Chuck Not Running True?

PAturner said:
Also, the chuck is a three jaw-
Could I possibly get around any runout issues if I got my hands on a 4 jaw independent chuck?
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Yes, you can dial a 4 jaw in to any desired runout

a 3 jaw will always have some run out,
the best i have seen was on my (New) old Hercus- it had .001" runout when i got it
i have not checked it's accuracy since but it has very little runout by eye
 
The questions that come to mind for me are:
1. What is the make and model of the lathe?
2. How far on are you able to thread the chuck?
3. Do the thread pitches match on the backing plate and the spindle?
4. Does the spindle diameter match the recess cut into the backing plate?

I would confirm that the backing plate was properly made before I tried to force thread it on
 
Ulma Doctor said:
1) YES
2)YES
3) see below

if you can remove the chuck, do so

just place a piece of wood (or thick cardboard doubled up) to prevent the chuck getting dropped on the ways
inspect the spindle threads for damage and bits of metal, clean with a brass wire brush
inspect the chuck threads for damage or bits of metal, clean with a brass wire brush
if there is no damage seen, apply a drop or 2 of light oil to the spindle threads and try to reinstall the chuck

4) YES! you sure can :grin:
Click to expand...
Mike, I hope that's not your video.
The first no-no shown in the video is the spindle is locked in using the back gear.
Yeah, I know, we are all guilty of doing that and in most chuck removals works fine. It's the situations where the simple bump to break loose the chuck where you are having to use a big hammer of six foot cheater pipe and brute force to get it broke loose. This is where you could loose a tooth off of one of the back gears in the head stock.
Just a word of caution here to those that have never experienced the sound of a tooth breaking off on a gear during chuck removal..... Ken
 
Update on everything- removed the backing plate this morning and checked everything out. First issue I saw was that the bur thrown up from threading was never knocked off. This was on the side that mates with the chuck. I got that taken care of.

Also checked how far the chuck is threading on, and it's definitely getting stuck right at the rust line. So I'll soak it in vinegar today and see if I can get it to thread on properly, check the runout and update again.


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4gsr said:
Mike, I hope that's not your video.
The first no-no shown in the video is the spindle is locked in using the back gear.
Yeah, I know, we are all guilty of doing that and in most chuck removals works fine. It's the situations where the simple bump to break loose the chuck where you are having to use a big hammer of six foot cheater pipe and brute force to get it broke loose. This is where you could loose a tooth off of one of the back gears in the head stock.
Just a word of caution here to those that have never experienced the sound of a tooth breaking off on a gear during chuck removal..... Ken
Click to expand...

Yes it is my video,
i know the video and sound quality are poor.
i agree to not put too much pressure on the gear teeth.
i did warn against putting too much pressure on the geartrain and only used a slight bump from a 2x4 to back the chuck off.
thanks for the clarification!
 
I am not particularly experienced with threaded spindle lathes although have owned 2 in the past, I suspect that the flat shoulder past the thread relief controls the axial position of a chuck or faceplate, the thread controls the radial position. This is exactly why tapered spindles were developed. Also changing threaded spindle attachments is a chore.

One may easily skim cut the shoulder in place. In an effort to find exactly where the thread interference is color the threads with a sharpie marker or blue lay out fluid, screw the chuck on tight, remove and inspect, there will be witness marks where the problem lies.

Good Luck
 
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If you have thread pitch gauges, check the threads on both pieces. You may be trying to thread metric onto sae.

Sent from somwhere in east Texas by Jake!
 
I can see the pic you posted jpfabricator, so whatever you did worked, cause I always get the red X's.
PAturner, you are probably experiencing the same problem I had. Although the back plate and spindle have the same threads, the narrow "register" on the spindle is sometimes a different size. My Logan Lathe came with a 3 jaw chuck mounted, it too had runout. The PO never noticed that the back plate was made for a Southbend and the register was about .015" too small to fully seat on my Logan's spindle register. Once I turned approx. .016" off the back plate register, it screwed on all the way and has been much better ever since. It still has some runout, as all scroll chucks do, but it is much improved. If you want no runout, you need a 4 jaw independent chuck that you dial in every time you mount a part in it. Hope this helps, happy machining, JR49
 
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