# Atlas 618



## bama7 (Feb 1, 2020)

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?


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## DavidR8 (Feb 1, 2020)

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


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## mattthemuppet2 (Feb 1, 2020)

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.


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## bama7 (Feb 1, 2020)

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.


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## DavidR8 (Feb 1, 2020)

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


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## mattthemuppet2 (Feb 1, 2020)

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.


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## bama7 (Feb 1, 2020)

mattthemuppet2 said:


> 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:
> 
> ...


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.  ?????????


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## bama7 (Feb 1, 2020)

DavidR8 said:


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


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## mattthemuppet2 (Feb 1, 2020)

bama7 said:


> 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.


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## bama7 (Feb 1, 2020)

mattthemuppet2 said:


> 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.
> 
> ...


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.


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## RJSakowski (Feb 1, 2020)

When you release the pin, M6-256 on my lathe, you should be able to rotate the bull gear, M62-241X separate from the pulley, 2140-10.  The pin has two detents for engaged and free.  There is a ball and spring followed by a set screw which rides in the detents.  If the set screw is turned too far in, you won't be able to move the pin to the free position.  With the pin in the engaged position and the back gears engaged it will lock the spindle. 

It is possible that the previous owner permanently pinned the bull gear to the pulley.  The pin will work against the Zamak pulley and wear tyhe pulley to the point that you can no longer lock the pulley to the gear. Also using the pin and the back gear to lock the spindle to change the chick can shear the Zamak if too much force is applied.  A solution, albeit a poor one, would be to pin the two together.  This would permit direct drive but prevent not driving with the back gears.

If you can rotate the spindle and the gears in the gear train are properly engaged, you will be able to turn the lead screw.  If the carriage is not moving with the lead screw turning and the half nuts engaged, the problem is the half nuts.  Looking at your photos, the lead screw looks OK but the half nuts need cleaning.  You can remove the half nut assembly by unscrewing the two screws on either side of the half nut lever.  Clean the half nuts with a fine wire brush or a toothbrush and some WD-40.  You can clean the lead screw in the same way.


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## bama7 (Feb 3, 2020)

mattthemuppet2 said:


> 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:
> 
> ...


I will try to do better on my answers today.  Yes, I can turn the spindle by hand with the back gear engaged. I can also turn the spindle by hand with the back gear disengaged as well. The oil screw is not tightened, but just covers the hole. Yesterday I was basically just putting my hand on the chuck and felt the "tension" and did not try any real pressure to move it. It works fine.
I still have the same problem. What I did find this morning was the front lead screw bracket screws were loose allowing the gear on the lead screw shaft to disengage. This would cause a slight noise. I tightened both screws and the noise is now gone. When I engage the back gear the thread dial still does not move and the carriage does not move when I engage the half nut lever. 
I went back to the shed for another look. By putting "some pressure" on the half nut lever I could get the carriage to travel some in both directions. The dial still did not move. I am still inclined to believe the lead screw is worn.


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## bama7 (Feb 3, 2020)

RJSakowski said:


> When you release the pin, M6-256 on my lathe, you should be able to rotate the bull gear, M62-241X separate from the pulley, 2140-10.  The pin has two detents for engaged and free.  There is a ball and spring followed by a set screw which rides in the detents.  If the set screw is turned too far in, you won't be able to move the pin to the free position.  With the pin in the engaged position and the back gears engaged it will lock the spindle.
> 
> It is possible that the previous owner permanently pinned the bull gear to the pulley.  The pin will work against the Zamak pulley and wear tyhe pulley to the point that you can no longer lock the pulley to the gear. Also using the pin and the back gear to lock the spindle to change the chick can shear the Zamak if too much force is applied.  A solution, albeit a poor one, would be to pin the two together.  This would permit direct drive but prevent not driving with the back gears.
> 
> If you can rotate the spindle and the gears in the gear train are properly engaged, you will be able to turn the lead screw.  If the carriage is not moving with the lead screw turning and the half nuts engaged, the problem is the half nuts.  Looking at your photos, the lead screw looks OK but the half nuts need cleaning.  You can remove the half nut assembly by unscrewing the two screws on either side of the half nut lever.  Clean the half nuts with a fine wire brush or a toothbrush and some WD-40.  You can clean the lead screw in the same way.


