Re: [CAD_CAM_EDM_DRO] mini-mill and motors

Danny is right, based on my experiences.
48 V is the way to go.
A gecko or other modern (morphing) stepper is the only way to go.

Going to a better drive, like from a Zylotex type one to a better one
like gecko will get you about 30-50% better top speed and acceleration.
And going with any drive from under 30 V to 48 volts, will approx double
your top speed and acceleration.
And going to a hw pulse generator (Centipede, Smoothsteper) will get you
from 30% to 100% better top speed and acceleration. Here the variance
depends on your mechanics, with a linear mechanicals load, ie linear
guides and ballscrew, being approx 100% better than ways and acme screws..

I have (had) all above combinations in use.

So, if you go to a gecko you get about 130% x 200% your current top
speed and acceleration for about 2.6 times performance improvement.
Like always, steppers will work better and your overall accuracy will be
much better, if you gear the steppers to 1:2 - 1:3.
The only reason not to do so is lack of ability to run high pulse rates.

I run 100 kHZ to 300 kHz, with Centipede and Smoothstepper, both with
gecko 203Vs at 58V, servo geckodrive 320, on a lathe.
My lathe is optimised for real-world 1 micron resolution, with actual
microstep sizes being 0.2 and 0.1 microns or so. Top speeds and
acceleration are way more than is safe or desirable, and I use way less.
I use 1:3 gearing.
This is a near-optimum configuration, with a 0.750 ballscrew at 1:3 on x
axis. X-axis is 14 times stiffer than a std lathe (double preload
oversconstrained. The screw is in tension).

My mill uses g251s and 48 V DC.
The table masses about 250 kg, with loads being theoretically about 250
kg as well. I have never had a heavy load on the table (above my
bodyweight around 80 kg + vice at 20 kg).
It runs very well on Nema 23 steppers, even from the parallel port.
However, I am again using 1:3 and it´s on linear ways, with a 0.750
ballscrew.
This is an optimum configuration, if price is an issue.
Real world mechanical resolution is about 0.01 mm, which is perfect for
a milling machine (limited to about 0.02 mm). Microsteps are of course
theoretically much less.

> If you get a Geckodrive, the 48V Sun 25A supply is not only much more
> appropriate, it's actually almost the same price!
>
> ~$35 on eBay with shipping INCLUDED. Versus $20 from Allelectronics +
> shipping isn't much less, and I wouldn't even recommend that supply in
> the first place.
>
> Danny
>
> On 11/14/2011 8:03 PM, turbulatordude wrote:
>
>> Hi,
>>
>> first off, the mini-mill has a horrible design flaw. you cannot easily lube the ways on the longitudinal travel.
>> if your machine is getting tight at the ends, then the center is worn and the ends are not. that is a mechanical problem that motors might or might not solve.
>>
>> if you are open to driving the motors harder, then you do need to ditch the xylotex and put on something more robust.
>>
>> the geckos will run the machine better.
>> what I would offer is that you get the $20 power supply from allelectroncis and keep the control panel. remove it from the mini-mill and put it on a small table top router type of unit.
>>
>> Dave
>>
>>
>>