The Art of Reverse Chucking (Jam, Vacuum, etc)

[Glen Blanchard]

As a new turner, I have purchased many instructional DVDs. Most of these demonstrate how to reverse a bowl or hollow form and place it against a secondary chuck designed for this purpose. I seldom am able to get the piece to turn true after doing this even after I spend some time tweaking it. I ran across a reverse chucking alignment adapter today in The Woodturner's Catalog. This has a morse taper on one end and allows attaching a chuck to the other, and is designed for use with vacuum systems. The premise is that you move the chuck from the headstock (bowl or HF still within its jaws) to the tailstock and then engage the vacuum. The claim is that the piece will be precisely centered. The primary chuck is then removed, and the tailstock moved out of the way so that the bottom of the piece can be accessed. It is supposed to then run perfectly true on the secondary chuck. Pretty nifty if it works. So here are the questions I ask the group:



If you have used one of these reverse chucking alignment adapters, how well do they work? Is the piece dead-on against the vacuum chuck? This whole concept makes me want to get into vacuum chucking.
Other than tapping and slightly tweaking how a bowl or HF sits in a jam chuck to get it to run true, do you have any secrets on how to get it so precisely centered? Any gadgets, jigs or gizmos to make the job easy?

[Jim Burr]

2) You nailed it...tap tap tap. Then it's Sanding 101.
1) A vaccum chuck is bomb!! Unobstructed access to the face or base assuming either side is free of defect.

[Steve Schlumpf]

Glen - I find that if I leave the divot caused by the tailstock live center when first forming the tenon - recentering is usually no problem.

[Bob Bergstrom]

If you used the tail stock to turn the tenon, you can use the indent from it to center the bowl on a jam chuck. The chuck reverse mandrel works about the same. No mater what you use the uniformity of the interior of the bowl will affect the centering. Get it close and few will ever notice.

[Glen Blanchard]

Yeah, I leave the indent from the tailstock center, so that indeed helps - but in only two planes. Placing the primary chuck in the tailstock (it would seem) would align in all 3 planes. I was hoping for a near perfect, quick, down-and-dirty method. Perhaps something that thus far has alluded me.

[Eric Gourieux]

Glen,
the tailstock chuck adapter is great and will give you the best alignment of all IMHO. i use it with the vac system and it works great.

[Mark Levitski]

Glen, as others have implied, it's never exactly centered. So accept it and you will be more at ease. "Happiness is accepting what is." Zen of Turning. I have a friend who is a machinist and makes aircraft parts in various metals. This is not that. Get it close and blend it in with what you had before it was reversed.

Mark

[Fred Belknap]

Glen I have used the tail stock adapter from Penn State and it worked great. When I got a larger lathe with 8.25" thread on the spindle it wouldn't work. I had the Oneway live center so I got an adapter to screw the chucks on it and it works. Sometimes I get a little misaligned. I have a vacuum but it doesn't work with everything I turn so I use whatever I can get to work. Doughnut chuck, cole jaws, jam chuck, vacuum, whatever works. I don't think any one is perfect.

[Scott Conners]

If you have a through-bored spindle, run a tight fit drill bit down it and put a fresh center mark on the back of the tenon before removing the piece from the chuck to reverse. Works good when I need to remove the original tailstock mark for some reason.

[Rick Markham]

I have to agree with the others, Fred especially. I generally use whatever method is going to work the best. I don't have a vacuum set up (yet) but I do use the reverse morse taper adapter with the donut chuck (when I have to). I don't think there is a one best method. You do have to just go with what inaccuracy occurs, anytime you remove a piece from a scroll chuck there is going to be error created (regardless of method.) You just go with it and blend it with what you have. For hollowforms I've been using my Rubber Chucky reverse chucky, nearly exclusively.

[robert baccus]

The rubber chucky no doubt works but it is a copy of an old handmade chuck. about 2 bucks. try a length of 1/2" ID galv. pipe with a padded block on the end. Fit perfect in most chucks(inside jaws) to drive with and tailstock with a smallish tip>

[Robert Henrickson]

If the piece has gone out of true while turning -- such as turning a greenwood bowl -- centering on a vacuum chuck may be a bit problematic. Even dry wood can run out of true when internal stresses are released by turning (e.g., I found the rim of a 1" x 12" plate developed a 1/8" wobble while still chucked). Using the center indent as a guide is easiest, but it can only be a guide. Adjustments may be needed. Absolute precision isn't needed. As was pointed this is not machining parts for aircraft.

[Bernie Weishapl]

I agree and like the accuracy of using a tailstock adapter for your chuck.

