Vacuum Holddown Questions

[greg_russell]

I am a new shopbot owner and intend to eventually use a vacuum holddown system. I want to be able to use a shopvac in combination with a mask and gasket material. I would like to rout vacuum channels in the table. I am wondering what depth and width these channels should be? IE should they be an 1/2 inch deep and 3/4 inch wide or what works best? I would also appriciate any suggestions on how far apart these channels should be as well.

I will be holding down primarily 3/4 and 5/8 baltic birch (5x5 sheets).

Thanks for any help or suggestions you can provide.

Thanks,

Greg Russell

[kerrazy]

All your info is right here
ftp://ftp.shopbottools.com@ftp.business.earthlink.net/PartFiles/vac2.sbp (ftp://ftp.business.earthlink.net/PartFiles/vac2.sbp)

Dale

[bjenkins]

Dale,

I have not been able to access these files in the past from the download site. Now I can't get your link to work. I seem to have an ftp access issue. Could you possible email the file to me?

[kerrazy]

Done Deal
Dale

[slendon]

Hi Bud,

I have the same ftp problem, can you forward to me Dales e mail files if they arrive safely.

Ta
Steve

[kerrazy]

I have posted the files at this site: http://makingdust.ca/downloads.htm

Dale

[bjenkins]

Dale,

Thanks for the files. I got them last night and they are very helpful. Steve, I just sent them to you.

BTW, Dale, that is a nice website you have there. I had no trouble getting the files off of your link there-- I checked even though I already got them.

[gerald_d]

In case people can't find the files on Dale's website....scroll way over to the right side.

[simon]

Hi
I have just lucked into 3 X 805 cu ft/min roots blowers in an auction.
Two of them have 30 HP motors, and they have spent their lives pumping air into a water treatment plant. The third was a spare.
I am not sure how many inches of mercury they will hold, but I suspect they will be extremely powerful The flow is over twice that of the BIG one supplied by shopbot.
I am designing a system round one of them. My question is, will ordinary drainage type 4 inch PVC pipe be strong enough to hold the vacuum and flow these things are going to pull? Or do I have to source extra thick walled pipe?
Also, since I had to get all three in a job lot, anyone in New Zealand want to buy one of them off me? They are quite large, english made, 40 years old, extremely well maintained by a government department.

[Brady Watson]

Simon...Make sure you keep your shirt tails tucked in and small pets far away!

30 HP is nothing to sneeze at...It's going to run up the electric bill for sure.

I found this online: "CAUTION: When using PVC pipe or any static enhancing material
for exhaust piping, make provisions to safeguard against arcing
from static electricity. Arcing can ignite oil vapor that may be
present."

A few other sites showed smaller pumps running 27" Hg (@-13.3 PSI) in a 1/4" PVC chamber. I think you should be good with 1/4", but I would check an engineering book to be sure. The only drawback, which is inapplicable in your case, is the outgassing of the PVC that you get when the vacuum leaches it out. This is probably only of concern if you are doing chemical mixing and degassing.

You should probably consider exactly how much vacuum you intend to pull for various materials. I don't think that you need to run 29" HG for most things. It's good that you have the CFM to overcome leaks.

-Brady

[gerald_d]

I get worried about the future of my planet when guys want to burn 30 HP to replace a couple of g-clamps.....

[elcruisr]

Simon, one thing to remember when running a blower like this for a vacuum application is you will need a "safety valve" so to speak. It is a spring loaded air relief valve adjusted to the maximum vacuum the pump is designed for. That way when that vacuum is reached it will start to allow some air into the pump and maintain the vacuum. Not having one will over heat your blower and ruin the bearings. Talking with a rep who sells blowers he considers 4" schedule 40 pipe to be the minimum for a 15 hp blower. If you can you might want larger but I suspect even at 4" you will be OK, you'll just lose a little flow but not vacuum.

