Now that we have the flexibility of stepper motors
and widespread computer availability at our disposal,
is there perhaps a much, much simpler way to address
the generation (not forming) of any gears?

Already there have been articles on the adaption of
electronic techniques to simplify gear trains for hobbing
(especially when prime-number gears were to be cut for
which the corresponding prime-number master wasn't
available). But is it possible that even this approach
is unnecessarily complex?

I have a proposal, and it is based on the idea that
the need to cut gears by the model-maker (but perhaps
not the professional) is few and far between, and that
therefore there is nothing lost if it were to take
an hour, say, to cut a whole gear.

The idea is based upon the generation of teeth by
using a rack, and realising that the whole principle
that applies for a many-toothed cutter that is the rack
could be applied to a single toothed cutter, and then
applied many times over, with suitable increments in
rack position, rack traverse, and blank rotation.
(And hence providing the necessary flexibility
in a number of dimensions to be able to generate
helices)

Only one cutter is needed for the whole range of
involute gears from 12 to rack, and that same cutter
can be used for gears of differing DP's. That
cutter is also simple to manufacture, either as a
wheel or as a vertical milling bit as it has straight
sides at the pressure angle.

How to vary the DP? Simple - a small enough cutter
for the smallest DP you wish to work with can then
cut either flank by two separate generating actions?

Takes longer? Sure - but that case is argued above.

wrote:
Hi,

Has anyone here built up the castings set for a gear hobber that's
available from College Engineering ? I heard that it's an improved
version of something called the Jacobs hobber which I've seen described
as "flimsy" and I'm interested to know if the CE version is better in
this regard ? Also, what is the maximum diameter gear size it supports
and can it cut helical gears ?

I'm aware of the yahoo group dealing with gear hobbers and know I could
email CE with my questions but I was just interested to know the
opinions of anyone here who has actually used the CE hobber.

Thanks,

David

On 21 Oct 2005 23:18:49 -0700, "Polymath"
wrote:

Now that we have the flexibility of stepper motors
and widespread computer availability at our disposal,
is there perhaps a much, much simpler way to address
the generation (not forming) of any gears?

Already there have been articles on the adaption of
electronic techniques to simplify gear trains for hobbing
(especially when prime-number gears were to be cut for
which the corresponding prime-number master wasn't
available). But is it possible that even this approach
is unnecessarily complex?

I have a proposal, and it is based on the idea that
the need to cut gears by the model-maker (but perhaps
not the professional) is few and far between, and that
therefore there is nothing lost if it were to take
an hour, say, to cut a whole gear.

The idea is based upon the generation of teeth by
using a rack, and realising that the whole principle
that applies for a many-toothed cutter that is the rack
could be applied to a single toothed cutter, and then
applied many times over, with suitable increments in
rack position, rack traverse, and blank rotation.
(And hence providing the necessary flexibility
in a number of dimensions to be able to generate
helices)

Only one cutter is needed for the whole range of
involute gears from 12 to rack, and that same cutter
can be used for gears of differing DP's. That
cutter is also simple to manufacture, either as a
wheel or as a vertical milling bit as it has straight
sides at the pressure angle.

How to vary the DP? Simple - a small enough cutter
for the smallest DP you wish to work with can then
cut either flank by two separate generating actions?

Takes longer? Sure - but that case is argued above.


Been done.
I have a vertical shaper with exactly that arrangement on it.
Unlike the idea above I only use one tool per DP, after all it's only
a simple Vee tool and easy to grind.
It is slow but remarkable accurate and if the machine is sturdy enough
as mine is then the quality is also very good.

I'm working off and on with cutting cycloidal gears by the same rack
method.
Making progress but slow going as it has to fit in with other work.
--
Regards,

John Stevenson
Nottingham, England.

Visit the new Model Engineering adverts page at:-
http://www.homeworkshop.org.uk/

This method has been described in the model engineering literature.
The teeth on the hob are circumferential (not helical), and can be used
without relief.

Cutting teeth is tedious, practically the same as using a single
milling cutter. Advantage is of course that you only need one hob to
cut all gear sizes of a given pitch and pressure angle. But accurate
indexing is required for decent results.

It does a good job. I've cut a bunch of 32 DP gears for Maudsley's
reversing gear on a steam engine.

