Universal Vacuum

[team08]

So let me get this straight... I can buy a vacuum pump, say 7.5hp, that will pull through my MDF spoilboard and hold down parts even when cutting through? This would be a perfect solution for me since I often cut 12"x60" UHMWPE sheets that are only 2mm thick or so. I double stick tape now but it is wasteful, messy, time consuming, and expensive over time. So I could in theory just lay this material on the MDF spoilboard, turn on the vacuum, and cut through and maintain hold-down? I was asking in the local forums since I want to see it in action but I guess there is no one around me with such a setup. Please advise as I dont need $5000+ wasted. Thanks!

[richards]

That's exactly right. Depending on your needs, you might be able to use a $300 Fein III vacuum to do the same job. I use two Fein III vacuums pulling through a spoil board for most of my work and a GAST 3/4-hp vacuum pump when I'm cutting small parts.

You'll want to search the forum before settling on any particular unit. What you're cutting and how you're cutting it will make a big difference. On my system, I leave a 'skin' about 0.03-inches thick. Others, using 15-hp and greater blowers can cut the same parts all the way through in one pass. There's a lot of information on this forum about vacuums, plenums, spoil boards, etc. that will help you understand how it all works.

[richards]

NOTE to Nancy: There was a question posted asking me to describe my spoil board. Is something wrong with the server? This post is in response to that question.


The support board is three layers of baltic birch laminated together with contact cement. Two layers of 1/2-inch thick material and one layer of 3/4-inch thick material. I cemented the two 1/2-inch layers of baltic birch together and used biscuits to align the common edge. The resulting 1-inch thick support board was bolted to the steel table frame using 3/8-inch carriage bolts that were sunk about 1/8-inch below the surface of the baltic birch. All holes were filled with Bondo and sanded smooth. Next, the top 3/4-inch layer of Baltic birch was laminated on top of the 1-inch thick bottom layer. (My machine is the 120-60 model, so I staggered the baltic birch to offset the seams between layers.) The baltic birch was sealed with three coats of polyurathane, top and bottom. I surfaced the baltic birch before top-coating it with polyurathane.

Four holes were cut in the support board for a four zone vacuum system. The holes are sized to fit $5.00 plastic shower drains from Home Depot. The plastic shower drains fit 2-inch white PVC pipe perfectly.

The spoil board was cut using Brady's design for a combined vacuum platen and spoil board. It is just one sheet of 3/4-inch MDF. The bottom side is divided into four zones with a vacuum grid in each zone. The grooves in the vacuum grid are about 1.5-inchs apart, 0.375 inches deep and were cut with a 1/2-inch cutter. I've used 3/8-inch wide, 1/16-inch thick ALLSTAR tape around each zone on the bottom of the spoil board. Then the board was flipped over and centered on the support boards, I used a Sharpie pen to mark a two-axis reference line on the support board to aid in lining up the spoil board without using pins or dowels or screws. Finally, I surfaced the spoil board by removing 0.030-inch of material. Because I had already surfaced the support boards, I could have taken off only 0.010-inch of material.

Because the spoil board is also the vacuum platen, my vacuum system requires the spoil board to function. When I cut the vacuum platen grid in the spoil board, I only used the four zone holes to hold the MDF to the support board. Although the MDF was held tight to the support board, the edges floated about 0.075 inch higher than the material directly over the vacuum holes.

My plan is to make various sizes of vacuum platen/spoil board as needed for different material sizes. Today, I shut off all but one zone, slapped down some scrap 1/4-inch thick melamine covered MDF and used my GAST pump/PVC puck vacuum system to cuts some plaques. The pucks have a single hole drilled through top to bottom so that the puck will hold itself to the something beneath and above it. The pucks have ALLSTAR gasket material top and bottom. The main vacuum system easily held the melamine material in place. The pucks tighly held themselves to the melamine and to the plaque material.

[team08]

Thanks for the reply. I understand most of the vacuum basics as you explained but I am a little weary of a system that pulls through MDF and holds the piece to that. Is the MDF smooth on top with no relief vacuum cuts? This would be ideal for me. And even if I cut through my material (I cannot onion skin my parts) it will still hold (my surface area is roughly 500 sq in)? Fein vacuums would be great and save a lot of money but I want to make sure whatever I choose works. Could I send someone some material to test for me? I would love to see this in action but if there is no one around me so be it. Thanks again.

[beacon14]

Sorry, Mike, I had asked for details about your spoilboard, then I remembered this post (http://www.talkshopbot.com/forum/show.cgi?tpc=27&post=32869#POST32869) so I deleted my message.

Thanks for the detailed info, though, that's real helpful - I'm still finalizing my own details even as I build the table.

