Re: [CAD_CAM_EDM_DRO] Bridgeport to CNC

bcnc2003 wrote:

>I have a bridgeport series 1 42x9 that i'm wanting to retrofit and i
>was wanting info from someone that has done this before, like how big
>of a motor to use,mounting,and controls, ect. (wanting to go
>servo/encoder with greco drives).
>
>

Well, I have done a round-ram Bridgeport with a 32 x 9" table. Will you
be putting
in ballscrews? That is highly recommended, for a number of reasons.
Primarily
accuracy, freedom from backlash, and greater efficiency converting torque to
linear force. The backlash may be the greatest improvement, as it
allows climb
milling without worry.

I used some 1/8 Hp (continuous) motors designed for 1800 RPM that were
part of
an existing servo system. That saved me making some brackets, etc. You can
match the speed/torque curve of the servo motors to the screws with
toothed belt
and sprockets. Big, high-torque, low-speed motors can be run at direct
drive or
near to that. Smaller, lower-torque, higher-speed motors can deliver
the same
performance with a belt reduction ratio.

Surprisingly small servo motors can really deliver a lot of power and torque
when matched properly to the load.

Given the HP at some speed, you can extract the torque the motor is
capable of.
You can then derive Oz-In / Amp (Kt) if you have a current rating at the
Hp rating
point. If not, you can easily measure the Kt with string, weights, a
power source
and a DVM set to read current.

Something that is hard to measure (and impossible without wasting a
motor) is
the peak current rating. So, it is always good to be sure you can get
that rating
before buying motors.

See what I wrote some years ago on these calculations at
http://www.timgoldstein.com/cad_cam/motor.htm

Jon