Vacuum Chuck questions

I use the chuck head part of that set, but I use a vacuum pump instead of the vacuum generator. (They both work well.) The Holdfast chuck head is very good. They also have a 3" diameter head here. You're correct about the diameter...a 6" chuck head won't hold anything smaller than about 6 1/2" in diameter.

You can also make your own chuck head with MDF, a short piece of PVC pipe, and some rubber o-ring or gasket material. I know Stu has made his own and posted pics here. I've got the parts to make some others for myself, but so far the 6" chuck head has handled everything I've needed. The few times I've had something smaller than that, I've dome up with other ways to finish the bottom of the piece.
 
Making vacuum bells is a very easy thing to do and a WHOLE lot cheaper than your reference.

I make mine out of PVC caps. Get a tap to match your lathe spindle thread. Hot glue a wood plug to fit inside the cap. Drill and tap though the cap and plug. Thread it on the headstock spindle and true up the edges of the cap. I taper the edge inward slightly and slightly round over the outside edge. You don't want the vacuum to leave a "ring."

Get some closed cell door/window insulation tape. 3/8" to 1/2" works well. Make sure the insulation tape is closed cell or it will leak air in. Cut a diagonal mating of the ends. Stick it on the edge of the cap. Make several of different sizes. Caps are cheap. The tap won't be but it is a one time purchase and will be handy again and again. I have a tap for the tail stock center as well.

Some folks use a coupler and turn an end plug to fit. That works too. To seal the plug in either application, run a bead of hot glue in the intersection of the plug and the PVC wall in the inside.
 
The vacuum adapter on my DVR looks like little more than a bearing that fits the hole in the headstock. They recommend a shop vac (a good one that has separate cooling - I use a Fein). Tiny pieces don't stick but a larger piece sticks fine to the piece of plywood and foam that I put on my faceplate.

With a good size piece (so there is plenty of area for air pressure/vacuum difference) a shop vac works great. For smaller pieces I have to dig out my vacuum pump to give enough suction to work. I have turned hunks of 2x4 as adapters between shop vac and the pipe I stuck in the bearing - to get the shop vac down to the pipe size, etc.

Total cost $25 for the "vacuum adapter" (aka sealed bearing) and almost no other cost.
 
Making the chucks is easy, but DON'T use MDF, that was my mistake, as it is as porous as a sieve :doh:I ended up having to soak, and I mean SOAK the entire piece of MDF with thin CA glue to get it to seal, what a pain. :(

Hardwood, or good plywood with a coating of poly would most likely work, I do like Carol's idea of the end caps, but the ones I've seen here the flat on the end cap is slightly domed, so that would be hard to use :huh:
 
I've made them with MDF and BB. Both types leaked like sieves but, an application of 1lb shellac under vacuum is sucked up right quick. And with all that air passing through it dries right quick too. ;)
 
If I understand it properly there is a hard line through the arbor hole & a connector of some kind that won't turn with the line & the chuck head what is it can it be built of off the shelf parts? Can someone please put up pictures of their shop built vacuum chuck with explanations. Also what is an inexpensive but good vacuum pump & where to purchase one?

Yes I want to build my own in Bart's above ground dungeon.
 
looong reply!

Bart, go to http://www.joewoodworker.com/veneering/vacuumchucking.htm.

That gets you to the heart of vacuum rotary adapters and chucks. Then poke around and discover how you can build the entire system.

I taught vacuum clamping in a woodworking class in the middle 90's, long before it became popular with woodworkers. I truly wish this site had been available then. It's got everything you need to know.

Lots of different ways to get a vacuum pump, but there are compromises whatever you choose. Most commonly available are the 220V rotary vane pumps from Surplus Center. 110v models used to be plentiful but not so much now. Avoid venturi models unless you have a really large capacity air compressor. Shop vacs have been used, but the motor has insufficient cooling to last long. Refrigerator vac pumps have been used, but usually the reason a refrigerator fails is the pump! My classes seemed to have tried them all. Bottom line was a rotary vane pump was the better choice from many standpoints. Relatively inexpensive, easily repaired.

Don't get wound up in either horsepower or CFM. Doesn't take much horsepower to turn a pump over. CFM is an issue for production shops where waiting a few extra seconds for the vacuum to be pulled is perceived to be an issue. Time is money, ya know!

Also don't get excited by how many inches of mercury the pump can draw. I have heard numbers bandied about that rival NASA vacuum applications! A used pump that will draw at least 24-25 inches of mercury will work just fine for a long time. If it is a rotary vane pump, when those numbers go down, simply get the repair kit and rebuild it.

Caveat: always filter the air going into the pump. The air comes from the chuck through the rotary adapter, into the pump, and exhausts to the atmosphere. Put the filter between the rotary adapter and the pump. It is exactly opposite of an air compressor. Sometimes it is hard to keep the ol' brain wrapped around that concept.

Also, with regard to tanks; for vacuum veneer press operations I can see their value. Not yet convinced for turning applications. Be happy to explain my thinking if anyone is interested.

Read Joe's site, and then if you have questions or comments, fire away. I'll be happy to share my experiences (and those of my students) with you. I have three pumps, plus the venturi (visual aid for the class).

Also understand that Joe's site is focused largely on veneering applications, so his pump systems are designed accordingly. Suggesting perhaps a bit of overkill for turning. ;) For the lathe I would design a much simpler and more inexpensive system.
 
I have a continuous duty vacuum pump from Joe Woodworker - works great for veneering, but is NOT good for vacuum hold-down - the dust around the shop gets into the vacuum line and plugs the filter that keeps the dust out of the pump. A real stinker to clean.

An intermittent pump might be okay, since the dust would accumulate in the vacuum tank, and may be easier to clean out (anything would be easier than the in-line filter on the continuous duty pump.)

If I were starting over I would get a venturi "pump." I was afraid of the high load on my compressor, but have later heard numbers that suggest it is quite efficient - much less compressor load than I expected, and no dust sucked into the pump or tank. The venturi systems can either be continuous (no tank) or intermittent (with vacuum tank)

On my lathe, I attached a piece of 3/4 inch ply to the faceplate, cut roughly round on the bandsaw, then refined on the lathe. I got some closed cell foam (no slip shelf liner) from Home Depot - provides an edge seal as well as closing any pores on the plywood. A hole in the center leads to the knock-out hole in my lathe headstock, and a bearing is put into the handle end of the headstock - outer diameter to fit the hole in the handle, inner diameter to fit a pipe with coupling to either the shop vac or vacuum pump. The sealed bearing is enough to prevent excessive leakage. The instructions with the bearing suggested a hole to "waste" part of the vacuum so it isn't pulled too hard on the faceplate; I plugged the hole.

As noted a cheap shop vac uses the airflow from the vacuum for cooling, and will burn out when used as a hold-down. Good shop vacs have separate cooling - I use Fein, but I hear Festool is the same. The shop vac works for larger pieces (say a 5 inch diameter bowl), but I get the vacuum pump for small pieces.
 
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