A blower MUST also have an intake side vacuum filter (which needs to be cleaned now and then)to match the flow of the pump. Even fine sawdust, such as from an accidental cut through the spoilboard, will be very hard on the vanes and can ruin the blower.

A vacuum gauge between the pump and filter is also a good idea, let's you monitor things.

Wish I was in NZ, I've got a 15 hp and I'm starting to look bigger. Checking out Becker and Travianni pumps for the not so distant future.

And no Gerald, a few clamps won't replace what a large pump can do in my operation!

Eric

[simon]

Gerald
Nearly every problem I have ever had was caused by shifting parts. I have broken bits to show for it. I have lots of ruined bits of perspex, ply etc.
6mm ABS can be secured all over the place but it still vibrates when being cut. Keeping work down is my ONLY big issue. I DREAM of being able to MZ-2mm and know it will really be -2mm, and not some arbitrary depth below a wavy board.
As far as the planet goes, Point taken. But all of what we do with our fancy machines has little to do with survival, it is gloss.
Nobody needs signs, or boats, or reindeer sculptures in the garden. But we like them, so we find fancy ways of making them better.

[simon]

These blowers came with big brass spring loaded pressure relief valves, maybe I can convert them from outies to innies...
Filtration is mostly taken care of by the spoilboard, I guess, but I also got some big washable filters with the kit which I will design in.
Another thing, These pumps are not helical, the vanes are straight. I suppose this means they will pulse and be really noisy?

[elcruisr]

Most of the pumps I've dealt with have straight vanes, it shouldn't be a problem. Don't trust the spoil board for filtration. I'm amazed at what I clean out of my filter every month. And the first time you have a crash that puts the tool through the table (don't worry we've all had it happen) you'll be sucking lots of trash for a few seconds!

Eric

[Matt Barinholtz, Covenant House Washington, DC (Unregistered Guest)]

I ran across something interesting in a book I got at the Thermwood area at IWF2004. In "The Furniture Network", (download the free PDF here - http//www.thermwood.com/twood_site/pages/books_and_multimedia/pdf/furn_network.pdf (http://www.thermwood.com/twood_site/pages/books_and_multimedia/pdf/furn_network.pdf)) written by Ken Susnjara, he mentions on p. 156 & 157 a technique that employs the use of two sheets of mdf - a base spoilboard up to 1" thick, and a loose sheet that's 1/4" thick, which when used increases the overall vacuum, and allows increased hold-down pressure on very small parts. It's a good read, so I'm going to quote:

"A handling sheet is a piece of ¼ inch MDF that is the same size as the machine tabletop. When it is placed on the Universal Vacuum table and the parts placed on the handling sheet, the amount of holding force securing the parts is almost doubled.

We discovered this by accident during a machine demonstration at our British office. We were having difficulty holding some drawer fronts. Actually, it wasn’t working at all and the customer was already there.

One of our people placed a second sheet of thin material on top of the table and then put the parts on top of this. It worked every time.

Neither we, nor he, is sure why he did that and we are not totally sure why this works as well as it does. We guess it is because the handling sheet reduces flow and thus increases the vacuum produced by the pump.
There is, however, something else at work here that we do not completely understand. If you make the spoilboard material ¼ inch thicker, the effect does not occur. There is something in the interface between the primary spoilboard and the handling sheet that make the technique work. Fortunately, the technique does make it possible to hold smaller panels for machining."

Anybody ever hear of this? Sounds really interesting, and I'm going to try it this weekend..Google searches of combinations of "handling, sheet, thermwood" don't pull up anything.

Best!

Matt Barinholtz
Covenant House Washington, DC

[Brady Watson]

Hey Matt! Hope to see you at Bill's Camp.

I haven't heard of the 1/4" trick with MDF, but I have heard of people using LDF to pull the vacuum through. I am still a bit leary of just using vacuum with no stops on the pieces to keep it from moving via cutting force. I'd be interested to hear about your experiment results.

