Re: Need advice on upgrading 2 existing CNCs

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "braidmeister"
<braidmeister@y...> wrote:

> At the moment I am running Vexta 2-phase motors putting out about
> 305in/lbs ea. I believe that they are either NEMA 32 or 34 size. I
>>
> My 1st thought is to look into servos, but I have concerns with
> there being interference with the Hypertherm plasma cutter machine.
> I am also at a loss how to properly select a servo that will be
> closest in mounting, torque and target speed. The other option is a
> hybrid type stepper like Oriental's AlphaStep or Animatic's
> SmartMotor with feedback like a servo.
>
> Can someone tell me if a servo will reliably run on a plasma

machine?

I can address that directly. I am running a servo/stepper mixed
machine. The gantry is run by two servo's driven with Gecko 340's;
the X is an identical servo with another 340 and the Z axis with
integrated THC, is a stepper with 201 driver. The whole thing is
hooked to a PC (8' away) running MACH2. I don't get missing steps or
bad cuts. My plasma is an old noisy HF start Miller 500.

The secret is proper grounding of the table and plasma and total
isolation of the controller and PC. Another dirty little secret is
that I mounted my drives close to each motor so the encoder leads are
less than 8". I made sure the Gecko's had nice big filter caps on
the raw DC and that the step and direction lines were buffered and
run in shielded cable up to each Gecko.

The Hypertherm is a a MUCH quieter machine than my old Miller.
As Jon pointed out, my upper IPM limit (200IPM) is a function of my
leadscrews and the whipping if I try to exceed that. I used 7' 3/4"
ballscrews for the best reason: I got them real cheap. My motors are
not brusers either being only 23 frame 120 oz/in Units with 3:1 belt
reduction. I could easily get 300 or 400 IPM if my ballscrews would
take it. My next machine will be either a rack and pinion or a
toothed belt drive setup, and while I am too chicken to run at 600 IPM
(10" /sec), I would like to be able to move at 250 or 300 on long
rapids. Moving a 100lb gantry (it was originally designed to be a
combo router and plasma....bad idea) at 600 IPM would make me want to
soil myself. There are two many times I have had to reach in and
grab a piece that hangs in the cut before the head has a chance to
move back over it. I fear I am not quick enough to do that with a
machine moving at 10"/sec

I would faint and fall in it if I had to spend 7 grand to retro fit
my machine. I only have about half that in it to begin with
including software!

Pop over to the MACH1MACH2CNC group and talk with some other
Torchheads (and router guys) that can show you how to get close to
what you want for a lot less. How about complete Torch Height
Control with dynamic corner sensing and anti-dive features AND the
software to run the machine (Controller software) for about 500
bucks? Check out www.sheetcam.com for a ultra low cost (free while
in beta) CAM program with extensive plasma features (will work for
router too).

>
> What would you suggest, a hybrid stepper with feedback or servo for
> both machines?
>
> What kind of ballpark $ am I looking at to upgrade the hardware on
> one machine? (Steppers~Servos/power supply/Geckos etc)
>
> Where would you recommend that I purchase my motors to get the best
> deal?
>
> Any and all help is greatly appreciated!
> Thanks!
> -B

There have been a lot of servo motors on ebay from time to time. You
need to stay with DC brushed perminate magnet units. Don't worry if
the encoders are not the right count or are missing. Rotary encoders
are cheap. Even DC PM motors can be used for servo if you can figure
a way to mount an encoder. A lot of the industrial DC motors (like
the Reliance Micro 100 series) have a rear shaft and mounting holes
for an encoder.

You are welcome to contact me off-list if you need specific help.

Also take a look at www.campbelldesigns.com (Bob answered you earlier
and is a friend)