Vacuum... Whats best?

[fishtrap]

I need a hold down system for a series of jobs. The parts may be as small as 10"x3"x1" maple/oak or as large as 4"X20".
I've been reading the various threads about vacuum clamping. Many swear by the ShopVac systems and others by pump or compressor driven setups. Without trying to start a war here, what are the pros and cons to each? Whats best as far as clamping power on smallish parts?

[ron brown]

Jim,

with vacuum clamping you only have atmospheric pressure for the start point. From there you subtract for less than perfect vacuum, leaks, leaks around the sides of the parts and countless other problems. If one understands that is the starting point and you have a limited and finate starting point - and it isn't a large number to begin with, you stand a chance to vacuum clamp.

Having made that statement, it appears to me you will need to clamp with a relativly high vacuum. If your 10" x 3" piece is clamped on that side and you get all the power teh atmosphere has to offer, you might get 430 pounds of clamping force if there is a gasket that seals to 1/4" from the edges and you loose a little bleed in the part you can be down to 1/2 that fairly quick. With a small but high power vacuum pump a pinhole would cause you to loose almost all hold-down force.

With "sheer stops" and a medium power pump you MIGHT be able to hold stuff down. Or, you could fail to seal the backer, or you could take to large a cut, or ... a list of other things.

If you could give us what you are trying to do - someone might have a method that will work for you. The problem is not so much starting a war as is there are several ways to approach vacuum clamping - and all work - and all can fail.

Feel free to contact me by e-mail and I will discuss the solutions as I see them. Others will have different views. What works for a system with 20HP of high vacuum may not work for a person with a small vacuum pump and pucks while a third or fourth person can make a shopvac do the job and still one more might never get it to work with vacuum and clamp the object with great success.

Let the war begin... I hope I fired the first salvo.


Ron

[fishtrap]

Ok,
Here is a "for example" part. These parts would be cut from 3/4" cherry or maple. I've created toolpath using a 1/2" cutter. This is typical of the type of part that I need to produce.
Any suggestions?

5258

[richards]

Jim,

Ron's post explains it pretty well. Small parts are hard to hold down with a vacuum (at least with the parts and vacuum systems that I've tried).

If I were cutting lots of pieces of the example that you've posted, I would either create a vacuum mask, take shallow cuts (to not disturb the vacuum) and then still leave tabs on the parts to hold everything together as a single unit, or I would use a method described by Morris D., Mike J. and Gerald D. in another part of the forumn today.

[lto]

Jim,

You could consider leaving a .100 skin when cutting these parts, then finish cutting them out with a laminate trimmer. This is not as elegant as having the parts completed on the router but if you plan on lots of repetition it deceases your time between cut files by allowing unloading in one piece.

[ron brown]

Jim,

Mike's description is near something I might try with even a low vacuum system and a proper mask/platten/pallet and tabs properly placed. I hope you need to make a bunch if you spend much time figuring the proper toolpath, sequence, clean-up and tabbing.

Ron

[fishtrap]

Hmmm... The tab idea looks promising. And LTO's method has worked for me in the past. In fact you can see the screw holes in the jpeg. I'd like to say "hasta la vista -baby" to the screws. (yeah, I'm from California) That alone would speed up production.

Mike, Where are those posts that you refer to?

As far as hardware goes, I have an air compressor that can deliver 12CFM @ 90psi. Would it be better to purshase a air/venturi system or go with a dedicated pump? There is about $500US available for work holding.

[ron brown]

I'd try it with a shopvac first.

Ron

[richards]

Jim,

The posts referred to are on "Assembly and Maintenance" under the topic "Getting the shopbot up and running". There's a section there on using alternate methods of holddown (T-rails, etc.). It's an excellent series of posts with detailed information including photographs and drawings to further illustrate the processes described.

The air/venturi system that I use costs somewhere in the neighborhood of $200 - $300 (sorry, it's been a while since I bought the parts and I'm away from the shop right now so I can't look up the invoices). The venturi system works well for me, but it keeps a 5hp compressor working nearly all of the time. For that reason, I bought a 3/4-hp GAST pump that costs less to operate over longer periods of time. For one-off projects, I use the venturi. For sustained use, I use the GAST (the dealer recommended a 10-minute no-load shutdown run to dry out the cast-iron parts on the GAST pump). Price wise, the GAST was somewhere around $700 for the pump and another $200-300 for fittings, so it might be a budget breaker on your particular project.

Ron's suggestion about using a shopvac is also very good. For larger pieces, I use a Fein vacuum that allows a little more leakage than the venturi or the GAST. However, almost any leakage will spoil the cut. So, be very careful with gasketing/masking if you use a low-volumn vacuum/pump system.

One last thought: Keeping the parts together with tabs/skin (per LTO's post) is still my preferred method of cutting small parts. Holding the entire 45 x 11.5 inch piece (with proper gasketing/masking) would be a whole lot easier than holding the individual pieces. Remember that the side-cutting force could be around 60-80 lbs. The 10 x 13 inch parts (9 x 12 after gasketing) that are shown in your example MIGHT retain enough vacuum to resist that side-cutting force - unless the wood is porous or the cells in the gasketing material leak (both conditions happen regularly to me). Having ten parts tied together with tabs/skin would multiply the resistance to side-cutting forces by a factor of ten.

-Mike

[davidallen]

if the small circles in the drawing are through holes, vacuum may not be the best option. each one will reduce the hold down force considerably simply because they will need to be masked off.

why not pre drill some or all of the holes then use dowels as fixtures or screws to hold the parts?

da

[gerald_d]

A curiosity....We are talking about 3/4" cherry or maple, 12" wide, 45" long, being cut with a 1/2" cutter. If something goes wrong, it is expensive. How flat can that slab of wood be expected to be during the cutting? Would the vacuum be expected to hold it flat if it does decide to warp/cup/bow?

[Brady Watson]

A shopvac with AllStar gasketing will definately work for this. I cut very small parts using just the Shopvac (IE~.625" X 1") and this is only at 3.5" Hg, but lots of CFM. I also have a high-Hg pump, but that is only good for perfectly sealed plenums and non-porous parts. If you get your gasketing setup right, a shopvac will do the trick for sure.

In the event that your parts are moving at the end of the cut, I would suggest adding a tab to the start point of the toolpath. I have found that you only need one at that point to keep the part from rotating at the last little bit and gouging the part.

-Brady

[gerald_d]

I presume that gasketing for this job would be a full sheet size - not only a strip around the edge. Which means that the gasket sheet must be cut as a mask, with a "manifold" to the right areas? And the gasket thickness/sponginess must be able to accommodate any problems with flatness?

The fact that All Star has such a very wide range of gasket products (http://www.allstaradhesives.com/cnc_products.htm) indicates that this subject can get quite involved.

