Vacuum tables for wood routers

[KSky]

I built a vacuum table for my CNC wood router and for the most part it works really well. It's just powered with a old blower from a 1980's computer (really!). It's basically a box with a bunch of holes in the top and various cutouts to hold standard size shapes. (Like a 7x7 square, 10x10 square) and so on, the vacuum just has to hold the part down, not necessarily keep it from moving side to side. I have some Mach3 macros and solid state relays to turn it all on and off so I only clamp when the spindle is on.

Anyway, on to my question. I finally got around to hooking a vacuum gauge to my blower and I get about 6" of vacuum. My shop vac can pull 8", and if I hook them together in series I can get 12" or so.

I'd like to build/buy a better blower but I have no idea where to start. I don't have (or want to spend) 5K for big commercial unit. Any idea's where to look?

[Geof]

How much are you willing to spend, 1/2k, 1/4k?

Blowers will never give you a lot of vacuum although regenerative blowers with big motors can be fairly good. They are also expensive. And very noisy.

But if you could pick up a clapped out compressor you could make your own:

http://www.cnczone.com/forums/work_f...ompressor.html

You will occasionally find just the compressor unit for sale below $100 and to run it as a vacuum pump you do not need a large motor. On my conversion I left the original motor in place but I am sure it would work with a much smaller motor, maybe even as small as 1/2 hp. After all acting as a vacuum pump it is only pumping against a maximum back pressure of 14.7psi as opposed to 125psi working as a compressor.

[ger21]

A lot of Shopbot users use these.
ShopBot Vacuum Motors

[JerryBurks]

Don't know your wallet but they have some interesting stuff:

Industrial Surplus at a fraction of the original cost

e.g. item 200089

I found a pretty good no-lubrication 2-cylinder 500 watts vacuum pump at a local industrial surplus shop for $50 or so. It pulls 25" vacuum(IIRC) but the flow is limited that means for a hold-down table you must control the leakage.

[HelicopterJohn]

Hi KSky,

Possibly another option may be to make individual vacuum fixture plates.

I have a Shopbot 48 X 96 PRT CNC Router and I drilled 1/4 inch holes in the table surface on 3 inch centers that are offset .125 in both the X and Y direction. This allows me to easily locate fixtures on the table for different operations. To align the fixture plates I just drop a couple of 1/4 inch bolts in the appropriate location on both the X and Y Axis and slide the fixture to the corner intersection. The fixture plates have several recessed holes around the parameter and I use drywall screws to hold it in position during the machining operation. If the holes get damaged for some reason I can easily change the X/Y locations in my CAD/CAM and move the fixture to a new location on the table surface. A larger plate could also be machined with several vacuum intake ports. Then you would just hook up your vacuum hose to the desired port on the Vacuum Fixture or design a valve system to change them via a push button etc.

When I program my CAD/CAM program I pick a location on the table where the fixture will be located.

I use a small GAST Vacuum Pump and make my fixtures from Plexiglas. I surface the plexiglas first and then cut slots for the vacuum and foam gasket material slot. Also, I cut an vacuum inlet port down into the plexiglas near one corner of the fixture. The outer slot is where the gasket material is inserted for sealing purposes. Then I cross drill a 3/8 inch hole from the edge of the fixture into the vacuum inlet port. This is where I connect the 3/8 inch hose from my Gast Vacuum pump. According to the gauge on the vacuum pump I am pulling around 26" of vacuum which has worked fine the holding plexiglas plates for engraving my LED Edge Lit Signs. I currently have a couple of fixtures I use. One is 11 X 13 and the other is 11 X 28.

This might???? be an alternative or something to consider for a future project.

I use Gerry's MACH3 2010 Screen Set and have the Gast Vacuum Pump and Dust collector hooked up via solid state relays that are turned on and off with GCode i.e. M7/M8 on and M9 off, or manually with the M7/M8 Buttons on the ScreenSet via my PMDX-126 Breakout Board.

I have enclosed a few pictures for your amusement. The little squares on Fixture Alignment Pins picture are locations where I intend to engrave reference X/Y locations, with my CAD/CAM system, into the table surface on 1 foot centers to make fixture alignment easy.

Just something that may be of interest.

John

[KSky]

That's pretty darn close to what I came up with for the holding fixtures. I cut 5/8 pockets every 1.5" and drilled a 1/4 hole into the vacuum chamber.

I use 1/4 low density boards to make the outside fixture board and then a piece of 1/8 inch below the part with the specific holes that match what shape I am cutting. Part of my issue is the volume of air in my vacuum chamber below the table so I am not sure that one of those smaller pumps would work, take too long. Maybe I could run both my fast vac and then a GAST one to get the vacuum up really high.

As you can see, I am still in the gear phase of wood routing. (Isn't that how it goes, you spend months thinking about it, years building it, and when you are done, you think, hmm, gears would be a really cool thing to cut with this...)

Not sure if you can see, but the middle picture shows the waste board. I cut all the way through the 12mm plywood and only left the faintest trace of the cutter. I'm accurate to the thickness of a sheet of paper.