Norton Style Gearbox Issue

ShagDog

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I have a Select 816b lathe that has what appears to be a Norton style gear box. I have trouble with the 2 tumblers falling out of the holes when running at the faster feed speeds. No problem on the slower ones. The left one is more problematic, again, at higher speeds. The longitudinal feed and threading are both operated with the half nuts on this lathe.

I do note, as you will see in the photos, that the pin that goes into the gearbox hole is pointed and bent on the left one, while the right one is cylindrical and straight. Also noteworthy is that the left one has apparently been brazed (see photos # 3, 4 and 5)).
I did try to take off the pin of the left one to fabricate another; but, it looks like the pin may need to be drilled out of the handle. Didn't want to do that since that may not be the problem. also, you can see that it appears that a previous owner attempted to hold the pin in, maybe with vise grips, as can be seen in the damage to the top of the left tumbler in photos # 2 and 3.

I guess what I am trying to find out is the root of the problem that makes the lever so jumpy (bouncy) and prone to pop out at the higher feed rates. Please help me get this figured out.
 

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martik777

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I think those pins are the problem, especially the left one. I've never seen those tumblers disassembled before but from this diagram may help. On my 9A the pins go all the way thru the casting and then some. If I pull them part way out (as yours are) they whole tumbler wants to pull down and out of gear. You may have to remake parts 27, 31 and 39.
 
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Mitch Alsup

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I agree that the pin is the problem, especially bent in the direction it is bent.

Is there a way to remove the pin and install it 180º from its current orientation ?

Otherwise
a) remove pin
b) use hammer to straighten pin or machine new pin or buy new pin
c) reinstall pin.
 

martik777

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Pin looks too damaged to straighten.
The pin on mine is 1/4" OD on the small end and 7/16" for the remainder of the plunger. One could mill the 1/4 part off and tap 1/4-28 into the 7/16" part and machine a new pin to thread into the 1/4-28. Holding the tumbler will be an issue.
 
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ShagDog

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I think you guys are right about the left pin. I just went out and tried it, and the left pin does stay in okay on the bottom holes. The top holes, not so much, under load. That is why I was thinking it could be the weld.

Here are some pictures of the left knob. I did take it off; but, the peening at the end appeared to be what was preventing the pin from coming out.
 

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martik777

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I found pin #27 on one of mine, on the front narrow un-kurnled part of the knob. I had to use a magnifier and strong LED to find it. If you can punch that pin out you should be able to disassemble it. I would remove the tumbler from the QCGB before attempting to punch it out.
 

martik777

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Last edited:

Tim9

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Yep, totally agree. Make new pins. And FWIW, if that’s grease on you gears, get rid of the grease. On a SB 9” that I rebuilt, I was shocked to find out someone smeared tons of grease on all of the gears. I went through the QCGB. And since the said lathe had tipped over, I had bent pins which I remade. Really a simple job. Just used regular leaded steel. Nothing special.
The only reason I mentioned the grease is that if there’s too much resistance in the gear transmission, then there’s also more pressure trying to move those tumble gears to pop out of gear. So make sure that the gears are lubed with the proper oil. No grease.
 
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