I'm a relative newby still trying to find out what I can do.
My must recent problem is that I'm having trouble holding cylinders on the lathe. I have a cylinder about 8" long and about 2 3/4" diam. whose tenon is held as tight as I can reasonably get it in a One-way Talon chuck and is supported by a Penn State steady-rest. Nevertheless, as soon as I start working on opening the end to a cup/goblet form, it comes out of the chuck.
What (simple) thing am I missing? Without the steady rest, it immediately came out. I thought that the steady rest would support it and help hold it in place.
You can undercut the shoulder a bit to protect yourself against the worse circumstance, which is out of square the other way. It'll get you 90 % of what you'd get from perfect.
Third possibility available if you have dovetailed jaws. Use the wedging action of the dovetail to help you keep the face of the jaws tight up against the shoulder. You already know that you want to make the tenon of a diameter which allows the most metal to be in contact with wood, rather than just those teeth, right?
As far as hollowing along the grain, you might consider a common cheat and bore a big hole to a bit less than the finished depth of the goblet. Allows you to work your way against the side grain. Open the area toward the rim and take successively deeper cuts bottom up and inside out. Fingernail ground gouge or full point are the ones I find best.
Pointy.
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Tale in the shavings.
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They're feathered on the side where the gouge exits the wood - toward the bottom - and square where it enters. That's where the taper grind helps. More support than a simple fingernail.
Before this gets out of hand, everyone please note that George, the OP, is not the same as George, the respondent.
To OP George: I tend to blame your steady rest. If everything runs smoothly until you start cutting, it is possibly due to the tangential force from the cutting tool. This can make the work move off center or possibly vibrate if the tires are too soft or the steady rest is not completely rigid. With the work in place, with the steady rest adjusted, and with the lathe off, can you push on the wood and cause it to move? This has happened to me.
ARE you using a tenon, or just gripping the wood in the jaws?
You want a tenon on the chuck end of the piece.. at least 1/4" smaller than the piece and square to the piece, and shorted than the jaw depth, so that you're gripping the wood AND the jaw faces are butting up against the shoulder/right angle of the tenon..
Turning without a tenon or having the tenon long enough to bottom out on the chuck will give you wobble and get knocked off true at the slightest catch or pressure..
I'm doing some goblets for a client and the damn things kept going out of true... very frustrating.. I finally realized that my tenon was about 1/16" too long and bottoming out in the chuck.. this kept the jaw faces from making square contact with the shoulder, so that every little bump would move the piece from one jaw to the other..
Hope that helped more than confused.. If you look on page 15 of the Talon manual, the pictures will explain it much better than my under-caffeinated words..
I very much appreciate all the feedback, especially that it began within 5 minutes of my original post. The common thread was to eliminate bottoming in the chuck and to be sure that the chuck was gripping squarely against the cylinder.
I checked the two cylinders I'm working with. One has a tenon that is not quite square and is bottoming out at one spot. That one has been put aside for further improvement.
The other one, though,... has a square tenon (and, yes, it is a tenon, not a grip on the whole cylinder), is not bottoming out, and is gripped tightly by the chuck. The chuck is flat against the base, and, in response to two suggestions, I can't budge it once it is chucked and with the lathe still off. (Also, I don't have dovetail jaws. But I do have Forstner bits to try drilling out the cup.)
I have made sure that the steadyrest is square to the lathe stays and that all three wheels are just touching the outer rim.
But ... as soon as I put my fingernail 5/8" gouge into the cup to cut, it was coming out of the chuck. FWIW, the lathe was turning at about 285 rpm, maybe too slowly. I guess it could be my technique, or lack of it, with the gouge.
Obviously, I took your advice to heart, and tried several things youse suggested. I am very open to any other and further thoughts. For the moment, I only have tomorrow to play with the lathe, because we have to go away for a couple of weeks.
well, george ms - you have an interesting problem, and since we can't see what you are or are not doing, and you don't know for sure what to look for, it makes it extra hard. Let's try an experiment
Do you have a faceplate (please say yes....)
ok, take a piece of wood like the one you are having problems with and screw it securly to the faceplate - Now, make the same exact cut you are having problems with at the same RPM - tell us if you get a big catch, or if it works fine or what happens - If it is a technique problem that is causing a catch and extracting the piece from the chuck, you will feel a catch and it will tell you it's not the chuck.
For what it's worth, I do what you are attempting to do with some regularity, as do many others, so I'm sure you will be able to do it too once you figure out what is going wrong.
I've been thinking about a small face plate, both for tenons and - what do we call an inverse tenon on a larger bowl? But, no, I do not yet have one, only the large face plate that came with the new Jet lathe.
FINGERNAIL? hmm... is it a 5/8" BOWL gouge, or spindle?
Are you getting a catch, or a vibration? Has to be SOME reason for it going out of true.. major catch or something to knock it out of the chuck...
My usual test, especially if you're working on one of those "project from hell" things that seems to have built-in demons, is to try a light pass with a sharp round nose scraper... If it sets up a vibration, I know that I have a wood and/or chuck problem..
a bowl gouge is the right answer, but you need to attack it with the flutes rolled way over so the sharp edge faces the headstock - if you have the sharp edge vertical you won't like what happens
I was asking what type of gouge you were using because I was afraid that you WERE using a spindle gouge on it..
I love scrapers... never catch, easy to sharpen, smooth surface later, etc.. Remember that you're not using an "edge" on a scraper, as you would with a gouge.. You're lightly shaving off wood with the BURR that sharpening creates.. So it's very sharp but goes away very quickly..
My personal preference is about a 4 or 5% angle on scrapers, and I've dedicated my 1" belt sharpener to them.. I keep the table set at the angle I want, but in NEGATIVE degrees, then lay the scraper upside down to sharpen it.. Might be my imagination, but I seem to get a much nicer burr this way, as the belt (or grinding wheel) is traveling in the direction that I want the burr, not against it.. YMWV
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