Everything works as it should except while in back gear. I cleaned and oiled the half nuts and they don't appear to be as worn as is the lead screw. Read my response above. Thanks


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## chippermat (Feb 3, 2020)

It's not clear to me. Does the lead screw turn, with the back gears engaged and lathe running/spindle spinning?


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## bama7 (Feb 3, 2020)

chippermat said:


> It's not clear to me. Does the lead screw turn, with the back gears engaged and lathe running/spindle spinning?


Yes


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## chippermat (Feb 3, 2020)

So if I get this right, the lead screw turns, both in back gear and direct drive?

And the half nuts engage and drive the carriage, but only in direct drive and not in back gear?


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## mattthemuppet2 (Feb 3, 2020)

hmm, sounds like your half nuts are popping open, maybe due to the lower speed in back gear. I think you mentioned that you can stop the problem by holding the half nut lever down, right? That would support that hypothesis. Couple of possibilities. One the ball detent that keeps the half nut lever in position isn't doing it's job (missing, stuck in its bore, ?) or two, the half nuts are so worn that they ride up and out of the leadscrew thread.

I very much doubt that your leadscrew is too worn, looks fine to me in the pics. Even if it was worn, the main effect would be thread pitch inaccuracy over long threads, not the half nuts popping out. The thread dial is not relevant here. It's a bugger to keep it engaged when tightening the bolt as doing so rotates the whole thing and the gear at the end out of engagement with the leadscrew.


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## bama7 (Feb 3, 2020)

chippermat said:


> So if I get this right, the lead screw turns, both in back gear and direct drive?
> 
> And the half nuts engage and drive the carriage, but only in direct drive and not in back gear?


Yes, except I did get the carriage to move by putting some pressure on the half nut lever while in back gear. I just said the heck with this and bought a lead screw from ebay for a really good price, if it is as described $29.00 shipped,  and a NOS half nut set for $40.00 shipped. The wait is on. I plan to change the lead screw first and see if that works, since I am hard headed and think that is the main problem.


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## chippermat (Feb 3, 2020)

OK, you'll get'er figured out one way or another. Best of luck, it's all fun


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## Voda2000 (Feb 3, 2020)

I had something similar and made a couple of small shims that went between the half nuts and the carriage. It seems like there was too much play in the half nuts when they were engaged. The shims tighter it up and solved my problem.


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## bama7 (Feb 8, 2020)

I got my lead screw and half nut set. Both are incorrect for my 618. The lead screw apparently came from a Craftsman with the crank handle on one end. I don’t know what the half nuts fit. They fell completely through M6-13A guide.


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## wa5cab (Feb 8, 2020)

The 618 and the 101.07301 have different part numbers for the lead screw for some strange reason.  I do not know what the difference is, if anything.  But the half nuts are the same.  And neither screw has a hand wheel on it.  So the parts that you bought must be off of one of the AA (Double-A) lathes that Sears sold briefly during WW-II and again from 1948 until 1959 or 1960.  So the parts that you bought could be for a Craftsman but not one built by Atlas.  Unfortunately, most people don't know this.  Whether you can get your money back may depend upon how the seller described it.  If he said that it fits any of these numbers, you should be able to:  101.07301, 101.21400, 101.21200 or 618.  If he only said that it fits one or more of the following numbers, it depends on how understanding he is: 109.0702, 109.20630, 109.21270.  Note that the first of these was sold under the Dunlap badge but the other two had Craftsman badges.


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## bama7 (Feb 8, 2020)

wa5cab, I contacted both guys about the parts. The lead screw came off a 109 style lathe. The guy I got the half nuts from said there were two types of half nuts for the 618 type lathes. He did give measurements on his ad when I bought them. I didn’t know there was more than one type. Both said to send them back and they would refund my money. I would much rather have the correct parts. Anybody in need of either before I send them back? The half nuts cost $40 and the lead screw was $20.


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## wa5cab (Feb 9, 2020)

OK.  I missed that the half nuts came from a different seller than the lead screw.

