# 40t Change Gear Rare?



## 38Bill (Aug 10, 2016)

I'm wondering if a 40T change gear for a Atlas Craftsman 10'-12" lathe is rare?  I like to use one setup for threading and another for running the lead screw at half speed. I decided to put together two gear sets on their own sleeves and bolts to make it easy to switch back and forth and I need one more 40T. There are a couple of 40T gears on the auction site but they are asking about twice as much as the other gears. Is that typical?


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## Rob (Aug 10, 2016)

You might give Clausing a call and see how much a new one is.  A lot of time new parts are cheaper than used.  You can also used steel or cast iron ones from Boston Gear.  Here is a 40T one https://www.amazon.com/Boston-Gear-...d=1470802919&sr=8-1&keywords=boston+gear+gb40.

Also some other ones https://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias=aps&field-keywords=boston+gear+gb


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## wa5cab (Aug 10, 2016)

I don't know of any reason for the 40T gears to be any different from the other standard ones.


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## cdhknives (Aug 10, 2016)

How do you arrange that to give you a half speed leadscrew?  I assume you need another bearing too...where to get that???


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## pdentrem (Aug 10, 2016)

I would contact Clausings first. I bought a few gears to complete the set and add the missing a ones for metric threads. I got them on the auction site and some from Clausings.


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## Mondo (Aug 10, 2016)

Whoopie!!!  9-101-40A listed at Searspartsdirect.com in stock for $161.49 plus shipping.  **GAG**
I have 17 gears that I can sell, but alas, none of them are 40 teeth.  Better to call Clausing, or get one from those currently listed on Ebay.


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## 38Bill (Aug 10, 2016)

cdhknives said:


> How do you arrange that to give you a half speed leadscrew?  I assume you need another bearing too...where to get that???



The 101.28900 12" lathe(with QCG) uses a 40T that drives a twin set of 48T gears.  If you remove the spacer and add a 20T on to the 40T hub and then drive the 48T gear with the 20T the speed in cut in half ( Note that one of the double 48T gears must be removed for clearance). Only one 20T gear is needed for the modification, everything else is already there. The half speed messes with the threading settings but in most cases all you have to do is set the threading levers at half of the threads you want so its not really a big problem. I just thought it would be handy to have everything  put together on separate mounting bolts so I wouldn't have to be swapping out each individual gear. Just loosen two nuts, remove the gear sets,  replace with the different gear sets and tighten their two nuts. I have everything I need but another 40T . I dont have to get one now so I will just wait and see what comes up.  I thought it was odd that the two I found were as expensive as they were.


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## wa5cab (Aug 11, 2016)

Hmmm.  I may try that on my 3996.  I very seldom cut threads.  And the slowest cross feed speed is a little fast for milling under power.


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## Uglydog (Aug 11, 2016)

38Bill,
I'm in Dayton MN. Not far from Annandale.
Are you interested in making your own 40T?
Spur gears go pretty easy.
You can use my mill and DH. I'll walk you through it.
You gotta promise to take your fingers with you when you leave my shop. 

Daryl
MN


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## 38Bill (Aug 12, 2016)

Thanks for the offer


Uglydog said:


> 38Bill,
> I'm in Dayton MN. Not far from Annandale.
> Are you interested in making your own 40T?
> Spur gears go pretty easy.
> ...



Thanks for the offer Daryl. That would be a fun project for the winter. I knew from your posts that you were fairly close by to me. I have done a lot of woodworking (not much metal) and I'm pretty careful with body parts so I could make that promise.


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## Uglydog (Aug 12, 2016)

Send me a PM if/when you decide you are ready.

Daryl
MN


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## cdhknives (Aug 15, 2016)

38Bill said:


> The 101.28900 12" lathe(with QCG) uses a 40T that drives a twin set of 48T gears.  If you remove the spacer and add a 20T on to the 40T hub and then drive the 48T gear with the 20T the speed in cut in half ( Note that one of the double 48T gears must be removed for clearance). Only one 20T gear is needed for the modification, everything else is already there. The half speed messes with the threading settings but in most cases all you have to do is set the threading levers at half of the threads you want so its not really a big problem. I just thought it would be handy to have everything  put together on separate mounting bolts so I wouldn't have to be swapping out each individual gear. Just loosen two nuts, remove the gear sets,  replace with the different gear sets and tighten their two nuts. I have everything I need but another 40T . I dont have to get one now so I will just wait and see what comes up.  I thought it was odd that the two I found were as expensive as they were.



Ok, after some study on my machine I see it now.  On my QC54 that is the 'sliding gear' allowing extra coarse (up to 4 TPI) threads and you are converting that spindle to a fixed 2:1 reduction gear.  After the conversion the actual TPI would be double the nameplate TPI, i.e. an 8 TPI setting actually cuts slower, to a 16 TPI.  I do see where that conversion would be nice if it were easily reversible as you are suggesting.  16 TPI is a pretty high minimum.  Adding another spindle sure looks nicer...let us know if you buy the Boston gear.  I'm curious how it turns out.


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## VSAncona (Aug 16, 2016)

I just sold one last month on ebay for $18 with free shipping. They come up for sale pretty frequently. If you're patient, you should be able to snag one in the $15-$20 range easily enough.


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