HP 46/81 idler gear

[RPZ]

Hello Duane,

Thought I posted a response to your post a long long time ago. Oh well. Sorry.

I am a hobbyist who enjoys repairing and using older HP calculators. Part of this is that I could not afford them years ago when they were introduced. I have no desire to sell parts or start a repair service. Just wanna have fun. I buy way too much on an auction site (must stop) and have yet to sell anything. The purpose of my posts was only to assist anyone else attempting to print 3d printer gears. Feel free to use or modify any information provided.

Due to the small forces and low usage, I don’t think wear is really much of an issue. I have tested my HP 97 gear for 40,000 cycles and can see no visible change. That’s over 6 rolls of 85’ paper. The usual idler gear replacement is made of aluminum driven by the steel pinion and driving the large plastic gear. Aluminum is very abrasive but no one has ever reported a wear problem.

PLA is short for Polylactic Acid and is often used for 3D printing and many manufactured items. This is the material I used for my gears. The tips of my gears are a little bit blunt due to the limitations of my printer but did not seem to matter in my testing. Sometimes this is done on purpose in gear design and is termed clearance.

Fine Detail Plastic from Shapeways is described as a resin-based acrylic material. It is not recommended for functional functional parts due to its brittleness. Brittleness is such a relative term. Cast iron is brittle but often used for gearing. Shapeways printed a really nice detailed accurate part with this material.

I don’t think any of the gears were meant to be sacrificial. My guess is that they picked a material for wear and sound. I’m sure they did a bunch of testing but there is no substitute for age. Thinking of the card reader gummy wheel.

I only printed the 46/81 gear as an exercise as I do not have one but you never know. Never thought I would have a 97.

If you would like some to test or use I would be happy to mail you some. Let me know.

Regards, Rick