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| Chuck runout question... |
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| picclock:
If there is enough meat left on the jaws of the 4 jaw, its not too hard to get them true if you have the time. Mine was never great from the start, but I guess it depends on what accuracy you are looking for. I experimented with the toolpost grinder way of doing the jaws but although things changed it was not an improvement. In the end I reasoned that for the jaw to be correct, in the bottom position it must be parallel to the ways. I checked this using a dti attached to the crosslide, and moving the carriage back and forth along the jaw soon showed where the high and low spots were. These were ground as shown in the pictures. http://s917.photobucket.com/albums/ad19/picclock/chuck%20jaw%20grinding/ When done the surface was like a mirror and the runout at 9" was 1/2 thou. Once you have one flat its probably a good idea to check it with the chuck rotated by 90 degrees to ensure that the spindle is true to the ways. If not, that's a whole new can of worms which you will have to sort out first. :doh: Obviously, once ground each jaw is only good for the jaw position it was ground in. Best to mark with paint or similar if they are not numbered.. This method certainly worked for me. I would have bought a new chuck if I could be certain that the jaws were truly accurate. Good luck picclock |
| AdeV:
--- Quote from: picclock on February 25, 2011, 11:07:46 AM ---If there is enough meat left on the jaws of the 4 jaw, its not too hard to get them true if you have the time. Mine was never great from the start, but I guess it depends on what accuracy you are looking for. --- End quote --- I took (one of) my 4-jaws to John, who had kindly offered to true them up on the surface grinder; which we (he, really) duly did. However, the runout was no better when I returned them to the chuck (the jaws were numbered, so no problems there); we can only think that the wear is in the "ways" of the chuck (and maybe the jaws), so that as one tightens up, the jaw is actually kicked outwards slightly by the pressure = taper. No, I think I'm just going to have to bite the bullet & risk buying a brand new chuck... Trouble is, I really need at least a 6" one, otherwise it won't fit over the spindle nose... and they get expensive quickly when they get big... Edited to add: I've just looked at RDG's site (the only co. I can find who do larger than 160mm), and actually a 200mm chuck is quite reasonable at 132quid, and 30 extra quid gets me a set of soft jaws... Very tempting..., but I guess I need a backplate as well? Any made-for-idiots tutorials on how to fit & true up a backplate? The spindle on my lathe is a simple flange, with 3 bolt holes; obviously the idea is the chuck backplate contains captive bolts, which go through the holes; the chuck registers on the outer edge of the flange, & one tightens the nuts from behind the flange (as the bishop said to the actress...). |
| picclock:
I suspect your right about the wear in the chuck, but using the method I outlined, this is mostly taken care of. I think this is why this method worked on mine so well. But, its a lot easier to get a new chuck than to muck about if you can get one good enough for your requirements. The only other thing that may cause your error is if the face that the chuck is fixed to is not at right angles to the spindle, but I'm sure you would have checked this. Hope you get it sorted Ok Best Regards picclock |
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