How to fix back gear separating from belt pulleys on Atlas 618

[markba633csi]

If there's enough threads so that you can put two setscrews, one on top of the other, that would help keep things tight if the original screw
keeps loosening up
Otherwise, loctite removable 242 is what I'd use- a very tiny amount or you'll have trouble getting it apart in the future

 

[skcncx]

If there's enough threads so that you can put two setscrews, one on top of the other, that would help keep things tight if the original screw
keeps loosening up
Otherwise, loctite

Thanks, I thought about that... I'll have to thread my extra down and see how many threads I catch. I did a fair amount of turning again tonight and everything stayed where it should so I'm glad it was an easy fix.

 

[wa5cab]

All of the Atlas-built lathes with back gears have a set screw in the hub of the bull gear that must be tight in order to keep the gear from "walking" out of engagement with the small back gear.

For an explanation of the oil plug screw in the cone pulley, including what will happen if you or a previous owner are dumb enough to tap the hole on through so that the set screw locks the cone pulley to the spindle, see the explanation up in the Sticky Area at the top of the screen in this Forum.

 

[wa5cab]

FWIW, the oil plug screw in the second to smallest diameter cone pulley groove, when new, could be snugged down to hold it in place over time. But a distressing number of all Atlas-built lathes are found with that hole tapped through to the ID. As the warning in Sticky I think says, anyone acquiring a new-to-them lathe should check this before starting the lathe the first time. To do it, starting with the set screw snug, measure the distance from the bottom of the pulley groove to the top of the screw. Be sure that you don't measure the distance to the bottom of the hole in the set screw if it is the Allen type. Then remove the set screw from the pulley and measure the hole depth down to the spindle and the screw length..

Sum the screw length and the first measurement (distance down to the top of the screw). If it is approximately the same as the distance from the bottom of the groove to the spindle, you have the problem. And as I think that I wrote several years ago, the only solution is to buy a bunch of nylon-patch set screws. The reason for buying several is that you won't get away with using them more than a few times.

Another consequence of the mistake is that if you need to pull the spindle, if locking the set screw to the spindle left marks, you will probably damage the right cone pulley bushing and maybe the bore of the bull gear, although you may get a chance to file the marks off after the marks clear the pulley bushing.

 

[skcncx]

FWIW, the oil plug screw in the second to smallest diameter cone pulley groove, when new, could be snugged down to hold it in place over time. But a distressing number of all Atlas-built lathes are found with that hole tapped through to the ID. As the warning in Sticky I think says, anyone acquiring a new-to-them lathe should check this before starting the lathe the first time. To do it, starting with the set screw snug, measure the distance from the bottom of the pulley groove to the top of the screw. Be sure that you don't measure the distance to the bottom of the hole in the set screw if it is the Allen type. Then remove the set screw from the pulley and measure the hole depth down to the spindle and the screw length..

Sum the screw length and the first measurement (distance down to the top of the screw). If it is approximately the same as the distance from the bottom of the groove to the spindle, you have the problem. And as I think that I wrote several years ago, the only solution is to buy a bunch of nylon-patch set screws. The reason for buying several is that you won't get away with using them more than a few times.

Another consequence of the mistake is that if you need to pull the spindle, if locking the set screw to the spindle left marks, you will probably damage the right cone pulley bushing and maybe the bore of the bull gear, although you may get a chance to file the marks off after the marks clear the pulley bushing.

Thanks for the heads up and tips. I hope to never have to disassemble the head stock (at least not for awhile), partly why I outfitted it with a mended urethane belt when I switched over to using a variable speed Consew CSM1000 550 watt motor and removed the extra pulley counter shaft. Ended up needing/wanting a shorter belt. Those melt and mend back together v-belts are pretty slick.

On the cone pulley oiler screw, I just snugged it up and backed it off. On mine, it's a flat head style set screw.... I though maybe the flat headed slot set screws are the ones you need to oil, while the socket head set screws were the actual set screws that need to be snugged down for the purpose of keeping things in place. On my bull gear, the deep set screw was a socket head, the one over the pin to engage/disengage the back gearing is a flat head. But who knows, factory likely interchanged screw head types throughout and who knows what previous owners swapped out with as they repaired... to my knowledge, I'm only the 2nd owner of this Craftsman 101.21400 / Atlast 618 model.

 

[aoresteen]

The backgear pulley in the Craftsman 109.21270 et al has a similar set screw that is for oil, not to bind the pully onto the spindle, From scar marks I've seen on some early 109 spindles (no key) people screw them down to the spindle when they should float free of the spindle shaft.

 

[wa5cab]

@skcncx,

I don't know how Atlas decided which head to use on the various set screws. I don't recall what the bull gear has in it. But the oil screw in the cone pulley is and as best I can recall after 40+ years always has been an Allen.