The gears in my head don't mesh

[Suzuki4evr]

I have a question. If I want to make 4 new gears but I only have the number of teeth of each gear, how do I calculate the OD's of the gear blanks if I have none other variables available? Because I am making new gears,I don't have any other variables. The gears are for my lathe and in the picture below it shows the configuration.

If I have the OD,I can work out everything else,but I just can't figure out how to get the blank OD's. I know some are going to give me formulas using the module or DP or other variables ,but remember I do not have any of that. I hope someone can shine a very bright light on this,because I am starting to feel stupid not being able to figure this out.

Thanks guys
Michael

 

[matthewsx]

This might be an unorthodox approach but how about cutting circles from thin plywood in about the size you think will work and seeing how they fit on the lathe. I'm not any kind of expert but if they fit in the physical space and have the right number of teeth that's all that should matter, right?

Cheers,

John

 

[Suzuki4evr]

John,I don't think it works quite like that. Making gears is actually a precise mathematical process from the little I know. But thanks for the idea. If all else fails........

 

[cathead]

Machinery's Handbook has a wealth of information concerning gears. There are drawings and formulas
that one can use to get the dimensions you need to make most any gear.

 

[Suzuki4evr]

I did page through it,but still could not get the answer I want seeing that I only have number of teeth.

 

[Suzuki4evr]

I count have missed it somehow.

 

[graham-xrf]

@Suzuki4evr :
Hi Michael
The final dimensions are precision, but the quick-'n -dirty check with a temporary plywood dummy, or bit of plastic can lead you straight to the correct gear, and remove ambiguity, if you only have the number of teeth.

An obvious question is.. does anything survive of the originals? If you can get at them, you can measure the pitch. Even an approximation may be enough to then figure out the rest of the gear - because the possible combinations are limited.

gear guide.pdf has a table of pitch comparisons on P602, various calculation examples, etc.

If you know, or can measure, the distance between the shaft centres, then the number of possible solutions that have the known number of teeth rapidly become fewer.

p-1930-bg_engineering-info-spur-gears has very complete tables and information about gears on P309 and P311.

Unfortunately, the madly comprehensive gear_guide1.pdf is 21.4MB, and so too large to upload to HM.

 

[Suzuki4evr]

Thanks Graham. I do not have originals,but can measure distance between centres of the shafts though.

 

[francist]

I think you will need to determine the pitch of the gears on your lathe first, either module or DP and what that number is, then you’ll be able to use a formula to derive the diameter easily enough.

Trying to match tooth profile of the existing teeth of another gear on your lathe is one way although subject to a lot of error. Or, seek out someone with same lathe who may know what the profile is? If you have a gear tooth profile gauge, this task is exponentially easier!

-frank

 

[RJSakowski]

inch: O.D. (inches) x diametral pitch = no. of teeth + 2
metric: O.D. (mm) /mod = no. of teeth +2

All the gears that mesh will have the same diametral pitch or modulus. From an existing gear, counting the teeth and measuring the O.D. will give you the diametral pitch or modulus. Then you can calculate the I.D.'s of the missing gears from the number of teeth.