Tumbler gear replacement questions

I’m just wondering if someone changed the size of one of the gears to cut a special thread
 
Alittlerusty said:
I’m just wondering if someone changed the size of one of the gears to cut a special thread
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I have only cut 'normal' threads and the QCGB is correct. The gears also match the Atlas parts list. The 24T gear runs the saddle L->R which is opposite normal threading and the 20T is engaged for L<-R.
 
In one direction the power runs through one of the idlers on the arm. Output gear turns same direction as input gear.
Flip the arm to the other direction and the power runs from input gear to one idler then to the other idler then to the output gear.
Output gear turns opposite direction of input gear.
 
Assuming a 48 tooth spindle gear in either position other than center, one revolution of spindle turns the 24 tooth gear 2 revolutions. Got it. Did u compare the diameter of the new gears to the old?
 
Alittlerusty said:
In the first pic the 20 drives the 24 then the 24 drives the rest of the gear train and in the fourth pic the 20 drives nothing and the 24 is driven by the spindle and drives the rest of the gear train in the opposite direction so in my head the elimination of the 20 definitely changes the ratio as well as direction of the rest of the gear train but I’m not fully coffeed up yet.
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If there are n teeth on the driving gear and m teeth on the driven gear, the ratio would be 20/n x 24/20 x m/24 in the first case and 24/n x m/24 in the second case. In either case, the overall ratio is m/n.
 
It looks like the detent plate in photos 2 & 3 still has some adjustment. Have you tried adjusting that? If you are at the end of the adjustment and clearance is still excessive, the tumbler detent pin may be worn or the spring weak. Either of those conditions would increase the tooth clearance. If that was not the cause. It looks like you can increase the travel of the detent by filing the slot longer. Barring that, I would just make a new detent mechanism with the holes moved slightly upward.

When I added a reversing tumbler to my 602, I set the tumble for the proper tooth clearance and marked the position of the tumbler. Then I drilled the detent holes.
 
The picture of the detent plate has it jammed to its stops. The end of the plate bottoms out before the groove. I could remake it or grind the end off. Right now if I get it just about perfectly centered the bottom of the slots acts like a second detent hole and the gears mesh better...but the detent pin does not appear to be fully engaged so I worry it will pop out at a bad time and ruin a threading project. I am still studying it. Different screws and a countersink might help too.
 
To reiterate the subject of spur gear trains, if you have two parallel shafts each with a spur gear on it, regardless of how many other gears you might put between them, so long as all gears are in the same plane, the overall ratio of the assembly is the ratio of the first and last gears (in this case the 32T spindle bear and either the screw gear (change gear lathes) or the first gear inside the gear box (32T input gear of Atlas QCGB). The only way that you can change the input to output ratio is to introduce one or more compound gears (two gears on a common axis with one driven and the other driving).
 
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