General Question

Jason,

Consider a 4 jaw chuck. They are a little more work to true up right off the bat but you get used to it quickly
and find you can do better work. I have both 3 and 4 jaw chucks and quite honestly, the 3 jaw is
busy collecting dust. It hasn't seen use for years. One could drill centers on both ends of a shaft and use a lathe dog
and that would have good repeatability. It just isn't my style...
 
I have a 4 jaw chuck. I will do give it some use and see where I land. Thank you for all the advice.


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A four jaw is a life saver when you need to turn your work around and still keep it accurate. It is still better to do it in one setup if possible, even with a four jaw.
 
First off, Assuming your spindle runs true. If not or you don't know, start from there.

Since you mentioned tapping on the chuck gives you no improvement, assuming you are loosening the chuck from the adapter slightly when doing so then retighten, I'm assuming your chuck mates the the adaptor's register pretty well. If that's the case as you know it won't do anything.

Now you can make your chuck an "tap-tru" but it's not recommeneded & I don't recommend it. I've done it to the stock 3-jaw that came with my lathe. But I only keep it around for dirty work like heaving sand, yada yada. I skimmed the register on the adaptor so it was slightly smaller than the register on the chuck. So now it's a loose fit. Now I can tap the chuck to run true. But if you do any heavy cutting or bump it pretty hard, it may run out again. That is why it's not recommened. For light use it will be fine.

Check the runout of your chuck using a a guage pin, shank of an endmill, or even drill rod. I use linear shafting. Remove the piece, chuck it back up & indicate again. Does it repeat your measurement fairly well or is it all over the place? This will tell you if you can just regrind the jaws or if your chuck is very worn.

If it repeats fairly well, what you can do in the mean time (should you decide to try & fix the issue), you might get away with indexing the part before removing it. Say you're working on a piece & you need to remove it for some reason. Mark a line on the part as well as on the chuck. I just use one of the jaws for indexing. When you put it back in the chuck, align the marks & then indicate. You can turn the part CW or CCW to get closer to where you were if off. But again, this only works if your scroll is not worn out.
 
I like the 4-jaw if it needs to be accurate. If I'm working in the "close enough zone," I mark the piece and put it back in the 3-jaw just the same as it came out.
 
Thank you for all the suggestions. Next time I am home I will try out the 4 jaw chuck and learn to use it. I like the idea of marking the work and chuck. I just didn't realize that There would be so much variance in that 3 jaw chuck. I assumed (yeah I know) that these would be fairly accurate chucks. Mine definitely is not. The wobble is visable, and very measurable. I will start over when I get home.


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Is the visible wobble that you mentioned of the chuck body or of a nominally round part when it is mounted in the chuck jaws?
 
A nominally round part when chucked up. The chuck itself seems to be true. The same part that I had center drilled and turned the outside to size when removed and reinstalled has wobble. So much so that a center in the tailshaft comes no where close to mating up.


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OK. With your machined part that you removed and re-mounted in the chuck and found it no longer had no wobble, did you carefully mark it with respect to one of the jaws and then as closely as possible put it back in exactly as it was before you removed it? If so, the culprit could be wear on the hole in the center of the scroll and/or on the spigot it runs on. In some cases (the wear needs to be uniform so that the hole and spigot are still round), that can be fixed or at least improved improved upon.

Have you disassembled, cleaned and inspected the chuck? I would do so. With the chuck front body lying on its face and without the jaws, install the scroll on the spigot with no lubricant other than something thin like WD-40 and see whether you can move the scroll other than in rotation. If you can, you may be able to shim the clearance mostly out. This may not (probably will not) reduce the runout to near zero but should significantly improve the repeatability.
 
Thanks for the help. I did not mark the work I just reinstalled it in the chuck randomly thinking since it was round it would be centered! It will be a couple weeks before I am home to do anything but I will definitely strip the chuck down and clean everything. This lathe lived unused in a wood working shop prior to me buying it. Everything else was covered in sawdust, why not the inside of the chuck! I will definitely look into it.


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