My Logan turning lathe's threading reversing gears shattered while attempting to make a worm drive with fast lead threads (5 1/2 threads per inch). The carriage hit the tailstock when I mistakenly started the lathe in reverse. New gears are very expensive and can cause other gears throughout the threading transmission to fail...so I decided to make a set of 30 tooth reversing gears from Taulman 910 alloy nylon to replace the cast iron originals. The nylon gears have several advantages. First they offer an inexpensive replacement. Second they run much quieter and most importantly they prevent any of the other gears from being damaged in the event of a crash of the carriage. (I have already tested this....twice) the only damage is to the nylon gears which are easy and inexpensive to replace. I now keep two replacements on hand at all times.