- Joined
- Dec 24, 2020
- Messages
- 1,042
Edited to correct the jaw numbers and add the clarifying question at the end.
I know this will be a lot of reading, so I'll apologize in advance! I've only got $85 total tied up in this, so I'm not at all worried about the outcome, just curious about what's going on. Here's the scenario:
I recently bought a used Buck model 4831 3-Jaw Adjust-True chuck (8"). It was at an auction I was able to preview and saw it was a Buck AT...the auction pictures didn't show the brand, and just said 8" 3-jaw chuck so I got it cheap. It came with inner and outer hard jaws. The inner hard jaws obviously came from another chuck as they were marked 1, 3 and 5, with the #3 being in the 2nd jaw slot and the #5 in the 3rd jaw slot, so I'm assuming they came from a 6-jaw chuck. I couldn't see this at the preview as it had dried cutting oil and dried dirt.
I had a backplate that would work, so I fit the chuck to the backplate, adjusted it to zero the runout and was okay with the results. The inner jaws have a trace of bell mouthing so I could only get the runout down to like .0015" which is three times what I get on my other 4831 that's on a different lathe. The outer jaws show runout well under a thousandth, so those are good and appear to be the original, correct jaws for this chuck.
While adjusting the runout I noticed I had to use pretty much all of the range available in one direction but didn't think much of it as I only left .010 clearance (diameter). When I ran the lathe with the inner jaws mounted (holding a piece of stock) I got a significant vibration at around 800rpm. If I slowed it to 700 or below, or went 900 or higher it was much better and at some speeds not noticeable at all. I stopped running it almost immediately...just enough to play with the speeds and check that nothing obvious was loose like one of the leveling pads...so maybe a minute of run time.
I put an indicator on the side of the backplate and saw well under a thousandth in runout. I put an indicator on the chuck body and it's like .010" runout. Putting a straight edge on the chuck body showed it was flush with the back plate on one side and a very visible gap on the opposite side. That tells me the vibration is due to the chuck being off center, so it's not balanced.
My initial thought is that the incorrect inner jaws are so far off that I had to move the chuck body a long way on the backing plate, but when I swap for the outside jaws they are spot on. I would have expected the outside jaws to be way off when the inside jaws are zeroed if the inner jaws are the problem. Clearly I'm missing something, but what?
I've got so little into it I'm not worried, and I'm considering talking to the folks at Kalamazoo Chuck Manufacturing as they mention being the service center for older Buck products. I expect it won't be cheap to have them go through the chuck and make new inner jaws, so before I head down that path I want to kick around what could be going on.
I'm not focusing much on the fix, as much as how it could be possible that both sets of jaws could be dialed in while the body is offset from the back plate. It would seem like if it was zeroed with one set of jaws the others should be off by a lot. Thoughts?
I know this will be a lot of reading, so I'll apologize in advance! I've only got $85 total tied up in this, so I'm not at all worried about the outcome, just curious about what's going on. Here's the scenario:
I recently bought a used Buck model 4831 3-Jaw Adjust-True chuck (8"). It was at an auction I was able to preview and saw it was a Buck AT...the auction pictures didn't show the brand, and just said 8" 3-jaw chuck so I got it cheap. It came with inner and outer hard jaws. The inner hard jaws obviously came from another chuck as they were marked 1, 3 and 5, with the #3 being in the 2nd jaw slot and the #5 in the 3rd jaw slot, so I'm assuming they came from a 6-jaw chuck. I couldn't see this at the preview as it had dried cutting oil and dried dirt.
I had a backplate that would work, so I fit the chuck to the backplate, adjusted it to zero the runout and was okay with the results. The inner jaws have a trace of bell mouthing so I could only get the runout down to like .0015" which is three times what I get on my other 4831 that's on a different lathe. The outer jaws show runout well under a thousandth, so those are good and appear to be the original, correct jaws for this chuck.
While adjusting the runout I noticed I had to use pretty much all of the range available in one direction but didn't think much of it as I only left .010 clearance (diameter). When I ran the lathe with the inner jaws mounted (holding a piece of stock) I got a significant vibration at around 800rpm. If I slowed it to 700 or below, or went 900 or higher it was much better and at some speeds not noticeable at all. I stopped running it almost immediately...just enough to play with the speeds and check that nothing obvious was loose like one of the leveling pads...so maybe a minute of run time.
I put an indicator on the side of the backplate and saw well under a thousandth in runout. I put an indicator on the chuck body and it's like .010" runout. Putting a straight edge on the chuck body showed it was flush with the back plate on one side and a very visible gap on the opposite side. That tells me the vibration is due to the chuck being off center, so it's not balanced.
My initial thought is that the incorrect inner jaws are so far off that I had to move the chuck body a long way on the backing plate, but when I swap for the outside jaws they are spot on. I would have expected the outside jaws to be way off when the inside jaws are zeroed if the inner jaws are the problem. Clearly I'm missing something, but what?
I've got so little into it I'm not worried, and I'm considering talking to the folks at Kalamazoo Chuck Manufacturing as they mention being the service center for older Buck products. I expect it won't be cheap to have them go through the chuck and make new inner jaws, so before I head down that path I want to kick around what could be going on.
I'm not focusing much on the fix, as much as how it could be possible that both sets of jaws could be dialed in while the body is offset from the back plate. It would seem like if it was zeroed with one set of jaws the others should be off by a lot. Thoughts?
Last edited: