Material for vacuum table

[tlempicke]

What is a good material to use for building a vacuum table? I have a Gast vacuum pump that will probably run about a two foot by two foot table.What I want to do is dowel a piece of flat stock to my table and then route out the piece leaving islands that will support a thin piece of MDF. I went to the local office of Cadillac plastics and he quoted me $850 for a piece of phoenilic 3/4 of an inch thick by 2 foot square. (I think I interrupted his coffe break and made him mad!)

Has anybody tried this? I am thinking about aluminum if platic is too expensive, but this would be hard to machine.

[bruce_clark]

Tom,

I have been told that MDF is porus enough that it
will let air through it. At $10 a sheet, it would
be worth a try compared to phenolic board.

Bruce Clark
bwclark@centuryinter.net (mailto:bwclark@centuryinter.net)

[tlempicke]

Bruce

What I plan to do is use the pocket feature of Bob Cad to mill the surface of my table while leaving a series of islands. Then put a piece of MDF on top of that and my material to be held down on top of the MDF. Air passing through the MDF would hold the material in place and the surface of the MDF would be sacrificial.

I bought a set of fonts from one of our other Shop Botters and found out that I can do credible engraving in letters as small as 1/8 inch high. this is all building up to instrument panels to use in airplanes.

[bruce_clark]

Tom,

Sounds good, but I have done a little engraver's
plastic and it works pretty good. Though, what I
did was engrave the letters then cut the parts
out. This might be a better way, though I could
be wrong (and I have not seen the parts you are
trying to do). What I did was do all the
engraving on all the peices then change the bit
and cut the parts out (a cut out in the center
and then cut the entire part out). I just
held the plastic down (a 4' X 4' X .125" sheet)
with some padded clamps. Worked like a champ. I
had to do 10, and I do one each time I improve
the machine to see the differences (this plastic
is GREAT for showing machine improvements).

Bruce Clark
bwclark@centuryinter.net (mailto:bwclark@centuryinter.net)

[jimt]

Tom,

I've used melamine for the vacuum table very sucessfully. Outline the part with 1/4" thick closed cell foam weatherstrip from the local hardware. Create you "islands" on top of this by gluing down 1/8" plexiglass in various spots with either dbl sided tape or hot glue. then drill a 1/4" hole somewhere in the center of the pattern and push a piece of polyethelyene tubing up from the bottom and connect it to your vaccuum pump. Done! Change the tape and "islands" as required by the job. The melamine surface is leakproof to the vacuum (a critical part as most small pumps have very limited CFM when drawing enough vacuum to hold something in place. For additional grip, put some used sticky back sandpaper on the top surface of the plexiglass.

Jim

[Ron B]

All,

Three coats of epoxy will seal a surface to the 28" of Mercury vacuum. There are 'liquid ring' vacuum pumps that will supply 30+ CFm @ 25" Hg on 3HP.

Ron

[pclscl@netup.cl]

Hi All,

I am new with a PR96, trying it and very happy about the many different possibilities offered.

With respect to vacuum holding, take a look into CARTER Products Co. web site : www.carterproducts.com
they offer an interesting but somewhat expensive solution to this problem, but their market is among H.D. and expensive CNC units. I agree with Ron about sealing properties of epoxy that makes good grade MDF an excellent alternative.

As for Vac. Pump, look for a DELTA Model Size EC25 (Prod. Code U43E-C025M-2) from NASH Engineering, Norwalk, CT.
This unit will give you :
@15"Hg. vac.:18 CFM / @28"Hg. vac.:8 CFM
w/3500 RPM 1-1/2HP TEFC motor (included )
Price Aprox. $1,000,00
This is a Liquid Ring Vac. Pump, which are very tolerant to solid contaminants such as sawdust.

[Ron B]

Bill,

The vacuum pump I mentioned was ~$350 from Surplus Center, new, less motor. A filter should placed before all vacuum pumps.

Check dairy supplys for used ones. I have been told they are available for >$500 for a large one.

Ron

[pclscl@netup.cl]

Ron,
Thanks for the tip on S.C. vac. pump. I am back in the woods down here (Chile, SA) so I am not aware of many, many good offerings as you mention. By the way, how can I get in touch with Surplus Center?.
We have been selling large (2.000/22.000 CFM) vac pumps for our Pulp & Paper and Mining Industries for over 30 years so we have lost the commercial feeling for the small end of the scale models. Anyhow, what will really be of utmost importance will be your leak-factor, because, if you have a good air-tight fit, any vac. pump, including small laboratory type, should be able to hold a good vacuum.
Thanks and regards,

Bill

[swims]

For my vacuum table I made a sandwich using two sheets of 1/2" MDO. After planing the surfaces of my 2X4 table to accept a full 4X8 sheet, I screwed the first piece down. I flipped the second piece upside down, laid it on the other sheet (my new table surface), and machined 3 large 'h' shaped grooves into it with a half round bit. These three grooves would eventually be the interior plumbing for the table.

I made three separate grooves because I knew that I wanted three separate zones, and the 'h' shape fit my requirements for where I would need future taps into the vacuum lines.

Next, I glued 1/8" closed cell rubber gaskets around the perimeter of each 'h' using contact cement. I added more strips of the rubber to help support the second sheet so that when I flipped it over there wouldn't be noticeable valleys in the final table surface.

Mentally 'flipping' the 'h' pattern, I then drilled holes through the bottom sheet of MDO at the point where the top most part of each of the 'h' shapes would be. From underneath, I epoxied copper tubing which I then connected to gas line valves. I sweated the three together in series, along with a relief valve, which was added into the line so that parts could be released from the vacuum without turning the pump off. All of this was connected to a 3/4 hp Gast vacuum pump which I had picked up from e-bay. After the top piece was flipped over and screwed down, I tapped into the interior 'h' plumbing lines(grooves) by drilling with a small router bit through the top.

When I finally scar up the top surface to where it becomes unserviceable, I will just discard it, get another piece of MDO, and rout in the pattern with the previous file and be on my way.

I should add that in order to get that tight vacuum, I cut a gasket out of the sheet rubber that runs the perimeter of whatever part I happen to be routing, while leaving a suitable open area underneath the part.

Adding in a $50 pump rebuild kit, I ended up with any easily configurable 3 zone vacuum table that can hold parts down so tightly they cannot be pried up with bare hands.

[hwcorian@gateway.nwt]

I used a sheet of 3/4" MCP(particle board with a layer of vinyl on both sides about $28.00) for the bottom layer then took 3/4" thick plywood strips 1" wide and made a grid on top of the mcp. I created three seperate zones with the plywood strips so I could controll 1/3, 2/3, or the whole table at once. On top of the 3/4" plwood strip gridwork i layed a sheet of 1/2" LDF(Low Density Fiberboard ) I then sealed the edges with laminate and contact cement. This LDf works great some times too great you have to close off the unused protions of the table or toomuch vacuum will be lost.

[rick reynolds]

TO SHOPBOTS VACUUM TABLE SEALED 100% i will sell you a cut 4 zone full covered system with white thermo foil in 12mil or 30 mil works better than anything you can make price 12.50 sq ft 12 mil 30 mil 20.00 sq ft ready to hook up call Rick 732 244 8758 for info