12" Commercial Reduction Gearing

M

mattygee

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Has anyone had any luck with a gearing setup on their 12" commercial to achieve a slowest feed rate of .0021?
I was able to do a double reduction gear on my 10F no sweat, but it seems like the banjo on the commercial is a little different and no matter what gear combos I try nothing will fit. I'm curious if anyone has tried the same thing.
 
Is your Commercial equipped with a QCGB or is it Change Gear?
 
OK. The same quadrant or banjo was used on all three versions of the 12" QCGB made from 1950 through 1981. So nothing changed there. However, the angle or distance between the AB slot and the C and D slots on the QC banjo is a little less than it is on the L3-58M banjo used on the Change Gear models from 1938 through mid 1962. Unfortunately, I don't have but two extra gears, or three if you count one of the two 48T gears normally on the quadrant. And none are small enough to be half the size of any of the others. So I can't experiment. But the sliding gear obviously needs to remain in the OUT position. It needs to drive the large gear of a 2:1 Idler. And the gear driving the gearbox must be an Idler, either driven by the small gear of the compound set, or by another idler driven by the small gear.
 
Yeah, I know what you're saying; I've tried any number of gear combinations to no avail. What I need to do is see if a 24/96 compound gear driven by the tumbler gear will fit. I think the larger tumbler gears of the commercial lathe must restrict the room just enough to prevent doing a double reduction gear setup.
 
OK. You may be right. But if I'm reading it right, look at Table II in a Version 8 MOLO at either 69 or 70 TPI, but with the levers in positions E 9. If you change the 46T gear on the line for 69 TPI to a 48 and the 48 to a 52, wouldn't that do it?

MOLO 1960-V8 Table II Odd Threads QCGB.jpg

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I did just find a YT video
where the gentleman uses a 64/32 compound gear with a 54 tooth idler.
I have the 64/32 combo which I'll try with a 56 tooth idler since that's what I have on hand.
 
You only need to purchase one gear to make it work.
Find a 24 tooth gear.
Use the outside 48 tooth gear that runs the QCGB, with the 24 on the inside in compound configuration to run the other 48 tooth gear and you cut the feed in half.
 
Well, I tried the 64/32 compound gear; which to me, as long as the ratio is 2:1, it shouldn't make any difference as to the tooth count.. Anyway, same deal. Still getting .0042 per rev on the carriage. I don't know why this thing is defying me, but I'm stumped.
 
You set them up as the 32 towards the lathe and 64 to outside, right?
The 64 should contact the outside 48 tooth that runs the QCGB.
 
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