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Gear/rack cutting

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Firebird:
Hi

I might have a go at cutting a rack and pinion. never done it before :headscratch: Looking at gear cutters the No. 1 cutter is listed as will cut 135 rack

Could someone explain that please



Cheers

Rich

crueby:
By the time you get to a straight line rack, the teeth to mesh with a normal involute gear approach just straight sided shapes. The 135-rack cutter in the set will work for the rack as well as any gear over 135 teeth. For the pinion, you would need the cutter that includes the number of teeth you need. For the smallest number of teeth, the teeth are shaped for the tighter curve around the gear, the more teeth, the more the shape squeezes in a bit.
Not sure if that helps?

Firebird:
Hi Chris

Yes that helps.

So the teeth on the rack are spaced ??????

Cheers

Rich

crueby:

--- Quote from: Firebird on January 18, 2021, 08:50:43 PM ---Hi Chris

Yes that helps.

So the teeth on the rack are spaced ??????

Cheers

Rich

--- End quote ---
Yes - looks like a series of flat top/bottom mountains/valleys. I cut one for my steam shovel, check out the pictures/posts here, this post and the next half dozen:
https://www.modelenginemaker.com/index.php/topic,7530.msg166377.html#msg166377
This one has a great diagram:
https://www.modelenginemaker.com/index.php/topic,7530.msg166232.html#msg166232

crueby:
Little further info - looked up racks in the Ivan Law book, and the distance from a point on one tooth to the same point on the next is the Circular Pitch value of the spur gear, and the angle of the sides (if you are using a flat sided cutter like I did) is the pressure angle of the cutters you are using (usually something like 20 degrees). If using the 135-rack cutter from the set, that is built into the cutter.
Chris
 :cheers:

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