12" Commercial Reduction Gearing

Hmmm. They don't give either the face width or the bore length. But at least, you wouldn't have to bore and broach it.
 
My 12" uses a 40T so I just added a 20T to the back of it and then removed the outside gear of the double 48T set that drives the QC. The compound gear drives the 40T and the 20T (mated to the back of the 40T) then drives the remaining 48T. NOTE: The outside gear of the double set needs to be removed as the other gear above it will hit it due to the difference with meshing the smaller gear to the 48T.
12 inch gears.jpg
 
Yes, that will also work. However, in my experience the 40T gear wears more than the 48's for three reasons. (1) it is loose on the bushing so the ID wears more, (2) it is engaging two gears while not being as constrained at the hub, and (3) it is running 20% faster.
 
wa5cab said:
Yes, that will also work. However, in my experience the 40T gear wears more than the 48's for three reasons. (1) it is loose on the bushing so the ID wears more, (2) it is engaging two gears while not being as constrained at the hub, and (3) it is running 20% faster.
Click to expand...

As the 40T is the standard gear on my 12" it isn't loose or turning any faster than than before. It has a spacer behind (on the bushing) it that is simply replaced with a 20T gear. The lower, outside 48T gear needs to be removed and replaced with a spacer. If you don't have a spacer you can use any gear with a small enough dia that will clear the 40T. Here is a sketch I made when I did mine for the first time.

Scan0003.jpg
 
Well, either way will work. But if your machine had a spacer behind it, some owner added it after the lathe left the factory. The 40T is the sliding gear, and is held in either front or back position by the metal disk that is between the 16T and 32T gears on the tumbler compound gear. That's the only reason for that disk. I have a 3996 purchased new which is that way, plus all of the manuals including the MOLO's show it that way.

My comment about wear rate was about the relative speeds or number of teeth engaged per revolution, or tooth wear rate, not the gear RPM. But the difference is only 20% and someone installed a spacer on your machine, so disregard.
 
songbird said:
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.
Click to expand...
I took the tip and got the one on e-bay, still waiting to receive it.
 
Has anyone tried threading with the single 24 gear setup? Also, has anyone found a source for the spacer?
 
Whichever small gear you use (20T with the second 48T not used as shown in the sketch in 38Bill's last post about four posts up the thread or 24T with the second 48T replacing the 40T), the finest thread that you can cut will be 16T with the gearbox set up for 8T. And all finer threads will be cut with the gearbox set for half of the desired TPI. And no odd thread pitches. Odd pitches and pitches coarser than 16 TPI will require setting the machine back to stock.
 
You must log in or register to reply here.
Back
Top