RE: [CAD_CAM_EDM_DRO] newbie needs advice

John,

As far as I know, if you ignore friction losses, etc., if you divide the
speed by X (2 in your case), you multiply the torque by the same number.
Basically you are trading speed for torque - as you multiply the torque you
are dividing the speed (by 2 in your case).

You spoke of "force" instead of "torque". We can't talk about force until
we go through the ball screw which converts RPM and torque to linear speed
and force by a ratio determined by the thread pitch - the courser the thread
pitch the faster the resulting speed but the lower the force available to
move/hold the work.

Note also that as you reduce the speed through the drive train you also
increase the "resolution" of the system - more steps per inch from a given
stepper motor. There is a limit to the effectiveness of this though because
of backlash and errors in belts, gears, lead screw threads, etc. - you're
not going to get a .000001 machine by just using a higher ratio drive! ;-)

I don't know the specifics but I do know that with ball screws you need more
torque to prevent the cutting forces from driving (i.e.: turning) the
stepper off position. I don't have this problem on my mill because I'm
using the original Acme screws that have enough friction loss that the table
does not shift. On the other hand I have to use a higher drive ratio to
overcome the friction so I pay for it with lower speeds - but this is a
hobby so I'm willing to trade off speed ....

Regards,

Chuck Hackett

-----Original Message-----
From: John Hudak [mailto:jh1221@...]
Sent: Tuesday, December 26, 2000 11:00 AM
To: CAD_CAM_EDM_DRO@egroups.com
Subject: [CAD_CAM_EDM_DRO] newbie needs advice

Hello, I am in the process of converting my bridgeport mill to cnc
control, and have already purchased the ballscrews, and the drivers
(gecko) at this point I am looking at the motors, and am a little
confused about the sizes that might be needed, I have seen some
conversion kits with 1200 oz motors that are reduced 2 times. Does
this give 2400ozs of force??? what is the minimum size motor that I
should use? I plan on using this mill for hobby work with a small
cash job thrown in here and there. Thanks; John


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