# Shaving Gears

How many teeth would be a good amount to shave off of a HS 36 tooth gear for a slip gear catapult. I want to hear your opinion because me and my team are debating on the number and we don’t want to waste gears. Thank you in advance.

It all depends on how far back you pull back your slide.
Test with different lengths then measure the number of teeth, then cut off the rest of the teeth that doesn’t have to make contact
There is no magic number really it’s all tailored to the mechanism.

just remember you can always shave more teeth off, but you can’t unshave…

Keep in mind that it doesn’t usually work using basic math. If you want to pull back your catapult 90 degrees (1/4 turn) it may take more than nine teeth (1/4 x 36 tooth gear is 9 teeth).

I wish I could explain this better but one of my teams went through numerous gears getting it right. It has to do with the teeth on the shaved gear approaching the driven gear. It may take a tooth or two to engage before the driven gear starts moving. Also, because the gears are round, the last tooth may let go earlier than you are expecting.

Depending on how fast your motor is going and the length of travel of your catapult you will probably need to remove at least six teeth as a starting point. (I don’t know your project so this is a best guess)

Make sure you axles are short so your gears don’t slip and test where the radius of your catapult has lots of room to move.

Thank you. I was trying to mathematically calculate it, but now i know that there may need to be an increase in the number of shaven teeth

Best way to calculate this is to just build the catapult with a regular gear that would be the slip gear, mark the initial point of contact, and then move the catapult to the point of release and mark that tooth. The take off the teeth in-between the marks; take off one less though just in case.