My hob was made of O-1 tool steel, machined in the lathe with
appropriate "threading" tool, heat treated, then finish ground on a
Quorn T&C grinder. Obviously this method leaves small flats on the
tooth flanks; nonetheless, the teeth mesh and run smoothly and quietly.

I can certainly recommend this for model / home use.

Regards,
Wolfgang

Polymath wrote:
Now that we have the flexibility of stepper motors
and widespread computer availability at our disposal,
is there perhaps a much, much simpler way to address
the generation (not forming) of any gears?

Already there have been articles on the adaption of
electronic techniques to simplify gear trains for hobbing
(especially when prime-number gears were to be cut for
which the corresponding prime-number master wasn't
available). But is it possible that even this approach
is unnecessarily complex?

I have a proposal, and it is based on the idea that
the need to cut gears by the model-maker (but perhaps
not the professional) is few and far between, and that
therefore there is nothing lost if it were to take
an hour, say, to cut a whole gear.

The idea is based upon the generation of teeth by
using a rack, and realising that the whole principle
that applies for a many-toothed cutter that is the rack
could be applied to a single toothed cutter, and then
applied many times over, with suitable increments in
rack position, rack traverse, and blank rotation.
(And hence providing the necessary flexibility
in a number of dimensions to be able to generate
helices)

Only one cutter is needed for the whole range of
involute gears from 12 to rack, and that same cutter
can be used for gears of differing DP's. That
cutter is also simple to manufacture, either as a
wheel or as a vertical milling bit as it has straight
sides at the pressure angle.

How to vary the DP? Simple - a small enough cutter
for the smallest DP you wish to work with can then
cut either flank by two separate generating actions?

Takes longer? Sure - but that case is argued above.

wrote:
Hi,

Has anyone here built up the castings set for a gear hobber that's
available from College Engineering ? I heard that it's an improved
version of something called the Jacobs hobber which I've seen described
as "flimsy" and I'm interested to know if the CE version is better in
this regard ? Also, what is the maximum diameter gear size it supports
and can it cut helical gears ?

I'm aware of the yahoo group dealing with gear hobbers and know I could
email CE with my questions but I was just interested to know the
opinions of anyone here who has actually used the CE hobber.

Thanks,

David

On 22 Oct 2005 09:21:21 -0700, wrote:

This method has been described in the model engineering literature.
The teeth on the hob are circumferential (not helical), and can be used
without relief.

Cutting teeth is tedious, practically the same as using a single
milling cutter. Advantage is of course that you only need one hob to
cut all gear sizes of a given pitch and pressure angle. But accurate
indexing is required for decent results.

It does a good job. I've cut a bunch of 32 DP gears for Maudsley's
reversing gear on a steam engine.

My hob was made of O-1 tool steel, machined in the lathe with
appropriate "threading" tool, heat treated, then finish ground on a
Quorn T&C grinder. Obviously this method leaves small flats on the
tooth flanks; nonetheless, the teeth mesh and run smoothly and quietly.

I can certainly recommend this for model / home use.

Regards,
Wolfgang

Wolfgang.
Not quite the same thing, you are describing hobbing with annular
grooves and cutting one tooth at a time, with the adjacent teeth
making an approximation of the involute shape.
Like you say it has small flats.

What our learned friend proposes is a modern version of the Sunderland
gear planer when the cutter [ in this case a short rack ] planes
backwards and forwards over the work.
At each stroke the cutter moves along slightly in mesh with the gear
blank which rotates.
In theory you get a many sided involute that in practice is a curve.

After the Sunderland has cut about 4 or 5 teeth it backs off, index's
round by 4 or 5 teeth and repeats the operation until complete.
These machines have been around since the late 1800's but work very
well.

Substituting the rack for a single vee tool, i.e. one rack tooth, this
works the same but takes a while longer.

Using Mach3 which is a windows 2000 application and a special wizard
screen you get to fill in various boxes like depth of cut, DP, number
of teeth and home points and it then automatically generates the code
to run three axis.
One axis controls the feed past the gear, one controls the infeed for
depth and clearance when backing off and the last controls the rotary
table carrying the blank.

The cutting action is done by a mechanical ram and the feeds are only
applied when the tool is at the top of the stroke, no feeds are
carried out whilst cutting.

