How to determine what gear you have

[Scott Riddle]

I have a old heavy duty drill that I want to pull the motor out of and replace it with a stepper motor. The problem I have is that the motor shaft has a gear cut into the one end of it to drive the gear reduction head. I want to make a adapter shaft to go on a stepper and then ride in the drills gear reduction heads bushing. The motor shaft gear has 9 teeth and has a OD of 0.380". How can I find the DP and pressure angle of the gear so I can find a prodcution gear that I can modify to fit my stepper. I found a bunch of gears at sdp-si.com but I could not find any 9 tooth gears that had a OD of around .380"
I would appreciate any help in figuring out what this gear is and a possible supplier of them.

Thanks
Scott

[Mike Everman]

Look in the metric gears. If it were english, Pitch=(teeth+2)/OD, which doesn't give a valid pitch in english.

[BillTodd]

Can you re-use the old motor shaft and gear - connect it to the stepper with an appropriate coupling ?

It could save you a lot of work.

[Scott Riddle]

I was thinking to re-use the motor shaft with the gear hobbed into the end of it but then I have to make a housing about 6-7" long to house the motor armature. I dont want to destroy the motor as I may want to put it back together some time and use is as a drill again. That is why I was trying to figure out what kind of gear this is so I can just put a stub shaft onto my stepper and make a adapter plate to hold it all together.
The thought on it being a metric gear I dont think would be correct as this drill is from the 1960's. I dont think they used metric gears back then.
I am thinking of pulling the head apart and measuring the mating gear and the motor gear to see if from the 2 I can get the numbers to point more to what it is. The pressure angle, I think, is going to be hard to figure out though.

Scott

[jimalb]

My guess is this is a 28DP gear.
9 tooth 28DP gear would have a 0.3928571 OD. (Textbook size)
I find a lot of gears a little smaller than textbook size.
Since you are measuring a gear with a odd number of teeth your .380 OD would be a little small, (I am assuming you measured the OD just outside to outside, Not center of gear to the outside of a tooth (radius) and doubled that, so you had one tooth on one jaw and two teeth on the other jaw of your mic(caliper).

[Scott Riddle]

I did just use a caliper and I bet I did get between 2 teeth on one side. I will have to measure again and rotate it a little to see if it gets any bigger. I will do some looking for a 9 tooth 28DP gear like you suggest. Do you have any good places to find small gears like this?

Many thanks!

Scott

[Scott Riddle]

I went and remeasured the gear teeth with a caliper. It measured .348" at a minimum and .353" as I rolled the gear. The smaller dia was with 3 points of contact. 1 tooth on 1 side and 2 on the other. What would that calculate out to for a Dp with 9 teeth?
What formula do you use?

Thanks
Scott