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

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Had a little spare time to today & decent temps outside to get the new half nuts installed on the Atlas 10100 Mk.2. I noticed before that the lead screw "flexes" or bows out toward the operator when engaging the half nuts. this also translates into pushing the threading dial away from the lead screw so that when then half nuts are disengaged the threading dial isn't making full contact with the leadscrew anymore. I set up a DI on the portion of the lead screw that was closest to the half nuts at the middle of the lead screw at the tailstock end of the apron. with the lathe turned off, engaging the the half nuts causes the lead screw to flex/bow 0.022 according to the DI.

Is there some type of adjustment I can make to remedy this or is it just a normal thing with the Atlas lathes and I'm worrying over nothing ?? As it sits now it has new half nuts installed & lead screw cleaned with brass brush and I also ran the carriage down the length of the lead screw with the half nuts engaged under power to allow the new half nuts to settle into the lead screw & further clean the threads in case the scrubbing with the brush missed anything. Flushed the new half nuts out with some spray lube, wiped the spray lube off, then re-oiled the lead screw & ran it again. None of the cleaning seemed to correct the flexing/bowing of the lead screw when engaging the half nuts...??
 
When I adjust the lead screw bearing on the tailstock end, I bring the carriage as close as possible and lock the half nuts before tightening the bearing. In your case, you need to move the bearing outward swo you you need to shim the bearing. Check your parts list. There may be a missing shim.
 
Was this a problem with the old half nuts? Is the shift the same at all carriage positions?
 
RJSakowski said:
Was this a problem with the old half nuts? Is the shift the same at all carriage positions?
Click to expand...

I believe it was a problem with the old half nuts too. I checked the parts diagrams included in the manual and there wasn't any mention of a shim. I haven't checked the deflection at multiple points on the carriage's travel yet as I didn't know how wise it would be to stress the lead screw bearings at the extreme ends of travel, thought I might break/crack something if I pushed my luck.
 
The lead screw should neither move in or out nor up or down when you engage the half nuts.

I would suggest re-installing the old half nuts temporarily to see where the problem lies. None of the parts lists from earliest to latest on 612, 618, 3950, 10100 or 10200 show any shims under either left or right bearing. And I don't ever recall anyone mentioning any. So something or several somethings isn't the right size.

After temporarily reinstalling the old half nuts, you will know whether the problem lies with the new half nuts or not. But I presume that you would prefer to get the lathe running rather than trying another set of half nuts. So reinstall the new ones. If you haven;t already, remove the change gears and change gear bracket (AKA Banjo) from the lathe. Crank the carriage to the right end of the bed and use feeler gauges to determine the required shim total thickness for the right bearing, make and install them. Note that the thickness may or may not be 0.022" and probably won't.

Crank the carriage as far to the left as it will go, back it up just barely, and repeat the process. Fortunately, there should be zero wear at either end of the lead screw, so you won't have to second-guess that. Reinstall, adjust and lubricate the change gear bracket and change gears. There should be no vertical or or horizontal bendingt of the lead screw with the carriage anywhere on the bed unless the screw is bent.
 
I have a MK2 and have zero movement of the leadscrew when engaging the half nuts. Something is way off. I suspect the half nuts/mechanism. The screw is pretty much fixed in position and has no adjustments on these lathes other than side to side and a slight bit of up / down due to slop in mounting holes.
-Mark
 
wa5cab said:
The lead screw should neither move in or out nor up or down when you engage the half nuts.

I would suggest re-installing the old half nuts temporarily to see where the problem lies. None of the parts lists from earliest to latest on 612, 618, 3950, 10100 or 10200 show any shims under either left or right bearing. And I don't ever recall anyone mentioning any. So something or several somethings isn't the right size.

After temporarily reinstalling the old half nuts, you will know whether the problem lies with the new half nuts or not. But I presume that you would prefer to get the lathe running rather than trying another set of half nuts. So reinstall the new ones. If you haven;t already, remove the change gears and change gear bracket (AKA Banjo) from the lathe. Crank the carriage to the right end of the bed and use feeler gauges to determine the required shim total thickness for the right bearing, make and install them. Note that the thickness may or may not be 0.022" and probably won't.

Crank the carriage as far to the left as it will go, back it up just barely, and repeat the process. Fortunately, there should be zero wear at either end of the lead screw, so you won't have to second-guess that. Reinstall, adjust and lubricate the change gear bracket and change gears. There should be no vertical or or horizontal bendingt of the lead screw with the carriage anywhere on the bed unless the screw is bent.
Click to expand...

Thanks...Would setting up a DI against the lead screw and running the lathe at low speed show if the lead screw is bent, or will I most likely be reading lead screw wear at the test location ??
 
Just did some checking based on the posts here... I reinstalled the old half nuts and the problem was still there, only to a slightly lesser degree,

JVCg1SVl.jpg


I grabbed a cardboard box top and wrote down the DI reading at the headstock (HS), mid point in the travel (M), and at the tailstock (TS). Starting with the old half nuts to rule out any variable introduced by the new half nuts and came up with the measurements in the pic. After replacing the half nuts each time I would engage the half nuts & then tighten the tailstock lead screw bearing in an effort to get it to run true. After replacing the old half nuts with the new ones again I retested and the measurements are shown in the middle line in the above pic.

The measurements stayed the same at 0.016in. in the middle of the lead screw and changing 0.002 at the tailstock (from 0.003in. to 0.005in), while jumping 0.004in. at the headstock. Next I inserted a 0.005 feeler guage under the tailstock end lead screw bearing and tested again (shown on the bottom line in the pic). With the 0.005 feeler guage inserted under the lead screw bearing at the tailstock engaging the half nuts resulted in 0 movement at the tailstock end, 0.011in. at the mid-point, and 0.016in. at the headstock end. All testing was done with the DI as close to the threading dial as possible without the half nut lever hitting the DI when engaging the half nuts as I thought being as close to the source (half nuts) would give the most accurate measurement.

I have yet to pull the change gears as wa5cab suggested but that's next on the list. Is there anything I could have done when I did the initial tear down and cleanup of the lathe when I first got it that could have caused the problem I have now ?? As it looks I'll need to shim both lead screw bearings.
 
I know nothing about the Atlas Lathe but on my cheapo 9x20 I have to move the carriage to the tailstock end with the apron loosley held in place, engage the half nuts THEN bolt up the apron else I get the problem you are reporting.
The first time I noticed the problem I released the tailstock end of the leadscrew and it required a 1/8" shim to get into alignment, which I did. This amount of resulting misalignment wore out the half nuts pretty fast.
Could this be your problem?
 
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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