-Brady

[elcruisr]

We've used 1/4", 3/8" and 1/2" MDF and LDF for spoil boards. Also tried the 1/4" overlay trick as well.

The 1/4 overlay sheet didn't do much for us, I suspect it depends on your exact system. We are getting the best results in our application with 1/2" LDF. We usually dress is untill it is about 1/4" then pull it and install a new one.

Since we have a 5 x 12 table if I'm doing a long run of 4 x 8 sheets I'll cover the top 12" of table with scrap laminate to help boost the vacuum.

Eric

[simon]

I have just had to get a sparky in to quote on putting in 3 phase for my new vacuum pump equipment. It is going to be very costly.
I had an idea. Anyone running a vacuum pump on a car or motorbike engine? It would seem a logical alternative, more control, and less installation cost, and it is easy to put the exhaust outside.

[conor haugh (Unregistered Guest)]

Matt
I read the same book and started using this system
about a year ago.Yes it does incease the holding power.In our case we use a 15mm mdf panel with a 4mm mdf sheet on top.I have been at a loss to understand the science behind this.The other advantages are that your 15mm panel remains intact
and you only have to replace the cheaper 4mm sheet.A big time saver has been the ability to slip the 4mm sheet off the table onto a trolley with all those parts and put another 4mm sheet
on and start cutting again While the machine is running you can be sorting out your parts.From our own testing I would say the holdig power has more than double.

[elcruisr]

Conor,
It's interesting that it is increasing your holding power. If you don't mind my asking what type of a vacuum pump and plumbing are you using? Do you have a vacuum gauge that can tell you what vacuum you are achieving?

We didn't really see an increase and it would be interesting to compare systems.

Eric

Dodging another blasted hurricane........

[conorhaugh (Unregistered Guest)]

Eric
A Becker Pump.The description is 250m3/h.The size of duct cable coming from it is about 80mm.The nature of the plumbing inside the machine I have not seen.There are 2 zones of vacumn on the table
which are independent of each other. The table itself is phenolic matrix table.Yes it is interesting that an arrangment that one would have thought should lessen holding power actually
increases it.I dont have a guage that shows a level of vacumn.Quite honestly I have a limited knowledge of the physics of vacumn.
Conor

[Matt Barinholtz, Covenant House Washington (Unregistered Guest)]

Conor -

What are you able to achieve with the increased vacuum? Also, how does it work if you are not using all zones of vacuun at once? We are running the FPZ blower that ShopBot recommends, and I would like to be able to learn the size of the parts you are cutting - we occasionally do a lot of parts less than 6" x 6", and have relied on tabbing or the chips left in the kerf from a downspiral cutter to hold the pieces. Using the handling sheet would be great. Do you seal the edges of the handling sheet?

Eric - you are using LDF, not MDF? IS that why you're pulling so much stuff through and into the trap? Does the LDF expand more or less than the MDF?

Thanks to all for the info!

Matt Barinholtz

[elcruisr]

Conor, that Becker is a fine pump! I believe it will pull much more vacuum than the 15 HP FPZ that I am running. I guess that there must be something going on with the higher vacuum and the thinner top sheet than I am seeing with my pump. We typically see 12" HG at the beginning of a sheet and it will often drop to 7" HG by the end of a typical sheet of nested parts (anywhere from 20 to 40 parts per sheet). Something to think about as we are starting to think about a pump more like yours.

Matt, we went to LDF (Trupan light) because we seemed to have better parts holding with it over just standard MDF and the price difference locally is small. Not really sure if that is why we get stuff in the filter or not but with either material we would experience "clogging" after cutting material that generates fine dust. A quick table cut of .01 would always bring it back though. Cutting melamine or MDF is always the worst!

As far as expansion I haven't noticed any difference between the two, as our shop is air conditioned things stay pretty stable though. I do usually cut the back side before installing a new spoil board, it really ups the holding power.

