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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

lathe chuck runout



 
 
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  #1  
Old March 17th 06, 10:08 AM posted to rec.crafts.metalworking
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Default lathe chuck runout

I just got the first 3 jaw chuck for my lathe. I was using a 4 jaw for the
last two years. It just got tiring trying to true up the work and not mar
it in the process. I never did get too good at it.
I put the 3 jaw on the lathe, checked the body for runout, and it did not
register any error on the dial indicator. Chucked up a 1.75" dia. piece of
steel, and made a light cut on it. It measured .001 runout after the cut.
Probably due to rough surface finish.
Then turned this piece around and chucked it in the 3 jaw, using the cut
surface as the holding location. When I measured the runout (still using
the cut surface to measure), I was indicating .020 out. I tried this
several times and it varied from .005 to .020. I found some rust on the
inside of the jaws I thought might be causing the problem, but removing it
didn't seem to help.
My lathe is a Reed-Prentice 16X54, the chuck a Skinner 8.5" 3 jaw I just
pruchased on Ebay. The chuck has an integral L01 spindle mount, and it
looks like it has sat and gotten a little rusty for most of its life.
Any constructive suggestions would be appreciated.


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  #2  
Old March 17th 06, 10:49 AM posted to rec.crafts.metalworking
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Default lathe chuck runout

Jim Reed wrote:

Then turned this piece around and chucked it in the 3 jaw, using the cut
surface as the holding location. When I measured the runout (still using
the cut surface to measure), I was indicating .020 out. I tried this
several times and it varied from .005 to .020. I found some rust on the
inside of the jaws I thought might be causing the problem, but removing it
didn't seem to help.


The chuck has one hole (for the key) indicated with a zero. Use this one
for precise (more or less) work. Also when turning the piece, don't
rotate it, but put a mark on it so that the same place goes to the same
jaw.

HTH,
Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO // Eigenbau-Digitalanzeige
http://www.yadro.de
  #3  
Old March 17th 06, 12:10 PM posted to rec.crafts.metalworking
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Default lathe chuck runout

....
Any constructive suggestions would be appreciated.



2.9. Why won’t this chuck hold parts exactly on center?
2.9.. No chuck or collet is perfect. Even a new three-jaw chuck is
only good to 0.002” or so unless it is adjustable. If your chuck won’t hold
parts that closely, something is wrong. Here’s a list of possibilities.
Any of these could cause a good lathe to wobble.
It could be that the jaws of the chuck are worn. Letting parts spin in the
jaws wears the chuck quickly.
It could also be that the scroll of the chuck is worn. The scroll is a flat
spiral metal plate behind the jaws.
Another possibility is that the chuck is mounted on the backplate wrong or
that there are dirt or chips between the chuck and the backplate. Take it
apart, clean it carefully, oil it, and reassemble it. That may help.
Still another possibility is that there is dirt or chips between the
backplate and the spindle. Unscrew the backplate from the spindle, clean
the threads in the backplate and on the spindle, oil both, and try
assembling it again. Screw it together gently. It should not be forced
together or spun on fast with a snap.
It could be that the spindle is bent. Put a dial indicator on the spindle
nose to check it.
It could be that the spindle bearings are bad or that the spindle is
improperly installed. Good bearings will feel smooth and have no play.
Logan spindles are precision machined to give the bearings a precise preload
when the spindle is correctly assembled. Preloaded bearings have no play.

Back to top

2.10. What can I do to fix a 3-jaw scroll chuck with worn
jaws?
2.10.. If the scroll is worn, there’s nothing you can do without a CNC
machine and a lot of time. If the scroll is worn and you fix the jaws, the
chuck will be true at the diameter that you used for the repair, but nowhere
else.
If you’re sure that the problem is just the jaws, then you can set up a
toolpost grinder or boring bar and regrind or bore the jaws true. However,
you must do this with the jaws pressing against something. One way to do
this is with a piece of sheet metal having holes for each jaw. Another way
to do this is to drill holes in each jaw for a pin or screw, and have these
pins or screws tighten down on a piece of pipe. Tighten the chuck on the
sheet metal or pipe and the jaws will be locked in the right place.
http://lathe.com/tips/chuck-jaw.htm


  #4  
Old March 17th 06, 02:36 PM posted to rec.crafts.metalworking
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Default lathe chuck runout

If I read your post correctly, you have the un-turned end of the stock
sticking out of the chuck, and that is the surface that shows the 5-20
thou run out.
Who says that the 1.75" diameter stock was round to begin with? I'd
turn that outboard end down and then measuure it.
I assumed from your original post (my problem, not yours) that the
chuck is new. If it used, all bets are off. I hassled with a couple
of used 3 jaw chucks for years and finally gave up and bought a set-true
chuck. I paid 3 times as much for the chuck as I did for the lathe 25
years ago, but it was worth it.

