Vacuum Chucking

Andrew Hilton

 

... And so then there was a knock at the door.  It was the deliveryman with my vacuum pump.  I had never used a vacuum pump before in my work with the wood lathe but I was quite interested in the new possibilities it promised to offer.  So began my little journey with it.  I've described a few of the things I've done to and with it so far.

Go directly to the updated Rotary Adapter information here.

DVC00038.JPG (58898 bytes) Here's the vacuum pump.  It's a Gast 1/4 hp, 4.5 cfm, 220V, pump capable of drawing around 26" of mercury.  It came mounted to a stainless frame and with the inlet and outlet filters you see.  All I did was add an electrical switch and a 1/4" elbow to the inlet filter.  You can see the clear reinforced hose come from it.
DVC00037.JPG (69852 bytes) The hose then goes to a few fittings that you see here. It's positioned next to the lathe so it's easy to reach and read while working at the lathe.  I'll mount it on a board behind the lathe soon.  You can see the vacuum gauge I got from Grainger for around $7US.  Also there's a 1/4" water gate valve.  That's for adjusting the pressure.  I used this kind of valve because it takes a few turns to fully open or close it.  This gives a great deal of control in just how much vacuum I want to get. To slowly decrease the pressure, I simply let a small leak into the system at this valve.  This is how I mount and unmount turnings instead of starting/stopping the pump.
DVC00036.JPG (62084 bytes) From the fittings in the above picture, the tube goes to my homemade rotary fitting.  It's just a block of wood with a bearing (the dark ring is part of it) that has an NPT fitting in it.  The block of wood, on the other side which is butted up to the hollow spindle on the handwheel side.  The block of wood spins with the lathe but the bearing just spins and keeps the hose from wrapping around (at terrific speeds!).
DVC00035.JPG (70259 bytes) Here's a wider view.
DVC00039.JPG (62868 bytes) On the other side is where the threaded lamp tube (used for making/repairing lamps) comes through the spindle to the working end of the headstock.  I've used a tapered washer that fits both the tube on the inside and the Morse Taper #2 on the outside.  The lamp tube screw fits snug up to the washer and holds the whole thing together. I'll have to add a drawing of this part of the system soon..... and here it is! <grin>
DVC00034.JPG (68009 bytes) Here's a wider view from this angle.  You can also see a simple and small vacuum chuck I made.
DVC00041.JPG (66438 bytes) UPDATE

Here's what I'm using now instead of the through-spindle rotary adapter described above.  I simply replaced the factory handwheel with my own.  This stays on permanently now.  There's no tube running through the hollow spindle.  I got tired (yes, within just a few weeks) of taking that other rotary adapter on and off when I wanted to use the morse taper of the lathe.

Dvc00042_1.jpg (23080 bytes)

Here's a shot of the double sealed bearing.  I made the handwheel extra long for a reason.  You don't have to do that. You could just make it short.  I used hard maple like on everything else with this vacuum system project.  I also sealed the wood with polyurethane just like everything else so I won't get leaks through the pores of the wood.

Dvc00048_1.jpg (18660 bytes)

A closeup of the outboard side of the lathe headstock.  On the Jet Mini, it's a 3/4" x 16 tpi right hand thread (UPDATE:  It is a LEFT HAND THREAD. Thanks to Clem for pointing this out to me. He should win a prize for catching my goof but I can't think of what.  Any ideas?  Send them here and we'll see what we can do for Clem.).  I just found a nut like that and glued it into a recess in the maple block that I turned for this.

Dvc00043_1.jpg (25094 bytes)

Notice nothing interfering with the morse taper. Nothing to take out when I want to use it.

Dvc00045_1.jpg (25992 bytes)

I did have to make a longer knockout rod since I made the handwheel extra long.  Just used some 5/16" (I think) rod of appropriate length and turned a small ball of hard maple for the end.  Notice that the knockout rod can be actually used!  Why?.....

Dvc00046_1.jpg (25835 bytes)

Because there's nothing in the bearing hole to interfere with it!  Unlike the other rotary adapter described above, I don't have the hose fitting glued into it.  I have the hose fitting permanently attached to the hose and just put the fittings' threaded end into the bearing hole when I want to run vacuum.

Here's a closeup of the hose fitting.  Notice the little black rubber ring / gasket on the threads of the hose fitting?  That fits snuggly into and against the bearing and creates an air-tight fit.  When the vacuum is on, the hose is held nice and tightly in the bearing.

Dvc00047_1.jpg (22035 bytes)

Like that.  I just pop it off there when not using vacuum.  I can then use my knockout rod as usual.

Here's a drawing of this new rotary adapter that's permanently attached to the lathe now.....