With my set up I am comfortable holding parts down to about a square foot when running 3/4 plywood at 10"/sec in a single pass. Beyond that we use tabs or if the parts are long and narrow we find we need tabs as well. We do alot of full sheet nests which are held fully together with tabs that can be pulled onto a sorting table as a single unit and cut apart with a laminate trimmer. Even then we find that good hold down is critical as there are so many vacuum leaks through the cut lines towards the end.

Eric

[conorhaugh (Unregistered Guest)]

Matt
The following are procedures that we also found to improve holdown.
When nesting a panel always position the smallest parts in the centre of table and start the cutting cycle with these first.As the cycle progresses the overall holdown is decreasing as the amount of kerf line is increasing.On the smaller parts cut a first pass down to .1mm at this the part is held securely. The final pass is exerting very little forces on the part.
Yes it is important to edgeseal the 15mm panel
both on the edge and a margin underneath and into meet the gasket.After each cycle vacunm down rather than sweep the 4mm sheet as even dust can keep the sheet to panel seperated enough to affect holdown. Apparently the vacumn exist only in a tiny distance (microns)
above the sheet.So it is important to keep the bottom of the panel within this area.We have followed the above as standard and have had little trouble with moving parts.I hope this has been of help.

[simon]

Hi all
I am now confused, as I suspect are all vacuum- holddown newbies. Correct me if I am wrong at any point about the following procedure.
1. Get a strong base board.
2 Screw a three-quarter inch MDF panel onto this.
3 Cut the channels and the holes with the Sbp program using a half-inch bit.
4. Paint the channels with PVA or something to make it airtight.
5. Skim the top skin off the remaining islands to allow air through?
6. Skim both skins of another three-quarter inch MDF board to allow air to pass through?
7. Screw it down to the channelled board.
8. Surface the board. Seal the edges
9. Get a "Handling" sheet of MDF, some thickness between 3mm and 6.4mm - about a quarter inch.
10. Skim both surfaces of this to allow air to pass through?
11. Connect up all the pipes to your system.
12. Put on your work and fire her up.

[lto]

Are any of you using a vacuum similar to that described by Simon to hold plastic? What about smaller or narrow pieces? Is there an advantage in using a table surface that has more slip resistance than MDF? Thanks in advance for your response, I hope to soon have my own shopbot and be able to contribute to this source of knowledge.

[elcruisr]

Simon, you're on the right track but, after cutting the channels and sealing them that's it for the vacuum plenum. I then cover with 3/8" or 1/2" MDF or LDF having first skimmed the down side with the CNC machine to give a good porous surface. Then I put it down with a small bead of silicone around the edges for a good seal. After the silicone cures you will need to recut the top to insure flatness and open up the pores. The extra, thin, handling sheet is used by some and not by others, experimentation will show wether or not it works for you. Remember most tables are built with several zones that are controlled by valves so you are not losing vacuum through open table.

LTO, we use vacuum to hold plastics on a routine basis. Small pieces require a little creativity to keep in place with jigs or clamps sometimes.

Eric

[lto]

Thanks Eric for the response. Have you ever cut/held the poly lumber manufactured by N.E.W. Plastics? Their description;Solid, premium recycled high density
Polyethelene (ReHDPE) plastic lumber. http://www.renewplastics.com/default.htm
This product has a slight textured finnish to appear like wood, which won't help the vacuum hold any. It is used locally for outdoor furniture, bird feeders, lawn ornaments, etc. I was looking into cutting and drilling this on a shopbot. My original plan was to cut to shape and ease edges in one operation, but I'm finding that I'd need to use a 1"CED cutter (according to Onsrud) which would increase my holding power needs and also mess up my yield on some parts. I may need to just cut to shape on the shopbot and ease edges on a router or shaper. I'm at the point where I'm anxious to order a Bot but feel like I need a test drive to make sure it will get me to where I'm going.