I will readily agree that tabs will be very useful to exploit the last square inch of vacuum area. If each part has 2 or 3 tabs, the whole board stays dimensionally stable, and the parts/offcuts hold each other in place (depends on the the tightness of nesting). The parts in the illustration look like a minimum of 10x3" giving 10x3x3.5/30x14.5 = 50 lbs holding force per part with Brady's Shopvac. This 50 lbs won't hold against a 1/2" cutter ploughing at speed if the maple is being sucked down onto a melamine bleedboard, or onto a plastic gasketholder - you will need tabs or non-slip gasket sheet.

[mikejohn]

Looking at Jim's drawing above, it seems it is the drawing of the pieces, not the toolpath for a 1/2" tool. If you made a toolpath from this drawing, both the required pieces and the waste would all end up as small bits, nothing would be holding the tabs together.
Refering to the hold down post here (http://www.talkshopbot.com/forum/cgi-bin/discus/show.cgi?tpc=7&post=23267#POST23267), I would be interested to see if it is actually possible to produce a practical vacuum system for this drawing.
...........Mike

[gerald_d]

Mike, that is why I added the caveat "depends on the tightness of the nesting". How flat/porous are your planks in the other example? (In this example as well) Would you consider having dedicated gasket boards/pallets for each job/plank layout? Have you got enough power/money to drive a 15HP pump? Can you live with tabs? Etc......I think it is a very personal choice whether something is practical or not.

[mikejohn]

Gerald and Brady
Again taking Jims drawing as a starting point, but seperating the pieces a bit more, otherwise it can't work, how much time, and what would be the cost in materials of making a vacuum 'jig' for this job?
Ignoring, for now, the actual cost of the vacuum system, there has to be point where the fewer numbers you are making means it is better to waste even expensive material, rather than create the jig.
I wouldn't trust my planks to stay flat enough to hold with vacuum. When we assemble the slices into blocks, there is always an amount of clamping to get the boards sticking face to face (and a few screws to keep them there)!
On the other hand, if I were in the business of making hundreds or thousands off of reasonably sized pieces, out of man made sheets (Ply or MDF for instance) then I would certainly investigate vacuum.
However, something inside me suggests that simple may in the end be best.
............Mike

[ron brown]

Lots of suggestions here - some by folks who seldom or never have used vacuum for parts hold-down. If one were to use a low-power vacuum (shopvac) and tabs, combined with masks it will take a custom mask/platten/pallet to hold the parts.

David's comment about the drill holes brings up a method that also might show promise, predrilling the holes and using pins to stabilize the parts held by vacuum. Brady is correct in the tabs and start/exit points need some thought.

As far as the expense goes, I'd use Jim's shopvac first, as well as Jim's bits and material. After I went through a bunch of material, I'd probably have it properly held. I might even dedicate one of the $16 vacuum motors I have to the project and really splurge on expense.

One would hope the board would be flat to begin with and stable enough to not warp, cup and bow. Here in the old Western colony kiln drying is used and much of the wood is stable. I'm not sure if that techonology got to the southern and eastern colonies of the English speaking places.

Ron


who actually preferrs air-dried and aged material for projects but seldom gets to use use the stuff

[bleeth]

I'm in the middle of a similar project right now in which I've been cutting a series of parts out of 6/4 Honduras Mahogany planks 8' x 6-10". I stepped my bit so there was a skin left and then cut the skin on the last pass. the planks were screwed down. No jigs, No masking, nothing but final sanding. The only justification I can think of for further engineering of process would be a huge number of multiples and even then I'm not sure what the gain would be.

Dave

[gerald_d]

If one drills the holes first, all the way through plus a distance into the spoilboard/pallet and then knocks dowels down through the holes into the spoilboard, that would probably be enough to hold the job if you are using a down-cutter. No screws, vacuum or clamps.

[mikejohn]

Ron says "some by folks who seldom or never have used vacuum for parts hold-down" which certainly includes me, which is why I asked "how much time, and what would be the cost in materials of making a vacuum 'jig' for this job? " So come on Ron, as someone who is well experienced in using vacuum hold-down, what is the true cost?

Ron also say " Here in the old Western colony kiln drying is used and much of the wood is stable. I'm not sure if that techonology got to the southern and eastern colonies of the English speaking places." I did say in the other thread mentioned here that I buy wood dried to 8%. I recognise that the trees I see out of my window as I write can not compare to anything grown in the Texan pine forests, but its still not bad quality


............Mike

[fishtrap]

The vacuum system in question here is not only for this specific task, but also for many other highly varied past, present, and future projects that may or may not resemble this in the least. However a specific example has been posted and a solution for said example is in development/discussion/debate. Thanks for all of your input.

This part is a staircase handrail rough blank. I need to make 40 of these units. These parts do not have to be perfect, as after assembly they will be run across a shaper to give them their final cross section profile. It will be installed into one of the many cookie cutter tract homes being built here in Southern California. In fact there are probably more of these tracts here than there are pine tree forests in Texas ;-).

The material that I use is of the “Western colony kiln dried” variety. It has proven to be quite stable in the past. Such material typically goes directly from the jointer, to the planer, to the ShopBOT with little lag time between.

Sooooo… what if I used a combination of not cutting all of the way through leaving .1”ish of material. This way I don’t spend my whole life making a complex mask/pattern/pallet. I’ll also have the advantage of having all of that wonderful atmospheric pressure exerting its might on an unbroken 489.5 sq in of surface area. Very few of the holes actually go through the stock. The ones that do could be partially drilled by the SB and chased through after machining. Or just mask around those holes.
Use surface mounted lever clamps around the edges for making certain that the stock stays flat and does not migrate during machining –none of those pesky screws. And then clean it up post machining with a router table/trimmer bit. The only places that need to be clean are the end of the pieces where they join together.

Yaddayathink?

[Brady Watson]

Gerald,
The AllStar gasketing in question is their 'Spoilboard' cover....not strips. I use this extensively and it works really well. You simply offset your part vectors to the inside about .2" and weed out the center, and drill a hole to the plenum. In many cases, I simply drill holes right thru the gasketing instead of doing an inside offset toolpath (keeping holes inside that.2" boundary) If you cut the parts in multiple passes, leaving a skin and then go back with a cleanup pass and tab, then there is no real issue with the parts moving. I have used this system quite a bit, and I am here to tell you that it works.

If you need to make a bunch of parts, then make a vacuum jig. You don't need a 15hp regenerative blower to do it either...my Shopvac only puts out 3.5" Hg, which is 1/2 that of the Fein (which I plan on getting soon)...You can go pretty far with a Shopvac if you just put the time into the R&D and recognize the limitations.

If I were cutting these parts, another option I would pursue would be outdoor/hi-traffic carpet tape. You can get it at most home centers for about $5 for a 50' roll. I am speaking of the type that has the fiberglass mesh running thru it. It works suprisingly well. I am NOT talking about DS foam tape here...as it has too much flex and results in vibration and poor edge quality.

-Brady

[fishtrap]

The tape residue can be quite a pain to remove if it decides to bond better to the wood than to itself. Been there, done that.

