# How do I identify change gears? (threading gears)



## 2manyhobbies (Feb 27, 2013)

I have a couple sets of unidentified change gears I would like to list on ebay but first I would like to identify what lathes they fit.
Any idea how I can ID them?

Thanks,
Steve Bennett


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## 2manyhobbies (Feb 27, 2013)

sssfox said:


> Steve,
> 
> The first thing I would do is to measure the diameter and number of teeth on a couple of them so I could figure out what the Diametral Pitch is.  Then, I would measure the shaft size and type and number of keyways.
> 
> ...



Steve,

  Yes I figured the first step would be measure them. But once I have the measurements how to narrow it down and match that to a lathe model?  You mentioned "Diametral Pitch". Is that how gears are standardized?
I know with threads there are standard sizes based on diameter and pitch but I'm clueless about what standards exist for gears.

I am hoping that:
 1)A standard exists to identify my gears as being some standard size. ( or was every manufacturer different?)
2) Somewhere there is a reference to lookup gear specs of various lathes of the period. (non-quick change gear box lathes)

If I at least know the specs of the gears I could leave it up to the buyer to research their requirements but ideally it would be nice to have that work done for them.

-Steve


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## DMS (Feb 28, 2013)

The great thing about standards is that there are so many of them 

Seriously, there are 3 main standards. Metric standards use "module", which is basically the number of millimeters per tooth, so for example, a module 1 gear of 30 teeth will have a pitch diameter of 30mm. Inch gears use "Diametral Pitch", which is basically the number of teeth per inch. So, for example, a gear with 30 teeth, and a diametral pitch of 30, will have a pitch diameter of 1 inch.

There is a further complication, and that is called the pressure angle. The two most common are 20 degree PA, and 14.5 degree PA. All that probably still won't tell you what lathe they belong to... but it will let you eliminate things (like, if it's a metric gear, it probably doesn't belong to an early American or British lathe).


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## Dunc1 (Mar 1, 2013)

An article here 
http://www.homemetalshopclub.org/news/10/newsletter1008.pdf#view=fitH
starting on page 8 that details how to determine the pressure angle.

Even with all the info I think that determining "which lathe" would be difficult.
Beyond determining from a  metric or an imperial lathe to narrow it further 
you would then need to know the number of teeth on each gear in a change 
gear set, total number of gears in the set, the bore diameter, etc in order to 
compare those results with the gears you have. One hint might be the increment 
in the number of teeth (teeth on the gears increment by 4, 5 or ?).

Are there any markings on the gear bodies?


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## British Steel (Mar 1, 2013)

*k*

If the plan is to put 'em on eBay, you'll have a bigger market if you *don't* specify the lathe - quite a few will use the same type of gears!
An eBay buyer is going to be interested in the DP / Module, pressure angle, width and number of teeth, they can (having a lathe, presumably) bore or bush the gears to fit their machine - tell 'em the bore and key dimensions anyway, if they match they'll possibly go a bit higher 

Dave H. (the other one)


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## rdhem2 (May 22, 2013)

Change gears---				 Over time I have accumulated an assortment of change gears.  They now all set in a box under the bench.  The other night I pulled them out and cleaned and sorted them just to see what I really did have.  For sales and trading purposes what do I need to post to get them back to use?  I would think, width, key size, bore, and number of teeth should pretty much get it.      OPINIONS?​


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## itsme_Bernie (May 22, 2013)

My $.05:

-Don't forget the thickness of the hub- like the hub diameter and keyway size, the hub thickness would be the next most standard measurement to specify a certain manufacturer since they have to be interchangeable on different parts of the geartrain.

-Then the material (cast iron, steel, Zamak(Atlas for instance))

-Also take a pic of one and try the google picture recognition search if it has any other distinguishing features.

-ALSO- if you have three gears that look like the same manufacturer, with say: 24, 48, 56, 37, teeth,  then Google "lathe change gear 24 48 56 37", since certain companies offered certain mixes of different #'s of gear teeth.  I threw "37" in there to make it more obvious, since that is a weird number.

-Google the number of gear teeth at the same time as any number stamped on it.




Bernie


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## Tonym47 (May 25, 2013)

2manyhobbies said:


> I have a couple sets of unidentified change gears I would like to list on ebay but first I would like to identify what lathes they fit.
> Any idea how I can ID them?
> 
> Thanks,
> Steve Bennett



Steve If you find that they are atlas/craftsman gears for a 12" lathe please let me know. Tonym47


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## kd4gij (May 25, 2013)

post up some pics an we may beable to help


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