That number is the total number of teeth on a gear . As the diameter of a
gear changes , the tooth profile does also . The cutters each cut a limited
range of teeth . There's a book called gears and gearcutting by Ivan Law
that's available on Amazon and maybe eBay . I bought it , and found it
*very* helpful . ISBN number is 978-0-85242-911-2 and I think I paid like 7
or 8 bucks for mt copy .
The number means it will cut a gear with 17-20 teeth total.
The cutter should be labeled for diametric pitch (the number of teeth per
inch of diameter)
Cutters come in a set of eight for each pitch. Each one cuts a range of gear
diameters to the same pitch as the others in the set.
Paul K. Dickman
On Wed, 4 Jan 2012 12:20:25 -0800 (PST), Paul Schiller
Here you go, Bitt. I got pissed at people who didn't care about 20
years ago and made the netiquette page part of my website.
Please do NOT top-post. Thank you.
P.S: Did you understand Jim's post? It went PSA on me.
Har! Good one, Paul.
It takes as much energy to wish as to plan.
The general "Emily Postnews guide for Nettequette" should be
somewhere on the net still. There is none specific to this group (and
a large number of people who would not follow it even if it did exist. :-(
That varies with the individuals, but *I* certainly prefer
interleaved answers/comments between parts of the properly trimmed
quoted text. And totally detest top posting.
Gears with 17 to 20 teeth total -- of the *one* diametric pitch
and pressure angle for which that cutter is made. It is *useless* for
other diametric pitches and pressure angles. (The best tooth shape is
probably at 18 or 19 teeth total from that one.)
The standard involute cutters come in sets, with each numbered
member of the set for a specific range of tooth counts -- the same range
for the same number in each set -- the fewer the teeth, the narrower the
range of counts because the angle from one tooth to the next changes
more. The largest number is for something like 132 teeth (IIRC) up to a
full rack gear of infinite length.
There are also extension sets with half numbers which cut a
better tooth form at the crossover between one standard numbered cutter
and the next.
Each set is made to cut a specific diametrical pitch, and a
specific pressure angle. The most common ones are 14-1/2 degrees
pressure angle and 20 degrees pressure angle.
Do you have a copy of _Machinery's Handbook_? It should have
all you need to know about the sets, the way to calculate the necessary
OD for a gear blank of a given number of teeth and a given diametric
pitch, and the way to calculate the total depth of cut for an involute
(Just looked them up earlier today to calculate the figures for
cutting a 32 DP, 14-1/2 degree pressure angle, 20 tooth gear to replace
one which disintegrated in an old Tektronix 7A13 plugin.)
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