Vacuum Clamping

Filled under: Fabrication

Date posted: March 4, 2010

Overview: Vacuum clamping is using atmospheric pressure to hold down material for machining. The material to be machined is placed on a vacuum clamp containing special neoprene vacuum tape and a hookup for air removal. The vacuum pump removes most of the air between the material and the clamp (the white slab of HDPE in the picture above) then atmospheric pressure firmly presses the material and clamp together.

The Pictures:  

vacuum_clamping_pump

 The vacuum pump.

 

Picture 328

Up close of the pump head with to top-plate removed showing the reed valve.

 The vacuum system is mounted on a slab of plywood for somewhat easy transport.

 

vacuum_clamping_side

A side shot shot showing the pump startup capacitor and solenoid switch.

 

http://www.joewoodworker.com/veneering/EVS/wiring.htm

http://www.joewoodworker.com/veneering/EVS/wiring.htm

Here is the wire diagram. The vacuum controller activates the mac valve and pump when a predetermined low pressure is detected.

Set up and ready for the vacuum.

 

The vacuum gauge indicates -20 inHG

inHG * .4912 = PSI

PSI = 9.824

The area inside the black gasket is 2.5″ X 2.5″ = 6.25 sq in

6.25 sq. in. * 9.824 PSI = 61.4 lbs of downward force

My complete CNC setup.

 

For the first cut an outline of the symbol for radiation is going to be machined. As you can see in Mach3 everything zeroed and the feed rates are set. It time to make the cut.

Success! The clamp performed great.

    The Parts:

  • Clamp: A flat, smooth, and nonporous surface such as HDPE (high density polyurethane) (HDPE is sometimes used in kitchen cutting boards.)
  • Gasket: The space creator between the clamp and the material. The gasket I use is closed cell foam PVC 1/16″ thick and 3/8″ wide which is specially manufactured for vacuum clamping.
  • Vacuum pump: The pump I use was found on eBay for $65 + S/H. Currently the pump gives -20 inHG with a good rebuild the pump should do -24/25 inHG.
  • MAC valve: The valve changes the path of the air from the tanks to open space when the pump is turned off. This takes pressure off the pump so when it won’t struggle to start up when needed.
  • Filter: Keeps the inside of the pump clean of debris. Needed in such a dusty environment.
  • Pressure switch: This turns on the pump when pressure drops to a preset level.
  • Check valve: You don’t want to lose pressure do you?
  • General fittings: A handful of brass fittings.
  • Reservoir tanks: Two solid foam core schedule 80 PVC piping creates great reservoirs to hold extra vacuum pressure. Without these tanks the pump would need to be continuously active.
  • Startup tank: A little tank so when the pump turns on it does not fight against a vacuum to begin rotation.
  • Electrical: Switches, wiring, and a cool red indicator light.

All the parts can be found at http://www.veneersupplies.com. There you can find extensive information on similar vacuum systems as well as a gallery containing dozens of home built systems like mine but presented much more attractively. The free plans and guide.

Advantages: Several key advantages of vacuum clamping versus mechanical clamping are having machining access to the full surface and reduced time in swapping out cut items with fresh materials. With the absence of mechanical clamps the whole surface area of the material is accessible by the router bit which reduces waste due to the needed area for mechanical clamps. In the production mind set, when tolerances are tight resetting mechanical clamps becomes tedious and the chance of the material becoming cracked or marred presents itself. It is very speedy to release vacuum pressure, remove the finished part, add new material, press go, and start the process over again. This makes for high volume production a breeze.

Limitations: There are a few limitation to a vacuum clamp system. One of which is that you can’t cut out profiles or drill through holes. Performing those type operations require huge industrial vacuums which are incredibly expensive. An observation is when the bit places downward pressure on the material the gasket compresses which sometimes creates low spots which is noticeable when machining acrylic. The problem can be rectified by placing shims between the clamp and the material to prevent compression.

Other Uses: The clamps are great to use when sanding parts by power sanders or using a hand router to machine the material. A popular usage of vacuum systems is gluing veneer.

Conclusion: I am pleased with the outcome of the vacuum clamping system. It really makes machining precut plexglass quite easy.