Re: [CAD_CAM_EDM_DRO] CNC Converting Questions

lcasey_lifestill wrote:

>Hello all,
>
>I am a new to the process of converting machines to CNC, but am very
>interested in learning as much as possible before I spend any money.
>
>I have read through a good part of this list and find a lot of this
>information educational, but overwhelming. I have not been able to get
>a firm grasp of how some of you determined the proper motor size for
>you conversions. Many of you, having the same mill (or similar) using
>different sized motors. Who is correct? Maybe all of them work, but
>what is the best way to calculate the proper size to be sure that the
>motor is not over stressed or under driven? With so many factors,
>where to start? Then on top of that, you have driver selection and
>servos or stepper. Can somebody please help me in figuring out these
>numbers?
>
>Machine to convert: MicroMark Mini-Mill
>
>How would you calculate the in-oz needed to hold, turn or turn to lead
>screw under load?
>
>

What is the highest cutting load you expect to need? I calculated the
absolute
worst-case load to be about 1000 Lbs for my Bridgeport Series-I mill, based
on spindle HP in the slowest back-gear range, applying all it's torque to
a 1" end mill, and delivering that through the side of the cutter to the
workpiece.

So, I designed the system for 120 IPM rapid feed and 1000 Lbs of linear
force
to the table.

>What is the best way to control these motors, Gecko or Rutted? Maybe
>some other?
>
>How about motor, server or stepper?
>
>
>

I have a minimill that I converted with size 34 steppers (I already had
them)
and Gecko 201A drives. I can run it at 90 IPM with this setup, which is
plenty. I use 1:1 belt drive. I did have to modify the Y axis bracket to
put opposed ball bearings into it. I don't know why they put ball bearings
in the X bracket, but sleeve in the Y. Servos become much more
attractive for the
larger machines. They give more power over a wider speed range than
steppers,
and can also deliver higher speeds. Who needs 400 IPM on a machine with
only 12" of travel?

Jon