Here’s a design that will run off an air compressor (so one of our air lines?)
and has a foot pedal to turn the vacuum on and off.
Doesn’t really say how easy to scale (his examples are only 6" x 12")
or how one would get around the problem of cutting through the work piece to cut a part free.
http://www.joewoodworker.com/veneering/vacuumclamping.htm
Parts as a kit (2 sub-kits, actually) seem to be about $300.
John2pt0
Tim,
One way to clamp down the vacuum clamp would be to put holes all the way through the clamp, and place the clamp on an impermeable bed.
If it was going to sit on MDF, the area of MDF in question would need to be sealed, but that would just involve a coat or two of finish.
John2pt0
Silly question:. If we're putting holes into the board, would it be just as effective to put clamps through the holes? Either cheap bar clamps, or much more expensive clamps made to go into holes. The holes would need to be about 3/4".
We could make the fixture with a sealed bottom (so we don’t need to seal the spoilboard) and hold down tabs off to the side. We may be able to create a bracket that reaches across the spoil board and grips the dead zone before the CNC mechanism.
I’ll look at it tonight.
John that is really awesome, I love how it uses the air compressor which already has a line to it right there next to the CNC. The foot petal seems like an interesting thought, We would want to carefully consider where we would place it.
So John is this your official proposal? 
Andrew:
Sorry I was unclear.
The holes go through the vacuum clamp, not the spoil board.
The idea is that the vacuum holds the workpiece to the clamp (through the hole in the top of the clamp) & the clamp to the spoil board through the holes is the bottom of the clamp.
John2pt0
Yes, as a vacuum clamp controller, I think it’s worth considering.
John2pt0
Maybe the pedal could be on a long enough line to be movable.
Brad
One challenge I see no matter what hold-down mechanism is used: how do we size the mechanism to the project?
Are all project boards required to be sized in (say) 2’ x 2’ increments, to match the (proposed) eight vacuum hold downs that cover the 5’ x 8’ bed?
How do we close off the unneeded area of the vacuum clamp? Eight valves (one for each 2’ x 2’ clamp)?
And another: are the eight clamps all of a piece, or eight separate pieces, to be used or stacked out of the way when the project is too small?
And this doesn’t approach another problem: what happens to the holding power (and the vacuum clamp itself)
when you cut through the project board (and into the clamp board - oops!) to separate the project from the project material?
John2pt0
John2pt0
Damned autocomplete!
Damned autocomplete!
John2pt0
John2pt0 ;^)
Good points.
I was thinking of a sheet of thin plastic film that was trimmed to block the vacuum around the part. It would then be thrown away after the job. You could use garbage bag material, just need to block off the exposed vacuum holes.
Wonder if a spoil board on the top of the vacuum box with holes could be created?
Might be fun to work on over the holidays. I should be much more available after this week.
No, I understand. So now we have a board with holes in it, which means that clamps like this would work:
http://images.toolbank.com/images/extralarge/BAH4201000.JPG
Basically you’d disassemble the clamp, push the bar through the hole, then reassemble.
Something like this:
http://jayscustomcreations.com/wp-content/uploads/2015/07/pulk-clamps-7.jpg
It’s a simpler approach, and one that won’t loose suction as parts are cut out.
Oh, and since the first objection to clamps is like to be clearance, this is probably about a 1/2" above the material, which should be plenty.
Good thought!
I like the concept, but I wonder what percent of users would be willing
to crawl around under the table to install the clamps & secure their project.
And those who wouldn’t, would end up nailing the project to the nice table top…
Also, any protrusion above the project is going to limit the Z height/thickness of the project material.
One now has to account for [stickout + Rapid Safe Z] as before [+ clamp height],
since one will want to set the Rapid Safe Z above the clamp height.
Maybe (If there is such a thing) a low-profile holdfast would (sorry) work. Except…hammer blows to set/release…still, with a thick enough top…
Just my 2¢.
John2pt0
Also, I stumbled upon two solutions for the “cutting through the vacuum clamp spoil board” problem.
1.) Don’t!
Oh, all right, in a little more detail: instead of securing the project with tabs and cutting all the way through the project material,
leave an onion skin. This would work for two sided projects, too.
2.) Cover the vacuum clamp with it’s own spoil board, made of “ultralight” MDF. It’s ultralight because it uses less glue in the manufacture.
This makes it more porous to air, and, thus, the vacuum pressure of the clamp, letting one secure one’s project to this spoil board.
When one cuts through the project board, scarring the spoil board won’t damage the actual vacuum clamp.
And one can replace the spoil board as needed.
John2pt0
Option 2 sounds like a winner
Hey, long term… something similar to this. http://lenzkesusa.com/ToolFiles/SideClamps.htm The neat thing out this company is you can request a sample set of the clamps, and try them before you buy them. Seeing as the Hive does have a business address… Just don’t show the metal guys the full catalog eh?
Coy discovered that the large cnc's top piece of spoilboard was actually never glued down. Not only was it never glued down it was flipped over and we are using the second side of it( maybe this predates anyone having a surfacing bit). It is currently held down with only brad nails... I believe this opens up many options for us on replacing the spoilboard or even better maybe even integrating something to clamp onto right into the spoilboard(which could possibly be vacuum board or clamps).
I think before we rush into replacing the spoiloard even in it's current state that we consider our options on the many possibilities that are available!
If the spoil board has been used on both sides, let’s replace it first, then decide how to install clamps or vacuum setups.
Home Depot has mdf as a 4’ x 8’ x .75" for $31 (approx.) (At .75" thick, it should minimize any nailing into the bed board.)
That’s even inside the Warden budget limits.
John2pt0
Although it kind of echos an earlier post, a problem with vacuum clamps or metal clamps is: who will maintain them?
Who will replace/repair them?
What will people use if there aren’t enough available for their project?
Nails or screws with an occasional resurfacing and even more occasional replacement of the mdf
seems like a more cost effective, more easily maintained approach.
Just my 2¢.
John2pt0