Polymath wrote:
Now that we have the flexibility of stepper motors
and widespread computer availability at our disposal,
is there perhaps a much, much simpler way to address
the generation (not forming) of any gears?

Already there have been articles on the adaption of
electronic techniques to simplify gear trains for hobbing
(especially when prime-number gears were to be cut for
which the corresponding prime-number master wasn't
available). But is it possible that even this approach
is unnecessarily complex?

I have a proposal, and it is based on the idea that
the need to cut gears by the model-maker (but perhaps
not the professional) is few and far between, and that
therefore there is nothing lost if it were to take
an hour, say, to cut a whole gear.

The idea is based upon the generation of teeth by
using a rack, and realising that the whole principle
that applies for a many-toothed cutter that is the rack
could be applied to a single toothed cutter, and then
applied many times over, with suitable increments in
rack position, rack traverse, and blank rotation.
(And hence providing the necessary flexibility
in a number of dimensions to be able to generate
helices)

Only one cutter is needed for the whole range of
involute gears from 12 to rack, and that same cutter
can be used for gears of differing DP's. That
cutter is also simple to manufacture, either as a
wheel or as a vertical milling bit as it has straight
sides at the pressure angle.

How to vary the DP? Simple - a small enough cutter
for the smallest DP you wish to work with can then
cut either flank by two separate generating actions?

Takes longer? Sure - but that case is argued above.

wrote:
Hi,

Has anyone here built up the castings set for a gear hobber that's
available from College Engineering ? I heard that it's an improved
version of something called the Jacobs hobber which I've seen described
as "flimsy" and I'm interested to know if the CE version is better in
this regard ? Also, what is the maximum diameter gear size it supports
and can it cut helical gears ?

I'm aware of the yahoo group dealing with gear hobbers and know I could
email CE with my questions but I was just interested to know the
opinions of anyone here who has actually used the CE hobber.

Thanks,

David

--
Regards,

John Stevenson
Nottingham, England.

Visit the new Model Engineering adverts page at:-
http://www.homeworkshop.org.uk/

John,

Thanks for the enlightenment! I guess I missed the bit about the
cutter moving along the gear blank pitch line incrementally, ie.
"rolling" with the blank.

I have thought of introducing this motion during hobbing with the
concentric hob.....this would reduce the size of the flats. Indeed,
for a small # of teeth I index the blank by 1/2 tooth and raise the
cutter by a commensurate amount. It improves the tooth form and
increases the # of flats.

As I said earlier gears produced this way run well together and with
commercial gears of same pitch and pressure angle.

I am not well versed in CNC machinery but, I would think that an
ordinary shaper, equipped with stepper motor driven cross feed,
similarly driven index head, and limit switches on the ram travel, with
appropriate controller, could produce good gears using simple,
rack-type cutters.

I would really like to try this, especially with rack-type cutters made
from mild steel commercial racks: At the cutting edge machine a 2
degree back-rake angle, and in the cutter holder introduce 1 degree or
so of clearance angle to prevent rubbing during the cutting stroke.
Case harden the rack, and machine. Should be OK for brass, bronze, and
leaded steel gears.

Could anyone here perhaps direct me to a book or web page that would
shed some light on the controller requirements, suitable for "rolling
your own"?

Thanks,

Wolfgang

On 22 Oct 2005 13:58:46 -0700, wrote:

John,

Thanks for the enlightenment! I guess I missed the bit about the
cutter moving along the gear blank pitch line incrementally, ie.
"rolling" with the blank.

I have thought of introducing this motion during hobbing with the
concentric hob.....this would reduce the size of the flats. Indeed,
for a small # of teeth I index the blank by 1/2 tooth and raise the
cutter by a commensurate amount. It improves the tooth form and
increases the # of flats.

As I said earlier gears produced this way run well together and with
commercial gears of same pitch and pressure angle.

Taking a few incremental cuts on each tooth will improve the shape of
the tooth.


I am not well versed in CNC machinery but, I would think that an
ordinary shaper, equipped with stepper motor driven cross feed,
similarly driven index head, and limit switches on the ram travel, with
appropriate controller, could produce good gears using simple,
rack-type cutters.

