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

On Fri, 14 Jan 2005 16:14:54 -0600, F. George McDuffee
wrote:


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?

Very common practice, even when using form milling cutters. Saves
some wear and tear on the cutters.

Greybeard

This subject is exhaustively covered in the British metalworking mags.

I know a guy who wrote a program to plot out an involute curve at 20X
actual size, and then he plotted that on a transparency and put it on
the screen of his optical comparator. He made a single-point tool and
used a round lap to remove metal, comparing with the transparency often.
He said it went really well and he made a whole set of gears for a
lathe. He did all of this at home, but then he's a really good machinist
compared to me. Seems like something you could do at a school where they
have programming guys, plotters, and optical comparators around.

GWE

F. George McDuffee wrote:

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

"F. George McDuffee" wrote in message
...
Our machining class needs information on generating single point

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.

I think there might be a small market for 127 tooth 1 module gears among the
owners of mini-lathes.

Like me.

jtaylor wrote:
"F. George McDuffee" wrote in message
...
Our machining class needs information on generating single point

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.

I think there might be a small market for 127 tooth 1 module gears
among the
owners of mini-lathes.

Like me.

Did you try compound gearing for a 80/63 ratio?
That is maybe close enough for hobbiest work anyhow.
Since 80 = 20 * 4 and 63 = 21 * 3 you can build a compound gear
train from a 20 tooth, 21 tooth, and another pair of gears with a
3:4 ratio.
Finding 20 tooth, 21 tooth, and either 15 tooth or 25 tooth
gears should be easier than finding 127 tooth gears.
80/63 = 1.2698 Basically this gets you within .0015 percent.

Maybe someone will have enough ambition to develop electronic gearing
for a mini lathe. Even if it doesn't have the ball screws for CNC
threading, it could work with electronic gearing and a stepper driving
the lead screw...
But I digress.

Pete

In article ,
says...

"F. George McDuffee" wrote in message
...
Our machining class needs information on generating single point

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.

I think there might be a small market for 127 tooth 1 module gears among the
owners of mini-lathes.


They're available from Ametric in 15mm face width...

http://www.ametric.com/catalogs.htm

Ned Simmons

A nice little book from the Lindsay Pubs - "Tear Cutting Practice 1937" Colvin and Stanley
Nice tables and drawings - lots of show and tell.
Martin

F. George McDuffee wrote:

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



--
Martin Eastburn, Barbara Eastburn
@ home at Lion's Lair with our computer
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder

Correct. You have to grind flats on the two cutters so they won't interfere
with each other. The radius given by the formula is needed only where the
two "circular cutters" actually cut.
-Dave
--
http://plumpe.home.mindspring.com
email:
ANTI-SPAM: To email, replace "lastname" with "plumpe"


"F. George McDuffee" wrote in message
...
Our machining class needs information on generating single point
(fly) cutters with involute geometry to cut spur change gears.
(snip)
== 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 anyone tried using a slotting saw to remove
most of the material and then cleaning up the slot using the form
cutter? "

This is a very old approach in watchmaking and it is still the preferred
approach for cutting pinions. Pinion cutters for clock/watches are very
dear (can't be had from MSC) and every effort is made to spare them.

In the very early days (1700) the wheel was divided with a slitting saw and
then a special file was used to shape the teeth. Later, this evolved into
the "rounding up" tool; a self indexing tool that is used to modify an
already divided wheel. When I have a wheel that does not conform to current
cutters (tooth is shorter or longer) then I divide the wheel and use the
rounding up tool to shape the tooth. Only when the wheel is too large for
the tool will I make a fly cutter.

BTW, in watchmaking/clockmaking we make fly cutters in the lathe out of
round stock. Since we use hand gravers (ala wood turning), we turn the end
of the rod to a profile that is an exact fit between two good teeth of the
wheel we are replacing. File the profile to the center line, harden and
temper. Grind relief on the tip and polish. Takes about 30 minutes.


