October 12, 2022
Backlash “adjustment” is just one of the many “frequently” encountered problems in custom manufacturing shops. Over time, most organizations develop an extensive “playbook” on what defects occur, what can be reworked, and how that rework can be accomplished. This is no reason for you to wash your hands of the decision-making process, however. As the engineer or designer, it is your responsibility to know what is actually going into your product. Even if you got out-voted in a scrap vs. re-work decision, you will be the first person called if the thing does not work as planned. We developed written policies on the chrome plating of diameters, for example. There were shafts we declined to plate — either because of customer requirements, application, or, more frequently, cost and delivery. Just because you can plate a diameter does not mean it makes economic or scheduling sense. But if you are going to plate something, you only want to do it once. The pre- and post-plating processing has to be done properly to get acceptable results. And “hard chrome” plating is much different from “show chrome” on automobile or motorcycle parts. Having a reliable plating shop is a critical thing too; price shopping is not always advised. Things remained more “fluid” with regard to heat treat “defects.” It was much easier back in the through hardened days when you could re-temper blanks until the measured hardness fell into spec. With surface hardened gears, things are much more complicated and extensive lab work is needed to verify what the actual problem is. If you are not cutting up parts you can never be certain you have met the requirements. Low-volume jobs seldom have the “budget” for cutting up parts. I used to tease our metallurgist that he would never be satisfied until we allowed 100% destructive testing. This does not mean that you should not have a thorough understanding of the thermal processes you specify. I have blogged about this topic frequently in the past but will re-visit it in my next posting to highlight the “fixes” that are often employed in an effort to “save” critical parts.