Re: [CAD_CAM_EDM_DRO] Motor sizing - revisited

Marv Frankel wrote:

>Guys,
> I've gone into the archives, and read the formulas for motor
>sizing, and some of the replies, but I have a further question. My
>Enco mill has pretty easy movement on the x-y axes, but I intend to
>make the knee the z axis, and the cranking required to raise and
>lower the knee requires considerably more torque. Do I use a
>different size motor on z, do I do it by gearing, or both. I'm
>thinking ahead to a particular project that requires drilling 10
>holes through a piece of steel tubing. Can I cycle the z axis quickly
>enough to do this in a timely manner? I don't want to use the quill
>fine feed as z, because of an excess of backlash. Any suggestions or
>experiences that might help my thinking?
>
>

You can figure the actual torque with a string and a fish scale.
Measure the radius on the
leadscrew handle, and attach a string to the handle. Pull on the string
with the fish scale
(make sure the string is at a right angle to the line formed by the
handle and the leadscrew
center line.) The force reading on the scale divided by the radius of
the handle will give
the torque (in In-Oz, in-Lb. or whatever your measuring instruments
read). Now, this is only
for the torque required to raise and lower the knee. On a full-size
knee mill, the table-saddle-knee
is so heavy, cutting forces are almost insignificant when raising the
knee. But, maybe
doubling the static torque would make a good safety factor.

Bridgeport mills already have a gearing factor in there, the knee is 10
turns/inch, the X and Y
are 5 turns/inch. You need to figure out the desired speed at the
torque already determined, and
select your motor based on that.

The overload clutch on the Bridgeport quill feed is set for 200 Lbs
linear force on the quill,
by the way.

Jon