# cast in  number 261 on thread counter gear



## Round in circles (Oct 17, 2014)

Part of my hobbies are photography ..I'm doing the first part of a four year course about digital photography .

 This last Tuesday we were taking about macro photography , so late last night I took a picture or three of part of the thread counter/ timer that's been siting on my desk for two months whilst I pluck up the courage to try and replicate it on my antique Sphere lathe ( From which it has come off ) 

On up loading the pictures to the computer & into my photo bucket tonight I noticed something I didn't find when I glued it together to stop any more bits falling off.    Cast in the metal is a casting or part number of 261 for the thread counting gear /cog.

  Now it appears to be the same metal as the thread cutting gears and apparently these gears were American made around 1943 & fitted to Atlas  lathes of the period .

 I understand that the gear may still be an available spare or used part in the USA , If anyone has an Atlas lathe of around that age would you be so kind and see if the thread counting/timing gear carries the same part number please.


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## wa5cab (Oct 17, 2014)

No.  The equivalent function part on the early Atlas of the period is 9-64.  Which doesn't necessarily mean that the Atlas part won't fit.


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## Ebel440 (Oct 18, 2014)

I have an old craftsman 109 which isn't an atlas but some people think it is. I checked mine just to see if that was the one you need but mine has a brass gear and no visible numbers.


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## Ebel440 (Oct 18, 2014)

I forgot to mention I have heard that the 109 uses the same zamack change gears as some atlases


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## Round in circles (Oct 18, 2014)

Ebel440 said:


> I have an old craftsman 109 which isn't an atlas but some people think it is. I checked mine just to see if that was the one you need but mine has a brass gear and no visible numbers.



Now that's interesting brass or phosphor bronze .

I think I can make the gear out of aluminium but if it's brass of phosphor bronze I might  enjoy doing it in aluminium first  to get a bit of experience then if accurate enough do it in brass or phosphor bronze and have a piece of art as well .


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## Nammar (Jun 20, 2015)

Dear David, I have only come across your posting now.

The dial thread indicator gear can be made of any material, as it basically does not take any load. The only load that it takes is to drive the dial shaft. The gears perfect meshing with that of the leadscrew is also not too important, as long as the gear does not bind when the leadscrew is turning. You will notice that there are 16 teeth on the dial indicator gear and that there are 4 numbered divisions and 4 un-numbered divisions on the dial face. What this all equates to is that your leadscrew has a pitch of 8 TPI (Threads per Inch) and when the thread indicator gear is engaged with the leadscrew, the dial will turn one full revolution for two inches of saddle travel along the lathe bed.

The rule of thumb for threading on your lathe, when cutting even number of threads (2, 4, 6, 8, etc.), engage the leadscrew on any line. When cutting an uneven number of threads (1, 3, 5, 7, etc.), engage the leadscrew on any numbered line. If you have to cut a thread with an odd number of TPI (1.5, 2.5, 3.5, 4.5, etc.) then you have to wait a little and engage the leadscrew on either 1 and 3 or 2 and 4. You do get threads with other pitches as well (1.25, 1.75, 2.25, 2.75, etc.), then you need to wait longer and engage the leadscrew on the same line that you chose, when you began cutting the thread.

Your aluminium gear will work a treat. Geoffrey.


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## francist (Jun 21, 2015)

I've got a couple of threading dials for my Atlas 618 and both the gears are either brass or bronze as well. What is really interesting though is the deterioration of David's gear. Anybody know what causes that -- for the zamak to almost self-destruct with all those cracks and such? I've got a change gear that looks like that (I don't use it anymore) that exhibits the same fracturing all over it and I've always wondered why. Anybody know?

-frank


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## Cobra (Jun 21, 2015)

This link may help.  Looks like the early alloys were not perfect.

https://books.google.ca/books?id=fg...ld zamak parts disintegrate over time&f=false


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## John Hasler (Jun 21, 2015)

francist said:


> I've got a couple of threading dials for my Atlas 618 and both the gears are either brass or bronze as well. What is really interesting though is the deterioration of David's gear. Anybody know what causes that -- for the zamak to almost self-destruct with all those cracks and such? I've got a change gear that looks like that (I don't use it anymore) that exhibits the same fracturing all over it and I've always wondered why. Anybody know?
> 
> -frank


"Zinc pest".  If it was made during the war they may not have been able to get lead-free zinc.


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## wa5cab (Jun 21, 2015)

The gear on the threading dial from an AA or Dunlap 6" lathe won't work on the Atlas 9". 10" or 12" because the lead screw pitch is different, regardless of what material it is made of.


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## ogberi (Jun 23, 2015)

Yup, zinc pest.  My Atlas mfc suffered from that.  99% of the zamak on it disentegrated, or swelled up and siezed in the bores.


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## wa5cab (Jun 24, 2015)

This seems to be the typical experience.  Maybe one in ten machines show the problem, and (assuming that all of the Zamak parts are from the same time frame), either all of the pieces or none of the pieces are affected.  My personal experience with three machines (two mills and a lathe) from the early 40's, early 50's, and late 70's is no problems.  Maybe I shoulda bought a Lottery ticket.


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