The Spoilboard cover looks rather nifty.

[bleeth]

Jim: I usually leave my skin quite a bit thinner than .1" -Usually more like .03-.04. If I do parts and leave them in the original piece instead of cutting through I like them to practically fall out of the "web" It makes clean up time oh-so-short and I can easily remove them with a utility knife.
I just have a problem with trusting a shop-vac rig to hold a plank being hogged out with the force of a 1/2" bit moving over 2ips through solid maple or cherry. I figure if the hold down system is complicated and means I need to reduce my cutting quantity and speed it just ain't worth it.
If I were going to use surface clamps I would want my lumber blocked from lateral movement as well and like Morris's T-track and pin rig on the other thread.

Dave

[gerald_d]

Jim, you mentioned "The material that I use is of the “Western colony kiln dried” variety. It has proven to be quite stable in the past. Such material typically goes directly from the jointer, to the planer, to the ShopBOT with little lag time between." I have no doubt that you are starting with a nice flat piece of timber, but does it stay like that during your cutting? We often find timber that moves dramatically once you cut a lot of grooves halfway into it - even mdf wants to warp. I have no experience with cherry or maple, but I have seen some determined woods that will not be held flat with 2 lbs/in2.

[mikejohn]

Gentlemen
I need educating.

5259
If I have a perfect vacuum on one side, no leaks on the other, then I have 1 atmosphere pressure at any point on the table.
I introduce a plenum (with perfect gasketing), and my material is 100% non-porous I still have my theoretical perfect vacuum.
Now, if I have a 1"(25mm) diameter connection between vacuum and table, and drill four 1/2" (12.5mm) diameter holes through my material, don't I lose all my vacuum?
I recognise that the amount of air the pump can remove comes in to play, but the size of the vacuum chamber seems imaterial. If the cross section area of the vacuum chamber inlet equals the area of the holes, does the table area become equal to atmospheric pressure?
My problem is this, obviously vacuum hold down works, but I can't see how once you start cutting right through your material.
Brady says "If you cut the parts in multiple passes, leaving a skin and then go back with a cleanup pass and tab, then there is no real issue with the parts moving. I have used this system quite a bit, and I am here to tell you that it works.
I have searched Google, tried to remember my physics (not sure we had pressure back in my school days, chalk and slate time) but keep coming up scratching my head.
Aerial cameras suck the film flat to the focal plain plate by vacuum, and I know the slightest leak caused problems.
Can anyone enlighten me?

............Mike

[gerald_d]

Mike, the answer is in here "The AllStar gasketing in question is their 'Spoilboard' cover (http://www.allstaradhesives.com/cover_gasket.htm)....not strips. I use this extensively and it works really well. You simply offset your part vectors to the inside about .2" and weed out the center, and drill a hole to the plenum. In many cases, I simply drill holes right thru the gasketing instead of doing an inside offset toolpath (keeping holes inside that.2" boundary) If you cut the parts in multiple passes, leaving a skin and then go back with a cleanup pass and tab, then there is no real issue with the parts moving. I have used this system quite a bit, and I am here to tell you that it works." The gasket covers the whole 45x11.5 area, and one drills strategic holes, and maybe even remove (weed) areas of gasket, so that you don't puncture the vacuum area with the cutter.

[ron brown]

"My problem is this, obviously vacuum hold down works, but I can't see how once you start cutting right through your material."

VOLUME as in more CFM/lm or, the proper mask/gasket and good design.

This one thing is why a lot of folks fail in vacuum holding. Well - not having sufficient airpassages as in your example and not having enough... of at least half a dozen things. It is a very simple, an elegant techinical solution or part of both.

Ron

[Brady Watson]

Mike et al...The best advice I could give you is to take some scraps laying around your shop and make a vac jig...try it. The vacuum works well even in situations where you don't use gasketing, although at this point in my development I insist on using gasketing.

You can't fairly judge the vacuum hold-down strategy without actually trying it or seeing someone else using it. I doubted it's ability (internally saying, "Vacuum Schmakuum") until I tried making a few test fixtures myself. While it isn't the right solution in all cases, it allows you to do things that you cannot do any other way. Clamps get in the way, and waste material...screws do the same as well. Plus, many times, particularly 3D carving, you can't really sink a screw without adding hours to the finishing process.

Here's one of the 1/4" 'masks' that I use covered in gasketing material. It sits into a universal plenum that sits atop my spoilboard. Rather than make 20 different plenum/jig combos to run repeat jobs, I simply make new masks that slip into the plenum.

This is a mask with 400 of the 5/8" X 1" pieces that I mentioned using nothing more than a Shopvac for hold-down. Since the pieces were laminated with 3M adhesive/paper that needed to remain on the parts, DS tape was a no go.


5260

Here is a pic of the plenum that the masks sit into. It is about 3" tall so that I can jack my 2.25" vac hose right into it. It is made of 1/2" and 1/4" solid surface material, and a few strips of 1/2" plywood. The plywood and the 1/4" standoffs were machined flat at the same time to ensure that there would be no dips in the mask when vac is applied. All upright pieces were dadoed and epoxied in. It works very well.


5261

Go try it...

-Brady

[mikejohn]

Gentlemen all
Thanks. I managed to confuse myself whilst reading some earlier posts on this subject which rather muddied the actually technique.
This is what I now understand to be the method.

5262
The blue box is the plenum chamber. The white square is a supporting board for the gasket sheet (green). 5 holes are drilled through the gasket and right through the support board in strategic places. The material to cut is now placed on top of the green gasket, covering all 5 holes. I can now cut out a circle of material by following the red toolpath, cutting into (or even through) the gasket but not cutting through the support board to the plenum chamber below.

Obvious, when you know how


................Mike

[gerald_d]

You normally enlarge the holes in the green part - with the shape of the holes in the green going nearer to the cutter and the edges of the job.

"Cushioned vinyl" flooring (upside down) makes an economical full cover gasket. We have "Novilon" here.

[harold_weber]

Mike, at the Durham Jamboree, the owner of Allstar Adhesives gave a talk on gasketing. Allstar has a little brochure that gives a lot of tips on how to make gasketed vacuum hold downs.

Their web site is allstaradhesives.com, but I don't see the brochure on the web site.

Try inviting Allstar to the European Camp. Even if they don't come, they might send a batch of their brochures and price lists for the attendees.

[billp]

Mike,
Harold has a good point, but if you DO ask for a price list be sure to ask for the "Shopbbot list" as John Murphy( the owner of All Star) has come up with a group of materials which he thinks would be more appropriate for most 'Botters ( rather than those owning mega buck machines with 50 HP vacuum setups).
He also has a pricing structure which allows us to buy just one roll of material at a time ,rather than having to purchase case lots.

[mikejohn]

Harold and Bill
I await with baited breath to hear about all that went on at the Jamboree.
Certainly for the European event I am looking to find sources for all those 'goodies' you seem to find aplenty on your side of the great divide (or at least the Atantic Ocean).

