My Simple CNC Vacuum Table

[jteneyck]

Not much enthusiasm here for CNC stuff, but I'll kill a few electrons anyway to show the few who do have an interest with the vacuum table prototype I made.  



It's 20 x 30 inches, and made for cheap plywood.  The grid pattern is 1 x 1", 3/16" deep.  The foam tape is just 1/4 x 1/4" weather stripping.  The hole is the port for my Fein shopvac.  It's amazing how much holding force this thing generates.  I absolutely cannot move a piece of stock that covers the top.   That might give those doing router, carving, etc work an idea on how they might hold their projects for unfettered access.  

The gasket is what seals the workpiece to the table.  For smaller work pieces, you install a gasket such that the workpiece covers the gasketed area.  



This 10 x 10" piece also is held so tightly that I can't move it.  My Fein vacuum generates about 3 psi of pressure, which means 300 lbs of force on that 10 x 10" area.  No wonder I can't move it.  



There is a size, however, where the surface area is so small that the holding force won't be enough to resist the cutting forces of the CNC bit.  For those parts, I'll have to use my prior methods of clamps or tape and CA glue.  I'm going to use this for awhile to see how well it fits my needs.  If it works as well as I hope, I'll make one, or two or three that sit side by side, to cover the entire top of my CNC.  

John

[FrankAtl]

I've thought about doing something like this for my CNC but haven't got around to it yet. Let us know how well you like it after using it for a while.

[EightFingers]

I like that, it would be great for non-through cuts. Clamping is the most important thing in cnc IMO

[BrentDH]

Very interesting.  A vacuum hold down would be so convenient and you have implemented one for minimal cost.

Do you think it is hard on the vacuum to essentially plug it up for an extended period of time.  This is not a criticism because I genuinely don't know if it matters.

[jteneyck]

Very interesting.  A vacuum hold down would be so convenient and you have implemented one for minimal cost.

Do you think it is hard on the vacuum to essentially plug it up for an extended period of time.  This is not a criticism because I genuinely don't know if it matters.

I wouldn't use a regular shopvac, but the Fein Turbos and some others known as extractors don't need the air being extracted to cool the motor.  They have some other mechanism to do that.  So you can run them for hours or days even deadheaded without killing the motor.  Also, motor load goes way down when no air is being moved, so the watts being drawn and, therefore, heat, is lower.  

I would prefer to use one of my vacuum pumps to do this, but with what I've built so far, including some smaller prototypes, they don't pull the level of vacuum that the Fein does.  That suggests there's too much leakage for their lower cfm capability to handle.  Rockler and others sell little vacuum hold down pucks that use a vacuum pump, so it does work if the leakage is small.  And AirWeights makes a 16 x 16" table that can be ganged together that uses a 3 cfm vacuum pump.  The common denominator is the bases are plastic/aluminum.  I need to build a small table out of plastic and test it again to see if I can get it to work.  If I still get too much leakage, then it must be through the seals (weatherstripping).  I'll figure it out.  

The ideal table would be aluminum or Delrin, but the cost is really high for either.  One option I'm thinking of trying is AZEK like board.  A sheet of that is maybe only 2X a sheet of Baltic birch plywood.  

John

[fixtureman]

I started out with 2 fein vacs on my 4X8 table and foun that that was all I needed

[jteneyck]

I made a small vacuum table out of 1/2" Delrin using the same 1" grid system, but this time so I could hook it up to one of my vacuum pumps.  It worked great.  Link  I don't how many db's it has, but it's really quiet compared to the Fein.  You have to listen carefully in the video to hear it until I moved the camera down close to it.  The area is about 32 sq inches.  At say 19" of Hg on the gage, that's about 9.3 psi, so over 300 lbs on that area.  That's 3X what the Fein does, so for smaller parts the vacuum pump clearly provides more holding force.  In this next little video, I cut the area down to 12 sq inches, and you can see that it mighht be approaching the minimum size where the vacuum will prevent the bit from moving the workpiece, although it's still about 100 lbs of holding force.  Another Link  Of course, it will depend upon what bit you use, how deep and fast you run it, etc.  

Note, I used the first vacuum table with the Fein vac to hold the plastic down for milling.  I cut the 3/16" deep grid pattern in one pass at 80 ipm.  The Fein held it w/o issue.  

So now the question is how large of a plastic table the vacuum pump will support.  The plastic doesn't leak, so it gets down to how effective the seal is and the leakage through the workpiece itself.  MDF, for example, is very porous, while solid wood typically is not.  This pump has a capacity of around 5 cfm, IIRC.  I have a larger one that I could use, or add, if needed.  Both are Gast rotary vane pumps, which are continuous duty, oilless pumps.    

My preference is to use the vacuum pump because it's quieter and draws a little less power, but mostly because it's quieter.  Now to see if I can find some Delrin or similar plastic for less than a king's ransom.  

John

[jteneyck]

I started out with 2 fein vacs on my 4X8 table and foun that that was all I needed

That's good to know.  What do you do to prevent cutting into the table?   


John

[fixtureman]

That's good to know.  What do you do to prevent cutting into the table?   


John

I use Trupan as my spoil board and shut the zones down when the parts on that zone are done cutting