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- Apr 23, 2018
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What's the big deal? Sorry, I measured from a different spot.
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Chuck question
- Thread starter jwmay
- Start date
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- Dec 3, 2017
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True. I bought it that way.
Well I don’t actually know if it’s a big deal or not. Sometimes I look at something and say to myself,”self, somethings not quite right here.” Perhaps it’s me that’s not quite right. It just seems like a lot of overhang. I don’t know that it is. I guess I’ll find some different thing to worry about for now.What's the big deal? Sorry, I measured from a different spot.
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- Apr 5, 2018
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- 105
I think it matters, especially with the little 1" spindle shaft and bearing on my 6" Atlas, to help minimize chatter and work climbing the cutter.
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- Dec 3, 2017
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Yeah I kinda feel like the first indication it did matter will be a bearing failure, or maybe just chatter. Time will tell. I’m getting used to the look of it now. Wishing I hadn’t sold off everything from my previous basket case Atlas now. Gonna have to bolt something to the compound and try out a cut!
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- Dec 25, 2011
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There are several reasons why chuck "stick out" should be minimized if possible. The obvious situation is that the farther out the chuck sticks, the shorter your workspace is. The common way to characterize spindle accuracy is to measure and quote the TIR (commonly just "runout") usually measured on the register area on the spindle nose or on a precision ground test bar gripped in the chuck. However, there is really more to it than that one figure (unless it is zero, which it never is).
The spindle runs in two bearings, not just one. Suppose that the runout measure at both ends of the spindle is 0.0020". Further suppose that at the time you measured them, the two runouts were exactly in phase. And that the headstock is exactly lined up with the vertical surface of the rear way. As long as the largest diameter that you turn the work piece to is smaller than the original diameter by an amount greater than the runout, everything should be OK. But if the two runouts are 180 degrees out of phase, the farther away from the front bearing you are, the worse the part becomes.
The spindle runs in two bearings, not just one. Suppose that the runout measure at both ends of the spindle is 0.0020". Further suppose that at the time you measured them, the two runouts were exactly in phase. And that the headstock is exactly lined up with the vertical surface of the rear way. As long as the largest diameter that you turn the work piece to is smaller than the original diameter by an amount greater than the runout, everything should be OK. But if the two runouts are 180 degrees out of phase, the farther away from the front bearing you are, the worse the part becomes.
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- Apr 23, 2018
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- 6,873
I realized I have been running my relatively heavy 6-jaw Pratt-Burnerd with the Burnerd 1" mounting plate on it for a year and a half as my primary chuck. I have been "proud" of my babbit bearings for having very low runout, and the indicator still shows it, but I measured a bit of "nod" in my head stock the other day. Like, a lot of nod, on the order of .001" per 1" of carriage travel. I see two possibilities, one, my bearings are just worn out, or two, the heavy chuck might not have helped. I still have shims to remove from the bearing caps, so I'll check the outboard bearing for that. I'll probably have to bite the bullet and mount up the Timken head I have on hand. With roller bearings, I would be much less concerned about the weight of the chuck.