--
Regards,
Dewey Clark
http://www.historictimekeepers.com
Restorations, Parts for Hamilton M21s, Products for Craftsmen
Makers of Historic Timekeepers Ultrasonic Clock Cleaning Solution

We have a version of the gear generation program written in lisp
for auto/intelli-cad called truegear by Eugene Kalney [see
http://www.cad.dp.ua/english/program-e.html to download as
truegear.zip w/ support files and coumentation] this seems to
work very well.

One problem is we don't have an optical comparator and we have a
zero budget. This is not all bad in that it forces us to do
machining projects that stress ingenuity over attachments.

One of my major concerns, given the current economic trends, is a
situation where industry and manufacturing is forced into
survival mode where replacement parts are no longer available,
either because the equipment is so old, a world wide economic
implosion has occurred or because the parts are only made
overseas and the suppliers will no longer accept worthless
American dollars. [Consider the situation of an Argentinean
manufacturer who has a failure of a critical part on an old
American made machine…]

It appears possible we can adopt the plans for a radius/ball
turning lathe attachment to use a pencil type die grinder to
grind the required radii in HSS lathe bits if the forming
information in Law's table is correct (or can be corrected).

Thanks for the suggestions - these newsgroups are the best
resource I have ever found.
==================
On Fri, 14 Jan 2005 15:31:44 -0800, Grant Erwin
wrote:

This subject is exhaustively covered in the British metalworking mags.

I know a guy who wrote a program to plot out an involute curve at 20X
actual size, and then he plotted that on a transparency and put it on
the screen of his optical comparator. He made a single-point tool and
used a round lap to remove metal, comparing with the transparency often.
He said it went really well and he made a whole set of gears for a
lathe. He did all of this at home, but then he's a really good machinist
compared to me. Seems like something you could do at a school where they
have programming guys, plotters, and optical comparators around.

GWE

F. George McDuffee wrote:

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

On 14 Jan 2005 20:27:53 -0800, wrote:

Several sources have suggested using a 37/47 gear combination
which is susposed to produce "2/100 of 1% accuracy"
[see http://www.lathe.com/metric_threading]

We can't find a source for those gears either.

GmcD
======================================
I think there might be a small market for 127 tooth 1 module gears
among the
owners of mini-lathes.

Like me.

Did you try compound gearing for a 80/63 ratio?
That is maybe close enough for hobbiest work anyhow.
Since 80 = 20 * 4 and 63 = 21 * 3 you can build a compound gear
train from a 20 tooth, 21 tooth, and another pair of gears with a
3:4 ratio.
Finding 20 tooth, 21 tooth, and either 15 tooth or 25 tooth
gears should be easier than finding 127 tooth gears.
80/63 = 1.2698 Basically this gets you within .0015 percent.

Maybe someone will have enough ambition to develop electronic gearing
for a mini lathe. Even if it doesn't have the ball screws for CNC
threading, it could work with electronic gearing and a stepper driving
the lead screw...
But I digress.

Pete

My numbers are more accurate with the 80/63 than the 47/37.
And most sets of gears should have a 20 and 21 tooth gears in them.
I posted that because I am sure that 20, and 21 tooth gears should be
cheaper, more accuarate and easier to find than the 47 and 37 tooth
gears,
If someone wants to go that route.

Pete

I'd try using a known good gear to compare the dimensions that you have on
the cutter and trim the cutter as needed to nicely wipe the layout dye off
of the gear.

--
Why isn't there an Ozone Hole at the NORTH Pole?

I am not sure but I think Scott Logan at Logan Actuator has the 37/47 gears
for metric threading on Logan Lathes.
Don't have a link right now but there is a web site.
Don Young

"F. George McDuffee" wrote in message
...
On 14 Jan 2005 20:27:53 -0800, wrote:

Several sources have suggested using a 37/47 gear combination
which is susposed to produce "2/100 of 1% accuracy"
[see http://www.lathe.com/metric_threading]

We can't find a source for those gears either.

