Hi all,

I have a gear wheel missing from my lathe and need to cut a new one from
scratch as they don't appear to be available any more.
Question is, given that I can measure for myself everything concerning
the leadscrew this gear needs to mesh with, can I from those
measurements, calculate the outside diameter (OD) for a blank to make
another gear wheel from? I'm guessing there must be a fairly simple
formula for this but I'm damned if I can find it. To keep things simple
and for the sake of argument, let's say the leadscrew's OD is 1", its
helix angle is 10 degrees and it has 10 TPI.

cheers,
cd.

On 12/06/15 19:35, Cursitor Doom wrote:
Hi all,

I have a gear wheel missing from my lathe and need to cut a new one from
scratch as they don't appear to be available any more.
Question is, given that I can measure for myself everything concerning
the leadscrew this gear needs to mesh with, can I from those
measurements, calculate the outside diameter (OD) for a blank to make
another gear wheel from? I'm guessing there must be a fairly simple
formula for this but I'm damned if I can find it. To keep things simple
and for the sake of argument, let's say the leadscrew's OD is 1", its
helix angle is 10 degrees and it has 10 TPI.

cheers,
cd.

Not enough information., What is the desired reduction ratio, or the
distance to the shaft its goes on?


--
New Socialism consists essentially in being seen to have your heart in
the right place whilst your head is in the clouds and your hand is in
someone else's pocket.

On Fri, 12 Jun 2015 19:50:26 +0100, The Natural Philosopher wrote:

Not enough information., What is the desired reduction ratio, or the
distance to the shaft its goes on?

Apologies NP and Gareth; I think we're at cross purposes here (my fault!).
I'm talking about the indexing indicator. This is the dial that tells you
when you can drop the half-nuts so you always re-cut in sync with
previous passes.
So if you can visualise it, I've got the indicator dial at the top, the
missing gear wheel at the bottom (meshing with the leadscrew when
screwcutting) and a plain shaft with a keyway coupling one to t'other.

On 12/06/15 20:14, Cursitor Doom wrote:
On Fri, 12 Jun 2015 19:50:26 +0100, The Natural Philosopher wrote:

Not enough information., What is the desired reduction ratio, or the
distance to the shaft its goes on?

Apologies NP and Gareth; I think we're at cross purposes here (my fault!).
I'm talking about the indexing indicator. This is the dial that tells you
when you can drop the half-nuts so you always re-cut in sync with
previous passes.
So if you can visualise it, I've got the indicator dial at the top, the
missing gear wheel at the bottom (meshing with the leadscrew when
screwcutting) and a plain shaft with a keyway coupling one to t'other.

Still tells me nothing iuseful.

To can have any sioze pof gear meshing with the leadscrew. Its diameter
and threadpitch are not by themselves defining factors. You need to know
the axis offset of the shaft you are mounting it on from the leadscrew.



--
New Socialism consists essentially in being seen to have your heart in
the right place whilst your head is in the clouds and your hand is in
someone else's pocket.

"Cursitor Doom" wrote in message
...
I have a gear wheel missing from my lathe and need to cut a new one from
scratch as they don't appear to be available any more.
Question is, given that I can measure for myself everything concerning
the leadscrew this gear needs to mesh with, can I from those
measurements, calculate the outside diameter (OD) for a blank to make
another gear wheel from? I'm guessing there must be a fairly simple
formula for this but I'm damned if I can find it. To keep things simple
and for the sake of argument, let's say the leadscrew's OD is 1", its
helix angle is 10 degrees and it has 10 TPI.

I fear that you are providing irrelevant information because the reason that
they are known as changewheels is that they get changed in order to give
different feedrates to the leadscrew, either for cutting screw threads of
different sizes, or for giving a smooth feed for cutting.

So, to try to answer your question in the sense that you have put it, for
a start, we need to know the arrangement of the other gears from the
main shaft, and what TPI of the screw thread it is that you wish to cut.

Also, for one of the existing gears, we will need to know the outside
diameter
and the number of teeth in the gear, from which we could estimate either the
DP or the module of the gears that you already have.

It would also help tp know what make and model of lathe that you have,
as that gives us a firmer base for knowledge.

On Fri, 12 Jun 2015 20:05:06 +0100, gareth wrote:

It would also help tp know what make and model of lathe that you have,
as that gives us a firmer base for knowledge.

Harrison M300.
I've come across a couple of equations from Ivan Law's book on gear
cutting which *might* be of use he

OD=N+2/DP

or:

CP(N+2)/pi

Does that help at all?