It was the link to All Stars site that sent me off on the wrong foot trying to understand the vacuum system. Talking about there Spoilboard cover material they say
The procedure is simple:

Cover one side of a sheet of MDF or LDF with SBC gasketing.

Put the foam-capped board on your CNC router.

Cut your pre-programmed tool path.

Have your router drill the vacuum holes (in a grid pattern, perimeter pattern or utilize a pocket cut) for your parts.

Place your substrate on the SBC Spoil*Board and begin cutting.


It was the lines in red that made me think they were cutting the same toolpath as for the piece to create the 'hole' for vacuum hold-down.

But now I understand how its done.
In my drawing above, what width of gasket would you leave between the enlarged centre hole (as per Geralds instructions) and the red tool path?

..............Mike

[Brady Watson]

It's not that hard Mike...again I encourage you to make one and try it for yourself. Typically, allstar recommends at least a .2" offset from the gasketing, depending on geometry and parts to be cut, from the vacuum hole/plenum port.

Now that you have your bot working...cutting a few test setups shouldn't be much work. Here's and illustration of how it all looks from the top down:


5263

Note that, depending on the part size, it is sometimes necessary to have bridging/webbing in the center of the part to keep it from bending the material towards the plenum. Using the example above, the blue area is area that is offset .2" to the inside. The Black band is both the extent of your part and the edge of the gasketing....if using AllStar SB cover, then that band would most likely be cut to the cover board that sits atop your plenum...which is the red toolpath boundary.

Hope that helps...don't over-think this one, Mike. Just go and do it.

-Brady

[gerald_d]

Brady, in your photo above for the 5/8"x1" pieces, what material (type/thickness) are you cutting with what size bit and step-down? Are you leaving a skin or tabs? (I think I can see a cutter mark and a tab)

[Brady Watson]

Yes, Gerald on that particular mask (1st gen) there is a tab on it. 1/8" carbon fiber laminate with 1/8" bit cutting full depth @ 1.2 IPS.

My subsequent runs have eliminated the tabs...amazing what some duct tape around the seams on the shopvac can do to increase vac suction...

-Brady

[gerald_d]

With that setup, what minimum part size would you go to, for cutting 3/4" hardwood with a 1/2" cutter?

[Brady Watson]

Gerald,
That depends. If I were trying to cut 3/4" material as small as the pieces that I cut in 1/8", I would definately do multiple passes on it, then go back with a cleanup pass and possibly a tab. Depending on which way the grain is running, the tab at the start point is fairly critical. I tab at the start point to avoid allowing the part to rotate/gouge at the last second. If feeling particularly crafty, and the run of parts justifies the effort, multiple overlapping drilling pecks are very effective at breaking out the tabs without rotating the parts...since the tool exerts no lateral force, only Z force.

-Brady

[beacon14]

Let's back up a step. Why is it critical to use a 1/2" diameter bit? Can't we cut 3/4" hardwood with a 1/4" or 3/8" bit and reduce the waste while exerting less sideways force on the blank?

And speaking of sideways force, why did no one question Mike R when he said: "Remember that the side-cutting force could be around 60-80 lbs"? I've cut 3/4" hardwood with a handheld router and while I had to push the router I can't imagine I was putting 60-80 lbs of force into it. Just because the SB is capable of 60-80 lbs doesn't mean it always cuts at that level; it's more a function of material, cutter geometry (and sharpness) and feed speed. If I had to guess (and it would be only a guess, anyone care to test it?) I'd say no more than 20-25 lbs of sideways force, if that much, to cut 3/4" hardwood with a 1/4" bit.

[Brady Watson]

David I agree with you 100%. I believe that Gerald was just playing devil's advocate for the sake of discussion.

-Brady

[gerald_d]

Jim started this thread wanting to cut 3/4" hardwood with a 1/2" cutter, presumably because he wants a certain production rate. I think the message is becoming clear - he would have to be careful of forces and speeds if he wants to use a ShopVac, which is going to limit his production rate.

Edited to add: This cross-posted with Brady above.

[richards]

David,

You're right about the side-cutting force. I've only gestimated the side-cutting force from the Shopbot literature and from cutting too fast and too deep when I first got my Alpha. There were several times that I stalled the Porter-Cable when trying to cut Baltic Birch too fast and too deep.

Something has to give when the cutter stops turning and the steppers keep stepping. Either the steppers stall or the material breaks vacuum as it is literally pushed around the spoil board. In the beginning, I've 'pushed' a full sheet of MDF several inches before I could hit the KILL button. I'm not enough of a physicist to calculate how much side-loading that produced, but it was significant.

Now I take shallow cuts at the proper feed speed/RPM to get the proper chip load. Unless my programming is messed up, things work much better than they did in the beginning. The school of hard knocks has tyrants for teachers.

[ron brown]

Is this off topic?

Getting a floor up - http://tinyurl.com/bsoyg

Enjoy,
Ron

[paco]

Hi all!

I just made some basic tests with a 4" diameter zone and a 15 year old Shop-Vac (small unit) on HDU and hardwood carving and I'm really impressed as how it can be a stong hold... without any clamps in the way!!! I plan some more testing next days coming... this might solve some issue that I had about material staying flat like Acrylic sheets and multi-tool bit usage in some intricate pocketing not being "Z" accurate...

Thanks to Ron Brown and Brady who lead me to believe simple design CAN be effective!

[gerald_d]

Ron, what happens if you break wind in that elevator?

[mikejohn]

Look accusingly at the person next to you

[gerald_d]

...after the elevator has lurched 6"

[bob_lofthouse]

I've got the shopbot set up and running and I'm very impressed with my 5 zome 15hp vacuum. I'm cutting 2d profiles from 9mm + 6mm okoume ply and have been expecting to see a part wiz past my head, but the hold down has been spot on so far.

[mikejohn]

What Robert says about parts wizzing past his head has had me pondering for a while. Brady is only cutting 1/8" material with a 1/8" bit, which I suspect will have a different effect in case of vacuum failure to someone cutting 3/4" hardwood with a 1/2" cutter.
Over the years a lot of my hand held electrical tools have stopped working suddenly for one reason or another, so I guess a vacuum failure is likely at sometime. The advantages for holding thin material flat is quite apparent, but wouldn't safety clamps be wise to insure against the wizzing parts effect?
...........Mike

[Brady Watson]

Mike,
The example I posted with 1/8" material is just one instance. I cut just about every material and thickness in my shop. I have used vacuum when milling 4/4 hard maple with a 1/2" bit...No pieces went flying with the shopvac setup...They did however go flying using tabs & clamps and no vac.

It is important when speaking in terms of vacuum within the confines of CNC part fixturing, to realize that a high CFM vacuum source performs much better than a high-vac/low CFM unit, when milling porous materials such as hard woods etc. The hi-vac pumps are only good where there is a solid material being held to an air-tight fixture. Any leaks...and I can tell you parts WILL go flying when the vac seal is broken. This is not really an issue when using a shopvac as the source, since when there is a leak, it is not catastrophic ~ Unless you have a serious leak, the parts will still have a partial vacuum holding them down.

