Fixing my 3 jaw chuck with a reamer ?
So my new expensive 3 jaw d1-4 chuck has a TIR of 0.30mm. The jaws are hardend. What if I try and correct the runout by using a reamer. Reamer goes in the tail stock, spin up the chuck and slowly ream. Stupid idea ? Any suggestions ?
Good way to ruin a reamer. Bad way to reduce runout in a chuck.
First thing to do is check the runout at several different diameters of stock. Make sure the jaws are clean and free of burrs when you do this. Check using perfectly round stock. The scroll will always vary a bit.
Various sources of runout include the mounting, the scroll, and the jaws. You're not going to do much about a bad scroll (big differences in runout and location at different diameters) beyond returning the chuck.
If it's out the same at every diameter, or even just the diameter you do most of your work at, it might be either the mounting or the jaws. If your chuck body has a lot of TIR, it might be the mounting. This is corrected by opening up the bolt holes between mounting plate and chuck a bit, plus the recess, and carefully nudging things back in place to get near zero TIR at a diameter you commonly turn at. Then tighten it all up, checking the indicator as you go. You've basically made your chuck a really inconvenient "Adjust-Tru" or maybe "Adjust-once-and-check-now-and-then" in this process.
If it's the jaws, they can be ground in place. Probably other threads on that if you do a search.
First off you need to verify its not in the scroll --- try a 1/4" piece of stock - a 1/2" a 1" and so on and mark the chuck where the deviation takes place on the low or high side,,,
if consistent then you might try something to true it up but a reamer is not the tool for the job as the three jaw is an interruption that would reek havoc with the reamer flutes,
Rig a little dremmel grinder and also keep in mind the jaws have to be loaded with something and kept under pressure during the grind --- its a hat trick as you have to load the jaws exactly where needed to be ground, someone might chime in with a how too - if not I'll try to post in the monyatta...
Ohhh... Baaadddd idea.
Unless you like ruined chuck jaws and pieces of reamers flying towards you.
This is the way to do it:
I've trued Pratt-Burnerd jaws using a carbid boring bar. The jaws are not that hard. Just keep the RPMs low and use decent feed but light depth of cut. Be sure to preload the jaws somehow.
TR, if the chuck is new I would be wary of grinding the jaws, and I am sure a reamer would be a disaster, until all other causes have been eliminated.
I am a fairly raw newbee and I dont even know the TIR on my chuck so I assume there is some and work accordingly, when using the three jaw and concentricity is important I try to do all the processes without removing from the chuck. If it is a new piece I try to plan the job so that the last action is to cut the part from the stub of scrap that stays in the chuck. From what I can gather this is the best way to handle inaccuracies in a 3 jaw.
Otherwise, for instance making changes to an existing part, I use my 4 jaw (while thinking how nice it would be to have two lathes so I did not have to heave the heavy chuck around).
No idea if your chuck can benefit... the newer the chuck the less I'd think so.
I'd reserve grinding for a chuck that is bell-mouthed.... but you must suit yourself.
Here is how I have done it. I use a dremel or toolpost grinder to do the actual grinding. Depends what is available at the time. You need to "spark out" really well. Idea is from Rich Carlstedt.
Drill some holes in the jaws with a carbide drill, and set the ring.... puts a load on the chuck virtually identical to actual clamping load.
That's thinkin, good Idea JT and Rich, and nice jig Macona...
Just did mine as well not long ago. I should have dressed the stone first but it came out fine anyhow.
Last edited by vpt; 12-09-2010 at 09:24 AM.