Bull gear issue

[John Lestelle]

I have an Atlas Craftsman 12" lathe and the bull gear keeps unlocking itself when I am using it. Very annoying, does anyone have any suggestions for a fix?
John L.

 

[RJSakowski]

As I recall on my 6", there is a pin or ball which engages the drive dog. A set screw adjusts the detent force and can be tightened fully. The set screw exits on the circumference of the gear opposite the drive dog.

 

[pontiac428]

Just of the top of my head, you could try making an oversize pin. But more likely if it's popping out under power there is excess wear on the pin lock holes on the zamak bull gear itself. Do you have any photos?

 

[markba633csi]

Another thing to check for is excessive wear in the step pulley bushings which can give an eccentric wobble and possibly contribute to the pin working it's way out as the spindle rotates, but as Pontiac mentioned, check for pin wear and bull gear wear
The detent ball and spring might also be gunked up with dried grease- maybe try some solvent spray or liquid wrench
There should be a positive click that you can hear and feel when the pin is actuated
-Mark

 

[Bi11Hudson]

I don't recall any detent feel on mine (101.27440/12X36) I always thought it was a slightly "over center" mechanical motion so that once fully engaged, any slop would force deeper engagement. That's just my perspective of it though. I don't fully load, hell, I don't load it at all. Just a speed reduction for me. Wish I had a good answer.

.

 

[pdentrem]

Should have a pin/ball and a spring to hold the Pin in position.

 

[John Lestelle]

Thanks to everyone for the help, I don't have any pictures to show the pin and I don't see any means of retention. More ideas will be appreciated.

 

[wa5cab]

The 10-256 Direct Drive Pin that you push in to lock the cone pulley to the bull gear is a nominal 1/2" diameter. by 1.35" long. It has near one end a 1/2" wide slot cut across it to a depth of about 0.1". Adjacent to each side of the slot is a dimple made with a 3/16" diameter ball mill. The visible end of the pin has a groove turned around it that a special tool or a screwdriver can be hooked into to pull the pin out with.

The 9-60 detent plunger is 3/16" diameter with one end being a ball end. There is a 3/16" diameter hole drilled between two adjacent bull gear teeth that goes through the 1/2" diameter hole through the bull gear web. To assemble, you first drop the 9-61 detent spring into the 3/16" hole and then drop the plunger on top of the spring, ball end up. With a special tool, you push the plunger down against the spring and slide the direct drive pin into the hole through the side of the gear, ending with the plunger in one of the dimples. To disassemble, you first rotate the direct drive pin 180 degrees, place your thumb or probably safer something like a putty knife blade over the hole between the gear teeth (to keep from losing the detent pin) and slide the direct drive pin out. To retrieve the plunger and spring, use a small magnet.

There is a reverse engineered drawing of 10-256 in Downloads.