Vacuum table and Two Feins

[jwelin]

I've constructed the 4 zone vacuum table per Shopbots plans and have had success holding parts with a Fein vacuum connected to one zone as a test. Now comes time to install the piping to all four zones and I've come by a second fein vacuum. I wonder if the both vacs should be connected to the 4 zone pipe system, or if I should dedicate each vac to two zones. I assume two vacuums connected to a single pipe system will not double the vacuum pressure, though I think it will double the CFM. Any sage advise?

[jthelen]

John,
I have 1 Fein vacuum connected to my 4 zone vacuum system. It works great to hold sheets and smaller parts as long as you don't cut through the parts. Otherwise it can't pull the CFM and looses vacuum. I am planning to try the multi-Fein system.I don't think the Vacuum will increase but think the CFM should. The big Fein pull 100 inches of water or about 7 inches of mercury. If having two allows an increase in CFM and holds the 7 inches of vacuum, I thought of using a vacuum switch to control addition Fein's to make up for lost vacuum do to CFM. You can get 4 of the Fein vacuums for about $1200. Maybe its a pipe dream so any input would be appreciated. I would love to have a big vacuum pump but can't justify it yet.

Jim

[richards]

Why not build a bypass-T between the zones so that you can use both vacuums independently or in series. Piping could be as simple as screw-on caps or a little more elaborate with ball-valves. In either case, the cost should be minimal.

[jthelen]

Mike,
Thanks for your input.
I have 4 quadrants each with a ball valve going into a main manifold.
Q1 Closest to 0,0 is divided into two more zones for small parts. If the part is smaller then the smallest zone I just cover the balance with plastic sheeting and tape air gaps with packaging tape.

My idea is to have the multiple Fein vac's hooked into the manifold. Since I don't need any more vacuum when everything is sealed, I would not have the others kick in until I get a vacuum loss.

I do remember reading somewhere that if you put one vacuum in an air tight box and then use another to keep the box at a vacuum you can increase the vacuum beyond the capacity of just one vac. Kind of a parallel / series kind of deal with electricity I quess. My problems is more with loss do to air leaks after cutting through and breaking the seal, then total vacuum in inches of X.

Jim

[richards]

Jim,

In my system, I have one Fein vacuum hooked up to a 4-quadrant system - probably similar to yours. Each quadrant has a ball-value to enable/disable the quadrant.

Like you, I've masked off smaller areas with tape and sheeting. Sometimes it works and sometimes it doesn't.

What I've found is that the vacuum fails if there is a 'small' leak. By small, I mean 1-inch by 3/8-inch break-through (either caused by routing too deep or by having too much suction on too small an area). Using three vacuums, one Fein and two shopvacs, didn't give enough capacity to keep the parts in place.

Using better procedures helped. I cut all parts to a maximum depth of 0.65 inch (assuming .75 inch thickness for the material) and then ran a finish pass to leave at least 0.030 inch of material. Most of the time it worked.

When I have to cut entirely through the material, I use a vacuum mask that overlaps the cut by 1-inch on all sides, which means that small parts can still be a problem.

If I have a lot of small parts to cut, I usually turn to my 3/4-hp Gast vacuum or to one of the pumps where the vacuum is generated by a compressor. Using some weather-stripping material and a vacuum mask gives fairly good results. I've found that routing at least two passes works best. The first pass removes most of the material and the second pass makes a clean-up cut.

One trick that I use frequently is to spray a little adhesive on the vacuum mask when the parts are small or the temperatures low. (I learned that low temperatures and low humidity can cause a lot of grief - at least here in Utah where 20% humidity is rare.) Slowing the feed rate, taking lighter cuts or increasing the vacuum would probably all work equally effectively.

- Mike

[jthelen]

I looked on ShopBots website at the comparisons between
FEIN Turbo III $395.00
7.5hp 230v/single-phase power (Cascade) $4495.00

It said the Fein "Will hold 126CFM @ 7.3"HG 14 gallon capacity"
The Cascade Will hold 14" Hg @ 144 CFM.
What do these numbers mean? I know from experience that the Fein holds really well until you start leaking air. What does the extra 7HG and 15 CFM get you? Can you cut through parts and they will hold even with the air leaks. Or is this not enough information?

Can someone with a 7 plus HP vacuum system help me out or point me to some past posts?
Thanks

Jim Thelen

[ron brown]

I built a 6 zone vacuum system for my last table and used 2- $15 vacuum motors from surplus center. I also built check valves where one or both could be run at a time. It would have been easy to build a safety switch using the deflection of the vacuum plenum so the second pump would switch off and on automaticaly.