  END UPDATE
DVC00052.JPG (65544 bytes) Here's the same chuck but without the rotary adapter in the spindle.  It's just a homemade screw-on wooden faceplate that I modified to work for vacuum work.  I just hollowed out the inside to reveal the hex nut.  I rounded the outter edges so it wouldn't mar the turnings used on it.  I also added some closed-cell foam to get a good seal.  This is about the minimum size of vacuum chuck and only certain things can be held on it.  The greater the surface area that the vacuum is acting on, the greater the hold (pressure exerted for a given level of vacuum).  It holds spheres and some eggs for sanding but not much cutting with the tools.
DVC00042.JPG (60359 bytes) Here's the backside of the large faceplate vacuum chuck.  It's just a hex nut (1" x 8 tpi in the case of my Jet Mini lathe) glued with a polyurethane glue into a recess of a maple board.  This arrangement works quite well and is strong.
DVC00043.JPG (56881 bytes) The front side.  Just a small hole is all that's needed.  What's not shown is the closed-cell foam that covers this face of the faceplate vacuum chuck.  Bowls or other turnings with continuous and even rims (not natural edged pieces) work well on this chuck.  It takes a bit of fiddling to get the piece on there just perfect though.
DVC00050.JPG (67076 bytes) Now, I'm starting to make what I call the "long neck vacuum chuck".  It's designed to reach down inside of a bowl or other turning in order to get a nice, round, continuous place to get a good seal.  Things like natural edged bowls for instance.  You need the long "neck" (the white PVC in the picture) to give you clearance so the rim of your turning doesn't hit the headstock or even the chucks' base.  So, I start out by measuring the PVC diameter.
DVC00049.JPG (65401 bytes) I then take one of my homemade screw-on wooden faceplates (with a hole in the middle of it) and cut a grove to match the PVC's diameter.
DVC00044.JPG (61796 bytes) There it is.  The faceplate is about 3/4" thick so I made the groove around 1/2" deep.  I tried to make it so it's a very snug fit for the PVC pipe to fit into. However, at the bottom of that groove, I made it a little wider than at the top (near the outside) of the groove. I did this so that it would give the glue a little more "bite" and surface area to hold onto the wood.
DVC00045.JPG (65165 bytes) About to be mated.  (The song "Together .... Forever ..." is going through my head right now. Yes, it's sick and twisted but then I've been smelling fumes most of the day!)
DVC00048.JPG (65875 bytes) Here's the glue I used. It's just a polyurethane. Brand doesn't make much difference.  I've found that polyurethane glues do well when bonding dissimilar materials such as metal / wood / plastic and so on.  You get foaming but it's not a problem in this case.
DVC00051.JPG (68674 bytes) Spread the glue in the groove.
DVC00046.JPG (59560 bytes) Pop the PVC neck in there.
DVC00047.JPG (61802 bytes) A view from the inside.
DVC00053.JPG (60261 bytes) I let that set up for a couple of hours and then go over the PVC / wood joint with more poly glue.
DVC00054.JPG (57859 bytes) Inside too.
DVC00072.JPG (61287 bytes) After overnight, it foams up and it's set.  Not pictured is the closed cell foam that I put on the PVC rim so it doesn't mar the woodturnings.  By the way, this chuck works VERY well for balls/spheres but they have to be sized just right so that they just barely slip inside the PVC.  Enough to get a good bit of suction on them but not enough that it gets sucked too far inside and you can't work on them ... or get them out!
DVC00071.JPG (61391 bytes) That's it! Well, not quite.  The last step with any vacuum chucks (or any of the wooden fixtures in the system for that matter) I make is to seal them.  Yes, wood is porous to some degree and I want to eliminate any leaks from the system.  So, I simply coat all of the wooden parts to the vacuum chucking components with a film building finish. I'm using just a few coats of a wiping urethane (thinned polyurethane).  It seals the wood so air won't escape from that direction.  Please Please Please do wait until the finish is really dry.  If not, you'll get some of that gooey finish sucked right into your vacuum pump and/or filters.  Nasty and could ruin your pump!

 

As I make more chucks, I'll add them here.

 

 

 

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3/24/07 10:33:36 AM ... Thanks for the article. Good details that I can understand. Thanks
12/28/07 7:21:18 PM ... Simply brilliant. Can't wait to try this myself.
2/16/09 3:38:42 PM ... Where did you get the nut? 3/4" 1TPI left handed thread? Thanks
2/16/09 3:39:13 PM ... Sorry I meant 3/4" 16 TPI left handed thread?
3/2/09 9:06:56 PM ... I got that 3/4" 16 tpi left handed thread nut from an old, dead lathe I had laying around. But, you can get one from other places .. example: Fastenal part #: 0175066
6/26/13 9:05:43 AM ... Hi Andrew, It looks to me like you made the adapter about 6 inches long. I was thinking of making one just long enough to hold the bearing and fit on the spindle (in order to avoid getting a longer knockout bar). Is there a benefit to the longer length? Thanks! Dan
6/30/13 7:21:31 PM ... No, there's no advantage to the longer length. You should be able to shorten things up by about 2" with no problem.
2/17/14 7:56:44 PM ... nice, thanks!
7/18/14 10:15:31 PM ... mpeFV9 Im thankful for the blog article.Thanks Again. Much obliged.

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