Broke Craftsman 109 gear while pulling

[ericc]

Hi. As some here know, I have been trying to get one of the change gears off the lead screw. The gear was stuck on the shaft, and kept the lead screw from turning freely even when the tumbler was disengaged. Anyway, there were some suggestions to use a gear puller to remove the gear. A quick puller was fabricated, and an attempt was made to pull the gear by its hub. It appears that this was not really a hub, but, as some have pointed out, a semi-permanently pinned spacer on the lead screw shaft. That was not going to come off.

So, the gear puller was set up to pull against the gear. Staying away from the teeth, the force was applied closer to the center. There was a horrible "POP" anic: and the gear came off. Closer inspection showed that something had sheared off. This gear does not look like any of the ones on sale on Ebay. The outside (left side) of the gear is round with no evidence of keying. The right side of the gear has a fracture which shows the male outline of the keys. For some reason, it looks like the gear had protruding keys that went into the spacer. This is very strange. It may be that there was some kind of intermediate keyed coupling that mated with female key slots in the gear and the pinned spacer.

Are there any hints of how to salvage this situation. It seems that the gears on Ebay are not suitable replacements.

 

[iron man]

Is it steel or the zamak? I have a pile of gears maybe i can help you out give me the tooth count and the pitch if you know what it is. Ray

 

[ericc]

Hi iron man. Thanks. It is a 64 tooth gear. There are a lot of these on Ebay, but they have the bore with the two key ways all the way through. I am attaching a drawing of the break. The grey area is the area of the fracture. It is amazing that such a thin section is in the casting, and this also supports torsional stress, not just abuse when some beginner is trying to pull the gear. :angry:

 

[ericc]

I cleaned up the gear and it appears that the gear is not really broken. Instead, there is a sleeve inside it, also made of zamak, that is sheared off. The sleeve could be pressed out with a rod of the appropriate size. It looks like a cylinder with the two keys protruding out the sides. So, the other half of the keyed sleeve is sheared off flush with what looks like a steel collar on the lead screw. This collar or spacer seems like it should be removable. It just doesn't seem to want to come off. It is really easy to mangle the end of the lead screw with the gear puller, because there is a threaded hole in the end. Even heating the collar to bronze will not help. This burned a lot of oil out of the gap, but even with the puller on the spacer, while heat is being applied, does not seem to help. I am going to leave the puller on the end for a couple of days, then I'll make a custom end to screw in that can withstand more force.

This is getting kind of difficult. Looking at a manual, it looks like the collar is pinned on with a longer sleeve. This is absolutely wrong. Also, since the threading requires that the lead screw gear be placed in either the left or right position. That pretty much requires a movable spacer. I cleaned and scraped off the outside of the spacer, and cannot see any pins. It looks like the washer is slightly damaged from some pulling attempts, possibly mine? Somebody at work suggested enough heat to melt the zamak. It is possible that the collar is "welded" on. He suggested that 500F should be enough to pop the sleeve out, since zamak gets pretty weak when it is hot. I think I heated the shaft to almost this temperature, but it did not budge.

Blacksmiths typically do not put up with this crap. Out comes the air arc, and no shaft will be stuck for long. But then the lathe will start looking like an anvil. )