Atlas 618

[bama7]

I made what I believe to be a really good deal the other day on a 618 lathe. It looks good, paint included, and runs really smooth. Came with a good selection of cutters and tool holders. Decent rolling stad and tool box. The only thing I found wrong is in the lead screw. I put it in forward or reverse and engage the thread dial and it works normally. But, if I put it in backgear the thread dial does not move nor does the carriage. I am in hopes the lead screw and or half nuts are dirty. Hope to take it apart today. According to printed catalogue I saw the lead screw is 1/2” x 16 tip acme thread. I cannot fing a die to chase threads to clean them. Anybody got a solution?

 

[DavidR8]

Nice find!
The lead screw on my South Bend was completely gunked up with sawdust, oil and grease.
I put it in a slow speed and held a small brass bristle brush against the screw.
I went the full length several times and now it’s very clean.


Sent from my iPhone using Tapatalk

 

[mattthemuppet2]

have you released the locking pin in the bull gear? Does the spindle rotate ok when you put it in back gear? If the leadscrew rotates when it's in direct drive, then it should rotate when it's in back gear.

 

[bama7]

I took it apart a little while ago and cleaned the half nut and the lead screw. It was a little nasty, but did not affect or correct the problem. I think the main problem is the lead screw. I cleaned it with a wire brush as it turned as well. Sure would like to find a “die” to chase those threads before I spend the money for another lead screw.

 

[DavidR8]

Can you shoot some clear photos of the lead screw? At the tailstock end and then near the headstock end?

 

[mattthemuppet2]

with all due respect, whether or not the back gear is engage or not has no effect on leadscrew rotation. The lead screw is driven off the end of the spindle via a forward/ reverse idler. All the back gear does is to reduce spindle speed and increase torque, by driving the spindle via the back gear and bull gear.

Before you do anything to the leadscrew, check this out first:

1. with back gear engaged, does the spindle turn by hand?
2. If no, is the bull gear pin (hard to see, it's in the large gear next to the spindle pulley) engaged?
3. If yes, pull it out and go back to #1.
4. If no, check that the screw in the middle of the pulley isn't screwed all the way into the spindle (it's an oil screw)
5. If yes, unscrew it and go back to #1.
6. If no, sounds like your spindle pulley is seized to the spindle and you need to dissassemble the head stock.

I've had these lathes apart numerous times and have owned a 618 for 4 or 5 years. There is no way that the half nuts will engage and drive the carriage in direct drive but not in back gear.

 

[bama7]

with all due respect, whether or not the back gear is engage or not has no effect on leadscrew rotation. The lead screw is driven off the end of the spindle via a forward/ reverse idler. All the back gear does is to reduce spindle speed and increase torque, by driving the spindle via the back gear and bull gear.

Before you do anything to the leadscrew, check this out first:

1. with back gear engaged, does the spindle turn by hand?
2. If no, is the bull gear pin (hard to see, it's in the large gear next to the spindle pulley) engaged?
3. If yes, pull it out and go back to #1.
4. If no, check that the screw in the middle of the pulley isn't screwed all the way into the spindle (it's an oil screw)
5. If yes, unscrew it and go back to #1.
6. If no, sounds like your spindle pulley is seized to the spindle and you need to dissassemble the head stock.

I've had these lathes apart numerous times and have owned a 618 for 4 or 5 years. There is no way that the half nuts will engage and drive the carriage in direct drive but not in back gear.

I too have had a few of these lathes apart and have never run into this problem before. Maybe the back gear position puts pressure on the lead screw and causes it to flex????
I have refurbished a couple of these lathes, Craftsman/Atlas, 2 Southbend model 9a, a Logan 1825, and a Montgomery Ward Logan model 200.
On this lathe with the back gear engaged you cannot move the chuck by hand. With the back gear disengaged the chuck spins freely by hand. With power on everything operates as it should when back gear is not engaged. With back gear engaged the lead screw turns, but the saddle will not move when the half nut lever is engaged. The thread dial will not move when half nut lever is disengaged while in back gear. When not in back gear the saddle will travel when the half nut lever is engaged as it should, and the thread dial moves when half nut is disengaged and stops when thread dial is engaged. ?????????

 

[bama7]

Can you shoot some clear photos of the lead screw? At the tailstock end and then near the headstock end?

 

[mattthemuppet2]

I have refurbished a couple of these lathes, Craftsman/Atlas, 2 Southbend model 9a, a Logan 1825, and a Montgomery Ward Logan model 200.
On this lathe with the back gear engaged you cannot move the chuck by hand. With the back gear disengaged the chuck spins freely by hand. With power on everything operates as it should when back gear is not engaged. With back gear engaged the lead screw turns, but the saddle will not move when the half nut lever is engaged. The thread dial will not move when half nut lever is disengaged while in back gear. When not in back gear the saddle will travel when the half nut lever is engaged as it should, and the thread dial moves when half nut is disengaged and stops when thread dial is engaged. ?????????

you've got a whole bunch of things going on here and it would help to isolate them to work on one at a time.

First, forget about the thread dial, it's not important. Loosen the bolt, swing it out of the way. Doesn't matter for testing purposes.

Second, did you do what I suggested above? I don't understand how you cannot move the chuck with the back gear engaged (belts loose, right?) but it does turn under power with the back gear engaged.

Get that clear first, then worry about the lead screw/ carriage/ half nuts.

 

[bama7]

you've got a whole bunch of things going on here and it would help to isolate them to work on one at a time.

First, forget about the thread dial, it's not important. Loosen the bolt, swing it out of the way. Doesn't matter for testing purposes.

Second, did you do what I suggested above? I don't understand how you cannot move the chuck with the back gear engaged (belts loose, right?) but it does turn under power with the back gear engaged.

Get that clear first, then worry about the lead screw/ carriage/ half nuts.

Thanks, I will have to wait until Monday to get the time to check it out. I really did not pay attention to whether the belt was engaged or not.