[richards]

Greg,

My two Fein vacuums pull about 5-inchs of mercury, which translates to about 2.5 lbs per square inch of force holding the material to the spoil board. I like to have a minimum of 100-lbs of force holding my parts, preferably much more. You would have over 1,000-lbs pushing down on your part, which should work perfectly. However, be aware that the 'slipperyness' of the material can play a big part. Semi-rough material is held better than slick plastic. Neither you bio nor your web page gives any information of where you are located. I would be happy to run a test for you if Salt Lake City isn't too far away.

[gerald_d]

Mike, a broad formula of 100-lbs per part is good if those parts are "square-ish". If they were long narrow strips, and a bit flexible, then it is back to the drawing board. Greg's 2mm thick sheets are not going to need a lot of cutting force, but the shape, size, flexibility, friction of the final cut piece all play a big role in deciding how much vacuum, tabs and gasketing are going to be needed.

[mikejohn]

If the edges of the sheet are held in place by putting the sheet up against blocks,( or clamping), then this would take the whole of the lateral forces, the vacuum would then just be needed to hold things flat.
I guess this assumes tabbing.

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

[terry]

Greg,
MDF is porous. It is not air tight, so the vacuum pulls air right through the mdf. The more powerful the vacuum pump the more air it will pull through. As you lay your material on the mdf, the vacuum pump continues to try to pull air through the mdf, thus creating a vacuum under your peice. The peice is then held in place by the weight of the "air" or atmosqhere above the peice. How much weight, or hold down force is being applied to your peice is determined by the amount of vacuum being pulled, so a larger vacuum pump pulls more vaccum which means more atmosphereic pressure pushing down on the top of the peice. Others can and have provided more detail on the science of this on this forum. But the bottom line is that you can make this type of vacuum hold down system work for your material. Start with a Fein vacuum if you want. You may have to adjust cut speed and cutter diameter to lessen cutting forces on the sheet, or make other adjustments, but this beats your current method hands down, besides having use for other types of material. Go for it.
Hope this was helpful.
Terry

[terry]

Greg,
Sorry, forgot this point. Yes, the MDF is smooth on top. The groves that Mike is talking about are cut either in the support top of the table and then a peice of 1/2" mdf is place on top of the groves to make the hold down surface (most common), or the grooves are cut on the bottom side of the spoil board (which is a new thought for me but I can see has it's advantages) and then flipped over as Mike explains in his post above. Doing it Mikes way may be the easiest way to try out the system without major table modifacation.

Terry

[team08]

Thanks for the the replies! So basically if I have a vacuum that has enough CFM, it doesn't matter that there are gaps in the material (after cut through)? With my Gast, as soon as I have even a little hole or porosity, vacuum is lost (low CFM but high vacuum). But with high CFM, I can cut through, but vacuum wont be lost? Is this because the MDF is porous but also still restrictive so you dont lose total vacuum once cutting through?

I am in Mass. Guess I need to update the profile!

[richards]

I wish that I could take credit for the combined vacuum plenum/spoil board, since it is such a good idea, but the credit belongs to Brady.

The chief advantage to me is that I can have a vacuum plenum/spoil board that is sized for what I'm cutting. Usually I cut 97x49 sheet material, but often enough I cut 60x60 baltic birch, and occasionally, I cut small stuff where I only need one zone. Brady's solution makes it easy to shift from size to size. The 'grip' is slightly better than the 'standard' system of using a vacuum plenum under a surfaced spoil board. Perhaps the better performance is due to a sealed support board, Allstar gasketing tape around the plenum/spoil board, or something else, but it works better than I expected.

[jay_p]

One thing that I have learned here on the forum, is that there are a million ways of creating a vacuum holddown system and there is a new idea coming along every day. At some point you simply have to take the leap and try some type of setup, knowing full well that you may eventually decide to change it all around again, or maybe even scrap it.
I put together a Fein/pvc/four-zone/plenum/mdf bleeder type setup in December using what was a hybrid of ideas that I picked up here. It has worked great for some things and not so well for others, but it has changed the way I approach hold down.
I never run any screws into the bleeder any more for instance. I either vacuum the pieces down, or use another removable 1/2" mdf spoil board or pallet, or use double stick tape a la Brady.
I have also collected a pile of 1/4" melamine scrap that I use to close off unused sections of bleeder and to block pieces in.
Every day I get better and better at onion-skinning. It is easier now, because without all of those screw mushrooms, my bleeder surface stays much flatter and so my dinmensioning is more accurate.
I like Brady's new development though. Maybe I will change it all around again...

