Th54 Back Gear Operation?

[WesPete66]

Well it's spring, and some of the spring work out of the way it's time for hobbies again.
I am in process of setting up my Atlas TH54 lathe. Have just completed the rebuild of the QCGB and bolted it back in place. Was looking at the machine in general and am not clear as to how the back gear operates.. On the spindle are two gears, a large one right of the pulleys and a small one left of the pulleys. It is this small left gear that has my attention for now. This gear (#10-242 in parts list) has a set of notches on the side next to the pulleys. The gear is free to slide on the spindle, maybe .180-.210", enough to engage these notches into the pulleys. This gear freewheels when the back gear is not in use. But if the back gear is engaged, and this gear is locked to the pulleys, nothing can turn. Locked tight.
I don't understand this. Is something not right? What keeps this small gear from sliding/locking during operation?
Help please? and thanks!!
(ps; my forum search function is not working right now..)

 

[ELHEAD]

Do you have the Manual of Lathe Operation for your lathe? It goes into detail on the operation of the back gear.
Dave

 

[cdhknives]

You should not be able to slide the gears and 4 step cone pulley on your spindle back and forth. There is a collar with a lock screw on the left and the set screw in the bull (big gear on the right) should pretty much fix the 2 gears and cone pulley in place.

Make sure the oiler screw in the second step of the cone pulley is NOT tightened down. It will score the shaft...and it is not intended as a set screw.

Pull the direct drive lock pin that locks the bull gear to the cone pulley to use back gear. Disengage back gear and push the direct drive pin back in for high speed operation.

 

[WesPete66]

Dave, Now that I look, no I don't have that book. Is it available somewhere?

CDH, I'm glad now I didn't try to power up the lathe yet! I didn't think that sliding gear looked right. I need to do some research on this all..
When you say to pull the direct drive lock pin, is that the pin that stops the bull gear from turning?
Thanks!
Wes

 

[eeler1]

Not an atlas, but similar in concept if not in practice, this may help;

 

[wa5cab]

Pete,

Just FYI, if you have a TH54 with QCGB installed, technically that makes it a QC54.

Between 1937 and 1988, there were supposedly 32 printings of the Atlas MOLO (Manual Of Lathe Operations). In these 32, there are 9 different versions. Up through 1954, the only way to tell the versions apart is to look at the first page (if any) in Chapter 7 - Threading. For a brief history of the contents of the MOLO, there is a PDF file in Downloads and a selection chart (MOLO version to lathe Model Number). There is also a link to both in a post at the top of this forum (in the Stickies) that I put there before we got Downloads running again. There are two or three PDF scans around of the 1937 Version 1 (covers 10D and earlier and the early Craftsman 12" models). And maybe one or two of later versions. AFAIK, there are none around of the 1955 V6 that you need. Your best bet is to set up a search or two on eBay. Be prepared to get a fair number of hits that are not the one you want because most eBay sellers don't know what they have or don't know what is important enough to include in title or text of their ads. However, finding the correct 1955 edition is simpler than finding the correct one out of the 15 or so printings where the Copyright page just said Copyright 1937.

 

[wa5cab]

I forgot that this thread started out about the small spindle gear. As previously stated, it shouldn't be able to move on the shaft more than about 0.003". The bull gear pin referred to earlier is the one in the large spindle gear. Pull it out. See procedure correction below. You should probably first remove the oil plug in the pulley (looks like a set screw) and oil the pulley and gear bushings thoroughly as they may not have been oiled in decades.

 

[WesPete66]

Thanks all for your replies!
I did find I had A copy of the manual on my flash drive, so did some reading. (will now check which version I have)
Went to the lathe for a look, and it all clicked. Loosened and slid the bull gear and pulleys to left against the small gear. Mainly because this lined up with the back gears best. Now it is easy to see how it all operates! (it made no sense before) Nice!
This brings up a question though. Is there a "proper" location left-right for these gears/pulleys? Am I ok just by lining up with the back gears, or can they move left/right as well?
Thanks,
Wes

Oops, just reread the above.. Slide the pulleys against the step in the spindle. Got it! Thanks!

 

[wa5cab]

CORRECTION TO SECOND POST ABOVE.

I've been looking at too many 6" drawings lately I think. Procedure that I wrote above was backwards for 10" and 12". Pull out the direct drive pin and loosen set screw in bull gear (large spindle gear). Loosen both set screws in collar next to small spindle gear. Slide collar against shoulder or step in spindle and tighten both set screws. Then slide small spindle gear against collar, pulley against small gear (engaging dogs), and large gear against pulley, and tighten set screw in large gear. Confirm that pulley and small gear spin freely with minimal end float. Re-engage direct drive pin. The back gears should fairly closely line up with the spindle gears. There appears to be no adjustment provided for the longitudinal position of the back gears. If they were much too far toward the tailstock, I suppose that you could move the 10-255B Washer to the other end of the shaft. Or decrease its thickness and add a second washer the thickness of the adjustment. However, a little misalignment won't hurt anything.