More progress!

Carol Reed

In Memoriam
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Coolidge, AZ
I love simple, eloquent solutions.

So I was designing a vacuum hold down table for the CNC. Actually there will be two of them. I am working on the vertical one. I got some vacuum ball valves from MP Power. Then came the plumbing. The table is HDPE plastic. Thought about routing a depression between vacuum pods and screwing on a boss. My experience with keeping bosses from leaking is not stellar. So I found a nylon tee with hose barbs. But the ball valve didn't fit. Needed a bushing. Enter a short length of 1/2" clear tubing. Press fit. Pretty snug. Should not leak. Eloquent!

I love it when a plan comes together, even on the fly.

Now to rout a counter bore on the back to make the vacuum ball valve flush with the front surface. Then drill and tap with 1/2" pipe tap. Cut some foam rubber washers out on the laser and screw in the fittings. Add hose lengths and done. Then on to the off/on ball valve for each zone and into a manifold and on to the vacuum pump.

Vacuum tee.jpg

More pictures soon.
 
Vacuum clamping works extremely well - if you follow the law of physics! Joe's PODZ are made of HDPE which is a spendy plastic, especially in 3/4" thickness. I had an almost full sheet left over from my router jig making days that I am using for the CNC. The point being, the material has to be impervious. Air moves through wood and wood products at various rates, meaning an air leak in the vacuum clamp. Not good. Good place to use plastic.

FWIW, I created the syllabus and taught classes on vacuum clamping back in the days I was teaching woodworking. Long before Joe Woodworker! My students did try sealing wood like MDF with varied success. It has to be a really good seal! The tape that creates the vacuum space must be closed cell. I used to be able to buy closed cell door and window seal foam PSA tape. Lately I could not find packages labeled as such so I got a roll from Joe. The tubing has to be of sufficient wall thickness so as not to collapse. I also got that from Joe as his price was very fair and I had an order going.

If you use the ball valves your substrate has to be be at least 3/4" thick to accommodate the length of the valve. If you made doubled sided pods, the surface you are sticking the pod on must also me impervious. This is much more problematic. And the material you are trying to hold must not leak air too bad. Closed cell wood works best. Red oak is the worst!

There you are, the short course in vacuum clamping. Vacuum BAG clamping is another ball game not to be confused with pod clamping.

There is more to know about applying vacuum and intentionally breaking vacuum and vacuum pumps in general. Holler if you really want to know.
 
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