12" Atlas Reverse Tumbler Gear Stud

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paul s

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Just got a 12" Craftsman/Atlas, going through it and making it usable.

Regarding the two smaller single gears - were the nuts on the back side staked? I took the assembly apart for cleaning, and there doesn't seem to be any provision for keeping the nut from tightening all the way against the casting. There's a shoulder on the stud where it meets the front of the tumbler casting, but not on the back.

Also, why does the headstock pulley have indexing holes, just like the bull gear?

Paul
 
To answer your second question first, in any given year up until the end of WW-II (roughly the Summer of 1945), Atlas built three models of 12" lathes, 101.0736x, 101.0738x and 101.0740x. where "x" = 0, 1, 2 or 3. The first group of four models had no back gears, so the right face of the step pulley had the indexing holes. The first two groups had babbit bearings and the third had Timken bearings. There is probably no way to prove what happened, but either the factory installed the wrong pulley (either by mistake or because they had a lot of them in stock after production of the babbit bearing lathes ceased) or a PO somehow damaged the pulley and maybe the factory was selling off the pulleys with the holes cheaper to get rid of them.

On your first question, no. The two nuts are torqued against the back side of the Tumbler which locks the L3-48A Shoulder Bolt against the tumbler and prevents it spinning with the gear and double keyed bushing. The two gears are standard A-suffix Change Gears with 20T and 24T. Although the parts drawings have never shown it, the A-suffix gears still have the same 3/8" face as the original no-suffix gears supplied on the x=0 and x=1 models but they have a 1/2" long hub, which sticks out from each face or side of the gears, 1/16" to each side. Note that all of the parts shown for the tumbler and change gears with an "A" suffix have the 1/2" hubs or are 1/8" longer than the original parts. These are used on all machines with x=2 and x=3, which includes your 101.07403.

Not that it matters to you, but the change gears and 1" long bushings were all carried over to the late 12". For some reason, they changed the two tumbler gears on the late 12" instead of using change gears there.
 
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Regarding the pulley; anything's possible on this machine - I pulled it out of an estate and the history is unknown. The bull gear was rubbing up against the index pin and I couldn't turn the spindle, until I loosened the set screw and moved the gear inboard. So, I suspect it's not completely original.

Regarding the tumbler gears; you're saying the shoulder bolt is stationary, while the gear and keyed bushing rotate? That's what I would expect, but that doesn't seem to be the case here. The gear will not rotate with respect to the shoulder bolt, in fact, it appears to be a press fit. I put it on the arbor press and pressed the shoulder bolt out roughly 1/16" and there's still no relative motion. I notice that my tumbler casting is L3-21A, while the parts list shows what appears to be L6-21.

Meanwhile, I've almost got the spindle out, but I'm fighting the woodruff key on the bull gear.
 
Remove the gears, bushings and shoulder bolts from the tumbler. Press the shoulder bolts out of the bushings and clean up the bolts and the bore of the bushings until the bushings will spin freely on the bolts. Then reinstall and tighten the bolts and then install and tighten the nuts. And confirm that the gears still spin freely on the bolts. Apply a few drops of SAE 20 oil to each bushing and bolt.

As to the question of L3-21A or L6-21, I will try to remember to call Clausing and see whether anyone knows what the story is. All of the 12" flat parts lists that we have show L3-21A, the "A" appearing with the appearance of the "A" suffix gears. The later Illustrated or exploded view parts lists show L6-21. The one model where we have both types of parts list shows L3-21A on the early one and L6-21 on the later one. And to further confuse the issue, back in 2012, I started downloading all of the parts lists off of SearsPartsDirect. And all of those lists still show L3-21A,
 
Thank you, Robert.

One of the gears/bushings had some old lubricant that hardened - I used isopropyl and 4/0 steel wool. The other, however, had more issues. The bore was distorted slightly near one face of the gear, which was remedied by forcing the bolt through and turning with a wrench, repeatedly. The distortion was enough to keep the gear from freely turning. Even worse, the shoulder of the bolt did not protrude through the gear. I fixtured the gear with an expanding arbor on my South Bend and took a few cuts off the face. I was surprised at how far off square the faces were to the bore. And I don't think it's a consequence of the bore being distorted, I think it's still on-axis. I put the tumbler back together, and there's no binding between the two gears, everything turns freely.

Any advice on that woodruff key on the backgear? I tried prying up the outboard end with a screwdriver, tried needlenose pliers, wouldn't budge. I thought maybe I could rock it back and forth, so I hit with a pin punch on the inboard end, no go. When I hit it with the pin punch on the outboard end, it rocked a bit - of course, that doesn't help much, maybe even worse off now.
 
I assume you are trying to pull the spindle. Although this works best if you are using a drawbar and receiver (which keeps the spindle centered), try moving the bull gear and everything else on the spindle to the rear. Then extract the spindle until most of the key is visible. Dribble a little penetrating oil down both sides of the key. Wait a few minutes and then use a pin punch on top of the rear end of the key.
 
Back on the original subject, if one of the shoulder bolts is too short, it is probably the original "non-A" version.

The gear with the damaged bore sounds like a hammer blow damage.
 
wa5cab said:
I assume you are trying to pull the spindle. Although this works best if you are using a drawbar and receiver (which keeps the spindle centered), try moving the bull gear and everything else on the spindle to the rear. Then extract the spindle until most of the key is visible. Dribble a little penetrating oil down both sides of the key. Wait a few minutes and then use a pin punch on top of the rear end of the key.
Click to expand...
Yes, I need to replace the two spindle gears that interface with the backgear, apparently, the zinc "pests" got to them. I don't think I can expose any more of the key at this point - it's all the way up against the inner bearing cover and the gears/pulley/collar are all the way up against the other inner bearing cover. I've tried penetrant and I'll try the pin punch again.
 
Regarding the short shoulder bolt - do I have mixed parts from different versions? The SN on the bed is 30478.
 
If the short shoulder bolt looks like the long one except for length, that would be my guess. Most commercially available shoulder bolts are socket head. So if the too short one is hex head, it's probably an Atlas part. But the gear hub length change dates from about 1938 and your lathe from early 1951. So it is unlikely that the mistake happened at the factory.
 
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