# Atlas 618 Thread Dial gear



## bama7 (Feb 25, 2020)

Does the 618 have two different Thread Dial gear options? Is there a 16 tooth and a 32 tooth gear for the 618?


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## RJSakowski (Feb 25, 2020)

My Atlas/Craftsman 6x18 has a 16 tpi lead screw and 32 teeth on the thread dial gear.  The P/N is M6-64A.


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## bama7 (Feb 25, 2020)

That is what mine has as well. Just curious if there was ever a 16 tooth gear used. Thanks


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## wa5cab (Feb 25, 2020)

No one at Clausing knows why the M6-64A Pinion is 32 tooth  but to answer your question of was the pinion originally 16T, yes.  I called Clausing and found unfortunately that the M6-64A is on the discontinued list but they were happy to send me its drawing and also the one for M6-64.  The change was made 11/06/1946.  The drawing was redrawn 02/19/1973 and if there was any explanation, it wasn't copied forward.


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## RJSakowski (Feb 25, 2020)

wa5cab said:


> No one at Clausing knows why the M6-64A Pinion is 32 tooth  but to answer your question of was the pinion originally 16T, yes.  I called Clausing and found unfortunately that the M6-64A is on the discontinued list but they were happy to send me its drawing and also the one for M6-64.  The change was made 11/06/1946.  The drawing was redrawn 02/19/1973 and if there was any explanation, it wasn't copied forward.



Did the earlier models list an 11.5 tpi thread in the thread chart?  A manual for my 101.21400 lathe dated 1959 states that for even numbered threads, use any of the four marks and for "all other threads", use opposite marks, suggesting that at some point, half integral threads, e.g 11.5 tpi, was not an option.  The manual dated in 1969 shows the 11.5 tpi thread setting in the change gear table.  The description for use of the thread dial is consistant with a 32 tooth gear.

With a 16 tooth thread dial gear running on a 16 tpi lead screw, there would be no position on the thread dial that could be used and the description of use would be incorrect.


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## bama7 (Feb 26, 2020)

I was working on a Craftsman 6x18 about a year ago and the 32 tooth thread dial was not working very well. I think it was bent. The box with extra parts I got with it had another thread dial, but with the smaller gear. I put that one on and it worked great. Just curious, but don’t the 10” Craftsman lathes have the smaller gear? My thought is the smaller one came from a different model lathe. I just checked eBay and the 109 lathe also have the 16 tooth gear.


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## wa5cab (Feb 26, 2020)

The Atlas 10" and 12" have a lead screw that is larger in diameter (either 5/8" or 3/4") than on the 6" and 8 TPI.  So 1/8" pitch.  And a 16 tooth pinion of a diameter such that it meshed with the lead screw.   So the threading dial from the larger lathes will not fit any of the 6" because the teeth are too wide.  

The early 6" (both Atlas and Craftsman) up until 1946 had a 16 tooth threading dial gear of a diameter such that it meshed with the 1/2" dia. 16 TPI lead screw.  The later 6" had a larger diameter 32T threading dial gear so that it also meshed with the 1/2"-16 lead screw.

So although the early 6" and the 10" and 12" lathes all have 16T threading gears, the gears are not interchangeable.  And why they changed from a 16T to a 32T no one now at Clausing knows.  But I assume that it must have had to do with wear or breakage.


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## RJSakowski (Feb 27, 2020)

wa5cab said:


> The Atlas 10" and 12" have a lead screw that is larger in diameter (either 5/8" or 3/4") than on the 6" and 8 TPI.  So 1/8" pitch.  And a 16 tooth pinion of a diameter such that it meshed with the lead screw.   So the threading dial from the larger lathes will not fit any of the 6" because the teeth are too wide.
> 
> The early 6" (both Atlas and Craftsman) up until 1946 had a 16 tooth threading dial gear of a diameter such that it meshed with the 1/2" dia. 16 TPI lead screw.  The later 6" had a larger diameter 32T threading dial gear so that it also meshed with the 1/2"-16 lead screw.
> 
> So although the early 6" and the 10" and 12" lathes all have 16T threading gears, the gears are not interchangeable.  And why they changed from a 16T to a 32T no one now at Clausing knows.  But I assume that it must have had to do with wear or breakage.


The 32 tooth gear allows the use of the thread dial for 11.5 tpi threads.  With the 16 tooth gear, you can only cut whole number threads.  The actual dial remains unchanged but the rules for using it changed.  16 tooth gear: odd numbered threads, use the same mark for each pass mark, even numbered threads, every other mark.  32 tooth gear: odd numbered threads use every other mark, even numbered threads, use any mark, and half numbered threads, use the same mark for each pass.


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## wa5cab (Feb 27, 2020)

OK.  Makes you wonder now why they didn't do that to begin with, since the larger lathes that had been in production for a few years when the 6" models came out were already made the later way.


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## RJSakowski (Feb 27, 2020)

The larger lathes with their 8 tpi lead screw are already set up with the 2:1 ratio.  Perhaps the designer didn't think that being able to cut half integral threads was important enough.  The 11.5 tpi thread is used on tapered pipe threads. and then only on pipe 1" and larger.  It was probably thought that this would be an uncommon use for the end user in the '30's and '40's, typically a small repair shop or a blacksmith.

Then the light bulb went on as Atlas realized that the additonal cost would be minimal and the change was made.  It is interesting to note that the user manual didn't necessarily reflect the change.  My user manual for the Atlas/Craftsman, dated 1969 shows the 11.5tpi in the thread gear chart but the rules for use of the thread dial don't mention half integral threads.  Curiously, a threading manual put out by Atlas c.a. 1940 does have the 11.5 tpi thread and does give the correct use of the thread dial (although the photo immediately above that paragraph shows what appears to be the 16 tooth thread dial gear.  I haven't seen concrete evidence but it appears that the M6-64 part was the 16 tooth gear and the M6-64A part was the 32 tooth gear.

Here is a link to the publication.
http://vintagemachinery.org/pubs/51/19942.pdf  (By the way, this publication contains a wealth of information on thread on the 618 and threading in general.  Far more than I have seen in any other publication.)


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## wa5cab (Feb 27, 2020)

Yes, as I wrote yesterday, M6-64 is 16 tooth and M6-64A is 32 tooth.  I have scans of the original M6-64 drawing and of a 1973 re-draw of the 1946 M6-64A one.  When I get them cleaned up, I'll upload them.  Unfortunately, whatever change notes were on the original 1946 M6-64A drawing were not copied over to the 1973 redraw.  And the redraw only shows applicability to the 3950 and another 4-digit number that I don't recognize.  It ignores the fact that for 27 years the 32 tooth gear had been used on the 618 and either the 101.07301 or the 101.21400.


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## wa5cab (Feb 27, 2020)

This 6" threading handbook is also in the rather rare version of the MOLO where Chapter 7 covers the Atlas 6".  Too bad that it doesn't have a print date anywhere in it, as that would date that MOLO version, too.  However, we do know that it can't have been printed any earlier than 1946, which is the original date on the 32 tooth threading dial gear drawing.  I'll put the booklet in Downloads.


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## wa5cab (Feb 28, 2020)

Also, the 6" threading handbook almost certainly came out in 1946 or later, after the switch to the 32T gear.  Unfortunately, like the earlier similar publications on the 10" and the 12". it is not dated.


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