Atlas/Craftsman 12x36" lathe...questions

The bull gear has a set screw and is keyed to the spindle shaft. When in back gear, that pulley drives the small gear on the left through those “clutch dogs, which drives the back gear assembly, which drives the bull gear, which drives the spindle. Slide the pulley back into engagement with the small gear on the left, and tighten the set screw in the bull gear that is on an angle after it’s all together and your two spindle gears are in line with your two back gears. Before you tighten it, it may behoove you to remove the set screw and drop a small piece of brass or copper wire into the hole, to avoid upsetting the spindle where the set screw bears. But before you do any of that, wait for Wa5cab to reply, just in case I’ve missed something.
 
Jason280 said:
Another question, trying to figure out a few things with the back gear assembly that changes to direct drive/low gear. My understanding is you pull the pin on the main gear, then roll the eccentric to engage the two back gears to lower the speed. Is this correct?
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Yes, that is correct. When in back gear, the pulley will make about six revolutions while the bull gear and spindle are making one.
 
There is a shoulder on the spindle against which the collar to the left of the small spindle gear should sit. Loosen the set screws in the collar and push the collar toward the tailstock without rotating it and re-tighten the set screws. Pull out the direct drive pin and confirm that the pulley is free to spin on the spindle.

There is an oil plug at the bottom of one of the pulley grooves. There have been a few reported cases where a PO has somehow forced the set screw/oil plug on down and against the spindle, which locks the pulley to the spindle. If you pull out the direct drive pin, engage back gear, and try to start the motor, either the motor stalls, the belts slip, or the pulley slips and the screw damages the spindle. If this has been done to your machine, back the oil plug out three or four turns, and find a short (3/16" or 1/4" set screw to put down in the hole and lock the oil plug. But hopefully this hasn't happened to yours. If it has, there is nothing to do about it at this point but if you ever pull the spindle, you will almost certainly have some difficulty in getting the spindle through the pulley. And you will need to replace the damaged pulley bushing that results when you pull the spindle through it.

At this point, since odds are that it hasn't been done in years, oil the pulley bushings. Pull out the direct drive pin and slacken the belts. Remove the oil plug from the pulley groove. Put about three squirts of SAE 20 ND through the hole and reinstall and tighten the plug. Tighten the belts, start the motor and let it run for 10 or 15 seconds. If you haven't done this in the past month, repeat twice.

Slacken the belts, pull out the direct drive pin, and check the end float of the pulley. The books don't give a figure but there should be definite movement, maybe 0.003" to 0.010". The only adjustment would be to move the bull gear, which might take it out of alignment with the small back gear.
 
My personal rule of thumb is to chuck the chuck. Well, I mean that many older lathes are sold with chucks that are so worn they have done their best work and need to be retired. You might be able to improve it a bit but I wouldn't spend a lot of time and effort. Use your 4 jaw for accuracy until you can afford a decent 3 jaw
Mark
 
Part of what Mark is alluding to is that the scroll disk wears both in the threads and in the spigot and hole that it runs on. The common way of re-grinding the jaws using a pre-loading jig plate is not really satisfactory in my opinion as the gripping surfaces end up with a radius ground on them instead of the original flat. There is a way around this as all of the Atlas lathes have a 60-hole index in the bull gear but it still doesn't do anything about the scroll.

So he is saying that if the chuck is worn out, it is just worn out.
 
Any suggestions on a decent 3 jaw replacement? Shars lists a 6" 3 jaw for 1.5x8 spindles for $150, and I'm sure prices go up from there.

Actually, now that I think about it, doesn't a South Bend B9 have the same spindle thread? If so, I could always try the 3 jaw chuck from the one I have...

Also, and I assume this is pretty straightforward, any special technique for removing the spindle adapter?
 
Yes, the SB 9A, B and C all have 1-1/2" - 8 spindle nose threads. So anything that will screw onto an SB 9" spindle should also fit the Craftsman 12".
 
My plan was to try my SB 3 jaw chuck this morning, except it seems to be stuck pretty firmly in place. I didn't have time to try and muscle it off, so I'll have to try again tomorrow. Hopefully the runout on the SB chuck is much better, it would definitely make things easier.
 
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