# Large Spur gear design

Hi, Im new to this forum so forgive if i am mis posting or multi posting. I am in the process of designing a 44 inch gear to cut on my shop bot cnc machine. I have been up and down calculations but i end up with tiny teeth and can not find the right formulae to calculate an oversize spur gear. Any thoughts ?

What exactly are you trying to calculate? What do you mean by "tiny teeth"?

What exactly are you trying to calculate? What do you mean by "tiny teeth"?

I am trying to build an oversize gear with large teeth. Given a Pitch Diameter(D) of 44" I am trying to find how to base the number of teeth (N) in order to calculate Diametral pitch(P)

Pitch Diameter is D=N/P

Number of teeth is N=D x P

Diametral Pitch is P= N/D

Based on that, we have D but I am not sure what to do about knowing what the propper amount of teeth would be or do ya just pick em and go with it.

I picked a number and went with it for fun and when i was done calculateing addendum, dedendum etc I ended up with teeth that were around 1/2 big. It would work, but i need larger teeth for this project.

I also need to check to see about the radius used to make the sides of the teeth. I read that there is a chart of info on this . Need to find my machneries handbook!

Doug Huffman
Gold Member
Pi is irrational, where do the left over digits go?

Pi is irrational, where do the left over digits go?

doug, what the hell ya want me to do with that statement ?

Doug Huffman
Gold Member
I am traveling at the moment and for the week. I don't have my library handy. ISTR I seem to recall that there are formulas in The Machinery Handbook for setting up gear cutters. The extra digits of irrational numbers are a typical problem for real world problems.

I am traveling at the moment and for the week. I don't have my library handy. ISTR I seem to recall that there are formulas in The Machinery Handbook for setting up gear cutters. The extra digits of irrational numbers are a typical problem for real world problems.

im just trying to find my copy of MHB right now

QTC has their http://www.qtcgears.com/Q410/Q410Cat.htm" [Broken]. The spur gear calculations are universal.
http://www.qtcgears.com/Q410/Q410Cat.htm [Broken]

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