Jay

[team08]

I agree I need to take the leap and try, but my needs are the following:

-I CANNOT make gasket fixtures, my parts are all different.
-I NEED to cut through, no skinning whatsoever
-The material is thin UHMWPE with surface area for the part around 500 sq in cut out of a larger rectange of material

I understand all the reasons for skinning and gasketing, I just need to know if what I need is possible, and what the requirements are for vacuum.

[richards]

Greg,
Have you thought about using PODS? They can be located anywhere on the table easily and quickly. They can be used with a GAST type vacuum pump that would produce 25-inches of mercury. More than one pod can be used with each piece that you're cutting.

I've cut very little UHMWPE. It cuts like butter, but it's too slippery to be held with my Fein vacuum system.

[handh]

Were do you get the pods and what is a GAST type vacuum pump?

[gerald_d]

Many people make their own pods - they are very elementary.

These are ALL Gast Pumps:

http://www.gastmfg.com/productinfo.html

[richards]

As Gerald pointed out, you can make your own pods. I make mine from 1-inch thick PVC. If you prefer to buy them ready to use, Morris Dovey has them listed on his web site:
http://www.iedu.com/DeSoto/vacuum.html

[gerald_d]

High-Tech vacuum pods/pucks/clamps:
http://www.schmalz.de/anwendungen/vakuumaufspannsysteme/branchen/vct/uebersicht.html.en
http://www.dabtech.net/vacuum%20clamping%20system.htm
http://www.m-powertools.com/products/mini-mach/mini-mach.htm
http://www.vac-clamp.com/

[team08]

I have looked at this solution but there is no way I can use this with 2mm UHMWPE. It would flop all over the place. The material needs to be on a true flat surface, no gaskets or anything.

[gerald_d]

Greg, why can't you have pods the size and shape of your cut pieces? With thin gasketing to offer friction? It would help if you gave us an idea of typical sizes and shapes of the final parts...

[Brady Watson]

I just made a setup similar to what you are looking for 2 nights ago...One of my customers ran out of time and needed me to cut some parts for the mouse in Florida...

Here (http://www.bradywatson.com/VacStuff.htm) is how I did it.

-B

[gerald_d]

Hey Brady, you mention after this photo...
http://www.bradywatson.com/images/Vac6Detail.jpg
....that it was machined on a Alpha. Is this the current Alpha or the 5:1 geared version?

[team08]

I make custom snowboards so image starting with a 12"x60" (or thereabouts) sheet of UHMWPE. Then cut out a large tounge depresser from that sheet. This is the basic shape but it varies with each board. The material is very thin and flimsy so it really needs to lay perfectly flat and not have the edges flex or anything.

Here is a picture of of somone doing this with a template by hand
http://grafsnowboards.com/preparation_files/image001.jpg

[mziegler]

The main trouble with vacuum pods is that they need to be accurately position so that they are not in the cutter path. This can be major headache if running small parts, different size parts and cutting out many parts out of sheet goods. The April 2006 CabinetMaker magazine has an article about using laser projection system to position vacuum pods on a CNC machine. The laser project the outline of the parts on the CNC table surface so the operator know were place the pods. I was wondering is anyone using lasers to do this? What is the good and bad points? Thanks in advance, Mark

[mziegler]

The link to that article in CabinetMaker http://www.cabinetmakeronline.com/Articles/0604CMlaser2.htm

[mziegler]

A laser projection system also could be use for positioning clamps, screws, and brads. Mark

[gerald_d]

Greg, it sounds like your application is ideal for vacuum through a consumable "bleeder" board that you re-surface from time to time. I can't imagine a more ideal application - what's holding you back? :-)

Oh, and definitely no need for a 7.5HP pump, a single "Fein" will do. Downcut spiral bits will also make your life a lot easier.

[beacon14]

Another technique not mentioned yet (at least in this thread) is to leave a thin skin on the first pass, then finish up with a cut along the same path removing just the skin. The reduced forces on the part from such light cutting may help the vacuum keep the small parts from moving.
Also if you tape or otherwise secure the edges of the sheet that will also help keep the sheet from sliding.
I agree with Gerald that this should be fairly easily do-able.

[jenijo]

These fein vacuums that you are talking about, are they shop vacs? If so, how do you keep them from burning up the motor when it's pulling a vacuum?

[Brady Watson]

Yes. They have a seperate cooling motor from the vac motor. These are industrial grade vacuums, not homeowner grade like those you find in regular stores.

-B

[jenijo]

Thanks for the info. j

[mikek]

Jeffrey, this is a Gast type pump system. The pump is actually a Rietschle Thomas which is a little smaller and cheaper than most of the Gast pumps but pulls down to 25 inches of mercury. It is built from a kit of parts from Joe Woodworker.com


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