Atlas 10100 Mk2 lead screw flexing when half nuts are engaged...

RJSakowski said:
Atlas lathe should have been built to better standards than the typical Asian lathe. I am not familiar with that particular model number. My 6" Atlas/Craftsman is an older model with a cast iron headstock but it would pemit shimming both the headstock and tailstock bearings to bring into better alignmnent with the halfnuts
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Don't see any reason why this model wouldn't be able to be shimmed but I'm curious as to why it's occurring in the first place, Doesn't seem to be a problem that I can find using search that's common to the Atlas 6" lathes. The 0.005in. shim at the tailstock lead screw bearing dropped the lead screw flex to zero at that end. It also dropped the measurement at the mid-point by 0.005in., though it only reduced the flex at the headstock end by 0.001in. More testing will be done to make sure it's not a bent lead screw I'm dealing with.
 
I can't think of anything that you could have done on the reassembly that would cause your problem. The carriage (saddle and apron) on all of the 6" Atlas lathes is one piece. So no adjustment there. I would guess that there is a grinding or milling error on one of the parts involved. If you had another Atlas or Craftsman 6" lathe from which to swap parts, you could probably find the culprit. I would start with either the carriage or the bed. But otherwise, it might be quite expensive to find out. Were it mine and I didn't already have another 6" to play with the parts from, I would shim the two bearings as required and get on with life. If you ever have to replace another related part (such as the half nut guide), I would check both with and without the two shims to see if the problem was still there. But otherwise, the two shims will not hurt anything.
 
I do have a spare stripped apron that I'm piecing together as I find parts. Still not quite sure how exactly to install the half nut lever once I get one. It looks to be staked in place on the apron. Once I get the needed parts together to complete it I'll check it against the lead screw both with and without shims to find the source of the deflection as you instructed.
 
On the 10" and 12" machines, the early ones all seem to have the lever staked to the scroll shaft. Later ones had the shaft center-drilled and tapped and the lever design modified so that it was retained by a rack-and-panel an oval-head counter-sunk screw. So if you were rebuilding one of those, you could buy one of the later levers and drill and tap the shaft. They may never have done that on the 6"' But you could still do it that way. All that you would need to do would be to locate a rack & panel washer whose OD was equal to or slightly greater than the diagonal dimension of the square on the shaft. And then to drill and tap the shaft for the appropriate rack & panel screw. I would use Blue Locktite on the screw as you may never need to remove the scroll again. But you could if you had to. The only down side would be that if you buy the screw and washer from a place like McMaster, you will probably end up with 49 or 99 screws and washers that you never have another use for. I would go to an Ace Hardware instead. If they have it, you will be able to buy one of each.
 
UPDATE..... Today was warm enough in the garage to finish troubleshooting the lead screw flex problem. Cannibalized a HF set of feeler gauges for use as shims, drilled some 0.250 in. holes in the shims (0.020 in. at headstock & 0.005 in. at tailstock). I now have around 0.001 in. movement of the lead screw when engaging/disengaging the half nuts according to the DI.
 
That certainly sounds much better.
 
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