Quick Change Compatibility

[Wildman326]

Will a Atlas/Craftsman 12” Commercial Quick Change Gear Box Assembly work on a non-Commercial 12” Craftsman Lathe?

 

[Ulma Doctor]

Modification will be necessary
The bed has no provision to mount the gearbox

 

[Wildman326]

Thank you.

 

[wa5cab]

Short answer is "we don't know".

There were three versions of the 12" Atlas QCGB. The second and third ones are functionally interchangeable. The two significant differencess between them are the change to the output shaft to accommodate the slip clutch and the addition of another mounting screw. The first one replaced the left lead screw bearing housing on the 101.07403. It is not technically correct to say that a 3/8" bed from an early 12" had no provisions for attaching the gear box. The tapped holes are there. We just do not know whether or not the holes are in the correct location.

 

[Wildman326]

OK. Well, that is tough. I have a 101.07403. I want a QCGB. They are not cheap, but they are very desirable. So, . . . I guess if I buy one and I don’t spend too much, I’ll be able to sell it and recoup my loss.

For what it‘s worth, I’m not afraid to modify as long as the gears are the same.

 

[wa5cab]

I still do not know whether it will or it won't. But I think that I have figured out one way to determine if it won't.

Using the Sears model numbers instead of the Atlas ones, there were three models of the QCGB conversion kit originally sold by Sears. These were the model numbers that you would buy if you had a Craftsman change gear model that you wanted to convert. They were

101.20140 (fit the 101.07403 and earlier models and were the ones that actually came on the 101.27430 and 27440). 3/8" bed.
101.20145 (came on the first version of the 12" that are generally known as "Commercial" (but no slip clutch). 1/2" bed.
101.201451 (had slip clutch, beefed up right lead screw bearing and lever cross-feed operator). 1/2: bed.

All three were attached to the side of the bed by two 5/16" socket head cap screws (one is covered/hidden by the thread settiings plate). On the latter two, the screws were approximately centered 3/4" below the top surface of the bed ways and the bottom of the headstock. In all three cases, the left bearing housing for the lead screw had exactly the same hole pattern as the appropriate QCGB main casting. Carefully measure the location of the two holes on your 101.07403. If the vertical location is 3/4" below the top of the ways, either of the two later models might fit. If the drop is only 5/8", then it will not. My suspicion is that it will not.

Note that the "Commercial" name didn't actually appear until 1972.