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12" Commercial Reduction gearing

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mattygee

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#1
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.
 

wa5cab

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#2
Is your Commercial equipped with a QCGB or is it Change Gear?
 

wa5cab

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#4
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.
 

mattygee

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#5
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.
 

wa5cab

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#6
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

END
 
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mattygee

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#7
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.
 

roadie33

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#8
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.
 

mattygee

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#9
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.
 

roadie33

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#10
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.
 

wa5cab

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#11
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.
 

mattygee

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#12
Definitely driving off 16 tooth gear of tumbler. Setup up exactly like the YT video I posted. Like I said, I'm stumped!
 

roadie33

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#13
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.

 

wa5cab

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#14
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.
 

roadie33

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#15
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.
 

mattygee

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#16
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>
 

songbird

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#17
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.
 

wa5cab

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#20
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.
 

wa5cab

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#22
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.
 

38Bill

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#24
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
 

wa5cab

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#25
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.
 

38Bill

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#26
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.
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
 

wa5cab

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#27
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

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#28
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 took the tip and got the one on e-bay, still waiting to receive it.
 

Gary Mundy

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#29
Has anyone tried threading with the single 24 gear setup? Also, has anyone found a source for the spacer?
 
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