I need to make a 12 tooth 20DP 14.5 degree involute spur gear.

I've cut plenty of low tooth count cycloidal clock gears, but this is
the first time I've tried to make an involute gear.  I started with a
blank (12 + 2)/20 = 0.700 inch diameter, and mounted this on a mandrel
on my dividing head.  I then cut 12 teeth 0.108 inch deep with a new
No 8 B&S type 14.5 degree involute gear cutter.

The resulting gear is not satisfactory, and does not mesh properly
with other 20 DP gears I have (e.g. the change gears for my Myford
lathe).  The gear also looks odd compared to my Myford gears, in that
instead of having flat-topped teeth, the teeth have sharp points
rather like cycloidal clock pinions.  It also looks for all the world
as if the teeth on my gear would need to be undercut at the bases in
order to mesh correctly, but clearly this can't be done with plunge-
cutting cutter.

I'd be most grateful for some advice.  The No 8 cutter is supposed to
be suitable for gears with 12 or 13 teeth, but looking through some
books just now I read that gears with so few teeth do need to be
undercut.  How is this possible?

TIA

Mike

On Aug 3, 6:54 pm, mikecb1  wrote:
> I need to make a 12 tooth 20DP 14.5 degree involute spur gear.
>
> I've cut plenty of low tooth count cycloidal clock gears, but this is
> the first time I've tried to make an involute gear.  I started with a
> blank (12  2)/20 = 0.700 inch diameter, and mounted this on a mandrel
> on my dividing head.  I then cut 12 teeth 0.108 inch deep with a new
> No 8 B&S type 14.5 degree involute gear cutter.
>
> The resulting gear is not satisfactory, and does not mesh properly
> with other 20 DP gears I have (e.g. the change gears for my Myford
> lathe).  The gear also looks odd compared to my Myford gears, in that
> instead of having flat-topped teeth, the teeth have sharp points
> rather like cycloidal clock pinions.  It also looks for all the world
> as if the teeth on my gear would need to be undercut at the bases in
> order to mesh correctly, but clearly this can't be done with plunge-
> cutting cutter.
>
> I'd be most grateful for some advice.  The No 8 cutter is supposed to
> be suitable for gears with 12 or 13 teeth, but looking through some
> books just now I read that gears with so few teeth do need to be
> undercut.  How is this possible?
>
> TIA
>
> Mike

Hi Mike

On the face of it, It sems that you have it all done correctly, I can
only suppose that you have made an error somewhere.
Lets go through it all, firstly check the blank OD , if OK then check
the dividing head, is it set for the right number of teeth, as this
could lead to the results you have got, Alternatively, have you gone
deeper than 108",again you an check this on the gear you have cut. If
all this checks out OK you need to look at the cutter, offer it up to
a similar cout wheel from the Myford chain and see if it could have
cut the teeth.
I am happy to have a look at it all if you get them to me
Peter

On Aug 3, 7:14 pm, petercolma...@hotmail.com wrote:
> On Aug 3, 6:54 pm, mikecb1  wrote:
>
>
>
>
>
> > I need to make a 12 tooth 20DP 14.5 degree involute spur gear.
>
> > I've cut plenty of low tooth count cycloidal clock gears, but this is
> > the first time I've tried to make an involute gear.  I started with a
> > blank (12  2)/20 = 0.700 inch diameter, and mounted this on a mandrel
> > on my dividing head.  I then cut 12 teeth 0.108 inch deep with a new
> > No 8 B&S type 14.5 degree involute gear cutter.
>
> > The resulting gear is not satisfactory, and does not mesh properly
> > with other 20 DP gears I have (e.g. the change gears for my Myford
> > lathe).  The gear also looks odd compared to my Myford gears, in that
> > instead of having flat-topped teeth, the teeth have sharp points
> > rather like cycloidal clock pinions.  It also looks for all the world
> > as if the teeth on my gear would need to be undercut at the bases in
> > order to mesh correctly, but clearly this can't be done with plunge-
> > cutting cutter.
>
> > I'd be most grateful for some advice.  The No 8 cutter is supposed to
> > be suitable for gears with 12 or 13 teeth, but looking through some
> > books just now I read that gears with so few teeth do need to be
> > undercut.  How is this possible?
>
> > TIA
>
> > Mike
>
> Hi Mike
>
> On the face of it, It sems that you have it all done correctly, I can
> only suppose that you have made an error somewhere.
> Lets go through it all, firstly check the blank OD , if OK then check
> the dividing head, is it set for the right number of teeth, as this
> could lead to the results you have got, Alternatively, have you gone
> deeper than 108",again you an check this on the gear you have cut. If
> all this checks out OK you need to look at the cutter, offer it up to
> a similar cout wheel from the Myford chain and see if it could have
> cut the teeth.
> I am happy to have a look at it all if you get them to me
> Peter- Hide quoted text -
>
> - Show quoted text -

Peter

Thank you for your advice.  I went through everything today, and as
you predicted I made a mistake.  Somehow I managed to cut the gear too
deeply.  Only .010" or so, but enough to ruin the meshing.  I've just
cut another gear to the correct depth (in my caution it's actually a
couple of thou under), and it meshes fine with my Myford gears.  It
also looks right, with flat tops on the teeth!

Thanks again

Mike