Our machining class needs information on generating single point
(fly) cutters with involute geometry to cut spur change gears.
Eyeball grinding of the tool ala Gingery produces entirely
useable gears but we are looking for something more exact.
Ivan Law in his book " Gears and Gear Cutting " [see
http://www.transatlanticpub.com/cat/workshop/gears.html for
details] [another US source for UK workshop practice series of
books is
http://www.powells.com/psection/Engineering.html ] shows
a technique to generate very close circular approximations to the
involute curve for both single point and circular form tools by
using two circular cutters of specific diameters spaced a given
distance apart. The tool blank is then fed to a specific depth
between the circular cutters to generate the correct involute
form.
Data take from Gears and Gear Cutting by Ivan Law ISBN
0-85242-911-8
Data to generate circular approximation of involute curve
For 20 degree pressure angle gears
Base table for 1" diametrical pitch gears
Inch
Cutter # Teeth Diameter C/C In Feed Width
1 135-R 51.300 49.600 17.790 4.000
2 55-134 32.150 31.600 11.470 4.000
3 35-54 15.070 15.510 5.870 4.000
4 26-34 10.260 11.030 4.270 4.000
5 21-25 8.550 9.400 3.710 4.000
6 17-20 7.800 8.700 3.440 4.000
dimensions in inches
Table for DP gears 25.400 == input DP Metric Module 1.00
Cutter # Teeth Diameter C/C In Feed Width
1 135-R 2.020 1.953 0.700 0.157
2 55-134 1.266 1.244 0.452 0.157
3 35-54 0.593 0.611 0.231 0.157
4 26-34 0.404 0.434 0.168 0.157
5 21-25 0.337 0.370 0.146 0.157
6 17-20 0.307 0.343 0.135 0.157
The same technique is shown at
http://www.metalwebnews.com/howto/gear/gear1.html , but with
slightly different dimensions for the cutters, spacing and
in-feed.
( I have an excel spread sheet to do the calculations if anyone
wants a copy - send me an email or I can post to the dropbox)
== The problem is that both charts show C/C spacing distances
LESS than the specified diameter of the two circular cutters for
the form tools for larger numbers of teeth.
Has any one used this technique? If so how are the #1 and #2
cutters formed?
We will be making 1.0 m/m module change gears out of 6061 T6
and/or phenolic / micarta, and possibly a 127 tooth metric
conversion gear.
Given that it takes some time to hand grind a form cutter and
this is a introductory machining class, we would like to minimize
tool breakage. Has anyone tried using a slotting saw to remove
most of the material and then cleaning up the slot using the form
cutter?
Using the advise from these NGs, our first attempts were done
using a spin indexer to make a 40T gear with entirely
satisfactory results. We just purchased a rotary table to
produce the gears the spin indexer can't divide. This is a WT
1990-0015 (see at
http://www.wttool.com/p/1990-0015 )
Any advise would be appreciated.
GmcD