Custom Vacuum Fixture

[EricSchimel]

Hey all, I'm working on making a custom vacuum fixture for a repeating HDPE job I cut all the time. Right now I use the universal vac/bleeder boared setup and I just onion skin everything. It works, but if I can through cut all the HDPE I can save a bunch of hand work.

I'm going to make some vacuum fixtures just like this:

https://store.shopbottools.com/produ...ant=6937750785

I get how they work, but the only thing I'm not totally clear on is how that little vacuum hose is actually fixtured into the HDPE board...

Are you folks using some kind of threaded screw in fitting for that little hose, or something like a Shark Bite adapter? I can't seem to find any images or drawings online... Any help would be appreciated!

[Gary Campbell]

Eric..
You will need a hole in the edge that goes into the fixture far enough to reach a deep spot in the plenum. Tap a 1/4 or 1/8 NPT thread at the edge. Then use a one touch or barbed fitting that fits your tube

[EricSchimel]

Ah that makes sense. I couldn't tell from any of the pictures if people were tapping fittings in, or shoving the hose in there and sealing it somehow. Thanks Gary!

[knight_toolworks]

as you know hdpe likes to take off so it may not stay put not sure really hard to say till you try it.

[Keith Larrett]

You can get a lot of the stuff you need at Veneer Supplies:

http://www.veneersupplies.com/catego...cuum__Clamping

The pipe tap also.

http://www.veneersupplies.com/produc...or-18-NPT.html

[tlempicke]

Also you might want to check Aircraft Spruce and Specialties. They use a ton of different vacuum fixtures to lay up aircraft parts.
For gasket material I have used http://allstaradhesives.com/home They have made a study of the whole thing and their stuff works quite well

[bill_l]

Not sure if this would be appropriate for your application but here is a jig I use to build guitar bodies. I have an eight zone vacuum tabletop that is driven with two Fein Turbo II's. The jig is simply a piece of MDF covered in laminate and then machined to what you see in the photo. The gasket material that you see on the jig is also used under the jig when mounting it on the table. In this way all the vacuum is isolated to the center hole of the jig. When I direct all the vacuum from both Feins to the jig I can't pull the blank off the jig for "love nor money".

Bill

[EricSchimel]

Bill sounds like we have nearly the same setup, I've got 8 zones too. Your jig would actually work very well for what I'm trying to do... The main reason I'm trying to go with a vacuum pump is noise. Ive got 4 lighthouse motors that run my table and they work well, but they are loud. With a little vacuum pump I think I can not only make my job easier, but a heck of a lot quieter too.

Keith, thanks so much for that link!

[jTr]

" With a little vacuum pump I think I can not only make my job easier, but a heck of a lot quieter too."

One more interjection regarding a vac pump - be certain it is an oil-free unit. I picked one up from HF that uses oil- took a while to realize what was going on, but the darn thing fogged my shop with oil vapor it emits as it runs...Ugh!

jeff

[Burkhardt]

I use custom made pods all the time. Usually from 3/4" plywood or solid wood scrap (must have no or tight knots and no cracks). I found MDF way too porous for a single low volume pump.
For 3d and vcarve I fly-cut the pod surface, not required for pure 2-d profiles. After that I scribe the outline of the parts with a very shallow tool path and a small end mill and stick the gasket on (McMaster https://www.mcmaster.com/#93675K16, 60 feet for $5). It is highly compressible but will recover for multiple use. Then drill through at 2 or 3 places to connect to the vac plenum.

When I am done I fly-cut the pod again to remove the gasket and scribe trace and re-use the pod material.

I have several refurbished oil-less GAST or Thomson pumps (1/3 or 1/4 hp). They are available on eBay from several sellers for about $150.

Nowadays I use a few of the t-slots of my extrusion table to get the vacuum to the pods and don't need hoses anymore. But when I do I just stick the the hose/tubing (typically 3.8" OD) into a tight fitting drilled hole. The vacuum (and friction) holds it in place and the leakage is negligible.

I find a vacuum reservoir with ball valve almost mandatory (I use about 5 gal) to get the initial suck-down effect and compress the gasket to seal properly. Another important thing is a good vacuum gage to check if your setup leaks. I do not have a vacuum switch to turn off the machine when a part moves or is cut through but that would be a good safety feature to avoid a fire. I may add that sometimes.