While a 1" X 3/8" break in the vacuum will cause part loss I expect the real reason is the path the air to keep that vacuum is much smaller than thhe hole itself. My grids were 3/8" X 1/4" and 1/4" X 3/16" on 2" centers. Anything larger than about 1/2 those cross sections would have lost holddown unless it was directly over a port.

Other features of the system I built was the absence of ball valves and extreemly short piping. My port covers, when not in use, eliminated vacuum losses. The large central plenum housing the two vacuum motors gave little or no loss to the central ports and two short runs of pipe kept the CFM loss to a minimum to the outside ports.

Bill Young had pictures of the thing posted somewhere. He even sent the link to me. I can't find it now... BUT, I seldom repeat the same project, I'll try and improve on the next one.

Ron

[richards]

I agree that there should be wide grids and large holes for the vacuum to work properly. Right now I'm out of the shop, but I believe that the 4-zone file from Shopbot is 1/2" wide x 3/8" deep on 1-1/2" or 2" centers (plus diagonal cuts).

With the Fein, and depending on the material that I'm cutting, I try to have a minimum part size of at least a 8"x10" if I cut all the way through the material. On smaller parts I leave tabs so that the parts never break completely free. Even with an 8" x 10" part, I always make two cuts. The first cut leaves about 0.10" of material to hold the parts together and the last cut either removes that 0.10" inch if I'm using a vacuum mask, or leaves a 0.03" sliver of material if I'm not using a vacuum mask. Results depend a great deal on the material being cut, the move speed and the cutter used. MDF and other relatively slick surfaces break vacuum easier than ply and other moderate to high friction materials.

It could be that I've misunderstood the theory of using a vacuum, but the way that I understand it is that if I have a nearly perfect vacuum i.e. 30 inches of mercury, then I should have 12-14 lbs of holding force per square inch. If the Fein produces aprox. 7 inches of mercury, I should have about 3 pounds of vacuum per square inch. I also understand that I should have at least 80-100 lbs of force holding a part down (to withstand the side cutting force of the router bit) which means that I should have a minimum surface of 30-35 square inches to enable that amount of hold down for the Fein. In practice, if I'm cutting ply and if I'm using a ply vacuum mask, I can cut 5"x7" parts (1/4 or 3/8 inch cutter). If I'm cutting MDF and if I'm using an MDF vacuum mask, I like to have a minimum of 80-100 square inches.

Bottom line. In my experience with the Fein, I don't allow any vacuum loss. (In reality there is always some loss due to dust and other debris trapped between the material being cut and the vacuum mask/platten.) The Fein is a great vacuum. It is well worth the price and it does a commendable job, but, I would never try to suck parts down through a piece of LDF (as is done with the large vacuums). With proper gasketing, masks or tabs, the Fein works well.

[dingwall]

Just a thought. Has anyone tried using a 1 hp dust collector blower as a source for vacuum for large areas?

[Brady Watson]

Sheldon,
In my experience, the ShopVac is a much better vacuum source than the dust collector. The DC has more CFM, but not nearly the same pull as the shopvac for material hold down.

-Brady

[waynec]

I've been reading posts on vac clamping using a shop vac. I need to ask a few questions.

I understand Brady's method best, and I think its what I want to go with. If I understand it correctly, you make a plenum, top it with spoilboard, put a layer of gasket sheet, and cut parts patterns in the gasket underneath where your parts will be cut. This allows the parts to be held down by vacuum applied thru the plenum.

My questions are;
1) is the sheet gasket stuff reuseable? That is, if I make a gasket on a spoilboard, can I then reuse this setup to make repetitions of the same cuts?
2) Do I have to make a plenum? My CNC table has the Shopbot 4 zone grid drilled in it. My idea is like this:

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I want to make a drilled spoilboard (instead of a plenum), put sheet gasket on top of that, cut that gasket to match my parts, and then place my material to be cut on top of that. The vacuum would pull thru holes in the CNC table, continue thru the part holes in the pallet/spoilboard, and hold my material. Is this right?

I might add a gasket to the bottom of the spoilboard to make a better seal with the CNC table.

3) Would a dedicated dust collector used for suction work better than a shop vac? That is, would a larger volume of air, at perhaps the same or less suction, work better than a shopvac or Fein? I'll be cutting adirondack chair parts from pine boards.

