Chuck Not Running True?

the boogers on the thread may be causing the issue.
a thread file or a small 60* triangle file may be lightly employed to improve any high spots
you could add some ink from a sharpie pen to the spindle and try to see where the interference lies
 
JR49 said:
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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What do you mean by the register? The unthreaded portion of the spindle threads?


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PAturner said:
What do you mean by the register? The unthreaded portion of the spindle threads?
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Yes, he means the axial control surface is defined by this surface, the radial control is dependent on many variables. A threaded lathe spindle is not the beat approach.
 
PAturner said:
What do you mean by the register? The unthreaded portion of the spindle threads?
Click to expand...



Yes, its the area at the end of the threads. In the pic that jpfafricator posted, follow the thread to the left, and right where it ends there is approx. a 3/8 to 1/2 inch of smooth surface. That is the spindle register, HOWEVER, on every spindle I've seen that register is higher than the top of the threads (max thread dia.), and on the back plate internal threads, the register is lower than the minimum dia of those threads, so that when the two parts are screwed together the two registers are a tight sliding fit. In your pic, the register looks to be level with the top of threads, which can't be right because then the backplate register would have to scrape over the top of the spindle threads in order to fit tightly on the spindle register. But I'm basing everything on that pic, which may look different than the actual spindle, but regardless, I'm hoping my explanation will give you some insight as to how they are supposed to fit together. As a novice myself, I'm basing my info on what I did to the southbend back plate to fit it on my Logan lathe. If this is no help to you, then don't worry, you can be assured that someone on this great forum will have the answer you need. Good luck, and keep us informed, JR49
 
After many hours of scrubbing, vinegar, and lubricating, there has been no improvement.

The backing plate still refuses to screw on. I don't think that the backing plate threads are metric since it screws more than halfway on with no problems and the part seems to be homemade anyway. I'm really blanking on what to do here, and I doubt my abilities to make an accurate backing plate as a first project.
Any advice on what to do next? I saw on practical machinist someone used a fine lapping compound on the threads and screwed the plate back and forth a few times and got it to fit all the way on. Would this destroy the threads or is it worth a shot?


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Backing plates come semi-finished in that the thread and machining mating surfaces are already done, they are inexpensive ($60-70). The only thing that is necessary is to cut a step in the front of the plate so it matches the lip on your chuck. This is actually a good thing to do, as it gives a specific alignment of the plate to your machine. Once you have done that, all you need to do is make/use a transfer punch to mark the holes for the bolts that hold on the chuck, it is very easy to drill these on a drill press. These might be threaded into the backings plate, so you would need to get a tap for the chuck mounting screws. This is one of the most basic steps in using a lathe, and is really the only practical way to fix your problem. If you let people know what lathe you have, the chuck and the size, people can provide you with more specific details.
 
I'm not sure where one might find these plates for that cheap. I'm coming up with prices in the 200 ish dollar range. The spindle size is 1-3/8", I'm not sure of the teeth per inch.


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PA, as I said in my previous post, there are many members here willing and able to help you BUT, you need to provide them with more information. I was about to say you need a pitch gauge, but actually all you need is a ruler to count the # of threads in one inch, both on the spindle, and on the backplate. Then you will know if the 2 threads are a match. If they are, then you need to screw it on until it stops, and figure out what is causing it to stop. No one can figure this out for you without being there at your lathe. I don't think that tiny gouge the needle is pointing to would stop the backplate from screwing on. As far as the plate being homemade, I've made 2 backplates at home and they work fine. You shouldn't be buying anything (except of course for some measuring, and indicating tools), until you figure these things out. I apologize if I offended you with my tone, but I'm sincerely trying to help. Good luck, JR49
 
PAturner said:
After many hours of scrubbing, vinegar, and lubricating, there has been no improvement.

The backing plate still refuses to screw on. I don't think that the backing plate threads are metric since it screws more than halfway on with no problems and the part seems to be homemade anyway. I'm really blanking on what to do here, and I doubt my abilities to make an accurate backing plate as a first project.
Any advice on what to do next? I saw on practical machinist someone used a fine lapping compound on the threads and screwed the plate back and forth a few times and got it to fit all the way on. Would this destroy the threads or is it worth a shot?


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Click to expand...
I don't believe that you have told us the make and model of your lathe. That will go a long way in enabling us to help you.

Check spindle thread diameter and thread pitch carefully. Grizzly, for example has been known to mix English and metric units for spindle diameters and pitches. 1-3/8" is very close to 35mm. You could get a reasonable facsimile of the internal pitch by pressing some modeling clay into the threads and carefully removing it. Compare to the spindle threads.

I don't recall your mentioning trying the bluing. This will definitely tell you where the interference is.
 
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