- Joined
- Apr 4, 2016
- Messages
- 963
A couple of years ago I dealt with this on a four-jaw combination scroll/independent chuck.
I purchased this chuck used on e-Bay several years ago and have never been really satisfied with it's performance but never took the time to really look into why it's accuracy wasn't up to par. The chuck is a quality piece made by Rohm in Germany and I have two other Rohm chucks that I have been very satisfied with so I thought it was unusual that it's performance was so poor. So, I decided to get serious about looking into the chuck. I have used it for chucking irregular work pieces and it seemed to work fine, but any time I attempted to dial-in something round, it was terrible. So, I took a piece of 3/4" ground HSS round stock and chucked it up. I could see daylight between the work piece and the outer ends of the jaws (obvious bell mouthing) I could slide a .004 or .005 feeler gauge in about half the depth of the jaws. I removed the jaws from the chuck body and tried to determine if there was any significant obvious wear in the T-slots that the jaws ride in and to see if I could detect any significant movement of the jaws in the T-slots that would give the effect of bell mouthed jaws. I was not able to detect any wear, so I decided it was time to try my hand at grinding chuck jaws.
Well, I don't have a tool post grinder and didn't want to invest in one for this one job, so I decided to see if I could set up my pneumatic die grinder to do the job (I know, not exactly the ideal tool for the job). I made a mount out of some scrap I had on hand, got everything dialed in concentric with the lathe spindle and proceeded to grind the jaws. It was a very slow process but I am very satisfied with the outcome. I can now chuck up that same piece of 3/4" HSS ground stock, dial it in to within .0005", remove it using the scroll and replace it multiple times and it will consistently dial in at .001 or less.
Some photos of my set up attached.
Ted
I purchased this chuck used on e-Bay several years ago and have never been really satisfied with it's performance but never took the time to really look into why it's accuracy wasn't up to par. The chuck is a quality piece made by Rohm in Germany and I have two other Rohm chucks that I have been very satisfied with so I thought it was unusual that it's performance was so poor. So, I decided to get serious about looking into the chuck. I have used it for chucking irregular work pieces and it seemed to work fine, but any time I attempted to dial-in something round, it was terrible. So, I took a piece of 3/4" ground HSS round stock and chucked it up. I could see daylight between the work piece and the outer ends of the jaws (obvious bell mouthing) I could slide a .004 or .005 feeler gauge in about half the depth of the jaws. I removed the jaws from the chuck body and tried to determine if there was any significant obvious wear in the T-slots that the jaws ride in and to see if I could detect any significant movement of the jaws in the T-slots that would give the effect of bell mouthed jaws. I was not able to detect any wear, so I decided it was time to try my hand at grinding chuck jaws.
Well, I don't have a tool post grinder and didn't want to invest in one for this one job, so I decided to see if I could set up my pneumatic die grinder to do the job (I know, not exactly the ideal tool for the job). I made a mount out of some scrap I had on hand, got everything dialed in concentric with the lathe spindle and proceeded to grind the jaws. It was a very slow process but I am very satisfied with the outcome. I can now chuck up that same piece of 3/4" HSS ground stock, dial it in to within .0005", remove it using the scroll and replace it multiple times and it will consistently dial in at .001 or less.
Some photos of my set up attached.
Ted