-Brady

[mikejohn]

I guess its time to ask a question that has puzzled me for a while. If I 'google' Shopvac I get a site (Shop-vac) for a range of wet-dry vacuum cleaners of different powers.
Is this what everyone means when they talk about shopvac?
Its not a brand that I am familiar with in the UK, but there are similar makes,and if this is what is meant, which model is the best for ShopBot use?
............Mike

[Brady Watson]

Mike,
In the US, we call them shopvacs...we also call tissues Kleenex.

The BEST vac anywhere for the bot is the Fein Turbo III. It has 2X the suction of a regular shopvac and some unique features like a seperate cooling fan for the motor. Google it...Over here the best deal is thru Amazon.com

-Brady

[gerald_d]

Seperate cooling fans for "shopvac" motors are pretty standard around here. I guess the Fein Turbo III has a 3 stage impeller similar to the last motor on this page (http://www.domel.si/products/products.asp?id=mokro). (From the specs can be seen that a 2x increase in suction is rather optimistic) You will probably find 3-stage impellers in other brands as well. Most of the ShopVac producers use generic vacuum motors from specialist vacuum motor producers. A google on "vacuum motor" will turn up dozens of these guys.

We buy only the generic vacuum motor for under $20, without buying the branded canister, filter and hose. (Ron does the same)

[gerald_d]

A word of caution when reading spec sheets of these vacuum motors: Some guys give the max "blowing" pressure as well as the maximum "sucking" pressure. The blowing pressure is a lot higher than the vacuum in terms of kPa or inches water. The best vacuums in "ShopVacs" will be around 30kPa, 120" Water, or 4 lbs/sq.in. (in the same holding power class as double-sided tape).

Interesting reading (http://www.ultimategarage.com/shopvacs.html)

[dvanr]

TA,

You've given me enough info to design my own "VINOvac" .(Drives me nuts that both the WAP and Fein models seem to only run on 110vac.) I know where I can get wine barrels cheap to slap those motors on . Who's with me to empty the wine barrels??

[mikejohn]

Send a couple of barrels to Gerald, he could do with some decent wine to drink


I was particularly impressed with those multi-barreled (more wine to drink) cyclone impellar type ideas.Any body have plans how to make such a beast?
.........Mike

[ron brown]

Well - while we are talking vacuum.... One of the things I try to do is eliminate the flow losses in the hose by putting the motor very close to the table. On one I built a plenum box with two vacuum motors and check valves so one motor could be used at a time. I also had plugs to close ports rather than valves. It did real well on pulling warped ply down.

Ron

[gerald_d]

We have plenty of wine and all our Fein, Wap and Kärcher, AEG, Bosch, Metabo, Makita, Electrolux and Hoover's run off 220V - the land of milk and honey

[gerald_d]

The www.ShopBotTools.com (http://www.ShopBotTools.com) web site offers:

"FEIN Turbo III $please call
Will hold 126CFM @ 7.3"HG 14 gallon capacity"

This is a problematic statement because the 7.3" HG will not be achieved at 126 CFM, it will only be achieved at nil (zero) CFM. Vice versa, the 126 CFM will only be achieved at nil (zero) inches mercury.

(7.3"HG equals about 85" Water)

[mikejohn]

Gerald
I would be realy pleased if you could Fein the time to Wap a plan together of a vac. I would Mak-it-a priority to build getting the power right with any (Electro)lux.Any Electrical Guidance would be appreciated. I would make it carefully, not Bosch it together.Hoo-(e)ver, please make the plans DIY simple.I Met a bo(er) once who was good at plans.
But I wont whine if you can't do it.
..............Mike

[gerald_d]

Poor old Kärcher got left out. Hey, havn't you also got Mother's Day out there today? Did you get permission to sit at the keyboard?

[mikejohn]

Mothers Day is 6th March in UK.
It's my day today. Roxana has a cold and has completely lost her voice. Heaven

............Mike

[bob_lofthouse]

Hi Mike,

Your welcome to pop up to lancs and take a look at our setup and see what you think.

[dirk]

I was planning on using this vacuum motor before I got my regenerative blower.
http://www.grainger.com/Grainger/productdetail.jsp?xi=xi&ItemId=1611764155&ccitem=
It's the most powerful vacuum motor I found. It will hold 145 inches of water. My blower only holds about 115, although I have more cfm.

[gerald_d]

Dirk, that is a brute of a vacuum motor! It has a separate motor cooling fan as well. Will probably suck a Fein through a 2" hole!


Spec Sheet for Grainger/Ametek 117500-12 (http://www.ameteklamb.com/support/prod/11750012.pdf).

Just a note of caution, shopvacs and "vacuum motors" have brushes and turn at very high speeds for a relatively short life compared to "regen blowers". Shopvacs, with their vacuum motors, increase speed when you use them for holding stuff and block off the inlet. If you look at the spec sheet above, you can see that this motor will speed up from 20 000rpm to 25 000rpm - more brush wear and noise. The regen blowers stay at a steady speed (probably 3 000 to 3 600rpm) and are happy to do this day in and day out.

[ron brown]

Another source for vacuum motors I have not used: http://tinyurl.com/755p6

Near the bottom there is a 140" 94CFM unit for $96.

These thing HAVE to make some racket.

Ron

[gerald_d]

Ron, that 140" $96 howler is on this page (http://www.imperialelectric.com/cgi-bin/wspd_cgi.sh/WService=imperial/itemdetl.html?item=122&lvl1=VM&lvl2=TBP&lvl3=&lvl4 =).

The full Grainger collection of 7.2" Ametek's (http://www.grainger.com/Grainger/wwg/viewCatalogPDF.shtml?browserCompatable=true&adobeC ompatable=true&CatPage=100) The footnote says: "Ideal for dental evacuators". Jeesh, I would guess these things could pull teeth!

[dirk]

It's a little strange to me that my regenerative blower increases in load and amps as the intake air gets restricted, where a vacuum motor is just the opposite.

[gerald_d]

Dirk, the regen blowers tend to behave more like "positive displacement" machines like piston/vane compressors. With centrifugal impeller vacuum motors (and water pumps) there comes a point where the impeller decides it is easier to "slip" than to bite off chunks of air (water) and spit them out. If no air is coming in, then there is nothing to bite and the motor relaxes. Very non-technical explanation.

[paco]

I just got the Shop-Vac indurtial line catalog and they have some quite interesting model; some pulling up to 105" with two stage motor (lower RPM)... one model fit a 44 gall. steel tank which you can buy only the motor (and lid); pretend to pull 100" with 109 CFM... I plan to inquire about prices...

