You do not always have to say “no” when confronted with non-conforming parts. Here are a few “fixes” I have been comfortable authorizing:
Custom keys and keyways
While standardization is expected in both the metric and imperial systems, larger-than-standard keys or step keys have long been employed to salvage otherwise acceptable parts. If you have a large pinion that moved during keyway milling, the shop is not being a bunch of hacks when they propose enlarging the milled slot to clean-up and then making a “step key” to allow a standard mating part to be mounted on it. You need to document the “as-built” condition for future reference, of course — and get customer approval if it effects the connecting couplings.
A damaged seal diameter can be quickly repaired with a hardened sleeve. Commercial sleeves are readily available in popular sizes or you may have to manufacture your own. It is usually faster and cheaper to do this than chrome plate the seal diameter. Document the change in your records.
High-quality thread repair inserts are widely accepted in most industries. They are preferable to welding up holes and re-machining because there is no worry about stresses induced during welding. As the inserts are permanent, I never felt the need for customer approval or recording in the build file.
Fabricated steel housings and gears — and, less frequently — cast steel gears, occasionally need repair welding. As long as the proper pre-heat, post-heat, and tempering operations are included in the process the end result will be indistinguishable from a “perfect” part. Some claim they can repair-weld cast iron; I remain unconvinced. Aluminum and bronze castings are also sometimes weld-repaired, I am told. Cosmetics, as mentioned previously, are a consideration, so get qualified welders involved, listen to the heat treaters on post processing, and make the extra effort to make the parts “pretty” again.
Bearing seat bushings
One of the underappreciated features of the inch series taper roller bearing system is the availability of a range of bore sizes in the cones. More than once this has allowed us to rework the shafts to accept a smaller bore cone and move along to assembly — after proper record keeping, of course. When using ISO-dimensioned bearings this option is not available. When fitting a shaft or pinion with bushings to correct an error, make sure the sleeve is shrink-fitted before finish machining operations. If you have concerns about axial forces displacing the sleeve, consider increasing the amount of interference or providing a keeper plate on the end of the shaft. As-built records are needed, of course.
There are a few “tricks” from the rebuilding side of the gear business to cover in the next blog posting before we move on to other topics.