[Pat Scott]

I have the tailstock adapter from Craft Supplies. I thought it would be the answer for using a vacuum chuck. Alas, it's not perfect. I have found that you really need to tighten it into the chuck (use a wrench), because for whatever reason it wants to start coming loose. I'll bring up a bowl to the vacuum, release the jaws and slide the chuck/adapter/tailstock away, and then notice the adapter is a little loose. Tough to perfectly center something when there is slop. Using a wrench helps. I think the accuracy of the adapter is about the same as using the divot made my the tailstock.

The adapter really helps when you forget to mark the center with the tailstock! A lot of times you have to remove more off the bottom of a bowl than planned, so you remove the tailstock and get rid of the excess. If I forget to bring the tailstock back in place to mark the center, that's when the adapter saves the day. I keep striving for perfection, but I've accepted that it's not always possible. Like everyone else has said, blend it and nobody will know.

[Michael Mills]

I don’t have a vacuum so I have never tried the tailstock adapter.
If you don’t leave a dimple from the tailstock make one of these. Professional ones are sold for about $18 for centering faceplates. I guess am lucky that the threads on my faceplate are the same size as the threads on my chucks. Will miracles never cease?:D

Before removing your chuck and reversing, drop into your chuck insert/opening and give a light tap to set the center dimple.

[Jeffrey J Smith]

I've been fighting this same issue since moving up to a larger lathe. The vacuum system works well, but centering with the reverse adapter was really hit or miss - mostly miss. Finally, after a round of frustrating attempts to get a decent centering job, I checked the reverse adapter and found it to be out of round (not centered well on the morse taper. I moved up to the oneway adapter since I'm already using a oneway revolving center and it helped. Also found that, at times, in my haste, I hadn't been locking down the tailstock before bringing the quill up to the vacuum chuck.

Now I take a little more time with my setup and get better results. Still checking with the center though, and accepting a little runout as inevitable.

As a footnote, I've noticed that with the new lathe there are significantly fewer leaks in the system. The pump will draw maximum or very near maximum vacuum on nearly every piece. With a 5" chuck on a larger open bowl you can actually see some pieces, depending on the form and the wood grain distort as the vacumm draws down if I don't bleed off a little. That was also causing some of my issues.

[Faust M. Ruggiero]

Jeffery,
That bleed you mention also helps cool the vacuum. Many vacuum pumps, especially the Gast 1/4 hp jobs need some fresh air to avoid overheating and having the overload protection shut down the pump....with bad results. I never fully close my bleeder.
I too use an adapter on the tail stock. It is helpful because the piece moves as the vacuum pulls it into the softness of the foam on my vacuum chuck, Not much, but enough to make a difference. However, if I am second turning a bowl and the tenon has become oblong, even the adapter and chuck method won't help. Someone said it best. Tap, tap, tap until it is the best you can get it. A good sanding job should take care of the rest.
faust

[Prashun Patel]

I have a cheap PSI reverse adapter. I love it. You can thread a chuck or faceplate on it, so it's good for reverse turning or remounting for hollowing.

[Thomas Canfield]

I have been using a loose jam chuck and rubber shelf liner to remove the tenon for most work lately. I make a MDF jam with either threads for the drive or tenon to fit chuck and then have a rounded edge that is about 1/3 to 1/2 the bowl diameter. A dimple is left in the tenon before doing the final turning and that in the live center almost always allows the bowl (or hollow form) to run true enough to remove the tenon. I do finish most of the bottom ahead of this, and any small alignment can usually then be rounded out in the sanding. I have recently bought the adapter for the live center to help when I do want to use my donut chuck for full bottom access. This has worked on 19"+ diameter.

[Don Doyle]

Robert,

I am the owner of Rubber Chucky Products, LLC

Yes, it is true that there are other reverse tooling aids. But I would like to relay some of the unique differences in the Reverse Chucky

The cone is molded from a durable urethane rubber. It doesn't slip, like a wood cone can and thus it doesn't burn your workpiece. The added gripping power of the urethane allows for less lateral pressure to be applied thus minimizing the chance of cracking a thin walled vessel.

It has a precision machined 6061 Aluminum threaded arbor with a MT2 taper and a threaded cone. Inside the cone is a flange nut that ensures that the cone will run true.

It comes with threaded drives (three or four depending upon the model) so that you don't have to configure something for the end of the arbor.

It also has a 1/4"X1" hole in the end so that various items (on mandrels) such as sanding disks, buffing pads etc. can be added.

There are many items on the market today that can be "homemade" and it is great that there are people who can and prefer to make their own. But, for the other woodturner's who wish to spend their time turning instead of making tools there are manufacturer's who provide such items.

Thank you,

Don Doyle
Rubber Chucky Products, LLC