[billp]

Paco,
That must be 100" of water, not mercury. I'm sure someone out there knows the conversion factor though.
I've used their "QSP superquiet" 10 gallon contractor's model for years with NO burnout. If it gets anywhere near the $300 mark you'd be better off with the Fein...

[gerald_d]

Yes, it must be 100" H20........ (13.6" H20 = 1.0" Hg)

Nothing will suck more than 30" HG (more correctly Hg = Mercury) because that is the most extreme vacuum that you can typically achieve at sea-level on earth, which is 14.7 pounds/sq.ft. or 1 bar = 1 kg/cm2 = 100 kPa.

[wayneo]

Hi Gerald,

Actually, I think it is 14.7 pounds/sq.in.
and that depends on the barometric pressure of the day......

Wayneo

[mikejohn]

and temperature ...

.......Mike

[cnc_works]

Hi Bill...
I bought the Fein III vac, then called the factory with some questions only to be told that for fine dust like MDF you must use a filter bag (at $3 or $4 apiece) in conjunction with the fine filter (an additional $50 or so with necessary retainers) or the warranty would be voided because the dust could damage the motor. I could fill several bags in a day so it would be a little expensive to use the Fein for a dust collecter.

That being said, it looked like a quality tool and sucked like a son-of-a-gun.

Donn

[gerald_d]

Thanks Wayne, 14.7 pounds/sq.in. ....it's Friday 13th.

[billp]

Donn,
I'd agree that for a dust collector it may not be the best tool, but in this case we're using it only as a vacuum hold down source. There should be minimal (if any) dust passing through the Fein if the vacuum pod/puck/jig is gasketed properly. MDF will eventually kill just about ANY tool by clogging it up if you run the dust through it's motor I bet.

[paco]

Bill,

yes, that's about water... but I just checked the Fein WWW site and it's too spec. with water... Fein III is spec. at 99" "static water lift"... The Shop-Vac industrial catalog says that the "Suction pressure represents how far up a glass tube a vacuum motor will lift a column of water."

QSP super quiet is a single stage motor vacuum pump... how good was the hold on this one?... I have a 6.5 HP single stage Shop-Vac that I might try first while upgrading my dust collector...

The Fein III is priced at 760.00$ CAD around here... still got to inquire about Shop-Vac price...

[billp]

Paco
Just as a test I stuck a vacuum guage into the hose on both my QSP Shopvac, and my Fein 3 units. Nothing scientific here,I just turned the units on and tried to suck the back of the guage off. The Fein was twice as powerful as the QSP. I am sure I lost vacuum as I had no gasket, etc. when I did this test, but the Fein showed about 7" hg and the QSP was 3.8"
I have used the QSP for quite some time and it held down almost everything I attempted. I wanted to go with the Fein because it had a lower DB sound rating, and the double fan on the motor. PLUS amazon .com had it on sale for under $300 (US) with free shipping last month.
I'll bet your 6.5HP unit will do much of what you want. At the least it would be a great place to start from and determine just how much vacuum you'll need for your work.

[David Arde (Unregistered Guest)]

I have an old milking machine vacume. I'm not surewhat kind it is but i will have to give it a try. What is a regen vacumn. This one could be a vane pump.

[richards]

Don,

I've been using a Fein III for about 9 months on a daily basis for hold-down only while cutting mostly MDF. To date there's been almost no dust inside the Fein. As Bill pointed out, there are other machines that work better for dust collection - although I'm beginning to wonder if anything works well with MDF; but, the Fein works very well for vacuum hold-down (if you use proper masks/gasketing).

[paco]

Bill,

Yes, I notice the Amazon.com price for sure!!!... but they wont ship to Canada else than book and CDs... I'll be back when I found out about thoses industrial two stage Shop-Vac prices... they too pretend about a MUCH lower noise level.

Did you only use the vacuum (QSP) to hold down sheet/things or added some screw?... I'm asking since so far my test reveal a good hold down for keeping sheet stock flat but not ideal for sideway hold; the material was keeping flat but the cutter could actually push the blank when machining aggresively...

[billp]

Paco,
If I have any real doubts I will use everything in the arsenal (screws, tape, etc.). Generally speaking when I cut full sheets of ply it's pretty nice ,flat faced marine grade, and about 6 mm thick. I have not found a piece of this where I needed to use anything other than the QSP. I think if I were planning to tey and cut very deep into .75" materials I'd use one of the smaller, more powerful rotary vacuum pumps.

[ron brown]

interesting - 6.5 HP = over 40 amps at 120 volts

That thing must have a cord as fat as a rattle-snake and rip breakers for breakfast. Or, it could suffer from advertising disease.

I bet on the latter.

Ron

[paco]

Yes Ron,

it's sick of pretentions... still, that's what the sticker on it says!

8-o

[paco]

Hi all!

I've just installed (and used some) my home made vacuum setup... and it SUCK!!!

Yes it really is! I'm very impressed from what I've test so far and I only use this Shop-Vac I had for my dust collecing system (this got me to upgrade my dust collector too and this one really SUCK too!!!). I have 14 zones on it, individually control; 8 zones that are 12" X 12" and 6 that are 24" X 24".

Here how it look like now... (I already plan some changes about the grid design; V grooves instead of flat bottom grooves.)


5264
I know, it does'nt look impressive like a high end tool setup but it working fine...

5265
I made the manifold with guess what?!... my tool!!! THAT'S impressive is'nt it?!

5266
Here you can see some of my previous vacuum tests... and I quite large redwood sign I made recently...

Thanks to thoses who convice me to try this... I wonder why I have'nt gone to vacuum before!!!

[fleinbach]

Great job Paco,

This is very similar to what I had planned when I purchased all the plumbing back in January. I really have to find time to get it all together. The only thing I see that I had planned differently was the placement of the valves. I plan on placing all my valves in line just under the front Xrail and running plumbing from there to each zone.

Maybe I will get the time to work on it now that I have hired three new people in the past two months. If they all keep working as well as they have so far I should start having some free time very soon.

[paco]

Frank,

yeah, I thought too to line up the valves but lining 14 of thoses was'nt easy on the designing part... since I was really eager to get it installed! I must say that reaching the inner most valves is'nt a problem... for me.

If I would have been a little more loose on the budget, I would have done it with 1-1/4" to 1-1/2" ABS draining pipe (and use bigger valves too)... if I would be rich, I would probably choosed brass valves cause they are MUCH MORE easy to turn!!!... but this would have been luxury! Why not electric selenoid valves with control switches installed just aside the keyboard?!?!

8-D

[fleinbach]

I purchased 12 each 1-1/2" valves and enough inch and a half pipe and fittings to reach each zone. For a manifold I purchased 3 inch pipe and reducer T’s from 3" to 1-1/2" pipe.
Altogether everything cost just over $300.00

[paco]

Frank,

what do you plan to use as for the vacuum pump?

I'm looking for something else already... if I could reach for 12-15 inch of mercury, that would be a very solid hold.

