Re: [Emc-users] Lost fractions of a step - Clock Wheels and Pinions

[Gene Heskett]

On Sunday 03 January 2016 12:37:55 Kirk Wallace wrote:

> On 01/02/2016 10:02 PM, Cecil Thomas wrote:
> ... snip
>
> > Several years ago I wrote a program to "generate" involute gear
> > teeth by making multiple cuts of the same tooth from differing
> > angles with a rack shaped cutter. This eliminates the need for the
> > different cutters when making only one cut per tooth.  I have used
> > it many times to cut relatively large gears with a relatively small
> > number of teeth with virtually no noticeable error.
> >
> > A few days ago a friend who repairs watches wanted to know if I
> > could figure out what gear (wheel to you watch guys) size, pitch or
> > module and number of teeth would be required to replace a missing
> > one. (the original was long gone).  I had no problem working from
> > the center distance and the matching pinion coming up with the
> > appropriate design.
>
> ... snip
>
> I have been looking at clock gearing off and on for a while. So far, I
> have found that clock tooth forms are cycloidal, but not really. It
> seems there is a British standard which is based on the ideal
> cycloidal form but uses a circular arc for the curved part of a tooth,
> rather than a cycloid, and clearance is added according to practical
> experience. I haven't been able to find the contents of the standard,
> but I'm still looking. My plan was to use a very small diameter
> (.015") end mill as a universal gear cutting tool for thin wheels from
> sheet brass. The wheel can be drawn in CAD, converted to g-code then
> cut in XY without using a rotary axis. I would appreciate any links or
> information that could get me closer to actually cutting wheels and
> pinions. Although, pinions are a different kettle of fish.
>
Yes, and recipes are scarce.

> I'm also working on a New Haven clock that seems to use custom screw
> threads (#3-40?) that don't appear in Machinery's Handbook or anywhere
> else.

Since all of our thread cutting canned software is infinitely adjustable, 
I would think some carefull measurements would lead to a G76 
configuration that could duplicate at least the screw.  But because the 
size isn't boring bar country, the threading tap may have to be made 
with G76 and some pretty precise flute cutting.  Probably involving some 
A2 rod that is subsequently hardened, something I don't have the heat to 
do here.

Yep, its starting with hemp or cotton seed to grow a rope, but...

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

--
___
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users

Re: [Emc-users] Lost fractions of a step - Clock Wheels and Pinions

[Dave Caroline]

The book which has a selection of standards is Gears for small
mechanisms by W.O. Davis, it was reprinted by TEE publishing ISBN
1857610156
Note the correct form has a rectangular root which stops the end mill kludge.
We just used the Thornton cutters to get it right.

The cycloidal form has a number of "standards"  swiss,black forest and
the british one based on the swiss.

http://www.clock-works.clara.net/cata/wnpc3.html

Dave Caroline

--
___
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users

Re: [Emc-users] Lost fractions of a step - Clock Wheels and Pinions

[andy pugh]

On 3 January 2016 at 17:37, Kirk Wallace  wrote:

> I'm also working on a New Haven clock that seems to use custom screw
> threads (#3-40?) that don't appear in Machinery's Handbook or anywhere else.

I thought it might be a watch pendant thread, or Progress, but I can't
find anything that coarse at that diameter:
http://www.bodgesoc.org/thread_dia_pitch.html


-- 
atp
If you can't fix it, you don't own it.
http://www.ifixit.com/Manifesto

--
___
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users

Re: [Emc-users] Lost fractions of a step - Clock Wheels and Pinions

[Kirk Wallace]

On 01/02/2016 10:02 PM, Cecil Thomas wrote:
... snip

> Several years ago I wrote a program to "generate" involute gear teeth
> by making multiple cuts of the same tooth from differing angles with
> a rack shaped cutter. This eliminates the need for the different
> cutters when making only one cut per tooth.  I have used it many
> times to cut relatively large gears with a relatively small number of
> teeth with virtually no noticeable error.
>
> A few days ago a friend who repairs watches wanted to know if I could
> figure out what gear (wheel to you watch guys) size, pitch or module
> and number of teeth would be required to replace a missing one. (the
> original was long gone).  I had no problem working from the center
> distance and the matching pinion coming up with the appropriate design.

... snip

I have been looking at clock gearing off and on for a while. So far, I 
have found that clock tooth forms are cycloidal, but not really. It 
seems there is a British standard which is based on the ideal cycloidal 
form but uses a circular arc for the curved part of a tooth, rather than 
a cycloid, and clearance is added according to practical experience. I 
haven't been able to find the contents of the standard, but I'm still 
looking. My plan was to use a very small diameter (.015") end mill as a 
universal gear cutting tool for thin wheels from sheet brass. The wheel 
can be drawn in CAD, converted to g-code then cut in XY without using a 
rotary axis. I would appreciate any links or information that could get 
me closer to actually cutting wheels and pinions. Although, pinions are 
a different kettle of fish.

I'm also working on a New Haven clock that seems to use custom screw 
threads (#3-40?) that don't appear in Machinery's Handbook or anywhere else.


-- 
Kirk Wallace
http://www.wallacecompany.com/machine_shop/
http://www.wallacecompany.com/E45/

--
___
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users