Thanks for the help all!

[gerald_d]

Wayne, your last sentence is the most important one: "I'll be cutting adirondack chair parts from pine boards." That puts the whole thing in perspective.....and immediately raises the questions; How flat/smooth are your pine boards? What size is the smallest part that you want to cut? How thick is the pine? How wide is the narrowest board that you are cutting the smallest part from? What is your envisaged cutter diameter and move speed? Up-spiral?

Many questions unfortunately, because you may be at the limit of what a shopvac can do. I think a "dust collector" is out of the question unless you have big parts, smooth/flat pine, multiple shallow cuts with small straight/down bit.

[richards]

When I cut lumber, instead of sheet goods, I usually use my GAST vacuum pump or a ventri pump and gaskets. The GAST pump or ventri pump both have much higher vacuum than the Fein shopvac. For narrow boards and small parts either the GAST or the ventri work better than the Fein.

My method is to make a jig that is either screwed to the spoilboard or held in place by the Fein vacuum and then use closed-cell foam tape to channel the air from the GAST or ventri.

You might want to browse some of the Shopbotter's web sites. Bill Palumbo has an excellent vacuum system that might be just the thing that you need.

[waynec]

Thanks for the quick replies!

I've had good success just brad nailing the boards to a fixed spoilboard. I just crawl on the table after the parts run and pry all the boards and parts loose.

But I have a new shop that will let me have space for both load and unload tables. So I want a pallet system. I thought it might be good to try vacuum clamping, but the pine boards are usually at least a little warped. So I think I'll just keep it simple, and make a pallet/spoilboard, and just brad the boards in place. I've gotten quite fast at it, and if I don't have to crawl on the table, it will be faster still.

I find that if I cut a very shallow final pass I can almost eliminate exit damage as the part is cut free. What little there is I can quickly sand off.

I'm always enticed by the idea of vacuum clamping, but I find it tough to justify the setup time for limited or one-off runs. Even with sheet good, I can brad a sheet or board down in seconds.

Thanks for the input!

Happy Thanksgiving. Gerald, you don't celebrate Thanksgiving in S. Africa, do you?

Wayne

[Brady Watson]

Wayne,
Go to the AllStar (http://www.allstaradhesives.com/) site and check out the pics on there. It will give you a better idea of how to hold down your parts. Vacuum hold-down, as you can see from this discussion, is a pretty broad topic. Using the AllStar stuff you can create purpose-build jigs with gasketing to use in conjunction with either a ShopVac or rotary-vane pump. There are advantages and disadvantages of both. For 90% of the things that I do, the Fein works ~ I have cut out thousands of parts as small as 5/8" X 1" and larger hardwood items as well. If you do not have an absolutely tight seal on the low cfm/hi vac pumps, it will not work. When using the hi-vac pumps gasketing and cleanliness become absolutely critical.

I assume that you have a shopvac of some sort. Gets some AllStar sheet gasket (spoilboard cover) and try it with the ShopVac 1st. Test it and see if it holds vacuum while cutting.

Somewhere on here I have posts and pics of the accessory plenum that I made that bolts to my spoilboard for use with a Fein.

-Brady

[gerald_d]

Hi Wayne - no, we don't have Thanksgiving here. We don't really eat turkey either - some of the "up-market" shops import them around Xmas only. These (http://www.info.gov.za/aboutsa/holidays.htm) are our holidays.

[mikejohn]

If Mike is screwing his jig down, why doesnt he by pass the vacuum and screw the pine board down?
.................Mike

[gerald_d]

Might it be that vacuum was the hold-down of choice before the days of cordless screwdrivers?

[richards]

Mike J.
Screwing the jig down means that I only have to use screws once and then the vacuum jig can handle the 200-400 parts with no further need to chew up the spoil board. That is the main reason that I use vacuum for small parts. If I'm only going to cut one or two pieces, screws would probably work, but needing to replace the spoil board every few pieces because the only practical places to insert screws have already been chewed up is frustrating.