Yes, on there having been two versions of the 618 half nuts.  I never knew exactly what changed because we don't have the drawings, just that something had changed.  If you look at the 1945 and earlier parts manuals that we have, you will see that they say part number M6-12 for the Half Nuts, M6-13 for the guide and M6-12X for the complete assembly.  The 1950 and later says M6-12A, M6-13A and the complete assembly is M6-12AX.  The difference appears to be the width of the half nuts and the width of the slot in the guide.  So those changed sometime between 1945 and 1950.  If I remember, next time that I talk to Tom at Clausing, I'll ask him whether the drawing gives the serial number at which the change happened.


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## WCraig (Feb 10, 2020)

wa5cab said:


> OK.  I missed that the half nuts came from a different seller than the lead screw.
> 
> Yes, on there having been two versions of the 618 half nuts.  I never knew exactly what changed because we don't have the drawings, just that something had changed.  If you look at the 1945 and earlier parts manuals that we have, you will see that they say part number M6-12 for the Half Nuts, M6-13 for the guide and M6-12X for the complete assembly.  The 1950 and later says M6-12A, M6-13A and the complete assembly is M6-12AX.  The difference appears to be the width of the half nuts and the width of the slot in the guide.  So those changed sometime between 1945 and 1950.  If I remember, next time that I talk to Tom at Clausing, I'll ask him whether the drawing gives the serial number at which the change happened.


Hi:

My Atlas 618 needed new half nuts.  When I ordered them, I didn't know about the changes to the part.  The following shows the old half-nuts in the (old) bracket and the new ones which would obviously not fit.  After I got the matching bracket, the parts installed without any issues.




I believe the half-nuts were enlarged to stop them from wearing out as fast.  More threads engaged on the lead screw would spread the wear, IMHO.

Craig


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## phubbman (Feb 10, 2020)

Go with the wider half nuts in the pic.  They are in MUCH better condition than the narrower half nuts.  The "V" shaped threads on the narrower half nuts used to be squarish, but have worn considerably.  This will result in a lot of slop / backlash between the half nuts and the lead screw - and a tendency to disengage, which of course is the very problem you've been having with your lathe.  

Given the rust pitting on portions of your lead screw, i'd still replace it, but i'm betting that everything would work just fine with the new half nuts and the old lead screw.  The lead screw threads look a bit rust pitted, but not significantly worn.  They are supposed to be squarish.


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## wa5cab (Feb 11, 2020)

First, I think that if you use a wire brush, the lead screw will clean up nicely.  I could be wrong but the rust visible in the photo near the right lead screw bearing looks like it would clean up nicely.

Second, the highest 618 serial number that we have in the database is 027421 from which I guessed that a total of about 28,000 were made from mid 1937 up through mid 1972.  We have no production figures to go by and it would be reasonable to assume that more were made in the 1940's than in the 1960's but I would guess that your machine was made in the 1960's.  We do know that the 1945 parts manual showed the narrow half nut and guide (M6-12 and M6-13) and the 1950 one shows the wide one (M6-12A and M6-13A).  So I would guess that your 618 didn't originally ship with the narrow half nuts.  You might, if you can, ask the previous owner when he bought the lathe and whether or not he remembers changing the half nuts.

However, it would appear that that problem has been fixed!


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## bama7 (Feb 11, 2020)

I have a very uneducated question. Is there a top and bottom half or are they, my belief, exactly the same?


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## wa5cab (Feb 11, 2020)

There should have been an instruction sheet packed with the two split nuts,  There was with the larger set that I bought for my 3996.  I just had a look at it and there is no mention of caring which one went on top.  If you didn't get an instruction sheet, the one for the 10/12 says to use a flat file and file a bevel on the four  corners where the two come together, and then carefully debur the filed areas..  The two parts may or may not be the same, but it doesn't matter which one goes on top.


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## bama7 (Feb 11, 2020)

Thanks for the info.


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## wa5cab (Feb 12, 2020)

Addenda:  the four corners are on the ID of the Acme threads.  Not on the outside of the two halves.  Unfortunately the note does not give a width of the resulting 45 deg. flat that should result from the filing.  So I would go for a nominal 1/16" X 45 deg. typ. 4 pl.


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## bama7 (Feb 15, 2020)

Bought a new set of half nuts from Clausing for $36.16 shipped. They surprised me again.


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