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Longworth Chuck Question

Pete Staehling

Pete Staehling

Joined
Dec 16, 2019
Messages
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Location
Tallahassee, FL
I am thinking of making a Longworth chuck and wonder if it would be a terrible idea to use a threaded wood block instead of a faceplate. This would be on a 1-1/4"/8 TPI spindle and the threads would be cut with a Beale tap. I'd harden them with CA or epoxy and recut them. The chuck would be only for light duty clean up of bowl and platter bottoms, but it would see long term use.
 
If I was going to go through all the precise machining to make a Longworth chuck, I would certainly consider spending a little more and put it on a permanent face plate. I just finished making a donut chuck and I got a faceplate from Highland Hardware for $20.00.

Something else to consider, if you make a wood faceplate, due to the weight of the Longworth chuck, it may unscrew itself off the lathe if you have power assisted braking. You'll need to consider a set screw.
 
You can also use a faceplate ring or faceplate tenon screwed to the back of your Longworth chuck to quickly fit onto an adjustable chuck. You could also turn a tenon or recess on a glue block and glue and screw the glue block onto the back of the Longworth chuck. A metal ring or metal tenon will provide an accurate mounting each time. A wood tenon or wood recess tend to change shape over time and expand and contract from humidity levels and normal wear and tear when clamping the jaws onto the wood..
 
Pete Staehling said:
I am thinking of making a Longworth chuck and wonder if it would be a terrible idea to use a threaded wood block instead of a faceplate. This would be on a 1-1/4"/8 TPI spindle and the threads would be cut with a Beale tap. I'd harden them with CA or epoxy and recut them. The chuck would be only for light duty clean up of bowl and platter bottoms, but it would see long term use.
Click to expand...

I don't know if it's a terrible idea, but I would say with some confidence that it's not a great idea. The threads will wear and compress over time and lead to a loose fit on the spindle threads. Also, metal to metal contact is needed for repeatable seating against the spindle's registration face.
 
Timothy White said:
Have you considered making the block to mount in your chuck?
Click to expand...
I had, but figured that it was as subject to wear as the threaded wooden block or maybe more so. I suppose that I could make one with a block for the chuck and threaded for the spindle as well. I could use the block in the chuck for normal use and true it up by threading it onto the spindle if necessary.

Bill Boehme said:
I don't know if it's a terrible idea, but I would say with some confidence that it's not a great idea. The threads will wear and compress over time and lead to a loose fit on the spindle threads. Also, metal to metal contact is needed for repeatable seating against the spindle's registration face.
Click to expand...
I guess when it comes down to it a faceplate is a pretty minimal expense.

Due to the amount of compression in the fibers and the amount of taper left in the threading, I have always found the wooden thread to remain tight and to register adequately for the amount of time I have used them. Of course that has been limited to the time it took to turn one bowl. I suspect it would probably hold up pretty well, but am not sure it is worth the risk of wasting the effort if it failed.

I think the Beale tap could tap something like a block of HDPE or I could turn an aluminum ring that could be held in a chuck. If I have the raw materials on hand for either I might consider doing one or the other, but if I have to order either it starts to make more and more sense to just buy a faceplate.
 
HDPE is soft enough that it will distort und torque. This could end up with it wedging onto your spindle, or spinning off easier- and on it's own. It has a high degree of lubricity. If I were choosing a plastic, I would look at some of the FRP (Fiber Reinforced Plastic) formulations out there. U.S. Plastics and Google may yield some information specific enough for you to decide which path is for you. One of the things I have considered is a large Longworth...to accommodate 20" +. But the mass of 2 - 3/4" 9 ply wooden plates rotating at even...200 RPM kind of makes me blink. There are some more "exotic" FRP materials which are stiff and light that may suffice - and save a lot of weight. As well, many carbon fiber reinforced sheet goods are available. But, be prepared for your ears to pop, and potential a nose bleed....as the prices can rise to stratospheric levels quickly.:D
 
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Pete Staehling said:
I am thinking of making a Longworth chuck and wonder if it would be a terrible idea to use a threaded wood block instead of a faceplate. This would be on a 1-1/4"/8 TPI spindle and the threads would be cut with a Beale tap. I'd harden them with CA or epoxy and recut them. The chuck would be only for light duty clean up of bowl and platter bottoms, but it would see long term use.
Click to expand...

Why go through the effort of building a Longworth chuck in the first place when there are so many other easier options? I don’t really trust the holding ability anyway. As I see it, the only advantage is the automatic centering – but if you already have a center mark on your foot or tenon you can use a form of jam chuck, friction chuck, or better yet . . . a vacuum chuck. :)

Mount a disc (by any method you desire) at the headstock. The disc can be covered with thin foam or rubber to protect the bowl rim. Use your revolving center in the tailstock to apply pressure (friction chuck) against the disc. If your disc(s) are only an inch or two larger than the bowl rim you can stretch strips of masking tape or duct tape from the bowl’s exterior over the edge of the disc (at least 4 strips or more for larger bowls). This will hold sufficiently for the final light cuts and sanding.

Better yet . . . cover the disc with pieces of rigid Styrofoam insulation (the pink or blue stuff found in building supply stores). Cut a groove with a parting tool to match the rim of your bowl (jam chuck) and press fit with the tailstock. This will auto-center your bowl . . . tape as above. Replace the foam as needed after many bowls. This is the method I used successfully before I rigged up my first vacuum setup in 1994. :D

Another option – flat jaws and/or repurposed Cole jaws. Both the flat jaws (especially if you use a dedicated chuck) and/or vacuum setup is going to cost you some bucks. Both work very well and might be worth it for ease and convenience.
 
Making a donut chuck is a lot easier than a Longworth chuck and holds the bowl much more securely. It only works for bowls with a trued up rim. Natural edge bowls need not apply. You can make several donut sizes for different size bowls.
 
Robert, what you say is true, but, a lot of the fun of woodturning is problem solving. I gave away my donut chuck after I made up a vacuum chuck so have no pics but I solved the natural edge limitations by drilling a hole, about 1 1/2 inches in the base of the donut chuck then turned the corresponding tenon on a 4 inch diameter cylinder, dished the top, added some fun foam, one about 5 inches and another about 8. Used as you would use a jam chuck but with the donut to hold and sandwich every thing into place.
 
Clifton, that's down right clever. That would work. I'll give that a try next time I attempt a natural edge bowl.

A vacuum chuck setup is on my wish list but I haven't gotten authorization from the CFO yet.
 
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