[CNCRob]

Over the past few months I have been working on a new vacuum table to hold some of my work in place. I have been through a lot of trial and error and have come a long way, but still have a long way to go. I have been reading just about everything I could find about vacuum systems and homemade vacuum tables. So I thought I would start a new thread to share some ideals and gain ideals from others. I am going to go through the photos that I have taken of my table so far and post a few of them and my experiences I have had been through so far on my quest to make a vacuum table. Feel free to weight in and share any ideals you may have. Also if you have a homemade vacuum system please share it with us, I would love to see how others tackle some of the challenges in making a vacuum system.

[kdoney]

I'd be interested. I've made a couple. One worked but it is just some pvc connected to particleboard with plumbing fixtures. All on or all off.

[Zippi]

I'm working on a vac-table, suction area will be about 36 sq in, it will be made from a 1" thick slab of 6061, ~5" x ~15". I'm planning to use some 1/4" EPDM foam cord for the seal, and will be dealing with non-porous surfaces.

One of the "unknowns" for me is determining the depth of the channel that the EPDM cord will sit in. If I remember right, it will compress 25% at ~10 PSI. The cord's diameter tolerance isn't great, so just using a 75% of .250" slot for the seal may not work. I'll test the channel depth on a piece of scrap before I mill the "big slab".

I built a venturi vac (thread in this forum), and am building a second one for a "how to" for this forum (got pictures of construction this time)- I'll finish that up when I get around to it...

I bought a vac-clamp (from www.vac-clamp.com). My design is losely based on the vac-clamp product, in aluminum. No grid structure for resizing of the seal as in the vac-clamp, I'll be dealing with the same size plate every time.

I'll gate the air to the venturi vac with a solenoid-actuated valve.

I've seen pressure switches, but haven't yet looked for economical "vacuum switches", something to tell me when the vacuum level is appropriate (a "yes" when the piece is properly sucked down). Initial thought is to take a vacuum gauge, rip off the front of it, and wire in an optical sensor pair to read the needle position. It'd be cheap, and somewhat adjustable, too!

[ger21]

I used this switch when I built mine. I managed to find a different source, and got it for about $15, but I don't remember where. http://www.joewoodworker.com/catalog...products_id=58

[2muchstuff]

Square D makes vacuum switches. Like pressure switches on an air compressor but in reverse.

[Zippi]

Thanks, Guys!

I had a "duh" moment- how else would one know to shut off a vacuum?

I checked the 1" alu slab, very true.

The 1" alu slab has a brushed finish, which I think will be advantageous as a vac-table. I'll cut "veins" into the table top within the gasketed area, I suppose you could call the brushed finish "capillaries".

No new work on this table as yet...

Thanks,
Paul

[Cold Fusion]

Any pictures?

[Zippi]

No pics as yet... I picked up an Asco 4-way valve (120v AC) and a Whitman vacuum switch off Ebay, arrived the other day. I had to loosen the switch and move it a hair to get the switch to actuate on a vacuum. I need to test the coil on the valve, but I'll probably be driving it with a Sharp S101S02 solid state relay (good for 1.5A at 125v AC, the solenoid is only 17 watts). I wonder how these SSR's will handle this solenoid...

[Ed_R]

I think vacuum tables are the way to go. I just don't know enough about them to build one yet.

[CNCRob]

Im glad to see all the interest, maybe together we can come up with some pretty good ideals.
I have some pics I will try to post when I get the image size changed.

[Geof]

I am in the process of outfitting a large machine with a vacuum table. Actually what I will be doing is 'tiling' a 5' by 10' surface with eighteen separate vacuum surfaces each 19" by 19". So far I have not progressed any further than a model of the vacuum tiles shown upside down in the picture. The four corner holes match up with an existing 4" by 4" array of holes tapped in the machine table and the tile will be bolted down with an O-ring gasket around the perimeter so the machine table forms the bottom of the vacuum cavity. Two indents can be seen where the perimeter wall loops in and this is where venturi vacuum generators will be fitted. Each tile will have its own controlled air supply. The aim is to install these tiles on the table, face and machine the top surface grooves for gaskets with full vacuum applied so that in use the surface is as true as possible and mark each tile with its location. It will then be possible to remove the tiles for non-vacuum work and replace them in the same location and go back to the same accuracy. My goal is flat to plus/minus 0.002" over the whole surface for engraving on large areas of thin material.

[ALpmc]

I'm normally a reader and not a poster but I do have a little experience with home made vacuum tables that I don't mind sharing. I'm not exactly sure where I saw the original design that mine is fashioned from but it seems to work really well! It's made from 1 inch 6061. It's base is 6" x 3.5". It's working surface is 5" x 3.5". It has 9 horizontal (Y) channels and 9 Vertical (X) channels. Each channel is 1/8 x 1/8 with chamfered edges. The gasket material is 1/8 x 5/32 leaving 1/32 above table level. There is a single 1/8 hole in the center of the table that provides vacuum to all channels. I don't have any details about the vacuum pressures. I just use a small vac/compressor without any problems. I use it for small engraving jobs or when I need to fly cut several pieces of stock when I work on multiple projects of the same piece.

This link will show you a page with one Quicktime movie at the top showing my first design in action. Click on the photo and see a page showing 8 short Quicktime movies of how I made the vacuum table. Click Here

[Cold Fusion]

What is the max depth of cut you can take with that table? I'm trying to get a feel for how much force you can put on these in relation to the surface area.

