Re: [CAD_CAM_EDM_DRO] Re: Info for a Newbie

For a bipolar driver you need bipolar motors.

The gearing is correct - 3:1 is good, 4:1 is ok.
You can also support the head with a gas spring, and should do so.
Its a *good idea*.
A counterweight may help, but you should have a rubber band in it.
The gas spring is better.

Motor quality and general guidance, some facts:

The best motors are new, square bodied, so-called rare-earth magnet motors.
The lower the inertia, the better they accelerate.

You want to use low voltage motors, and low inductance motors.
You want to use bipolar parallel, if your drivers can support this.
You want to use about 20x motors theoretical voltage.
There are huge differences in quality, and usefulness.
Your amps and volts are the limit, as determined by your drivers.
Most steppers will not run to 1000 rpm - your rapids will be slow,
especially if you gear down.
Many will only turn 300-600 rpm, or less sometimes.

Most old stepper motors will not work at more than 50%-60% of their
theoretical potential due to many issues.
You cannot get around this, due to electrical reasons.
Many times, a nema 34 motor will run your mill much faster than a nema
42 motor.With the same driver.
Most times, you cannot get full performance out of a nema 42 motor.

Some general milling machine advice.
You should gear the steppers down 1.5:1 - 3:1 with timing belts, due to
resonance and
accuracy issues and to make building the machine easy.
You can use couplers, like oldham, but they are more difficult to set up
(alignment is tricky) and they are expensive.
About 20 $ / axis and more.
You should plan to use 40-68 volts psu, and appropriate motors/wiring etc.
Avoid old, second-hand steppers. They may have been de-magnetised,
and in general give much less performance than the new ones.
Dont use steppers with 8v - 24 ratings, for a lathe, mill or plasma
cutter - they will run very slowly.
They are fine for table saws, bandsaws, astronomy etc where you speeds
and accelarations can be slow.

Shameless commercial pitch.
I have a few spare, very good motors I got for myself and for resale.
These are very powerful, new, rare-earth magnet 425 oz-in nema 23 size,
triple stack motors for 59$ each.
Shipping is 28 euros to japan, same for 1-6 motors.
They have excellent hi-speed performance, and just the right curve for
plasma cutters and milling machines.
Unlike most motors, they run at 1000 rpm with 50% torque.
They have the power of nema 34 motor, in a smaller, better nema 23 frame
size.
They are an excellent! fit for you.
They will run great with a 40-48 volt psu, like a 48v meanwell.

I got them for my lathe 9x14, and will put them on my 100x100 mill .

I can help you hook them up for you, if interested.

Btw - what drivers are you using ?
I can recommend options on the drivers - geckos are best for a mill, but
some kits may work well.
In general look for about 40 volts to 48 volts.
In the smallest size, xylotex in the usa is good.
They may not ship to your country.

> Stefan,
>
> Good luck on your project. You should check out the other yahoo
> groups, there is a cnc mini mill group, mini-mill group, grizzley/hf
> minimill group also & check out cnc zone.com lots of good stuff there
> too.
>
> I am using 325 oz/in motors on my mini-mill, I would not recommend
> anything smaller in the torque range.
>
> Arnie
>
>