Unintended asymetric turning

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That's more than enough material to hold a piece, even if the jaws are made of aluminum. Key to success is not having an overly long piece, which can be levered from the chuck, or to take excessive cuts, which may do the same thing. Also, there's nothing preventing you from running a live center with a plate on the item being held. That keeps it from pulling out of the chuck under adverse conditions. You'd put the center drilled plate against the part, then start the machine. Back off the live center ever so slightly, so the plate can find natural center as the part rotates. Assuming you have machined a proper pocket for the part to be turned, it holds the part securely against the back of the pocket. Only enough torque on the handle of the chuck needed to drive the part, with no fear of the part coming out.
If the part must be faced, you'd have to use good judgment as to how hard to tighten the chuck. It's all just a matter of having a little experience. You get a feel for these things pretty quickly.
If you do explore soft jaws, make sure you understand how they should be applied. If you don't follow the simple rules, they don't work worth a damn. No better than hard jaws in most cases.
Harold
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On Tue, 14 Dec 2010 09:42:19 GMT, "Harold & Susan Vordos"

It's boring and ID on such piece that had me worried.

[...]
Michael Koblic, Campbell River, BC
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snip-->

Piece of cake!
Once you've used soft jaws with success, you'll wonder how the hell you got along without them. They are, truly, the magic bullet of lathe work.
I use soft jaws in place of the hardened steel jaws with almost NO exceptions. I have a set that is bored through for gripping bar stock. It runs truer than the factory jaws in both concentricity and perpendicularity.
Harold
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On Dec 9, 11:23 pm, snipped-for-privacy@gmail.com wrote:

I believe your eccentricity is due to one edge of the ring being lifted up, you then get an angular section of a cylinder instead of a circle, an ellipse in other words. Has been a kink written up in old machinists' books to bore elliptical holes.
What you list as workflow wouldn't be my choice if I wanted concentric inside and outside. I'd start with flat stock, roughing out a blank on the 4x6 first. If your flat stock is that much out or you need machined surfaces, face off both sides first. Precision ground stock isn't that expensive, saves facing and possible "wedgies". With the blank still stuck in the chuck, bore your hole to whatever limit you care to. Make up a mandrel for between centers to fit your hole, I'd make up one with a shoulder and a retaining sleeve. Now finish off the outside to size. If you're doing multiples, make your mandrel long enough to put a bunch on and finish them all at the same time.
It always bugs me when somebody reverses the process. It's always much easier to get a precision hole bored and finished FIRST, then reference everything from that. You get much better results from putting a part on a mandrel between centers than trying to indicate a part in a chuck. Concentricity is pretty much guaranteed that way.
I've not seen any metal lathe supplied with such a flimsy 4 jaw chuck, even the 7x has a better chuck than that. Didn't cost as much, either. Reminds me of some of the faceplate add-ons I saw in The Model Engineer ads circa 1899 for treadle lathes. I wouldn't trust it on a wood lathe, either.
Stan
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On Sun, 12 Dec 2010 19:15:27 -0800 (PST), snipped-for-privacy@prolynx.com wrote:
[...]

It is a thought, however, to get a 0.007" error on 4.5" that way (without any flexion) the disk would have to be tilted over 3 degrees. Even I would have seen that :-)
I am still voting for the "lay chips" pattern :-)

Roger Shoaf suggested something essentially identical. I can see the benefit of doing the ID first even using pre-fabricated blanks as I do. I am still confused as to the benefit of a mandrel vs. 3-jaw chuck.

I am not sure why the need to indicate if the piece is clamped inside the hole by the 3-jaw self-centering chuck. Concentricity within 0.003" is fine for this application.

Which I guess is the reason they throw it in with the lathe. It is of comparable quality to their face-plates and the stand the lathe comes with for that matter. Not to mention the work one has to do on the lathe itself.
Michael Koblic, Campbell River, BC
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snip-

It's pretty simple. Any time you can avoid using a mandrel, you're likely better off. That would be especially true when attemting to turn what is, essentially, a large, thin washer. Chatter is an ongoing problem, as is driving the part without slippage. By preparing the OD of the part first, easily accomplished by pressing the part against a plug, using a plate with a live center. Once the OD is machined, the part can then be chucked in soft jaws and faced, bored and reversed with no issues. Best of all, chucking the OD pretty much eliminates chatter, especially if the part nests on a proper cavity. Soft jaws solve all the problems of holding large diameter thin pieces.
Harold
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On Tue, 14 Dec 2010 09:55:04 GMT, "Harold & Susan Vordos"

You said it! The piece I described certainly does that. I have got rid of the chatter by putting a spacer behind it.

I see your point, too. OTOH you gotta love the diversity of opinions on this group :-)
Michael Koblic, Campbell River, BC
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snip--

The only problem I have with that concept is that you often get advice that isn't very good, and if you are asking the question, you may well not be able to discern good suggestions from those that are troublesome. I face this problem all the time with well meaning but poorly informed people that think of themselves as machinists (yet they have no experience in the trade. Strange!)
In many cases, they've struggled through a tough project and succeeded to some degree, but don't have a clue that there's much better ways to approach the problem. There's nothing quite like years of experience, especially if they're spent running a (commercial) shop, making all of the decisions.
The biggest problem you'll face on an open discussion forum such as this is the guy that can't resist telling you how to do a job when he doesn't know, himself. I think it's a guy thing! :-)
Some guys just love to see their name in print.
Harold
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On Wed, 15 Dec 2010 07:09:20 GMT, "Harold & Susan Vordos"

So, no different from other spheres of life then...:-)
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