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| Chuck jaws - making them parallel...? |
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| AdeV:
So, I sling some bar stock in the 4-jaw chuck, line it up by eye, then pop an indicator on it - say 4" out from the chuck. After a bit of fiddling, I can usually get it indicating less than 0.002" runout. If I'm really trying, I can get it under 0.001", but that needs patience... Anyway, slide the DI down to just by the jaws, and suddenly it's reading "several" thou of runout (for a long - say 4" - piece, maybe as much as 0.010"). I can dial that out of course, but then I've got runout at the far end. I can only assume, therefore, that my chuck jaws aren't parallel any more. Is there a simple fix which I can do with the lathe itself, or do I need to investigate replacing the chuck? |
| Bogstandard:
Ade, What you are experiencing is one of the failures of smallish independent jaw chucks (or sometimes big ones, depends how white knuckle you can tighten things). With a self centring chuck, when they are tightened, all jaws exert the same pressure, so they all wear or deform the same. With an independent, pressure is applied to each individual jaw, so they don't wear or deform equally. This is usually caused by people applying pressure to get the piece into position rather than slackening the opposite jaw. If you know someone with a surface grinder, it is only a few minutes job to bring them back to like new by grinding them all square, together as a block. Bogs |
| DMIOM:
--- Quote from: AdeV on September 14, 2010, 08:18:04 PM ---...... Is there a simple fix which I can do with the lathe itself, or do I need to investigate replacing the chuck? --- End quote --- Ade, Have you whipped the jaws out and had a good look in case there's a ding or a burr? How is your chuck mounted? is there a chance that the mounting of the chuck body isn't square to the spindle, especially if its on a back-plate? (also assume you've tried this with several bits of stock in case the first one was just the type of over-bent banana/cucumber the European Union was trying to stamp-out) Dave |
| Stilldrillin:
Ade, I would grip onto a thin disc, held at the very back of the jaws. Then take a very light cut with a tipped boring tool. Same as soft jaws! :thumbup: David D. P.S. Nice to see you here again John! |
| No1_sonuk:
--- Quote from: DMIOM on September 15, 2010, 03:32:59 AM ---(also assume you've tried this with several bits of stock in case the first one was just the type of over-bent banana/cucumber the European Union was trying to stamp-out) --- End quote --- This was my first thought. One way to check is to mark the high spot on the stock and jaws with tape, then rotate the stock 90 degrees. Do the clocking again, and see if the high spot has moved round with the stock. If the high spot moves, it's more likely the stock. |
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