gearing identifying help

davidh

davidh

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I have a salvaged gear rack from something and would like to buy a pinion to match it. im attempting to build a slotting tool for my lathe.
I have determined by tape measure that there are 33 teeth in 8.25 inches of length meaning tooth centers are .25 inches. is there an easy way to measure or describe what I may have, for shopping for a pinion or do I need to just start carving / grinding a tool to the same profile as the rack ?? and cut my own pinion ?

if I could remember where I got this dang thing, I could just go to the tool breakdown and find the gear part number if its the proper number of teeth. .. .

the mind is one of the first things to go it seems :)
 
A true rack for an involute gear will have straight sided teeth. Can you get the included angle of one of the teeth or gaps? From the photo, I'm going to guess 20°, but that's a basic piece to the puzzle.
 
more information:
vertical angle is 30 Degrees.
tooth height is .300 inch

anything else needed tony ?
 
How old.is the rack, and how certain are you that it's 30 rather than 29 degrees included angle? 14.5 pressure-angle gears and racks used to be pretty common (and the Acme threads derived from 'em)_, so that would give 29 included... The other common (and more recent) standard pressure angle is 20 degrees, giving 40 included - should be easy to.tell apart!

There are.several ways of describing gear pitches, if the rack pitch is *exactly* 0.250" then you're looking at a "quarter inch circular pitch" rack, and need a pinion to suit. If it isn't exactly... Divide the pitch by Pi, the divide one by the result, that will give the diametral pitch of the rack and pinion , if that doesn't give a sensible whole number, measure in mm, if either the.rack pitch is a nice exact (possibly with decimal fraction) number or it is once divided by Pi, you have a metric rack, either.metric circular pitch or (if you had to divide by Pi) a metric module rack, again, you want a pinion to match! Metric.racks are.most.often 20-degree or (rarely) 30- degree....

Hope.this helps, rather.than confuses!
Dave H. (the other one)
 
pinion dim's

I've kinda figured out what size pinion I need, please tell me if im close to correct. . . .

.250 tooth spacing on the rack and I wish to move the rack 3" per turn of the pinion. that's probably satisfactory. meaning that 12 is the number of teeth required. . . . . so far so good ?

the pitch diameter would be roughly .9554 based on circum. divided by 3.14159. right ?

then if I measure the height of the tooth on the rack that I estimate @ .1718 high.

the bottom diameter of the pinion tooth is .7836 and that is of course not a diameter, really just a measurement.

should that information be enuf to make it function ?

I am only making a slotter mechanism for my lathe. . . . . .
 
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