I found a stepper motor not able to turn and would like to dismantle it to service. However, in order to do that, I needed to dismantle both ends of the motor in order to free the motor rotor shaft from the end bearing covers. Without a gear puller available, I knew I would certainly do some damage on the shaft, bearings or housing. I needed to keep these in good working condition because I would certainly wish to use them later.
Without wanting to buy a commercial gear puller, I searched around for the best options available to me. As always, I wanted something cheap and good.
I searched the internet and found a pretty good diy gear puller fabricated from steel hollow square bars with a tapped hole which was able to accept a bolt for jacking.
But I could not do the same because I did not have a suitable tap for threading the hole to take in the required bolt. I knew that I could weld a piece of nut in place instead of tapping the screw threads, but again, I did not have a welding machine.
Thoughts of filing a hexagon-shaped hole to slot the hexagon nut and then gluing it in place with epoxy entered my mind, but that would mean spending some extra time and effort in fabricating a contraption which might not work eventually. Similarly, I dismissed the idea of fabricating in wood because it might not be strong enough for such a small motor.
Then, I had a brain wave. I did not have thread taps, or welding machine, but I had a vise. And a vise could be used for jacking if I could work out some arrangement to make it work. The motor was not too big to fit into the jaws of the vise, so I decided to fabricate some simple parts just to jack the pulley out.
My idea was this: Instead of pulling out the gear from the motor shaft as in normal practice, I would be pushing the whole motor (including the shaft) out of the gear. That’s how the vise work – to push instead of pull – like a jack.
First, I would need a strong bar to hold against the gear. I did this by using a piece of 5 mm thick mild steel bar and ground a slot just big enough to allow the shaft to enter. I used a portable angle grinder for this. Next, I would need 2 spacers to support the motor. After measuring the total length of the motor, I cut 2 pieces of wood slightly longer. They had to be the same length in order for the strong bar to exert an equal force on the gear when jacking.
The diameter of the shaft was 5 mm. A piece of nail with the same diameter was cut and smoothen so that it was able to move freely into the bore of the gear when jacking against the shaft. The head of the nail was somewhat helpful in steadying the assembly when setting up.
I must admit that setting up the assembly was not quite so straightforward, but eventually I managed to put everything in place. The wooden support blocks were tied against the motor so that they would not fall apart, and also to ease the assembly.
With the assembly set up, all I had to do was to tighten the vise by turning the handle. With the gear resting against the strong bar, made immovable by the wooden spacers, the center pin pushed against the shaft and motor which caused them to separate from the gear.
It worked. It’s a Shaft pusher instead of a Gear Puller. And it practically costed me nothing.
Once the gear on the shaft was out, the motor housing covers could be easily removed to reveal a rotor which had been badly contaminated with iron rust particles. These particles had been attracted to the permanent magnetic poles of the motor rotor, causing them to jam up against the stator.
Once the iron rust particles were removed, the motor was able to turn freely.