[elcruisr]

I have not cut that particular product but I have cut HDE up to 3/4" in sheet stock form. Don't forget you can easily build a jig to hold your pieces and hold the jig down with vacuum. You can also cut it in multiple passes if need be with a smaller bit.

I would never use my table time to radius or ease edges personally. It's faster and easier with a router table or hand held router. That's not saying it can't be done but the trick is to remember that a CNC machine does not necessarily beat every old fasioned method of work in the shop, just some of them!

Eric

[simon]

Hi
After some enormous effort and long afternoons of head scratching I have finally conected up my vacuum pump to the machine and it is ...awesome.
To remind, I got 3 x 804sq. ft. roots blowers and 30hp motors off a local auction site, along with lots of cast iron pipes, filters, and other stuff. They have been been blowing air into water treatment tanks for at the last 50 years, but there is not a scratch on the vanes or a shake on the bearings.
I had to get 3-phase installed in my shop first off.
I was told by the local electricity suppliers that I couldnt start the motor direct online, because it would dim all the lights in the town, so after researching soft starters and prices I decided to buy a speed controller. I got an ABB one from M&E electrical in Australia who sell them at half the trade price for some reason. These arepricy but very worth it at $2,500 bux.
The outlet diffuses backwards through a filter which kills the noise almost completely aside from a dull rumble. This filter is made up of layers of perforated steel sheets of reducing diameter holes.
I have only got 6 layers of very fine screen mesh for an intake filter while I figure out how to put a proper one in, but I suspect that drawing air through 3mm of MDF is sort of okay... (Until I drive the bit through the table).
I only have a single zone, the pipe goes out the centre.
I cut the grooves in the plenum with a 19mm ballnose down to 8mm deep. I designed this with lots of radials to carry the vac to the edge.
I siliconed the edge, and pressed a 3mm MDF sheed directly onto this, with the vac running as it cured.
It is all hooked up, and I have not yet even run the pump to a third of max. speed.
I find that I can place a sheet in the centre, measuring only 2 ft square, and cut out pcs of under 4 inches a side, and it will still hold incredibly well when in good contact with the table at a quarter speed, using a quarter inch spiral upcut.
If anyone can explain the dynamics behind this I would be most interested - I have good grip with only about 10 percent coverage of the table. Leakage seems not to be an issue. No need to run around covering the cuts or crank up the vac.
As soon as I replace my digital camera, (ruined during a sailing race), I will send some pics of the setup.
Simon

[Brady Watson]

Simon,
Congratulations...It's been a long time coming.

That's quite a bit of potential vacuum with that setup...be careful that you don't suck the entire world into it like Tom & Jerry cartoons...LOL!

-Brady

[bleeth]

Simon- It sounds like you could use this rig to vacuum bag a 120 footer all at once!!
Go guy!!
Dave

[sales@vac-clamp.com]

A viable alternative to large vacuum pumps are Vac-Clamps. These run on compressed air (about 1 CFM per pad), can be sized to hold smaller items or chained together to hold larger items. No moving parts inside the clamps and they tolerate dust and grit.
They cost about US$54.00.

Website http://www.vac-clamp.com

[Brady Watson]

Errol,
A number of us botters make our own vacuum clamps by machining similar pockets on both sides (or all the way through like a donut) of MDF scrap laying around the shop...usually for no cost other than the gasketing material. A few pieces of MDF scrap and some epoxy resin to seal them and drill a vac port into the plenum and you're all set.

You can buy a venturi vac from Harbor Freight for $15 that hooks up to your compressor (almost certainly what they use...and charge you 10X that amount). For the price of one of their clamps with venturi vac, you can get a real vacuum pump off of ebay with more holding power.

-Brady

[ron brown]

Well said Brady. The sealing allows teh use of almost any porous matarial about. If one has some plastic scrap around they can make even more durable "pucks" and avoid the epoxy seal.