"Cursitor Doom" wrote in message
...
On Fri, 12 Jun 2015 20:05:06 +0100, gareth wrote:
It would also help tp know what make and model of lathe that you have,
as that gives us a firmer base for knowledge.
Harrison M300.
I've come across a couple of equations from Ivan Law's book on gear
cutting which *might* be of use he
OD=N+2/DP
or:
CP(N+2)/pi
Does that help at all?

Although 5 years ago I had read up on the theory of helical gearing (to
produce the "HobNail" spreadsheet, which is used by a few machinists
on such machines as a Barber-Coleman, I've no experience of the
production of wormwheels.

Also, on my lathe,I've never had a TDI so cannot visualise what you
describe.

Ivan Law's book has some suitable information but greater analysis is
covered in The Machinery's Handbook.

On Fri, 12 Jun 2015 21:09:58 +0100, gareth wrote:

Although 5 years ago I had read up on the theory of helical gearing (to
produce the "HobNail" spreadsheet, which is used by a few machinists on
such machines as a Barber-Coleman, I've no experience of the production
of wormwheels.

Also, on my lathe,I've never had a TDI so cannot visualise what you
describe.

This is eight mins well spent on the subject:
https://www.youtube.com/watch?v=jbRcs_Hhtuw

gareth wrote:
"Cursitor Doom" wrote in message
...
I have a gear wheel missing from my lathe and need to cut a new one from
scratch as they don't appear to be available any more.
Question is, given that I can measure for myself everything concerning
the leadscrew this gear needs to mesh with, can I from those
measurements, calculate the outside diameter (OD) for a blank to make
another gear wheel from? I'm guessing there must be a fairly simple
formula for this but I'm damned if I can find it. To keep things simple
and for the sake of argument, let's say the leadscrew's OD is 1", its
helix angle is 10 degrees and it has 10 TPI.

I fear that you are providing irrelevant information because the reason that
they are known as changewheels is that they get changed in order to give
different feedrates to the leadscrew, either for cutting screw threads of
different sizes, or for giving a smooth feed for cutting.

So, to try to answer your question in the sense that you have put it, for
a start, we need to know the arrangement of the other gears from the
main shaft, and what TPI of the screw thread it is that you wish to cut.

Also, for one of the existing gears, we will need to know the outside
diameter
and the number of teeth in the gear, from which we could estimate either the
DP or the module of the gears that you already have.

It would also help tp know what make and model of lathe that you have,
as that gives us a firmer base for knowledge.



He does not seem to be talking about the screw cutting gears.he is
talking about the indicator on the lead screw.
I would be looking at second hand machinery places or the maker of the
lathe maybe ebay or maybe too rare

Cursitor Doom wrote:

I have a gear wheel missing from my lathe and need to cut a new one from
scratch as they don't appear to be available any more.
Question is, given that I can measure for myself everything concerning
the leadscrew this gear needs to mesh with, can I from those
measurements, calculate the outside diameter (OD) for a blank to make
another gear wheel from? I'm guessing there must be a fairly simple
formula for this but I'm damned if I can find it. To keep things simple
and for the sake of argument, let's say the leadscrew's OD is 1", its
helix angle is 10 degrees and it has 10 TPI.

Check out Ivan Law's book "Gears and Gear Cutting" in the Workshop
Practice series.

OOI, what gear is it to mesh with a leadscrew? Thread Dial Indicator?

--
Scott

Where are we going and why am I in this handbasket?

On Fri, 12 Jun 2015 20:15:15 +0100, Scott M wrote:

Check out Ivan Law's book "Gears and Gear Cutting" in the Workshop
Practice series.

Oddly enough, I just have!


OOI, what gear is it to mesh with a leadscrew? Thread Dial Indicator?

Precisely.

On 12/06/2015 19:35, Cursitor Doom wrote:
Hi all,

I have a gear wheel missing from my lathe and need to cut a new one from
scratch as they don't appear to be available any more.
Question is, given that I can measure for myself everything concerning
the leadscrew this gear needs to mesh with, can I from those
measurements, calculate the outside diameter (OD) for a blank to make
another gear wheel from? I'm guessing there must be a fairly simple
formula for this but I'm damned if I can find it. To keep things simple
and for the sake of argument, let's say the leadscrew's OD is 1", its
helix angle is 10 degrees and it has 10 TPI.

cheers,
cd.


A better place to ask might be uk.rec.models.engineering or on the
WWW.MODEL-ENGINEER.CO.UK forums ... someone may even have one or offer
to make one ...