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JeffKranz
07-17-2009, 11:19 AM
Hello,

I just come into a boat load of Corian and other solid surface countertop material. I would like to cut shapes out of this material for some craft projects but most of them will not have holes in the area to clamp it to the table. I have tried to use double stick tape but some times it works and some times it lets go.

I could overlay this design in my CAD software and it will show me which ones to use and which ones will be outside the cutter path. I can then create cutterpaths based on what I want to cut - slap on the corian, turn on the vacuum, and hit the go button.

Here is my thoughts - an aluminum plate with a bunch of CNC cut o-ring grooves where I can add O-rings where needed and the center will have some type of SAE pipe plug on the others where I don't need them. Before I start out I was hoping to get opinions if this will work. There will be a series of gun-drilled holes to connect the vacuum path at the bottom.

Size of the plate will be 36" x 15” Each of these O-rings will be 1 1/2 or 2” haven’t decided on the size yet.

Here is an idea of the overall plate

http://i422.photobucket.com/albums/pp304/woodzy9370/vacuum.jpg

Here is a close-up of each o-ring groove

http://i422.photobucket.com/albums/pp304/woodzy9370/vacuum1.jpg

The next picture I have shaded an area where I think should be lower (.015) then the surrounding surface so you can build an vacuum chamber.

http://i422.photobucket.com/albums/pp304/woodzy9370/vacuum2.jpg

Any idea on how much force let say each 2" o-ring will hold it from moving? I have a vacuum pump that is a commercial one and should be me to around 28" of mercury. Any tips or suggestions would be greatly appreciated. One more thing - I have no idea on compression of o-rings so not sure on how much compression I should design into the o-ring groove. Would thicker O-rings be better?

Thanks,

Jeff

Jim Shaper
07-17-2009, 01:36 PM
Plastics guys often superglue the part to the table. A swift whack will break the bond and solvent cleans the residue.

Silicone is another option, but the cure time would be a drag.

Fasttrack
07-17-2009, 02:54 PM
Thicker O-rings are not neccessarily better. General rule of thumb for ASA vacuum flanges is as follows:

Use the thinnest section O-ring as possible - preferably less than .125"
O-ring groove width should be 1.35 times the actual O-ring section width
O-ring groove depth should be about 80-85% the actual O-ring section width

For a ~2" ID O-ring, about 30 lbs would be a realistic estimate for holding force. That would be about a 10 psi vacuum. This should be relatively easy to achieve. With appropriate pump and proper connections, you could concievably get to about 10 microns, but I don't think that is realistic for a workshop setting. If you were lucky, I would expect about 100 torr, or about 13 psi vacuum.

<edit> I suspect 28" Hg of vacuum is an over-estimation; that would be about 50 torr. Possible but unlikely given all the connections and contaminates. Remember the moisture in the system - i.e. from coolant - will gas off more quickly as the pressure drops, hurting your ability to pump down to the limit of the pump.

Yes you should undercut the area by about .015 or .02 like you suggested. This will allow a greater surface area to be held at vacuum and, thus, greater holding power.

Commerical vacuum plates are actually pretty clever. You could probably make a much more flexible plate in the "commercial" fashion with a CNC machine. They are basically a grid where the depth of the cut and width of the cut is designed to incorporate o-ring stock. You can buy square or round section viton and buna-n stock by the foot. This way you could outline the entire shape of your part and achieve better holding force.

see here: http://www.2linc.com/Vac_Vise_workholding.htm

Someone posted a better link on this forum. I couldn't find it though. That one should at least give you an idea of what I meant.

Greg Q
07-18-2009, 10:45 AM
http://www.taunton.com/finewoodworking/ToolGuide/ToolGuideProduct.aspx?id=30644

If the link doesn't work search "V4 vacuum clamp". It's an Australian product that does what you want. You could copy it in a larger size for your project.

A friend has a pair of these and they do a great job.

Also, if you are routing Corian have you tried some carpet underlay on your bench? This is the same stuff they sell as router mats and toolbox liners, only a tenth the price. I find a square yd of this pretty much grips anything.

Greg

Dragons_fire
07-18-2009, 11:43 AM
http://www.taunton.com/finewoodworking/ToolGuide/ToolGuideProduct.aspx?id=30644

If the link doesn't work search "V4 vacuum clamp". It's an Australian product that does what you want. You could copy it in a larger size for your project.

A friend has a pair of these and they do a great job.

Greg

Lee Valley tools had one of these on display the last time i was there. they had a chunk of wood sucked to it and there was no way i could move it... i even thought about ti for routing aluminum, but then figured it would get covered in swarf and cutting fluid and never be able to seal again!!