Re: [CAD_CAM_EDM_DRO] Servo/Stepper on a Surface Grinder

Use a micro-stepping driver for the stepper motors and the big jerks become
many tiny ones. If you're driving a lead screw it probably doesn't mater
anyway, since that is a major "gear" reduction already unless it has a
really steep pitch.
--Phil M.

----- Original Message -----
From: Alan Rothenbush <alan@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, April 26, 2006 1:36 PM
Subject: [CAD_CAM_EDM_DRO] Servo/Stepper on a Surface Grinder


>
> I have a small little Sanford Surface Grinder, 4" x 7", fully manual, and
an
> absolute jewel of a machine (after my friend Marcus spent a whole day of
his
> valuable time regrinding worn things back to wonderful with his nice big
SG).
>
> The problem is, being fully manual and with a rather small motor, there is
a
> LOT of hand cranking involved, and that gets old in a hurry.
>
> It's clearly time to automate it.
>
> Add a motor to the table, add another to the Y axis, add some (moveable)
> travel limit switches, build and program a controller, done. Really not
much
> more than a long weekend project.
>
> The controller will have a number of BCD switches
>
> table speed (TS)
> Y axis step distance (YSD)
> table traverse count before step (TTC)
>
> The usage is this. Set the switches and press start. The table will move
> forward then back, at the speed specified by the TS switch, as many times
as
> specified by the TTC switch.
>
> It's been my experience that when taking off 3-5 tenths, about 4 passes
are
> required before there are no sparks .. so set it to 6.
>
> Once 6 passes have been made, stop the X motion, then move in/out the YSD
> distance (.025", .050", etc). Begin traversing again. Repeat until a Y
> traverse limit switch is hit, then reverse Y direction and continue.
>
> Simple and should work fine.
>
> The real question is this .. I want a SMOOTH motion, and at the very low
RPMs
> the traverse motor will be running at, everything in the house (NEMA 17 -
34
> steppers, Sherline-sized to Bridgy-sized servos) seem to "cog" a wee bit
more
> than I'd like.
>
> (The electronics are designed to issue Step/Dir pulses for use with either
a
> Gecko G320 or a stepper controller)
>
> I like the idea of a servo to supply extra current if the grinding gets a
bit
> tough. I like the idea of a stepper because they have lots of power at
these
> sorts of speeds. I'm not as crazy about a simple DC motor, as controlling
> and maintaining the speed is not so easy as just wiring up a Gecko.
>
> Also, too big a motor is problematic .. this IS a small machine, and so
the
> size and weight of the traverse motor is a consideration.
>
> (There's a tach being added to the spindle motor; should it slow because
the
> grinding got really tough, power will be removed).
>
> But all the motors in the place of suitable size jerk jerk jerk at the 5
RPM
> or so rotational rates I'm talking about.
>
>
> I _could_ use a gear head motor (the lash in the gears not really being an
> issue in this application), running the motor fast (and therefore smooth)
and
> using the gears to slow it down, but now manual use is severely
compromised.
>
> A clutch might be possible, but I'd rather not, if I can avoid it.
>
> So I'm kinda stuck, in my own mind anyway.
>
>
> Any thoughts appreciated.
>
>
>
> Alan
>
>
>
>
>
>
> --
> Alan Rothenbush
> Academic Computing Services
> Simon Fraser University
> Burnaby, B.C., Canada
>
>
> The Spartans do not ask the number of the enemy, only where they are.
>
> Agix of Sparta
>
>
> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
> Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
> Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
> List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@...,
timg@...
> Moderator: pentam@... indigo_red@... davemucha@...
[Moderators]
> URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there, for OT
subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> bill
> List Mom
> List Owner
>
>
> Yahoo! Groups Links
>
>
>
>
>
>