Pete Stanaitis


Jim Reed wrote:
I just got the first 3 jaw chuck for my lathe. I was using a 4 jaw for the
last two years. It just got tiring trying to true up the work and not mar
it in the process. I never did get too good at it.
I put the 3 jaw on the lathe, checked the body for runout, and it did not
register any error on the dial indicator. Chucked up a 1.75" dia. piece of
steel, and made a light cut on it. It measured .001 runout after the cut.
Probably due to rough surface finish.
Then turned this piece around and chucked it in the 3 jaw, using the cut
surface as the holding location. When I measured the runout (still using
the cut surface to measure), I was indicating .020 out. I tried this
several times and it varied from .005 to .020. I found some rust on the
inside of the jaws I thought might be causing the problem, but removing it
didn't seem to help.
My lathe is a Reed-Prentice 16X54, the chuck a Skinner 8.5" 3 jaw I just
pruchased on Ebay. The chuck has an integral L01 spindle mount, and it
looks like it has sat and gotten a little rusty for most of its life.
Any constructive suggestions would be appreciated.


  #5  
Old March 17th 06, 02:53 PM posted to rec.crafts.metalworking
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Default lathe chuck runout


Jim Reed wrote:
I just got the first 3 jaw chuck for my lathe. I was using a 4 jaw for the
last two years. It just got tiring trying to true up the work and not mar
it in the process. I never did get too good at it.
I put the 3 jaw on the lathe, checked the body for runout, and it did not
register any error on the dial indicator. Chucked up a 1.75" dia. piece of
steel, and made a light cut on it. It measured .001 runout after the cut.
Probably due to rough surface finish.
Then turned this piece around and chucked it in the 3 jaw, using the cut
surface as the holding location. When I measured the runout (still using
the cut surface to measure), I was indicating .020 out. I tried this
several times and it varied from .005 to .020. I found some rust on the
inside of the jaws I thought might be causing the problem, but removing it
didn't seem to help.
My lathe is a Reed-Prentice 16X54, the chuck a Skinner 8.5" 3 jaw I just
pruchased on Ebay. The chuck has an integral L01 spindle mount, and it
looks like it has sat and gotten a little rusty for most of its life.
Any constructive suggestions would be appreciated.


I'd start with disassembly and chemical rust removal.
  #6  
Old March 17th 06, 03:14 PM posted to rec.crafts.metalworking
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Default lathe chuck runout

Jim Reed wrote:

I just got the first 3 jaw chuck for my lathe. I was using a 4 jaw for the
last two years. It just got tiring trying to true up the work and not mar
it in the process. I never did get too good at it.
I put the 3 jaw on the lathe, checked the body for runout, and it did not
register any error on the dial indicator. Chucked up a 1.75" dia. piece of
steel, and made a light cut on it. It measured .001 runout after the cut.
Probably due to rough surface finish.
Then turned this piece around and chucked it in the 3 jaw, using the cut
surface as the holding location. When I measured the runout (still using
the cut surface to measure), I was indicating .020 out. I tried this
several times and it varied from .005 to .020. I found some rust on the
inside of the jaws I thought might be causing the problem, but removing it
didn't seem to help.
My lathe is a Reed-Prentice 16X54, the chuck a Skinner 8.5" 3 jaw I just
pruchased on Ebay. The chuck has an integral L01 spindle mount, and it
looks like it has sat and gotten a little rusty for most of its life.
Any constructive suggestions would be appreciated.



..005" runout isn't too bad for an 8-1/2" 3-jaw. .003" is about as good as you
can expect even from a very expensive new chuck. However, there are some things
you can do. The first thing is to completely disassemble your chuck, and clean
it using solvent & compressed air. It's amazing how a tiny chip somewhere can
bollux things up. When you put it back together, pay close attention to the fit
between the scroll and the central boss. Any clearance there translates to
runout in the jaws. Older chucks can accumulate wear there. If it is worn then
chances are it is worn uniformly, so you can cut a suitable shim that fits all
around the central boss, like a wedding ring. Give it a little lubrication in
the back where the pinions go, and leave the jaws dry and clean, and reassemble
and test. When you test, shoot for a good finish. Pay close attention to how
your piece is oriented in the jaws (maybe mark it where the piece touches the
no. 1 jaw) and replace it exactly, and tighten it from the same pinion, and I'm
guessing a lot of your error will be gone.

Even with .020" error a 3-jaw is completely usable for many things and a highly
desirable addition to your lathe tooling. Many things can be turned entirely in
one setting.

GWE
  #7  
Old March 17th 06, 06:15 PM posted to rec.crafts.metalworking
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Default lathe chuck runout

--FWIW a decent new chuck should come with a certificate of
accuracy. This will allow you to pinpoint the runout problem a little more
quickly. If it doesn't have one, well.. ;-)

--
"Steamboat Ed" Haas : Concave, convex, con
Hacking the Trailing Edge! : carne: all is Zen..
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---
 




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