Runout problem when reverse chucking - Woodworking Talk - Woodworkers Forum
 
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post #1 of 11 Old 12-13-2011, 09:53 PM Thread Starter
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Runout problem when reverse chucking

New to turning...and need some advice. The other day I mounted a bowl blank (2" x 6") on a 3" faceplate and turned the outside bowl shape and turned a recess on the end. I removed faceplate and chucked with 50mm jaws (Nova G3) in the recess. When I started to turn I noticed radial runout .030" on the bowl. Last time I turned a bowl I used the woodworm screw in the chuck and then reverse chucking with 35mm jaws on the recess and had no runout at all. Any guesses to what might cause this? Maybe bad jaws?
* FYI...the faceplate has no runout, the chuck body has .001" runout (not bad). I'm not sure how to measure the jaw runout.

All comments are appreciated,

Paul
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post #2 of 11 Old 12-13-2011, 10:24 PM
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Quite likely from uneven compression of the wood when tightening the chuck. Sometimes this is unavoidable, sometimes you can rechuck it for better results.
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post #3 of 11 Old 12-14-2011, 12:37 AM
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I would say something moved when you had it on the faceplate. Can you reassemble it to the faceplate to see if that is the problem ?
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post #4 of 11 Old 12-14-2011, 06:20 AM
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Quote:
Originally Posted by Gary Beasley View Post
Quite likely from uneven compression of the wood when tightening the chuck. Sometimes this is unavoidable, sometimes you can rechuck it for better results.
+1 I agree

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post #5 of 11 Old 12-14-2011, 06:42 AM
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When screwed on the face plate you are dealing with side grain only, while expanding your chuck in the recess end grain becomes a factor, try to losing your chuck and rotate it just a little see if it helps. could also be moisture content of the wood changing making the wood shift. but I do prefer using the worm screw over the faceplate, so when i reverse chuck it my tail stock is use to keep it on center while expanding the chuck jaws..

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post #6 of 11 Old 12-14-2011, 08:37 AM
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The jaws are cut from a solid billet so I would not think it is the jaws. When you changed jaws did you leave the 50mmís a little loose close them down and then tighten? If not the jaws could be installed just a little off. Also check to make sure all mounting screws are tight and the jaws in the correct mouting location.
As other said, slightly loosening and rotating the item may solve it also.

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post #7 of 11 Old 12-14-2011, 09:31 AM
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Quote:
Originally Posted by pvechart View Post
When I started to turn I noticed radial runout .030" on the bowl.
Three one-hundredths of an inch -- less than 1/32".

If that's measured at the rim, it could be caused by the jaws not being at uniform pressure against the flat of the recess, or the wood compressing slightly different amounts under that pressure.

I don't have the same chuck as you -- are the jaws dovetail? If so, did you cut a perfectly matching dovetail recess?

TBH ... I'd just let it go, this is such a tiny amount, I wouldn't even see it.

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post #8 of 11 Old 12-14-2011, 04:44 PM Thread Starter
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Thumbs down

Thanks for all the advice. I have finished the bowl so I can't go back to check some of your items. I actually did loosen and turned the bowl to a few different positions with no noticeable change. I have noticed the 50mm jaws when fully closed are not totally flush from jaw to jaw. Between jaw #1 and #4 there is an offset about .010" on the front face and the outer surface. Should they fit perfectly flush or can you expect some small steps? I had expected the jaws to have very close tolerances when mounted on the chuck. Also do the jaw slides on the chuck normally have some wiggle play to them when they are open? Mine seem to be kind of loose (only when open). By the way I followed all the instructions in the Nova manual for installing the jaws. I have also gone over and checked for burrs and any left over machining chips on the chuck and jaws. My lathe is a new Delta 46-460 and a Nova G3 chuck. I really love this new hobby and am kind of a stickler for details. It's great to have so many experienced people to "turn" to for help!

Thanks again for any comments,

Paul
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post #9 of 11 Old 12-14-2011, 07:35 PM
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I know that you have done it but loosen the jaws (screws only finger tight) and run them in and out a little. They should seat against each other with no light between the jaw edges when fully closed. Then tighten. The edges are not machined after they are cut. Is your chuck the G-3 or G-3D? It could be that one jaw is not seated on "ring" fully. Again, I know you have already checked but the jaws are installed to corresponding numbers on the chuck.

Did you have this problem with them before? There could be a very small difference I suppose but again, the jaws are turned as a billet and then cut apart. It doesn't make sense that the 35mm line up and not the 50mm so it shouldn't be anything with the chuck itself.

I purchased a couple of used chucks made for Jet and Delta resell. The finish was different from a normal Nova chuck. They had black coated jaws instead of nickel(?) coated and the edges were much rougher. They do work just fine. Just speced to a lower finish so Jet or Delta can make more $$ I suppose.

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post #10 of 11 Old 12-14-2011, 09:40 PM
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I would also be checking on the wood itself changing dimension between the first cuts and reverse chucking due to moisture content changing. I've had that happen more than once.
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post #11 of 11 Old 12-15-2011, 07:56 PM Thread Starter
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NC...I went through the steps you suggested again and it is still the same. By the way I have the G3 model no D. This little offset I discribe has always been there. I might take the chuck and jaws back to the "Craft" store and show them.
Gary...As far as the runout it may be that the wood did change between reverse chucking because it sat in the lathe for at least 24 hour before I re-chucked into the recess although the wood was dried out. I'll be making many more bowls and will see if this continues with just the faceplate and the 50mm jaw combonation.

Thanks again Guys!

Paul
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