[Geof]

What is the max depth of cut you can take with that table? I'm trying to get a feel for how much force you can put on these in relation to the surface area.

It depends on how much vacuum you can pull. One atmosphere of pressure at sea level is 14.7 psi so if you can pull a perfect vacuum your work is held down by 14.7 lbs for every square inch or 2117 lbs for every square foot.

A perfect vacuum is not possible; good vacuum pumps with no leaks in your system can come very close so you can get a clamping force of over 14 lbs per square inch. Everything goes down from here; venturi vacuum generators using compressed air might get you 12 lbs per square inch, Roots blower type pumps will get to 5-3/4 or so and a regular vacuum cleaner might get to 2 lbs per square inch, maybe more.

All of the above was for a more or less leak free system or very small leaks. If you have porous material you have large leaks and the vacuum you get depends very much on how fast your pump can remove the air that has leaked through. In this case a regular vacuum cleaner may be the fairly good because it can move a large (ish) air volume and keep ahead of significant leaks. It is possible to get venturi vacuum generators that can move a lot of volume and still get to a clamping effect of 5 lbs per square inch or maybe more. But you will need an air compressor the size of a small car if you are working with large areas so this is not really practical. Proper vacuum pumps if they are large enough can keep ahead of leaks of course but then you are looking at big dollars. Roots blowers can handle fairly large volumes of leakage and still get to the 5 lbs per square inch region but they are also expensive.

[Cold Fusion]

I've got a welch vacuum pump capable of 10cfm and it will pull 29.5HG, or as close as is practical to a perfect vacuum. I've got an 11"x9" table in the mail. I'm hoping I'll be able to do profiling with 1/4" endmills at 15ipm with a .08" doc.

[CNCRob]

Here are some photos of the table itself. There is nothing really special about it, its just 2 pieces of 3/4" birch plywood bolted together with some vacuum seal between to hold in the vacuum. I modeled it after a few tables I seen on here and my table top on my CNC at work.

[CNCRob]

The way the table works is the vacuum comes in throught an opening one the bottom piece then follows the channels(also in the bottom piece). It then has holes in the top piece that allow the vacuum to flow through. On the top piece I have a grid of 1 3/8" squares that I can run vacuum seal between to mask off an area for a form. Then I cover the other exposed holes leaving the ones under the form open. I also have several inserts in the top piece were I can just bolt down forms with 1/4" bolts and screw the piece to be machined down to the form and not use the vacuum at all. I am currently in the process of sealing the top and bottom pieces to help hold in vacuum, make it more durable, and also so it won't stain as easily. I will try to post some photos when it is finished.

[ger21]

Rob, I'm guessing that part of the problem your having is trying to get a perfect seal over such a large area. The venturi vacuum system is not very tolerant of leaks. When I ever get around to building one, I was thinking of using a few valves to break the table into seperate, smaller zones that would be easier to manage. Especially with larger parts, where it might be difficult to get an initial seal. Looks good, though. Very well done.

[CNCRob]

Thanks Gerry,
I think building seperate vacuum zones is the way to go, I didn't even think about it untill a couple of days after I finished cutting mine. If I ever make another one I think I will make it with 2 seperate zones. I may just make a new bottom piece for mine with two zones, I should still be able to use the same top piece. I think I have mine fairly good enough to hold down most of the things I will be cutting. I screwed a vacuum gage into some of the holes on top, and I am getting about 10 - 12 Hg( or at least I think it is Hg). At work on my old pump I used to get about 8 - 15 Hg. Then they bought a new one and im getting bout 24-27. When I first started I was planning on using a regular shop vac, like I seen many others use. I built a large test setup to try it out, and the test pieces would not budge. Then after I build the real thing I couldn't get it to hold well enough. I tried a couple different shop vacs but still no luck. Thats when I decided to build a pump like on joewoodworker.com. Your right you need a near perfect seal to get enought vacuum. One of the ideals in my original plan was to use LDF spoil boards and cut large pieces of plywood, etc. I now know that is pretty much out of the question unless I find a more powerfull vacuum source. I had been in contact with a local industrial supply and they had several small industrial pumps for sale for $400 each. They seemed to be in fairly good condiction, but they are all 440 volts. The guy spoke of another pump that he may be about to get and sell me. That one is 220 volts, but I have yet to see it and have't herd from him in over a week. I have also read of alot of people using Fein shop type vacs. But about 50% of the people that have them say they have enough vacuum to hold plywood through a spoil board and about 50% say they don't. So im still kinda sceptical. And that would be alot of money to pay for something that may not work. What kind of pumps are the rest of you guys using.

[ger21]

Our router at work uses a vacuum pods, with a good sized pump. We tried to set up a spoilboard using LDF, but it didn't work very well. I talked to someone I know the other day that has a router with twin 5x5 tables, with spoilboards. Each table has it's own 25HP pump and each pump is bigger than your router. Jmo, but I don't think the spoilbard method would work too well. I could be wrong, though.

If you can't get it to work, I'd go with 3 or 4 zones. I was also thinking of making some double sided pods that you could just stick anywhere you want. You could make a couple different sizes, and use the push in quick disconnect fitttings to swap them out quickly. Just some ideas.