GmcD
======================================
I think there might be a small market for 127 tooth 1 module gears
among the
owners of mini-lathes.

Like me.

Did you try compound gearing for a 80/63 ratio?
That is maybe close enough for hobbiest work anyhow.
Since 80 = 20 * 4 and 63 = 21 * 3 you can build a compound gear
train from a 20 tooth, 21 tooth, and another pair of gears with a
3:4 ratio.
Finding 20 tooth, 21 tooth, and either 15 tooth or 25 tooth
gears should be easier than finding 127 tooth gears.
80/63 = 1.2698 Basically this gets you within .0015 percent.

Maybe someone will have enough ambition to develop electronic gearing
for a mini lathe. Even if it doesn't have the ball screws for CNC
threading, it could work with electronic gearing and a stepper driving
the lead screw...
But I digress.

Pete

"Bob May" once again asked in message
...

Why isn't there an Ozone Hole at the NORTH Pole?

Why, Bob?
Do you want one?

from http://www.al.noaa.gov/WWWHD/pubdocs...nt98/faq7.html
"The difference between ozone content in the two polar regions is caused by
dissimilar weather patterns. The Antarctic continent is a very large land mass
surrounded by oceans. This symmetrical condition produces very low
stratospheric temperatures within a meteorologically isolated region, the
so-called polar vortex, which extends from about 65°S to the pole. The cold
temperatures lead in turn to the formation of clouds, known as polar
stratospheric clouds. These clouds provide surfaces that promote production of
forms of chlorine and bromine that are chemically active and can rapidly
destroy ozone. The conditions that maintain elevated levels of chemically
active chlorine and bromine persist into September and October in Antarctica,
when sunlight returns over the region to initiate ozone depletion.

The winter meteorological conditions in the Northern Hemisphere, just like in
the Southern Hemisphere, lead to the formation of an isolated region bounded
by strong winds, in which the temperature is also cold enough for polar
stratospheric clouds to form. However, the geographic symmetry about the North
Pole is less than about the South Pole. As a result, large-scale weather
systems disturb the wind flow, making it less stable over the Arctic region
than over the Antarctic continent. These disturbances prevent the temperature
in the Arctic stratosphere from being as cold as in the Antarctic
stratosphere, and fewer polar stratospheric clouds are therefore formed.
Nevertheless, chemically active chlorine and bromine compounds are also formed
over the Arctic, as they are over Antarctica, from reactions at the surface of
the clouds. But the cold conditions rarely persist into March, when sufficient
sunlight is available to initiate large ozone depletion."

....but whadd'a they know?

--

Jeff R.

"???" wrote in message ...
"Has anyone tried using a slotting saw to remove
most of the material and then cleaning up the slot using the form
cutter? "

This is a very old approach in watchmaking and it is still the preferred
approach for cutting pinions. Pinion cutters for clock/watches are very
dear (can't be had from MSC) and every effort is made to spare them.

In the very early days (1700) the wheel was divided with a slitting saw
and
then a special file was used to shape the teeth. Later, this evolved into
the "rounding up" tool; a self indexing tool that is used to modify an
already divided wheel. When I have a wheel that does not conform to
current
cutters (tooth is shorter or longer) then I divide the wheel and use the
rounding up tool to shape the tooth. Only when the wheel is too large for
the tool will I make a fly cutter.

BTW, in watchmaking/clockmaking we make fly cutters in the lathe out of
round stock. Since we use hand gravers (ala wood turning), we turn the
end
of the rod to a profile that is an exact fit between two good teeth of the
wheel we are replacing. File the profile to the center line, harden and
temper. Grind relief on the tip and polish. Takes about 30 minutes.


--
Regards,
Dewey Clark
http://www.historictimekeepers.com
Restorations, Parts for Hamilton M21s, Products for Craftsmen
Makers of Historic Timekeepers Ultrasonic Clock Cleaning Solution


Nice website Dewey. You appear to be a true craftsman. Did you serve an
apprenticeship? I can appreciate working with small stuff. I used to run a
factory that made dental handpiece motors. Spindles, chucks, impellers, all
with seemingly zero tolerance. At a half million rpm .001 run out will waste
a bearing in a short period of time.

