vermicular engineering

[travis]

All insightful points, well taken.

Many people bring up worm gear efficiency as a problem. I looked deep into the roymech (great online reference by the way) page on gear efficiency and for single start 14.5° worms at 5krpm the efficiency is 89% -- pretty fair actually. Efficiency scales as v^-0.25 so you do worse while accelerating.

There was a lot said about reacting axial loads. Does anyone have experience using an E style retainer clip for this purpose? My friends over at Machinery's told me that an ANSI standard 1/2" shaft E clip will resist 600lbs of static load. I know you have to react that eventually, but I have something sinister in mind.

Several folks said they broke teeth. This indicates to me that worms are not necessarily inherently crummy (though one is suggested to use bronze, not steel gears), but perhaps the gut instincts that work fine for spur gear sizing need a fudge factor to be applicable to worm designs.

The final concern was alignment, on which I am going to just have to bite the bullet.

An alternative at this point would be a largish single stage spur gear reduction -- I just discovered Boston Gear's 5T(!) stem pinions -- followed by a smallish reduction and right angle transition using helical gears. Helical gears, being a somewhat special case of worm gears, should have a lot of the same challenges. Anyone have something good/bad to say about errr Crickian engineering?

Travis

[sanddrag]

Originally Posted by travis

There was a lot said about reacting axial loads. Does anyone have experience using an E style retainer clip for this purpose?

E-clips would probably work fine for this. Snap rings would probably work better. Your best bet would be to have a structural/geometry constraint such as shoulders on the shaft. flanged or tapered bearings, etc to avoid using a clip at all.

In supporting the axial load, the concern in addition to the support/constraint is the bearing. It can be done (has been thousands of times over, but it's just more work than the traditional spur gear setup. Typical single row radial bearings are really only intended for no more than about 25% of their radial rating applied in the axial direction. Angular contact bearings are fantastic, but can be expensive. Some teams get by by using bronze thrust washers/bushings and grease. Tapered roller bearings (similar to automotive wheel bearings, but smaller) could be another option.