[fleinbach]

Paco,

I'm not quite sure at this point. I was going to experiment with my shop vac and I also have a Gast 1 hp vacuum pump that pulls 27 inches of mercury but of course not at a high volume. From what I have heard the backing point will not work very well unless I use a gasket. I do not intend to use a gasket it would defeat my purpose. So if the vacuum pump doesn't work I will be looking for a higher volume vacuum.

[evan]

Paco & Frank,

My table is a grid of .25" channels .23" deep spaced 1.25" on center. Dividing the table into four quadrants I placed two 1.5" holes evenly spaced and centered in each quadrant ( centers @ 12,16 & 12,32 in the first quadrant). There is a four gang manifold with valves to each quadrant. I use gasketing from Allstar in the grid in order to isolate each quadrant, or I can turn off one to three of the zones and gasket an area as small as I need. I've even pluged one of the holes and used this system to hold a piece 4" x 4". The vacuum is powered by the Fein Vac. I don't know exactly what it pulls but when I'm doing sheet goods I use 1/2" LDF (which I edge band to reduce leakage) for a spoil board and I can cut a full sheet of 3/4 ply or MDF into 24" squares with a .375" bit in two passes @ 3ips (I only have a PC router if I had a spindle I believe I could do the same thing in one Pass)without throwing any material off the table.

PS I forgot to say I think your table looks great.
It's great not not having to use screws and clamps all the time. Once you've used a vacuum hold down you don't want to go back. All though I've still had to resort to screws, doublestick tape and or clamps on occation.

[richards]

I just installed a 1/2-inch MDF spoil/bleeder board surfaced both sides for a finished thickness of 0.3-inch on top of the basic Shopbot four-zone vacuum board. The thought of using a spoil board on top of the vacuum board seemed ridiculous, since I use a lowly Fein vacuum.

In the past, I've either used a vacuum mask with tabs for smaller parts or simply left ~0.030 material uncut to hold everything together. Lately, I've had to increase the ~0.030 to as much as 0.060 to keep the MDF and particle board from cracking and loosing vacuum. I learned in a hurry that 0.060 is too thick for my prefered method of 'snapping' parts apart. Unless I scored the cut line before snapping the parts apart, I often ended up with uneven breaks and ruined parts.

So, in desperation, I spent $15 for a sheet of 1/2-inch MDF, surfaced it both sides and found that it works great. Today, I cut ten sheets of 3/4-inch particle board with various sized parts ranging from 1-1/2 x 7 inches to 24 x 33 inches. Everything was cut twice. The first cut was to a depth of 0.65 inches at 5.5 ips with a 5/16-inch 2-flute cutter. The second cut was to a depth of 0.74 inches at 8.0 ips (meaning that there was a spot or two where I cut all the way through the particle board). Not one part shifted. Not one part was spoiled. Snapping the parts apart was almost unnecessary. If you haven't already guessed, I was amazed that a little Fein vacuum and a diffuser board could work together.

[Ryan Patterson]

Look on Ebay http://search.ebay.com/regenerative-blower_W0QQfromZR8QQpqryZREGENERATIVEQ20BLOAER You can get some good deals on a regenerative blower. I got a 15hp blower for $150.00 3 phase. Before I got the blower I used a 5 hp shop vac. When I got the blower I tested it by using my shop vac hose Stuck it in the intake of the blower and block the air flow. The regerative blower sucked the 2 1/2" shop vac hose flat. I also have a 4.5 hp regenerative blower that is still far better than a shop vac.

[ron brown]

Just a few comments on valves: I've never used them. I built one system with valves but found I always used a cover-plate. I soon machined recesses for the coverplates where the pockets were "recessed" and the coverplates were the same level as the table top. these systems were all high volume, low vacuum pressure systems.

I have long thought of exactly how I would setup a system if I had less limited funding. More vacuum might be the first step, both in volume and suction/pressure/mercury. I doubt I would invest in valves as I think plugs will work better. One could even make "O-Ringed" plugs of (insert desired or scrap plastic material here). The O-ring coule be oriented to the surface of the top or of the tube opening.

One would locate the manifold in the center of the table and keep "runs" as short as possible, using as large tubing as practical. Like Paco's arrangement one would want the tubes to enter above a "floor" where any stuff that gets sucked in would stop there for later cleanout. A hinged flap would seal but also be easy to open for cleanout.

I think polyurethane will stick to poluethelyne sheeting. One could bond the sheeting to the bottom of one's table (probably on the top and flip the sheet before install) and all but eliminate vacuum leaks. One would want to think about the penetrations of the vacuum openings if volume was a problem. This may occur on a small high-suction vacuum pump. And, permeability of the material to be held will become a problem in that case.

Jigs can (and have) been made using the vacuum ports on similar tables for parts that need masks and gaskets. O-ring style material can be found in various sized. This has included "caulk saver" expanded foam from the local box stores. I have also cut small grooves and used the self stick foam and "d-type" weatherstripping.

Blocking or "shear-stops" can be all one needs to stop parts from sliding while cutting. Proper tool-paths can help here too and, the shear stops can sometimes be held by the vacuum.

Well, I've rambled enough,

Ron

[gerald_d]

"I doubt I would invest in valves as I think plugs will work better." We use normal bath plugs - they keep the dirt out of the pipe as well. Super high-tech stuff.

[larryk (Unregistered Guest)]

Do you think this would work?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=11809&item=3867191 708&rd=1&ssPageName=WD1V

[richards]

Larry,
From what I read, the item listed is a blower. Can it function as a vacuum? (I'm not at all familiar with Regenerative Blowers.)

[Ryan Patterson]

If you used the blower in larry's post you would probably get sucked through the table I wish I had a spare $2,500.00. Would never have to worry about anything moving again.

[beacon14]

Hi all,

I've been accumulating ideas here over the last year and here's my first attempt at putting together the ones that made the most sense for me:


5267

Now that I've used it I realize I made it much more elaborate than it needs to be, but I kept the construction simple to virtually eliminate vacuum leakage. It's a piece of 3/4" melamine-covered particleboard with strips of 3/4" MDF glued into recesses routed just through the top melamine face. After cleaning up the edges with the 'bot I ran them through the edgebander, applying aluminum-faced laminate (leftovers from a recent job) around the perimeter. No leaks. The whole thing locates to the table with dowels for easy removal, and rotating stops locate the workpiece then swivel out of the way if necessary.

Notice I divided the thing into 4 zones using foam backer rod in a routed grooove as a gasket. My plan was to have interchangeable covers of 1/2" melamine board, customizing them as needed with holes and gasketing for each job. Never got that far. Since 98% of all my parts are rectangular, it turns out all I have to do is block off the uncovered area with scraps of 1/4" MDF (plentiful around here.) If I need max suction I run a strip of masking tape over seams and/or around the perimeter.


5268

I don't even bother with the foam gasket, and the suction is amazing. I can re-surface the MDF flat if needed, or re-rout the base layer and replace the MDF. I'm using a Ridgid shopvac (which is also convenient for cleaning up the dust after cutting).

