# Re: how deep do the coilers prefer doing it? : )

```Original poster: tesla popp <teslas_lab@xxxxxxxxx>

answers-  The best way to figure out how deep to cut
the flats, is the measuring distance between the
windings of the motor.  If you don't already know,
1800 rpm @ 60Hz= 4 flats exactly 90 degrees apart.
3600 rpm @ 60Hz= 2 flats exactly 180 degrees apart.
the motor will have gaps in between groups of
windings, a 1800rpm will have 4 main running coils and
4 gaps.  these gaps will control the phasing of the
armature.  I use a 1/2 winding cut in the armature. (a
cut half as long as the winding's width).  For this
motor I have, that divides the core in sections
exactly 1/8 the circumference of the armature.  It
locks at 50VAC of 120VAC.

You can figure to loose an equal amount of efficiency
to heat by figuring how much material you removed from
the armature.  if you cut down your flats to 1/2 of
the armature's surface area total, you will loose
lost energy, the more lost torque.  due to the
composition of different armatures and different Field
ratios, there is no "exact" equation for figuring
losses, nor is it important to know.  I truly don't
feel like writing an equation for this problem because
it it NOT an important issue.

If you don't have a machine shop, use a angle grinder
with a multi layered SANDPAPER WHEEL, to cut the
flats.  this will leave a smooth polished surface when

good luck...
Coiler Forever: Jeremiah Popp

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "Dmitry (father dest)"
> <dest@xxxxxxxxxxx>
>
> Hallo.
>
> yesterday i got a 1/2 hp, 2780 rpm capacitor run
> motor - you can see
> some pics of it here -
> http://himplast.ru/father_dest/temp/370w/
> this puppy has no "dead poles" at all, and was fully
> rewound by hands
> of some drunk electrician % )))
> i see that nobody on the list really know, how deep
> should one shave
> that poor rotor down to perform so called "salient
> pole" conversion.
> i mean nobody know any formulas, nobody can explain
> how wide exactly
> should one cut that flats, nobody know how one could
> verify that
> performed conversion was optimal in terms of lost
> torque and etc.
> am i correct on this?
> coz all that i can find in archives is something
> blurry like this:
>
> "The info I supplied is more of a general guideline
> than anything --
> you will inevitably see variations on the number of
> poles, etc."
>
> "Maybe the flats should still be 3/4" wide like the
> 1750rpm motor, I
> don't know.  There are various opinions."
>
> "In other 3600 rpm cases I made the flats narrower,
> but the motors
> seemed weaker.  But these were all different motors
> so it's hard to
> judge."
>
> does anybody know any real physics that stands
> behind all of this? what
> should one monitor in process - input currents, any
> phase shifts,
> something else?
> or coilers prefer just to cut 1/3 of od and don`t
> want to know nothing
> more? : )
>
> p.s.
>
> "If the cuts on the armature are sufficient, the
> motor will lock into
> salient-pole mode at roughly 75 to 85% of full
> voltage."
>
> i like this particular criterion, but what if the
> input current at 75%
> would be 2 times (for example) more than at 90%? or
> say torque would
> be 2 times smaller? then i`ll better go for 90% i
> think.
>
> -----
> Let the bass kick! =:-D
>
>
>

```