I came across a box of gear rack in my garage that were removed from equipment. The tooth pitch is .200" (tooth to tooth). Does any one out there know what the gear pitch number may be from the dimensions given above, ie: 8, 10, 12 etc. I seem to have lost my gear catalogs somewhere and will be needing to buy pinions to match up with the racks. I am in the process of gathering parts for my first cnc router and due to the size I will be using the rack and pinion method to move things around. Thanks in advance.

2muchstuff,

Sounds like you want the DP (Diametral Pitch - # Teath/Diameter) . You can get it with these formulas:

DP = N / D ; N = # of teath; D = pitch diameter

easier formula:

DP = 3.14159 / p ; p = circular pitch you measured

Hope this helps,

plm

You will also need to know the contact angle 20deg or 14.5deg.
Al

I came across a box of gear rack in my garage that were removed from equipment. The tooth pitch is .200" (tooth to tooth). Does any one out there know what the gear pitch number may be from the dimensions given above, ie: 8, 10, 12 etc. I seem to have lost my gear catalogs somewhere and will be needing to buy pinions to match up with the racks. I am in the process of gathering parts for my first cnc router and due to the size I will be using the rack and pinion method to move things around. Thanks in advance.

I may be missing something but I thought that the "8, 10, 12, ect" refers to tooth per inch, so that in your case it looks to me like 5tpi. But, hey, what do I know, I'm just an electrician. :D

I always thought that that you mark an inch distant on a screw and count the ridges and that gives you the tpi and that you have to divide this number by the starts if it is a multiple thread screw.

Yoram

pmurray, You know some stuff, that was exactly what I was looking for. I was pretty close on my measurment, just .004" off, it should have been .196". Plugging it in got me a diametral pitch of 16. Thanks. Now all I have to do is get one of the kids to let me borrow a protractor.

2muchstuff,

Sounds like you are on your way.

Indeed, you were close on your measurement. Ya, I forgot to mention that the value computed should come out to be an integer (whole) number. When I later used your .2" value in the formula, I got something like 15.7 and figured the DP was 16.

Good Luck,

plm