In article ,
says...
On 14 Jan 2005 20:27:53 -0800, wrote:

Several sources have suggested using a 37/47 gear combination
which is susposed to produce "2/100 of 1% accuracy"
[see http://www.lathe.com/metric_threading]

We can't find a source for those gears either.

Also available from Ametric..

http://www.ametric.com/catalogs.htm

Ned Simmons

A cylindrical cutter with multiple rows of teeth(about 5) in the shape of a
rack of the desired pitch (easily made on the lathe) will generate involute
gear teeth of good quality. There is info available on this gear cutting
method if you are interested.

Randy


"F. George McDuffee" wrote in message
...
We have a version of the gear generation program written in lisp
for auto/intelli-cad called truegear by Eugene Kalney [see
http://www.cad.dp.ua/english/program-e.html to download as
truegear.zip w/ support files and coumentation] this seems to
work very well.

One problem is we don't have an optical comparator and we have a
zero budget. This is not all bad in that it forces us to do
machining projects that stress ingenuity over attachments.

One of my major concerns, given the current economic trends, is a
situation where industry and manufacturing is forced into
survival mode where replacement parts are no longer available,
either because the equipment is so old, a world wide economic
implosion has occurred or because the parts are only made
overseas and the suppliers will no longer accept worthless
American dollars. [Consider the situation of an Argentinean
manufacturer who has a failure of a critical part on an old
American made machine.]

It appears possible we can adopt the plans for a radius/ball
turning lathe attachment to use a pencil type die grinder to
grind the required radii in HSS lathe bits if the forming
information in Law's table is correct (or can be corrected).

Thanks for the suggestions - these newsgroups are the best
resource I have ever found.
==================
On Fri, 14 Jan 2005 15:31:44 -0800, Grant Erwin
wrote:

This subject is exhaustively covered in the British metalworking mags.

I know a guy who wrote a program to plot out an involute curve at 20X
actual size, and then he plotted that on a transparency and put it on
the screen of his optical comparator. He made a single-point tool and
used a round lap to remove metal, comparing with the transparency often.
He said it went really well and he made a whole set of gears for a
lathe. He did all of this at home, but then he's a really good machinist
compared to me. Seems like something you could do at a school where they
have programming guys, plotters, and optical comparators around.

GWE

F. George McDuffee wrote:

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

On Sat, 15 Jan 2005 12:49:01 -0600, F. George McDuffee
wrote:

Several sources have suggested using a 37/47 gear combination
which is susposed to produce "2/100 of 1% accuracy"
[see http://www.lathe.com/metric_threading]

We carry those gears. Our online store is temporarily down for
maintenance, but you can call our office [(815)943-9500] for details.

We have two different sets available, both 16DP, 14-1/2 NPA.

One set is 7/16" wide with a 5/8" bore and 5/32" keyway. These are
designed for Logan 9", 10", 11" and some 12" Lathes.

The other set is 5/8" wide with a 15/16" bore and 5/32" keyway. These
are designed for Logan 14" and some 12" Lathes.

We also have available 100T and 127T gears with the same specs for
mathematically correct transposition. These gears are, of course,
substantially larger and more expensive.

The 37T gears are $60.50 each, the 47T gears are $74.50 each.

The 100T gears are $162.25 each, and the 127T gears are $213.25 each.


--
+--------------------------------------------+
| Scott Logan - ssl "at" lathe.com |
| Logan Actuator Co. http://www.lathe.com |
| Harvard, IL |
|++++++++++++++++++++++++++++++++++++++++++++|
| Parts and Accessories for Logan Lathes and |
| Montgomery Wards Lathes |
| Logan-Lilly Mine Hoist Safety Controllers |
+--------------------------------------------+
"Measure Twice, Cut Once"

RCM FAQ - http://w3.uwyo.edu/~metal
Metal Web News - http://www.metalwebnews.com/
Help squash SPAM: http://www.cauce.org/

Would greatly appreciate the information -- URLs? Books?

