12" Commercial Reduction Gearing

Right. It would seem likely that you are driving from the 32T tumbler gear instead of the 16T. When you do that, your first 2:1 reduction ratio is lost. So instead of a 4:1 reduction, you still have only 2:1 over all.
 
Definitely driving off 16 tooth gear of tumbler. Setup up exactly like the YT video I posted. Like I said, I'm stumped!
 
Yes, the 32 tooth gear, closest to banjo, should be the one driving the 16 tooth, the 64 tooth should be driving the outside gear that runs the QCGB.
Make sure QCGB is in E and 9

Watch this video and you'll understand better.

 
Well, I don't know what to tell you. Both videos show doing essentially the same thing, just with different tooth count gears. If you have just the basic QC lathe and no extra gears, the second version is the most economical, requiring only a new 24 tooth gear. However, the second guy did fail to mention one other part that you will have to have. This is what the threading charts call a Steel Spacer. It replaces the 48T that was removed from the front right position where it and the one in the back right position drove the long gear in the gearbox. I am trying to determine the part number of that spacer. In place of the 40T sliding gear, you put first the 24T in the back position and then the relocated 48T in front.

The tumbler gear (stud gear on a 10" change gear lathe) is a 32T/16T compound gear. The 32T part is driven by either the forward or reverse gear on the tumbler. The 16T part drives the relocated 48T gear. That is your first (normal) 2:1 reduction. The relocated 48T drives the new 24T through the 9-70A bushing that they are both mounted on. The new 24T drives the remaining original 48T in the Back position.(its original position). That is your second 2:1 reduction. Finally, the original rear 48T drives the gearbox as it always has. That looks like it worked. I am going to order a 24T gear this afternoon, and if we can determine the part number, a spacer. When they arrive, I'll try it.

I'll add that the slowest cross feed rate has always seemed to me to be too fast for power feeding for milling. This will help that as well.
 
I have done it that way and it works great.
I was lucky and had a 24 tooth gear.
I just made the spacer myself on the lathe and broached the key slots to fit the bushing.
It makes it easy to switch back to normal operation.
I never tried to thread with it setup like that, so I don't know if that works like they say in the vids.
 
Soooo... Today I checked my gear setup and instead of measuring linear travel with a DI, I set it up for threading and did a scratch pass, with the results being I have doubled the thread count per inch vs the QC placard... After that I rechecked linear travel with a different measuring method and I do indeed have the desired .0021 slow feed rate. Don't know why my DI doesn't seem to agree but that's another issue. All's well that ends well... Thanks all for the input. M>
 
I am trying to do the same set up, having trouble locating a 24 tooth gear. Did you find one on e-bay, or did you order one from Boston Gear? If so, what exactly did you order? Thanks, Jim.
 
I was talking to Clausing about some drawings for restoring a 900B Collet Attachment, and ordered one from them. Price was $42.92, which compares favorably with the cost of a plain gear plus cost to bore, face. and double broach.
 
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