# Craftsman Atlas QC54 - mounting motor underneath.



## Packard V8 (Jun 3, 2018)

I've just been given a mostly complete QC54 which was damaged during removal.  The bent tailstock screw has been straightened.  The motor mount bracket has been removed for welding.

In reading through the most excellent MOLO, page 2, fig 2A, illustrates a floor cabinet with underneath drive.  Throughout the remainder of the manual, I can find no other information as to the underneath drive.

Since there was no bench with the lathe, I'll have to build something.  What are the pros/cons to an underneath drive?  How complicated is it to convert from rear drive (broken mount anyway)?

jack vines


----------



## wa5cab (Jun 3, 2018)

The under drive cabinet models shown in the Version 8 and 9 MOLO's work quite well.  There were four Atlas and four Craftsman models (early and late, 12x24 and 12x36).   Several (probably all) of the parts manuals are in Downloads.  And the QC54 would work quite well sitting on top of the later cabinet.  

However, the only countershaft assembly parts common to both types are the cone pulley on the countershaft spindle, the large 2-step countershaft pulley, and the motor pulley.  Plus you could use the same motor.  You would have to pull the spindle and replace the spindle cone pulley with the 2-groove spindle pulley used on the cabinet models.  And find all of the other parts, including the cabinet.  The old spindle cone pulley would not be usable.  The only things that would make it practical would be (a) cost is no factor, or (b) stumbling across a cabinet model lathe  with a bad lathe for not too much cost.

Outside of those two scenarios, you are probably better off keeping it original.


----------



## Packard V8 (Jun 3, 2018)

Thanks for the clarification.  Obviously, there were considerations, but why make the two so different?

One reason for asking about the underdrive; I've read with the standard rear mount, the weight of the motor/tension on the belt can change the leveling/twist the bed.  Anyone have any suggestions as to how to ameliorate this?
jack vines


----------



## pontiac428 (Jun 4, 2018)

I don't think the weight of the motor can affect the bed leveling, since it is twice decoupled from the spindle drive.  The idler shaft when locked in sets the tension on the spindle to idler belt.  The support assembly for the idler is mounted to the bench, and bears the load from the weight of the motor (I support my motor weight with cedar shims to limit bounce on my setup).  With or without support, motor movement is well isolated from the spindle.  This should be true for the cast iron legs from Atlas that have a bracket for the idler shaft support.


----------



## wa5cab (Jun 4, 2018)

The weight of the motor is never supposed to be what sets the motor belt tension.  If you have the thing installed that way, think what is going to happen if you are doing an interrupted cut, like for example when you take a piece of square bar stock and start turning the end down to a smaller diameter round for a bearing or bushing.  four time per revolution of the spindle, the tension in both belts will increase as you make the short cut and then go back to the static value plus just enough to overcome the friction in the various bearings.  Under just the right conditions, you can get the motor bouncing enough that the motor belt will actually slip.  The motor mount should have either a hold down bolt or an adjustable stay or pair of stays to prevent this.


----------



## bill70j (Jun 5, 2018)

Packard V8 said:


> One reason for asking about the underdrive; I've read with the standard rear mount, the weight of the motor/tension on the belt can change the leveling/twist the bed.  Anyone have any suggestions as to how to ameliorate this?
> jack vines




On my Atlas QC42, I found that tensioning the belt definitely affected the leveling of the bed.  I made the mistake of leveling before tensioning only to find that the bed twisted under belt tension.

My bench top is made from 3"thick laminated hemfir 2x4's.  I should have made it out of hardwood, but didn't want to spend the money.  Big mistake.  Apparently the bed feet were digging into the top when tensioning the belt.

So I removed the lathe and secured 1/8" steel plates to the top under the bed feet.  That helped a lot.

Bill


----------

