4 ms·

Very nice. One perhaps counterintuitive thing about threads and gears is the optimal "tooth" size is a function of the material strength, not the geometry of t

by tejtm 5y ago

Very nice. One perhaps counterintuitive thing about threads and gears is the optimal "tooth" size is a function of the material strength, not the geometry of the object the tooth is on. Another is that when regular involute gears mesh, they press but do not rub, no sliding friction. Here I am not seeing how to avoid sliding friction which is a small price to pay for the extra degrees of freedom but one to factor in.

rfrey 5y ago
Slightly know-it-all, but in fact involute gears do rub against each other - they experience pure rolling motion where they contact at the pitch circle. That's the only point where the circumferential speed of the gears is the same. The purpose of the involute shape is to maintain constant torque transmission during tooth contact.
- jerome-jh 5y ago
  I believed like OP involute gears had true rolling motion with no slide however quoting Wikipedia (https://en.wikipedia.org/wiki/Involute_gear https://en.wikipedia.org/wiki/Involute_gear): "Where the line of action crosses the line between the two centres, it is called the pitch point of the gears, where there is no sliding contact." So I learnt something :) I also believed torque varied slightly because the point of contact between teeth was not at a constant distance of the gears centers. Illustration: https://en.wikipedia.org/wiki/Involute_gear#/media/File:Involute_wheel.gif https://en.wikipedia.org/wiki/Involute_gear#/media/File:Invo... Would you have sources for the affirmation "constant torque transmission during tooth contact"? BR
  - rfrey 5y ago
    I overspoke when I said "constant" - like everything, involute shape is a compromise, in this case (I think) between constant torque and manufacturability. I should have said "the shape is intended to minimize torque transmission ripple". I'll pull out my old textbook and see if I can figure out where I picked that up from.
    - jerome-jh 5y ago
      OK thanks actually I do not need the math. Just wanted to know I my beliefs were wrong on that point too.
codesnik 5y ago
I also see some locking positions which probably would require active rotation of the supporting gears in their brackets.

by tejtm 5y ago

rfrey 5y ago

Slightly know-it-all, but in fact involute gears do rub against each other - they experience pure rolling motion where they contact at the pitch circle. That's the only point where the circumferential speed of the gears is the same. The purpose of the involute shape is to maintain constant torque transmission during tooth contact.

jerome-jh 5y ago
I believed like OP involute gears had true rolling motion with no slide however quoting Wikipedia (https://en.wikipedia.org/wiki/Involute_gear https://en.wikipedia.org/wiki/Involute_gear): "Where the line of action crosses the line between the two centres, it is called the pitch point of the gears, where there is no sliding contact." So I learnt something :) I also believed torque varied slightly because the point of contact between teeth was not at a constant distance of the gears centers. Illustration: https://en.wikipedia.org/wiki/Involute_gear#/media/File:Involute_wheel.gif https://en.wikipedia.org/wiki/Involute_gear#/media/File:Invo... Would you have sources for the affirmation "constant torque transmission during tooth contact"? BR
- rfrey 5y ago
  I overspoke when I said "constant" - like everything, involute shape is a compromise, in this case (I think) between constant torque and manufacturability. I should have said "the shape is intended to minimize torque transmission ripple". I'll pull out my old textbook and see if I can figure out where I picked that up from.
  - jerome-jh 5y ago
    OK thanks actually I do not need the math. Just wanted to know I my beliefs were wrong on that point too.

codesnik 5y ago

I also see some locking positions which probably would require active rotation of the supporting gears in their brackets.