It's not a new solution at all. There were commercial attachments made
around the turn of the 20th century that bolted onto a standard shaper
for just this purpose.
Model Engineer ran an article in September 14th 1950 by 'BaseCircle'
describing this attachment.
There was a later article on the 20th January 1989 covering the same
ground.

I would really like to try this, especially with rack-type cutters made
from mild steel commercial racks: At the cutting edge machine a 2
degree back-rake angle, and in the cutter holder introduce 1 degree or
so of clearance angle to prevent rubbing during the cutting stroke.
Case harden the rack, and machine. Should be OK for brass, bronze, and
leaded steel gears.

Could anyone here perhaps direct me to a book or web page that would
shed some light on the controller requirements, suitable for "rolling
your own"?

Thanks,

The controller is easy, any CNC controller like Mach3 or Turbo CNC
that can run 3 axis will do this.
The code is quite simple.

You start off with the tool central on the blank and just touching,
this is X0.0, Y0.0

The code only runs when the tool is at the top, limit switches control
this.

N001 X0.0 Y0.0 [Sets zero ]
N002 G00 X-20.0 Y0.0 [ Moves tool clear of blank at rapid move]
N003 G00 X-20 .0 Y-3.0 [ moves tool in to depth ]
N004 M03 [ starts stroke motor]
N005 G01 X20.0 Y-3.0 A20.0 F50.0 [ Moves tool past the blank by 40mm
whilst revolving it thru 20 degrees at 50mm/min]
N006 M01 [ stop motor]
N007 G00 X20.0 Y1.0 [ move tool clear on depth ]
N008 G00 X-20.0 Y1.0 [ Move to start point]
N009 G00 X-20 Y-3.0 [ moves tool back in to depth ]
N010 G00 A 360/N [ rotate for next tooth ]
N011 [ Repeat from line N004 ]
Etc.

This code is quite long winded and done this way to explain the code,
many moves like G00 are modal and do not need to be repeated, same for
X and Y values that don't change.
Line N010 will be a fixed value for the number of teeth required, so
20 teeth will be 360 /20 = 18.0



Wolfgang

--
Regards,

John Stevenson
Nottingham, England.

Visit the new Model Engineering adverts page at:-
http://www.homeworkshop.org.uk/

Welcome back, John! We've missed your posts; it has been quite a while
since we've heard from you. Stick around, OK?

Bob Swinney
"John Stevenson" wrote in message
...
On 21 Oct 2005 23:18:49 -0700, "Polymath"
wrote:

Now that we have the flexibility of stepper motors
and widespread computer availability at our disposal,
is there perhaps a much, much simpler way to address
the generation (not forming) of any gears?

Already there have been articles on the adaption of
electronic techniques to simplify gear trains for hobbing
(especially when prime-number gears were to be cut for
which the corresponding prime-number master wasn't
available). But is it possible that even this approach
is unnecessarily complex?

I have a proposal, and it is based on the idea that
the need to cut gears by the model-maker (but perhaps
not the professional) is few and far between, and that
therefore there is nothing lost if it were to take
an hour, say, to cut a whole gear.

The idea is based upon the generation of teeth by
using a rack, and realising that the whole principle
that applies for a many-toothed cutter that is the rack
could be applied to a single toothed cutter, and then
applied many times over, with suitable increments in
rack position, rack traverse, and blank rotation.
(And hence providing the necessary flexibility
in a number of dimensions to be able to generate
helices)

Only one cutter is needed for the whole range of
involute gears from 12 to rack, and that same cutter
can be used for gears of differing DP's. That
cutter is also simple to manufacture, either as a
wheel or as a vertical milling bit as it has straight
sides at the pressure angle.

How to vary the DP? Simple - a small enough cutter
for the smallest DP you wish to work with can then
cut either flank by two separate generating actions?

Takes longer? Sure - but that case is argued above.


Been done.
I have a vertical shaper with exactly that arrangement on it.
Unlike the idea above I only use one tool per DP, after all it's only
a simple Vee tool and easy to grind.
It is slow but remarkable accurate and if the machine is sturdy enough
as mine is then the quality is also very good.

I'm working off and on with cutting cycloidal gears by the same rack
method.
Making progress but slow going as it has to fit in with other work.
--
Regards,

John Stevenson
Nottingham, England.

Visit the new Model Engineering adverts page at:-
http://www.homeworkshop.org.uk/