Gears That Time Forgot

My consulting practice covers a very wide range of products — from 4-inch circular pitch mill stands to 180-NDP handheld medical devices — I see them all. Most of the articles and papers that find their way to this magazine cover the latest advances in gears for energy or transportation equipment. We seldom see articles for fine pitch (less than 20 NDP) gears, however.

After more than twenty years away from that particular product niche, several clients requested my help in resolving problems with small devices. And by small I mean a six- shaft mechanism that fits into a plastic housing the size of a quarter. Wading back into the swamp, I was surprised to learn that very little of the advanced technology we take for granted in the “big gear” world had made it down to the little stuff.

Many of the “problems” were exactly the same as I had left behind in 1989; e.g. — heat treat distortion, residual burrs, and high costs. CNC was limited to blank preparation where the labor-intensive multi-spindles were supplanted by bar feed multi-axis machines; the machines actually took longer per part, but were more suited to the smaller lot quantities on order. Rooms full of skilled technicians still worked on the burrs, fully aware that one wrong stroke of a file could turn a part into junk; indeed, deburring costs often exceeded tooth cutting costs. Teeth were still being made on the same equipment that I remembered. Quality control was a roll tester next to the hobber or shaper.

Few of these shops could afford new equipment, even if it were available. I wonder if grinding teeth from solid might reduce the deburring problem, but I have not identified a CNC grinder small enough. A client managed to get a roll tester rebuilt and computer-fitted to collect and analyze the charts. Another found someone with a CNC inspection machine capable of doing lead, involute, and spacing charts on teeth as small as 220 NDP. It was amazing to see a probe that small but frustrating to find “defects” on parts too small for a grinder to fix.

Eventually someone will make that grinder. I hope the fine pitch sector survives long enough to see it. There were not many young people in those crews and operator skill takes years to develop. It would be interesting to see a few more technical articles from this community — even if they are just reviews of methodology that is no longer commonly used on larger gears.

 

About Charles D. Schultz 605 Articles
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

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