Ron

[phil_o]

Brady, do you have any pictures of the vacuum clamps you've made?

[billp]

Phil,
Here's a shot of some pucks which Bill Imschweiler brought to the NJ Camp last year. I have since seen pucks made out of plastics, and Delrin and as Ron mentions this eliminates the need for a sealer coat. You just need something the gasket material can stick to.
Errol's Vac Clamps are production models of similar modules, and we had one on display at last year's Jamboree. If you don't want to get into the manufacturing end of these pucks, his unit is a nice alternative. I also believe he can do custom sizes if you have special projects.
Ron -Surplus Center has some more vacuum modules listed again, not sure if they are the same as your previous units...
5306

[stickman]

Guys,

I am working on some vacumn pucks. 3/4" or 1" UHMW with EPDM foam seals top and bottom. Venturi vac generator, with a simple toggle switch valve or a slide valve. I am finding I can build them at a reasonable price. I'll post more, when I get them done.

Jay

[jthelen]

Bill,
I have a couple of 1"x 2'x4' sheets of UHMW left from a job. I would like more information on how to build these pucks. Or is it as simple as it looks in the picture. (the shape, the groove for the gasket, the slot, and holes either end for the tubing connector.) I assume the slot is cut through to suck it self down to the work surface. This must mean the other side looks similar to the top? How big of vacuum pump do you need?

Jim

[Brady Watson]

Jim,
You are correct...It really is as simple as it looks. You could just as easily take a piece of 4" PVC pipe, and if you could get a gasket to seat on the top and bottom, all you would need to do is drill a hole for a 1/4" NPT nipple to pipe your vacuum source to....or 2 ports so that you could daisy chain them together.

-Brady

[billp]

Jim,
I've seen these pucks in a variety of shapes and sizes, so I don't think there is any formal rule of thumb for making them. Most people have told me they do exactly as you stated; they cut holes in the top for suction , and on some models have a matching bottom hole to "grab" the table. Other people make chains of them to hold larger items. With the newer, thinner gasketing materials available from places like All Star adhesives you can get get great holding power on any non porous surface.
I've heard of pumps ranging from 1/6 HP and upwards doing the job. I am guessing that larger pumps will evacuate the air faster. I just ordered a 1/4 HP pump from the Surplus Center ($90 before they added shipping, etc.), and I also bought a 3 gallon air tank to use as a resevoir with it. I plan to have the tank ready as an instant vacuum, and then let the pump keep the vacuum level constant. I'm going to try some pucks, and a few designated jigs as well. My 6HP Shopvac still works pretty well on most applications, but I think the ability to provide pin point placement of the pucks will be a great time saver, not to mention eliminating most of the clamping headaches...

[billp]

I've finally got the vacuum pump up and running. So far it's done everything I've asked it to. Obviously as with ALL vacuum devices it works better with non porous materials.
I think another issue which has made it perform better is that after trying out a few different configurations I've gone to a "one sided" "puck/pod"instead of the two sided version.The new pods are made of 1"thick PVC which is incredibly dense, and can be tapped/threaded to hold the fittings.
I was finding out that if there was ANY dust/dirt/debris on my table, OR if I had place the pod in an area where I had previously screwed into the table I was NOT getting full vacuum. With the one sided pod I can now either screw it directly on top of my table, or mount it/them on a piece of plywood, and then clamp the plywood (with the clamps now able to be well out of the cutting path) to my table.
The initial period to evacuate my 3 gallon "surge tank" takes about 17 seconds, and I may swap that out for a larger tank in case I want to use this rig for full sheets of plywood on my existing table.
I'm consistantly getting close to 24" of mercury according to my guage, and even after it bleeds down a little (I think there is still one tiny pinhole leak somewhere in my "manifold" which I'll track down..) the vacuum switch kicks back in at 16.5"and it takes 16 seconds to get back to the 24". I could probably tweak the pump to pull a little more vacuum, but it seems happy at these levels.SO if my math is correct, my pump shouldn't run longer than 17 seconds for most operations which should mean a pretty long pump life. I've posted pix/specs/suppliers/prices on my web page- http://www.baycraftdesigns.com (on the Shopbot page)

[Brady Watson]

Nice setup Bill!