[mikejohn]

Now I have an idea about this

I will try and put it together over the weekend.
Mainly for not so flat pieces of board.
.....................Mike

[mziegler]

Wayne, where are you locating the brads on the boards or sheet goods? Are you use drilling program or a first cutting pass or a old part as a template to accurately to place the brads? I use plastic nails in mine shop and they have some advantages over brads. The nails do not need to be removed if located in the part, you do not need to pry the boards off the spoil board and also the nails can be place in the tool paths. Mark

[jhicks]

New photos of the "Waffle iron" vac table base here at Wellhouse Woodworks. Fantastic with 2 separate vacs ( 5.5HP and 6.5HP)and 8 zones which we can manipulate for sizes from 1' x 4' to 5' x 10' and increments between.
Cut with 1/2" Ball nose leaving 3/4" top squares, shellaced 2 coats everywhere, drop in Allstar gasketing around zones, drop on TRUPAN and its holding parts or zone pucks like magic.
Simple and effective. Not sure why we waited so long but we're nowable to place, turn on the zones/vac, and run. fantastic!
No more fences, screws, tape or clamps.Eureka!

5375
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[harryball]

Simple and surprisingly effective. Each head nurses the 2" port directly. I'm going to be building some sound enclosures in the near future. A cardboard box cut the sound by about 1/2.



Robert
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[gerald_d]

Realise that those vacuum motors are designed for filtered air and that you shouldn't be dropping chunks into them. Maybe screw some mesh between them and the table - then you could pull big litter out from the top. We use bath plugs to seal the holes when they are exposed.

[harryball]

I use an MDF spoil board on top so the chambers stay sealed, but point taken. The original webbing is still in the head, it would stop very large items, over .25" from dropping in.

I also discovered there is a foam silencer in the head, thinking of removing them when I put the cabinet cover on. That should improve airflow once again. I'm still surprised at how well it works.

Robert

[baltic_birch]

The shop vac heads directly mounted is great!!

I'm still trying to figure out my hold down sytem before I buy my shopbot.

That looks like a great idea.

[harryball]

I completed the sound cabinets today. I completely removed the heads from the plastic housings and the foam. They don't look like shop vacs anymore. On the front of each sound cabinet is a switch for each motor inside. So I can choose to run any mix of quadrants.

I ran a file on a complete sheet of particle board with an upcut bit today without any holddowns other than the vacs running. There were four 7" diameter circles cut out at various places along with 5 panels about 11" x 10". All of the parts stayed in place. When finished cutting I could not remove the circular blanks or the 11x10 blanks from the table without turning off the vacs.

These are 4.5HP heads, as I mentioned I already had 2 so it made sense to me to just get a couple of more. I suppose I could go with the 6.5HP heads if I thought it would help... but I'm not sure how much better it could be with just shop vacs.

Robert

[patricktoomey]

Robert, do you have any pics or specs on the sound cabinets? I would like to see what you did there as this whole thing seems like a good idea. I have been waiting to get my new granite table top installed before switching to some industrial vacuum motors I got from Grainger. One thing that has been concerning me is the sound. I was going to run hoses to the new pumps and put them in a sound deadening cabinet of some sort but mounting them direct and then putting something around them may be better.

[digitalwoodshop]

Are there any over heating issues with mounting the motors in a sound enclosure? I like the idea of mounting the motors under the Shop Bot.

I am still building my business with Laser Engravers and Sublimation. Would love to be able to add a Shop Bot by this time next year.

Enjoy reading all this great info every chance I get.

[harryball]

I'll get photos and upload them. The heat build up has not been too bad, it does get hot but the boxes are large enough and have a side vent. I don't think it'll be any worse than how they were originally in the plastic housings.

I had a sheet of 3/4" cabinet ply that was warped on it today. Laying on the table at the 0,0 location the sheet was about 1/2" off the table, at 96,48 it was over an inch off the table. Not as bad as I've seen it, but basically a large potato chip. I figured I was out of luck and would have to flatten the sheet in storage a while. I was shocked when I pushed the sheet to the table and it held it in place! I ran my file and it did just fine.

You can still find me at the table with the vacs on trying to lift a part from the table or slide it... I'm just amazed it pulls that well through the MDF.

Robert

[david_beede]

Robert,
This seems like a great approach. I would love details on your sound attenuation. I'd like to try this with Fein heads. Do you by any chance have the specs on your shopvac heads? Was wondering how they compare to the Grainger replacement for the Fein vacs. which pull 107" water & 110 CFM. The 4.5 HP shopvacs I could find on line were 57" & 165 CFM
http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?ItemId=1611622037
How thick is your spoil board? And is it MDF or LDF or...?

And Patrick.... Granite table top! Yikes!
How much will that weigh and cost? I was toying with the ea of finding some sheet plastic or Corian or some such to solve the flat and level problem once and for all.
Thanks for all the great experience and research you are all sharing.
David