Sunday, August 16, 2015

Patching a Broken Pulley

I’m sure that most of you have come up with at least one problem with a damaged pulley on a shaft that you needed for a restoration. You have just found a nice jackshaft for your mill and you either damaged a pulley or a piece was already broken out of its circumference. This will require you to TRY to remove the pulley, then find another pulley the same size and then finally attempt to reinstall the new pulley. We had such a situation happen when we were restoring a jackshaft on a 20-stamp mill. In this case we had a pulley that had (2) pieces broken out of one of the pulleys. We did not have another pulley of the same size and the pulley was frozen on the shaft and would require removal of the shaft from the mill to press the pulley off of the shaft. We really did not have much choice to fix the problem.

We found another couple of pieces of broken pulleys that had came from our bone yard. It would have been nice if we had the original piece that broke off, but we came up with similar pieces with the same curve. The first thing we did was to take the pieces and scribe a line on them and cut them to fit into the broken area.  The picture below shows the notching of the pulley where it was broken.
Next we cut the pieces so they would fit into the broken area.

The next step is critical. We drilled 1/8” holes in the pieces and placed pieces of welding rod into them. The picture below shows holes being drilled into the piece:

The next picture shows the piece being fitted into the broken space and notches being ground to hold the piece in place:


We had to decide how to fasten the pieces to the pulley. This has to be strong enough to hold the pulley together during operations. We tried both brazing and using an epoxy called JB Weld. Actually, both methods were very strong and would make a good repair. We decided to use the JB Weld since it would not require heat to make the mend. Brazing might cause the cast iron wheel to crack. This is a common issue when repairing old cast iron components. The picture below shows both repairs:

The next picture shows the JB Weld being applied to the mended pieces. This took several coatings and grinding to make the transition between the main pulley and the repair pieces.   

The final work was to grind the surfaces so that there was no unevenness across the pulley. It worked very well and we did not have to remove the pulley or obtain a new pulley.


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