It seems to me that it would be a perfect fit for those of us that don't really need a 15HP pump...and aren't getting enough performance out of our shop vacs (the boat I am in now)

I really like the fact that the pump shuts off automatically...not that the little pumps are that loud, but it's nice to extend the life of the pump if you can. Thanks for sharing the info!

-Brady

[davidallen]

you can also find thick PVC at the depot as floor flanges in the electrical and plumbing dept.

it will have holes in it so you may have to 'face' it with acrylic or make 2 sided pucks.

[Brady Watson]

David,
One nice thing about PVC is it welds nicely. It would take about 5 min to weld up the holes so that they are air-tight. You can get a plastic welder with rods from HarborFreight for $30.

Nice tip on the accessible PVC source!

-Brady

[jthelen]

Bill,
The 1/8 inch gasket material from All*Star Adhesive Products looks like their On-board type. This comes in different densities, what density did you find to work best?
Jim

[billp]

Jim,
I spoke with John Murphy of All Star last week, and he seemed to think that the lower density foams would work better for Shopbotters using lower powered vacuum rigs, (as compared to guys running larger machines with correspondingly larger pumps). I am afraid that I can't give you a specific answer as to which density I have here as it came from the sample pack John was good enough to send us for the NJ Camp, and I wound giving away all but a few small strips of it to "campers" who attended so I don't even have the wrapping it came with.
John, and his son Mike, are now well aware of the Shopbot community and they will be adding a special 'Shopbot' designation to some of their product line which they feel would be most appropriate for our needs. They will also be offering the tape in single rolls (rather than case lots) knowing that many 'Botters do not really NEED to buy 24 rolls at a time.
I've found that they are really helpful on the phone when you call and ask specific questions, and so we have invited them to come down to the Jamboree to show some of the ways good gasketing can improve performance on a vacuum rig, as well as being "resource" personnel for anyone wanting to learn more about vacuum hold downs/clamping...
Please keep in mind that everyone's needs might be a little different, so I don't want everyone to think that THEY need the 1/8"gaskets, it has just worked out fine for me...

[jthelen]

John Murphy helped me design my vacuum table and spent lots of time explaining the ins and outs of using vacuum. He runs a good company. I use his Spoil*Board Cover Gasketing and it works very well. He is a great resource.
Jim

[billp]

I just got an e-mail from the company I get my "pods" from. Someone apparently screwed up when posting their web page listings, and a bunch of pricing got transposed. The latest prices are now accurate... http://www.nappyproducts.com

[gerald_d]

Nappy Products? to the English speakers outside America that comes across as Diaper Products. Our babies wear nappies.

[billp]

Gerald,
I asked about the name already myself (it also has certain connotations about hair texture..). Apparently it comes from a childhood nickname of "Napoleon" (whodathunkit?).....

[mikejohn]

Have they met their Waterloo trying to sell this side of the pond?

[billp]

Sometimes Euro humor can be as dry as a used nappy....

[gerald_d]

I take my hat off to a guy that sticks with his nickname, even if there may be a slight whiff to it. May Nappy Products go from strength to strength!

[tony@nappyproducts.com]

I am impervious to Humor go or bad.

[mikejohn]

It's the nappies that we hope are impervious.

[gerald_d]

As some may have noticed, I am on a mission to limit thread drift (hijacking). This thread is on vacuum holddown systems. How can we hold a baby down while changing its diaper/nappy? Should we put a vacuum puck inside the diaper/nappy for "extraction", thus reducing the need to change the diaper/nappy?

