OT : CNC mills

These stepper motors don't really like getting hot do they?

When I first got this of WUN I accidentally left the motor driver box
turned on overnight (WUN had given me strict instructions to never leave
it on if the PC wasn't driving it).

Next morning entered the garage to the delightful smell of burnt
electrickery stuff. Damn.

Controller box had burned out its mains transformer. Both of em (kind of
a Heath Robinson affair). Sorted by ripping out all the AC power supply
and powering it off my 35A 13.8V PSU. That appeared to fix it.

In preperation for knocking up the new bracket for the 10R I've just
stripped the whole mill down and rebuilt it (dishwashers rock for
cleaning all the crap of stuff .

Then stripped the smaller bits down and rebuilt them.

Stepper motors still sticking when cold.

Stripped the motors down.

Bugger. Seems that when I left the control box on it heated the motors
up to such an extent the "paint" used to hold the laminations together
on the rotor had sort of turned slightly less than solid and oozed down
just enough to sit proud of the rotor and cause it to slightly jam when
cold.

Sorted with a light dusting of sandpaper.


The control box is of ancient design though, I'm tempted to replace it
with 3 new stepper motor controllers that use micro steps and a chopper
drive.

Using the current control box the motors get too hot to hold after about
an hours use, will using new design controllers reduce the heat?

(thankfully the software lets you pause the program so I can let them
cool down as needed)

 

frag wrote:

<snip magic smoke story>

hmm that doesn't sound right. Seems like the controller is supplying
too much current (perhaps to try and ensure that no steps get missed
etc. - basically overrating what the motors are capable of).

So I guess the choices are to continue with the resting duty cycle, a
new controller better matched to the motors, or rig up some cooling.
(Or if you've got a load of time and/or money, convert it to 'proper'
servo drives ;-) )

My concern with new drive electronics (that may not overheat) would be
that then they don't supply enough current and the motors start losing
position - but you won't know that until you try it. Not very well
written but I hope YSWIM. Could you try one axis at a time?

 

Reading up between the difference between the chopper types of controller
and the old fashioned types I can see why the chopper ones use less power
and drive the motors better (constant current to overcome the inductance on
ramp up and down Vs. constant voltage).

I know that I run these at 14.5V, but even at 12V they still get very hot.

I suspect the drive circuitry isn't too well as the Z axis motor (which 95%
of the time just holds position) only gets warm. The X and Y get hot, and
I'd expect a static motor to draw more current and get warmer?

A cold compress on the motors did me tonight

Good suggestion about trying one axis at a time. I'll probably change the
motors too as others have found out that the motors Taig use aren't the
best.

Heh, the rest of the machine isn't worth spending that much money on

ISWYM no problem.

There is a bit of wear in the middle of the Z axis, and all axis are a PITA
to set up right (I'm still learning - this piece has oval holes!), so I
either get a visible amount of slack or the motors haven't got enough power
to move through the full range.

More power needed + new controllers!

(looking around I'm a little bit suprised at the cost of stepper motors,
they ain't cheap!)

 

Using the patented Mavis Beacon "Hunt&Peck" Technique, frag

I'd be very surprised at that, the machine has done very little work.
Have you adjusted the gibs properly?

 

is this some sort of toy milling machine?

The Bridgeport CNC[1] rig I used to use in the '80s would run pretty
much 24/7

[1] for values of "C" that = "Commodore Pet"

 

I am more Setanta than Cu' Chulainn, I fear.