So (finally) to my question: I'm ready to make a full 4' x 8' 4-zone table improving on this setup, and the link to these pictures from Bill's corner (http://www.shopbottools.com/bciowatrip/brownshop.htm) which Bill posted in this thread (http://www.talkshopbot.com/forum/messages/28/9164.html?1125292721#POST27295) caught my eye. The 5th picture shows the system that I believe Ron is referring to above:

On one I built a plenum box with two vacuum motors and check valves so one motor could be used at a time. I also had plugs to close ports rather than valves. It did real well on pulling warped ply down.

Can you give us a little more info on which motors you used and how much noise they made? If it can pull down warped plywood that should be plenty as I am a recent convert to the system of leaving a skin and then using a finishing pass. I had been thinking about a 4-zone system with 4 Fein vacs, one for each zone, and just turn on the one(s) needed for each job, but after re-reading this thread I wonder if one would be enough, or if it makes more sense to just mount a vacuum motor or two as Ron did? How would the noise level of the Feins compare with a supply-house motor(s)?

As for the idea of using 4 vacs/motors vs just one: certainly in a perfect set-up with zero leaks extra motors would offer no advantage but in the real world we need more suction to overcome leaks from gasketing (or lack thereof) and throughcuts. Am I correct in thinking that for a given area, the following two options would behave identically? A) 2 motors each connected to the entire area, or B) 2 motors, each connected to one-half the area. If the vacuum loss per square inch is uniform on average over each motor's area the overall suction should be the same. So by mounting 4 motors I can use only one most of the time when cutting small parts, but have 4X the suction when holding a full sheet. I also have a cabinet-side drilling routine where I have to mount/dismount one part while another is being routed. I don't want to open a valve to "add" the second part to the system while the first part is being routed, and risk losing the seal. I also like not having to pay for the power to run a huge pump when I don't need that much suction all the time.

Sorry for the ramble. I've been meaning to post this for a while, so here it is. All feeedback is appreciated.

Regards,
David B.

[ron brown]

David,

I'll take a little more time to answer this afternoon - I have Jury Duty this morning -

BUT, I used some LOUD motors - If I had a Fein, I might use one or two to pull the warp out then use the Fein to just hold them - would be auto switching so a failure would trigger the loud motors.

Ron

[billp]

David,
I'll throw these thoughts into the mix based on systems I've been experimenting with over the last few months...
A Fein has a comfortable sound range. It does NOT sound like a rotary version of nails on a blackboard the way most other vacuum motors/blowers seem to. According to my VERY unscientific tests ( I stuck a vacuum guage into the mouth of the vacuum hose with a gasket on it, and turned on the machines...), I was pulling about 4 inches of mercury for a 6HP QSP 6 hp Shopvac, and 7.5 inches from the Fein Turbo 3. The Fein had twice the suction, at about a third of the sound. Of course then it's also 3 times the price of the Shopvac model...
If you were really trying to break your system down into smaller units which could be
'hot swapped'in the middle of a job, why not line your "zones" with some gasketing, and instead of using blowers, use individual rotary/diaphragm vacuum pumps ? These pumps have a lot of benefits over the larger models.
Since you are looking for the option to do a simple zone setup (no valves, just on/offs?) you could have 4/6/8 of the smaller pumps installed for MUCH less than the price of 4 Feins, and you would get three times the suction as well (most of these pumps pull close to 25 inches of mercury...)
Since you have already described the use of smaller areas to draw your vacuum from these would be perfect as they would now only have a relatively small area to control, and this would speed up their "grab"time to be competetive with the LARGE CFM school of thought.....In both schools ( Large/Small CFM ) the issue of "breaking through" a piece is equally serious, and care should be exercised in the design phase to avoid such incidents....
So I see; less noise (almost nothing above conversation level...), less power requirements (most of these pumps draw 1-4 amps each), THREE times the suction/holding power (which is really the bottom line in any discussion regarding vacuum hold downs...)And the ability to control as many zones/small areas you would like with minimal setup time...I think that's where my next table design is headed

[gerald_d]

A few years back there was a lot of talk (http://www.talkshopbot.com/forum/messages/27/581.html) here of little spring-loaded valves that the blank would push down to open vacuum to the right area. What happened to that idea?

[billp]

I thought there was some report of dust/debris getting in the seal of the ball valve after cutting for awhile. At least I remember someone telling me that at one of the Camps. If anyone has first hand experience it would nice to know if this is real, or just another "CNC Urban legend"...

[scott_smith]

Paco,
Do you think the extra small vacuum zones in the above post was worth the time and effort? Or do you find that you keep most of them on together? I was thinking of an 8-zone table powered by the mini Fein vacuum. 2) 12x24 zones, 2) 24x24 zones, and 2) 24x48 zones.

5269
Scott

[paco]

Scott,

it all depends on your needs. I still like a lot my setup, but the more valves the more money! The effort for me is to turn thoses #!@? plastic valves, I've come to hate 'em because they are VERY stiff to turn and it does'nt get any better with some lubrification tests I've made... I wonder if it would'nt worth the extra expense for brass ball valves instead.

[beacon14]

Scott,

If you keep a few scraps of 1/4" MDF (I like the stuff with white vinyl on one side, it's used for cabinet backs and is completely airtight), you can cover the unused areas of a larger zone easily, and maybe get by with fewer zones.

[gerald_d]

Paco, you need a tool like this:


5270

Overall height about 600mm. Top and bottom materials about 12mm steel round bar - bottom one bent U-shape. Vertical is 30mm pipe welded between round bars. The upside-down-U goes over the plastic valve handle.....you can figure out the rest.....

We always have them in factories, at refineries, on ships, etc. The tool allows you to reach difficult valves and to turn them with a good force. Also works for round valve handles - just put the fork over one spoke of the round wheel. We sometimes had them 2m long for valves in the ceiling or down in holes.

[jay_p]

Are you guys with Fein vacs letting them run for extended periods as might be required for 3D machining?
Thanks also to Mike for answering some questions while the forum was down.

Jay

[Brady Watson]

Jay,
Yes, I have...however carpet tape is probably a cheaper and better option if it's just 3D. Since there probably isn't much force on the part, tape is usually fine.

-Brady

[jay_p]

Thanks for the reply, Brady.
I finally have a Fein-powered vacuum system put together, and it is suprising how well it works. I am using a spoil/bleeder board like Mike's (and others) that started out as 3/4" mdf, but after milling is just under 5/8".
I have been using a Gast pump with pucks and so on for a couple of years, but for many things the new table is proving much easier.
I really appreciate all of the info available here on the forum.

Jay

[scott_smith]

Thank you Gerald!

The tip was for Paco but I took it anyway.
I’m familiar with T handles for valves but it took a reminder from you to build one for the vac table.
It works great!

5271

[gerald_d]

, especially for the instructions written on top.

and, for posting a top quality picture.....