design of a cup chuck

[Perry Hilbert Jr]

I want to make a cup chuck for my lathe which has a 1x 8tpi head stock. I will be using 1 x 1 bass square stock. the diameter of the square stock with out compression is 1.414 inches. Will an interior diameter of 1.25 inches be sufficient compression for holding the bass wood?

[John K Jordan]

I want to make a cup chuck for my lathe which has a 1x 8tpi head stock. I will be using 1 x 1 bass square stock. the diameter of the square stock with out compression is 1.414 inches. Will an interior diameter of 1.25 inches be sufficient compression for holding the bass wood?

It sounds like you mean driving it in square without first turning a tenon on the 1x1 basswood. If so, how well it would hold would depend a lot on how compressible/deformable the wood is, of course, so you might have to just try it. If you are holding the end with the tailstock you won't need much grip in the headstock.

I have never been a fan of holding square stock by jamming into a round hole. I know some people drive square stock directly in to the spindle morse taper socket but I like to turn a short #2MT on the wood first. Some old timers would first roughly trim the corners off square stock with a knife or hatchet before driving it into a cup chuck.

Is there a reason not to use a scroll chuck with jaws sized to tighten on the square stock? I do that a lot and it's very secure. Alternatively, it's very quick to turn a tenon on the square wood held between centers (using a bedan, peeling with a small skew, or even a parting tool.

JKJ

[Perry Hilbert Jr]

I ran into a young fellow, who was obviously not trained in the US, that turns little Christmas trees about 7 inches tall. I watched him turn a half dozen small trees. He had 2 inch bass wood and just bumped it into a cup chuck with the heavy shaft of his skew and used only a skew to round the stock, turn the tree and part off the piece. The stump in the chuck, was then bumped out with a knock out rod, from the left of the head stock. The knock out rod was held in the lathe by a spring. It took him a second to mount the stock. Sometimes he didn't even stop the lathe. When he got down to the place where the chuck was spinning, it was smooth. no jaws to knock on knuckles or to catch edges of tools etc. He put his hand over the chuck to catch the stump coming out, again, often without stopping the lathe. He also had a line of people waiting to buy at $10 each. I figure it was taking him 3 or 4 minutes each. BTW, there was no tail stock on the lathe. I am certainly not in that class for speed, but there are ornaments I make that take less than 2 minutes on the lathe. It just seems that a cup chuck would be faster and easier to use. Also, it is one of those throw back Techniques that seems to be lost today.

[Dave Fritz]

Perry, so it was basically a friction fit? It must be tapered so the wood can jam securely into the chuck. I'm not sure I'm picturing it correctly. https://www.woodworkersinstitute.com...-cup-chucking/

[Perry Hilbert Jr]

Yes friction fit. figure D from an 1842 text book. Holds by friction, same as turning a piece jammed into a MT of the head stock spindle, but larger and less tapered so the piece is not likely to work loose as when using the morse taper. . In eastern Europe some cup chucks are approximately 6 inches in size.

[Dave Fritz]

Thanks, that's what I was picturing. Be fun to see a video of someone using one. I would think it would take a skilled turner to use one. Certainly a light touch without a tail stock.

[Robert Henrickson]

I ran into a young fellow, who was obviously not trained in the US, that turns little Christmas trees about 7 inches tall. I watched him turn a half dozen small trees. He had 2 inch bass wood and just bumped it into a cup chuck with the heavy shaft of his skew and used only a skew to round the stock, turn the tree and part off the piece. The stump in the chuck, was then bumped out with a knock out rod, from the left of the head stock. The knock out rod was held in the lathe by a spring. It took him a second to mount the stock. Sometimes he didn't even stop the lathe. When he got down to the place where the chuck was spinning, it was smooth. no jaws to knock on knuckles or to catch edges of tools etc. He put his hand over the chuck to catch the stump coming out, again, often without stopping the lathe. He also had a line of people waiting to buy at $10 each. I figure it was taking him 3 or 4 minutes each. BTW, there was no tail stock on the lathe. I am certainly not in that class for speed, but there are ornaments I make that take less than 2 minutes on the lathe. It just seems that a cup chuck would be faster and easier to use. Also, it is one of those throw back Techniques that seems to be lost today.

That is the method used by the traditional turners in the Erzgebirge region of Germany. It is very much alive there.

[Perry Hilbert Jr]

To the contrary they go to it. The Russian Matryoski Dolls are turned using cup chucks and no tail stocks. See at 4:26 https://www.bing.com/videos/search?q...tail&FORM=VIRE

[John K Jordan]

...Be fun to see a video of someone using one. I would think it would take a skilled turner to use one. Certainly a light touch without a tail stock.

Dave,

This is the thread where Perry talked about this a few years ago. It links to a video of turning the Christmas trees (and other things). The later comments in the thread still stand.

https://sawmillcreek.org/showthread....7684-Cup-Chuck

I've made Christmas trees like that (but with the wood held in a chuck and they are quick and easy. (for several reasons I still recommend using a scroll chuck unless going into production). You can airbrush them with dye for a little color. I've also made little Christmas trees from cedar but by carving instead of turning. Each shaving with the knife makes a curled bough. The shavings got shorter towards the top. The cute little trees were quite popular.

A little skill with the skew is needed but that's not hard to acquire with just a bit of directed practice. If not currently adept with a skew, JKJ's free skew lessons are on sale this year.

As before, note that lathe manufacturers generally recommend to NOT pound anything towards the headstock on today's lathes due to risk of eventually damaging the bearings. It is even recommended to remove drive centers and pound them into the wood rather than pound the wood into a drive center mounted in the headstock spindle.

BTW, another way to make a cup jam chuck is to mount a piece of hard wood on a faceplate or in a scroll chuck and turn an appropriately sized socket, perhaps slightly tapered. Even if machining a meta cup chuck, the one from hardwood could function as a prototype to test the size needed for the intended wood blank.

JKJ

[Perry Hilbert Jr]

Or here beginning at 1:25 https://www.youtube.com/watch?v=DWEEJhdcyMQ
and again at 10:45