[mikejohn]

Before trying any experiments with full nappies, make sure you wear the correct mask

A lot of my cutting, when I get my ShopBot (somewhere on the high seas at this moment) will be on birch ply, 4mm or 6mm (1/6" or 1/4") of many small pieces, within a rectangle 480mm x 305mm. I understand that vacuuming with many small pieces is difficult. Should I cut the file 20 times (4x5) from a full sheet, clamping the edges, and risking the sheet lifting in the centre, or should I make a couple of simple 305mm x 480mm holding jigs, letting the machine cut one whilst I set up the other?
Or should I make a fancy jig that holds down the waste material rather than the cut pieces? The waste material ends up as a single piece with lots of holes in it.
.........Mike

[gerald_d]

Why is the 480 x 305 rectangle important to the question? Is this the way that you did it before? Or is this the "full sheet" that you are referring to?

If I think that I know what you mean, we would cut with a down-spiral cutter, slightly into the spoilboard (Good finish on top and bottom edges and no "lifting" issues). Only clamp one edge (x=0) of a full table-sized sheet. Use one cut file that does the whole job. No vacuum involved - unless the stock sheet is warped and it needs sucking down to flatten it. But then you do need a very good cut file where you determine the exact starting point and sequence of each part to work back towards the clamps.

[mikejohn]

Gerald
To prevent further thread drift, I have started a new thread here (http://www.talkshopbot.com/forum/cgi-bin/discus/show.cgi?tpc=29&post=21284#POST21284)
.........Mike

[iranpu@yahoo.com]

Dear
how are you?
my name is Amir.i am a searcher in surface coating.i would be glad if any one wants to hepl
me in these fields:
1-dip or water transfer printing
2-decoral or heat transfer printing
3-pvc foil laminating
4-veneering
looking forward for your mail


your new firend
Amir Taheri

[jim_ludi]

An interesting website that details veneering vacuum systems can be found at: http://www.joewoodworker.com/veneering/visitorspress.htm. You'll find plans for home brew systems and many pictures of completed home built systems.

Also, you'll find some videos of completed systems in action - check out the venturi system video: http://www.joewoodworker.com/catalog/vacuum_press.php?osCsid=f466c6f5be8e6405f4f8ac0574 3c4bf2) - it draws about 20" vacuum in a few seconds on a system with two 3" x 14" PVC reservoir tanks.

[errolvacclamp]

Previously in this forum I had mentioned our compressed air powered vacuum clamps as a viable alternative to large pumps. We now have a couple of new additions that will be of interest to those who need a ready made solution to vacuum hold downs.
Our VC5 clamp will hold itself down to a surface, and then hold a workpiece on top. It has two low consumption vacuum generators built in. The faces can be configured to hold down almost any shape, and no moving parts inside to wear out.
Link http://www.vac-clamp.com/vc5.htm

The other product is a face plug for the VC4 or VC5 vacuum clamp. This is a shim or packer that clips into the face of either clamp. It elevates your workpiece by 3mm to allow you to cut through the workpiece, but not damage the clamp face.
Link http://www.vac-clamp.com/vc%20cnc.htm

[bcammack]

Interesting product, Errol.

Us backward American aren't good with the metric system, though.


What is the compressed air consumption in CFM at the recommended PSI? What are the noise measurements, on a single unit in operation, in dB at 1, 3, and 5 meters?

[errolvacclamp]

Hi Brett,
Air consumption for the VC4 is approx 1cfm at 80psi. Double that for the VC5
Specs for VC4 link here http://www.vac-clamp.com/vc4spec.htm and VC5 here http://www.vac-clamp.com/vc5spec.htm

We have very usable vacuum levels at 60 psi and much lower air consumption at that level (I will post exact stats later)

Have not done noise testing at 3ft, 10ft or 16ft, but a conversation can be had while demonstrating the units at trade shows. Not shouting, talking.

Errol