Craftsman 6" 101.07301 tear down and rebuild thread (and some questions)

Ah, the infamous 'idle gear' mystery.

Between the driving gear and the driven gear you can have any number and sizes of idle gears. The actual ratio is defined by the driving/driven gears only.

If you imagine a 40 tooth driving, and a 40 tooth driven (end of a chain), and a 40 tooth idle, then for each tooth of the driving that passes, one tooth of the driven passes.

Now imagine a 100 tooth idler instead of the 40 tooth idler. It remains that for each tooth of the driving that passes, one tooth of the driven passes. The tooth count of the idler(s) is irrevelant.

On your lathe, the driving gear is, of course, the spindle gear.
The driven gear is the first gear in the chain that uses a mated step-up or step-down gear (or the final leadscrew gear), and its mated gear becomes the driving gear for the next chain.

If you had no step/up or step-down mated-gearing, just idlers between the spindle gear and leadscrew gear, then the ratio would be just (spindle gear) / (leadscrew gear).

Edit: However, having an odd number or even number of idler gears controls direction, forward or reverse...

Fun stuff, huh?
 
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Matt,

One of the thing hard to get your mind around (because it seems intuitively wrong) is that if you have a train (three or more) of simple spur gears, the only two that matter are the first and last. Take three gears with different tooth counts at random. Calculate the ratio between the first and the third. Then calculate the ratio from first to second, then from second to third. If you didn't get the same answer, you did the calculation wrong. Or think about this simpler case. Both the spindle gear and the larger end of the compound gear on the tumbler are 32T. The speed up ratio between the 32T spindle gear and the 20T gear is greater than between the 32T and the 24T. So, when engaged, the 20T spins faster than the 24T. But the ratios between the 20T and 24T gears and the second 32T gear are the reciprocal of the first ratios. So the slowdown is greater for the 20T than the 24T and the second 32T turns at exactly the same speed as the first one.

The exception to this rule is a compound gear (two gears on a common axle, like the 16T/32T on the tumbler), with one end of the gear driven and the other end driving. If you drive another 32T gear with the 32T end of the compound gear, it will turn at the same speed as the first two 32T gears. But if you turn it with the 16T gear, it will turn half as fast.

Some of the Atlas tumblers have two of the same size gears and some have two different gears. This is simply because of the relative locations of the two tumbler idler gear axles and the tumbler pivot point and the tumbler angle or position at Neutral. Sort of a cut-to-fit arrangement. Apparently, when they built the late 12" headstock, they were able to locate the tumbler pivot point in the proper location to need two of the same size idler gears.
 
Thanks guys, that does make sense but I'll have to ponder on it to properly understand :) math is an anathema for some reason - I can do developmental genetics but simple math ties me in knots!

Got a bit more done today but no pics yet as I'm on my tablet. Chuck is done, couple of bits painted and the motor needs another coat of paint before it gets put back together.

Quick Q - I found some 4 core sprinkler wire at HD today to go between the drum switch and the motor, but it's only 18g solid core. Is that thick enough? It's about 0.3mm thinner in the core than the existing perished wire, but that was the thickest they had. Opinions?
 
No. Not unless you have a 1/4 HP motor. #18 AWG is only rated at 3 amps continuous or maybe 4 amps intermittent. Tables that say otherwise should be deep sixed. For a 1/2 HP you need #16 or #14. For 3/4 HP #14 or #12. And I wouldn't use solid core wire, anyway. If you don't have a decent electrical supply house in your town, I think that you can buy wire in lengths as short as 10' from McMaster. 300 V rated is adequate. And Type SJOOW outer jacket.
 
Hmm, I think it's a 1/4hp motor from memory but I can't check until I finish painting it :)

I'll check around locally to see what I can find, there has to be some kind of electrical supply around here. Ace hardware didn't have anything suitable. Why not solid core? Does stranded give a better connection with crimp on connectors and post terminals?
 
Yes, stranded wire does generally make a more secure joint with crimp fittings. And as it spreads out when you tighten a screw down on it, a marginally better connection there. But the main reason is that unless it is in conduit or running along a surface to which it is attached frequently, it is or may be subject to getting moved around, bent or flexed repeatably. Which will eventually work harden it and it may crack. However, if the switch wiring is inside the headstock or cabinet and tied down at a few points, the #18-4 solid would probably be OK if it were large enough. Find the motor nameplate and see what the rated full load amps is.
 
I also checked your Ace and to my surprise they don't seem to carry three conduct appliance cord. Depending on what length you can go and buy an inexpensive power bar or cord set like for an air conditioner which are usually 16 or 14 awg. Cut the female end off and use the rest of the cord to attach to your lathe motor.
 
If you just need flexible, multstrand cable 16 awg or similar and you can't find it from Ace, just get a couple of inexpensive extension cords.. or one long one and cut up the cable as required.

I agree with Robert, always best to have flexible multi strand cable. We can buy extension cords quite cheaply at our buck store.
 
Good points Robert, I hadn't thought about work hardening. 10ft of 16-4 from McMaster is $12+postage, so that's always an option if I can't find anything locally. Any point going heavier? I'll take the tape off the motor plate tomorrow once I've put on the last coat of paint.

Thanks David, I got a nice replacement power cord from HD with a plug on the end which will go to the drum switch.
 
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