Cheap 3 jaw lathe chucks

Anyone else had trouble with the $150 three jaw chuck?
About 4 years ago I bought a used 13 X 40 Jet lathe. Sweet machine compare
d to the Smithy 3in 1 I had. It came two three jaw chucks and each of the m had 20 mill run out. I bought a new cheap 3 jaw and was thrilled to see it had about 2 mill run out until the 2" diam Al rod jammed when I was par ting it out. Now I have 3 cheap 3 jaw chucks with 20 mill run out.
The new chuck (Christmas present) is arriving in a day or two and it is su pposed to be a step up from the cheap ones. I am also going to be way more carful doing cut off operations.
Anyone have some rule of thumb for cut off operations?
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On Fri, 04 Jan 2013 15:35:52 -0800, d32 wrote:

Uh -- start with a cheap chuck that's already beaten up?
:)
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Anyone else had trouble with the $150 three jaw chuck?
About 4 years ago I bought a used 13 X 40 Jet lathe. Sweet machine compared to the Smithy 3in 1 I had. It came two three jaw chucks and each of them had 20 mill run out. I bought a new cheap 3 jaw and was thrilled to see it had about 2 mill run out until the 2" diam Al rod jammed when I was parting it out. Now I have 3 cheap 3 jaw chucks with 20 mill run out.
The new chuck (Christmas present) is arriving in a day or two and it is supposed to be a step up from the cheap ones. I am also going to be way more carful doing cut off operations.
Anyone have some rule of thumb for cut off operations? ==================================================I bleeve you can grind the jaws pretty simply for zero runout. Dumont-type grinder (or improvisation) in tailstock.
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When in doubt, finish on the bandsaw.
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Anyone else had trouble with the $150 three jaw chuck?
About 4 years ago I bought a used 13 X 40 Jet lathe. Sweet machine compared to the Smithy 3in 1 I had. It came two three jaw chucks and each of them had 20 mill run out. I bought a new cheap 3 jaw and was thrilled to see it had about 2 mill run out until the 2" diam Al rod jammed when I was parting it out. Now I have 3 cheap 3 jaw chucks with 20 mill run out.
The new chuck (Christmas present) is arriving in a day or two and it is supposed to be a step up from the cheap ones. I am also going to be way more carful doing cut off operations.
Anyone have some rule of thumb for cut off operations? =========================================I'm not really a fan of parting, except on tubing. Thick solid stuff is a pita. Imo, better to cut thick stuff on a saw (band, RAS, abrasive, whatever does the job), and then face it. But then, ahm no 'spert, I just get thru the day.
Lest the 'sperts don't reply:
Don't have the parting tool too low below center. Don't have it stick out any farther than necessary. Be prepared to move the carriage in X bec of tool drift -- I've never parted anything that didn't wind up convex or concave, unless it's very small diameter, or tubing.
Make sure you have the right rake etc on the tool. Use oil, coolant, make sure rpm is appropriate for mat'l, diameter. Some people don't realize that even tho alum is easy to work, it's low melting point/gumminess can cause its own problems with tool breakage. So watch the rpm on large diam stuff.
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Whenever I have to loosen the toolpost or compound I reset it square with the parting tool holder pressed against the end of the spindle.
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wrote

Oh yeah, I knew I was forgetting something. Which is proly why all my shit comes out convex/concave..... lol
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wrote

I should add that my parting tool holder is hardened Chromoly, precision-ground to aerospace tolerances by elves in Switzerland.
Very large, well-armed elves.
If yours came from a Chicom prison factory the blade may not be so precisely parallel to the end of the holder.
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wrote

never

very

with

Indicate it parallel to the axis travel, unless you are already certain that the spindle is accurately trammed to the cross slide.

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wrote in message

If the cross slide axis isn't square to the spindle the cut will still be concave or convex. My lathe is good old American iron and suffers from wear and student abuse rather than poor manufacturing.
I bevel the end of the cutoff bit -very- slightly, as little as possible by hand grinding really, to leave the teat on the work, the opposite of conventional advice. Then if the bevel deflects the cut the work has extra metal I can remove rather than being spoiled, and the concave stock end is easily faced square before making the next piece, and doesn't have a protrusion that deflects the center drill. jsw
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All
There are some great ideas here. Thanks!
I like the idea of grinding the jaws square. I am looking at making a tool post mount for my die grinder. Bearing seem to be pretty good and it should work but I will have to make sure the jaws are indexed or bad things will happen.
The other idea I like is to turn down the centering shoulder on the mounting plate then re set center, I am a bit worried the chuck will move as the only thing holding it is friction.
Thanks all
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On Friday, January 4, 2013 5:35:52 PM UTC-6, d32 wrote:

red to the Smithy 3in 1 I had. It came two three jaw chucks and each of t hem had 20 mill run out. I bought a new cheap 3 jaw and was thrilled to s ee it had about 2 mill run out until the 2" diam Al rod jammed when I was p arting it out. Now I have 3 cheap 3 jaw chucks with 20 mill run out.

supposed to be a step up from the cheap ones. I am also going to be way mo re carful doing cut off operations.

You can modify the back plate to make it into an adjust true type chuck... So VERY easily.
Turn the back plate smaller than the mounting register on the chuck, make s ure you have clearance for the mounting bolts, and add adjuster screws to d ial it into position.. Even easier than making a new mounting plate for the new chuck..
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wrote:

the Smithy 3in 1 I had. It came two three jaw chucks and each of them had 20 mill run out. I bought a new cheap 3 jaw and was thrilled to see it had about 2 mill run out until the 2" diam Al rod jammed when I was parting it out. Now I have 3 cheap 3 jaw chucks with 20 mill run out.

supposed to be a step up from the cheap ones. I am also going to be way more carful doing cut off operations.

I can't see how a chuck can go from .002" runout to .02" and can't be adjusted back to the original .002" I don't know what your chuck looks like but it probably mounts to a backplate that in turn mounts to the lathe spindle. If this is the case then loosening the bolts that attach the chuck to the backplate and tapping the chuck with a soft hammer or similar back to center is the solution. Make sure to re-tighten the bolts. Do you have a link to a picture of your chuck? I have more than once converted standard chucks to adjustable chucks. It is pretty easy. Eric
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wrote:

the Smithy 3in 1 I had. It came two three jaw chucks and each of them had 20 mill run out. I bought a new cheap 3 jaw and was thrilled to see it had about 2 mill run out until the 2" diam Al rod jammed when I was parting it out. Now I have 3 cheap 3 jaw chucks with 20 mill run out.

supposed to be a step up from the cheap ones. I am also going to be way more carful doing cut off operations.

I could never part off work with any real sucess on any manual lathe. Now on my CNC I have very good luck. Mostly I think because I no longer use a HSS cuoff blade. I'm using Manchester carbide inserts. Exspensive at $18.xx each, but I think the complex chip contol molded into the top of them makes parting off work way better than any sharpen job you can do on a HSS blade.
Remove 333 to reply. Randy
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