Craftsman 12" question

The photo shows both pins as described above. But as to which is which, therein lies the question. . .

The "inner" pin, below the rim of the gear, is a "dog" pin to use the back gears. Pull out to release, maybe 3/16-1/4 inch. Do not remove it, there is a detent when it's out enough. Do this before engaging the back gears. Reinsertion is not so easy, the spindle must be rotated a ways to find a hole for it to plug into. I think there are four, I never bothered to count. Almost a guaranteed pinch if your mind is somewhere else.

The second is attached to the frame of the headstock. It is for a "primitive" indexer. There are 60 holes around the edge of the gear. Any number that will divide evenly into 60 is achievable. DO NOT power on the machine with this pin engaged. If the machine is started with this pin engaged, it will snap off, damaging the machine. Handy for scribing indeces and with a toolpost Dremel, capable of primitive milling.

The 60 holes is for an Atlas 10 inch / Craftsman 12 inch. The 6 inch machines may have them, but a different number. The gears and original pins are ZAMAK, a Zinc/aluminium alloy. The alloy is not so strong as steel and will fail easily if jammed. This applies especially to the gear. It is not currently available, so I've been told. Replacement will be a PITA on a good day.

In both cases, the machine should be powered off. Be sure the switch is clear of anything that can start up the motor. The dog pin for the back gears is the more hazardous of the two. Very easy to get your hand squeezed or crushed if the machine moves. My machine (101.27440) has a drum switch mounted on the front of the chip pan, very easy to bump. The stock switch is not so dangerous, but still a hazard.

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shadetreedad said:
As pdentrum said pull the pin & engage the lever for using the back-gears. Also, I highly recommend unplugging the lathe while doing this maneuver. Your fingers are in a very vulnerable position either pulling it out or pushing it back in. I've pinched a finger just moving the spindle with my left hand while reseating the pin with my right.
Mike
Click to expand...
Oh BS.. I never unplug to change to backgear or reverse.
 
All of the gears in an Atlas built machine are Zamak V except for those in the QCGB. If they weren't there probably would be no Atlas machines around. However, most if not all pins in an Atlas are steel. The reason that the indexing pin is relatively easy to shear off is that it is quite small, not that it is made of Zamak. The gear that can shear it off is made of Zamak.

The proper name for the 2-position pin the you pull out for operating in Back Gear is "Direct Drive Pin".
 
Unplugging the lathe before engaging/disengaging backgears might be a bit overdoing it in the safety department, but make very sure you can't accidentally turn on the motor while your fingers are in a risky place
-Mark
 
I often chuckle to myself for imagining the worst when I rely on machines not turning themselves on. Like reaching into a garbage disposal, etc. I think since the 80s movie Maximum Overdrive where machines came to life, it’s always been in the back of my mind.
 
I always pull the plug before disengaging or reengaging the "direct drive pin" on my Atlas lathe. At least that is my story and I am sticking to it!
 
My Atlas 3996 has two holes located 180 degrees apart. I have never seen the Bull Gear drawing so I do not know whether this is and has been true of all 10" and 12" since the beginning. But mark both of them if two are present. And don't make any effort to always use the same one. The cabinet models have a 2-groove pulley and next to the bull gear is a flat area where it is convenient to use a center punch for a permanent locator. If I had a 10" or bench model 12", I think that I would loosen the set screw in the bull bear and move it away from the pulley and use a triangular file to make a permanent locator groove in the front edge of the pulley. If you only use a black felt-tipped marker, it will eventually fade away.

And don't forget to slide the bull gear back against the pulley and re-tighten the set screw.
 
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