Re: [CAD_CAM_EDM_DRO] Smithy CNC

At 08:27 AM 5/11/00 -0000, you wrote:

>At any rate- I'm thinking real hard of getting a Smithy. I've seen
>the machies in person and they loog good to me--of course they weigh
>about 10X as much as the Sherline too. I'm thinking of the Midus
>with
>the CNC conversion. Does anyone have any expericence or coments on
>this? Thanks in advance
>
>Craig

I purchased the base Midas about 6 months ago with the intentions
of maintaining manual operation with the addition of hanging some
surplus steppers on it and writing my own software for CNC.

Here's my impressions so far...

All three axis have *lots* of backlash (on the order of ~.040)
making it IMHO, unsuitable for an open loop system using steppers
only. I've worked out some of the backlash but ball screws will be
required on the X and Y axis if I pursue my original intentions of
stepper motors. The Z axis is worm screw driven so of course the
ball-screw option is out. Most of the backlash here can be corrected
by removing the front "drill press" manual levers, removing the
useless dial cover and attacking the manual engaging device with
a MIG welder. You lose the manual drill press option and it's rather
crude, but it eliminates the majority of the backlash problem. I
also removed the Z axis takeup spring and extended the smaller side
hand crank to give me more leverage. This retains manual operation.

I removed the front facing X axis fast crank assembly, as again IMHO,
it's useless for actual work - way to much movement from hand crank
to table motion to suit me. As the lathe is configured "out of the
box", the addition of a motor to the X-axis disables the ability to
use the lathe manually. So, I modified the end of the X-axis to take
both the CNC gear and an extended handle. Hey, what can I say, I
like leverage.

Most of the Y axis backlash was found to be in the slop of the cheezy
nut the screw rides in. I split the nut with a bandsaw and squeezed
it together taking up most of the backlash.

Overall quality is ok for Chinese I guess, of course; 'ya gits what
ya pay fer'. Since I use the lathe for semi-production of aluminum and
plastic work, it's ok and I have no real regrets.

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Here's something the rest of the group might me interested in...

As it stands now, I'm currently using the lathe manually as I've
become disillusioned with adding steppers to this lathe. My biggest
complaint besides the backlash, is the nuisance of being able to feel
the stepper motor while using the lathe manually. My intentions are
now to remove the steppers and replace them with reversible DC
gearhead motors that are somewhere in the neighborhood of 100 rpm.
From there I plan to manually control all movement of the lathe
electrically via a pendant. With the future addition of a computer
readable DRO and an interface to the pendant I'll have a closed
loop system. Ultimately I'll be able to use the lathe manually for
most of the work but allow the computer to control such tasks as
radius turning, tapers and the like.

Later -

O-Tay (tm)
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Mark A. Taylor (U$UA 15484)
http://www.esper.com/taylorma