worm gear emergency

[Bill Gold]

The Martin Sprocket (www.martinsprocket.com) cast iron part numbers appear to be W1218 and WG12 on page G-69. Motion Industries and Applied Industrial Technology can get you Martin stuff. Out here on the west coast we can get them next day, if they're not stocked by the local outlet or another nearby. I'm not sure about the east coast, though. Best of luck on your search.

-Bill

[Andrew]

My experience with worms and worm gears is that you often have to replace them as a set. The lead angle on the worm+worm gear is usually a custom number.

So, be careful trying to mate a "Stock Drive" worm with a "Boston Gear" worm gear of the same pitch, leads, and number of teeth.

My advice, look at your pitch distance between the worm and worm gear, and buy a set with the same gear ratio and pitch distance.

The next issue, if you failed the original system because the shaft was deflecting (cast iron gears throwing teeth?), you will probably fail the steel system in "low cycle fatigue". In other words, if you passed the ultimate strength of cast iron, you will probably be at a significant fraction of the strength of steel that, after 20-50 cycles, you will fail the steel gear due to fatigue.

I'm assuming that your shaft was not doubly supported, over a short length. You might want to consider a redesign (not sure how much time you have) to get that shaft better supported and therefore remove the chance of failure.

Good luck and sorry that I only have cautions and not much positive,...

[ClicheCow]

Originally Posted by Andrew

My experience with worms and worm gears is that you often have to replace them as a set. The lead angle on the worm+worm gear is usually a custom number.

So, be careful trying to mate a "Stock Drive" worm with a "Boston Gear" worm gear of the same pitch, leads, and number of teeth.

My advice, look at your pitch distance between the worm and worm gear, and buy a set with the same gear ratio and pitch distance.

The next issue, if you failed the original system because the shaft was deflecting (cast iron gears throwing teeth?), you will probably fail the steel system in "low cycle fatigue". In other words, if you passed the ultimate strength of cast iron, you will probably be at a significant fraction of the strength of steel that, after 20-50 cycles, you will fail the steel gear due to fatigue.

I'm assuming that your shaft was not doubly supported, over a short length. You might want to consider a redesign (not sure how much time you have) to get that shaft better supported and therefore remove the chance of failure.

Good luck and sorry that I only have cautions and not much positive,...

The shaft was supported on both ends, with a thrust bearing on one over 3 inchs. We only think that it is bent, but our lathes aren't properly centered (as we discovered trying to test the shaft) so we can not confirm that. But then again, if the lathes are not centered, and they were used to machine the shaft, thats probably our problem.

Seeing as we ship tuesday, and will only be able to work from 9 - 12pm on monday (the alarms in our school will be turned on after then), we don't have time to re make our gear box. Buying multiple sets of steel gears that will only last 40-50 cycles seems much better than what we have now, which will last us less than one match, but I still have been unable to find one. We may have to take the cost and have one custom made unless we can find a better option.