How do you get the clearance for the teeth? Simple eccentric
offset with only one "gash"?

Thanks

GmcD



On Sun, 16 Jan 2005 13:19:12 -0600, "R. O'Brian"
wrote:

A cylindrical cutter with multiple rows of teeth(about 5) in the shape of a
rack of the desired pitch (easily made on the lathe) will generate involute
gear teeth of good quality. There is info available on this gear cutting
method if you are interested.

Randy


"F. George McDuffee" wrote in message
.. .
We have a version of the gear generation program written in lisp
for auto/intelli-cad called truegear by Eugene Kalney [see
http://www.cad.dp.ua/english/program-e.html to download as
truegear.zip w/ support files and coumentation] this seems to
work very well.

One problem is we don't have an optical comparator and we have a
zero budget. This is not all bad in that it forces us to do
machining projects that stress ingenuity over attachments.

One of my major concerns, given the current economic trends, is a
situation where industry and manufacturing is forced into
survival mode where replacement parts are no longer available,
either because the equipment is so old, a world wide economic
implosion has occurred or because the parts are only made
overseas and the suppliers will no longer accept worthless
American dollars. [Consider the situation of an Argentinean
manufacturer who has a failure of a critical part on an old
American made machine.]

It appears possible we can adopt the plans for a radius/ball
turning lathe attachment to use a pencil type die grinder to
grind the required radii in HSS lathe bits if the forming
information in Law's table is correct (or can be corrected).

Thanks for the suggestions - these newsgroups are the best
resource I have ever found.
==================
On Fri, 14 Jan 2005 15:31:44 -0800, Grant Erwin
wrote:

This subject is exhaustively covered in the British metalworking mags.

I know a guy who wrote a program to plot out an involute curve at 20X
actual size, and then he plotted that on a transparency and put it on
the screen of his optical comparator. He made a single-point tool and
used a round lap to remove metal, comparing with the transparency often.
He said it went really well and he made a whole set of gears for a
lathe. He did all of this at home, but then he's a really good machinist
compared to me. Seems like something you could do at a school where they
have programming guys, plotters, and optical comparators around.

GWE

F. George McDuffee wrote:

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

snip
BTW, in watchmaking/clockmaking we make fly cutters in the lathe out of
round stock. Since we use hand gravers (ala wood turning), we turn the end
of the rod to a profile that is an exact fit between two good teeth of the
wheel we are replacing. File the profile to the center line, harden and
temper. Grind relief on the tip and polish. Takes about 30 minutes.
=====================
Sounds like a good idea. Cutter will automatically be centered
and both sides will be symmetrical. Does the tool have enough
strength for anything beyond sheet brass? What is the working
radius of the tool? Do you just have a flat on the tool to
orient in the holder or is there some special technique?

Do you use soft drill rod / silver steel and harden or grind
round hard tool steel? We are limited to a propane torch and a
bucket of water for hardening (but if the old timers could do it
… )

GmcD

On Sun, 16 Jan 2005 13:19:12 -0600, "R. O'Brian"
wrote:
A cylindrical cutter with multiple rows of teeth(about 5) in the shape of a
rack of the desired pitch (easily made on the lathe) will generate involute
gear teeth of good quality. There is info available on this gear cutting
method if you are interested.
Randy
========================
Thanks for the tip. I checked and some of the older machining
books [Lindsay reporints] show these cutters.

As usual, the details of use are sketchy at best.

When I make a 25 X CAD layout it appears with the smaller gears
the extra teeth on the cutter do not contact and thus the spaces
in the gear are too narrow. Do you have to make several passes
with the cutter with the gear slightly rotated and cutter
slightly displaced to get a involute curve (approximated by a
series of straight lines) and wider spaces? If so how many
passes?

GmcD