Another newbee needs help chooising motors

[P-4]

I am looking at building a CNC to do minor work, like PCB's and maby some light al. work. I went to my local surplus store and they had 3 decent steppers. I am wondering which one I should get. I am planing on using 1/4-20 threaded rod for the drive. Is this ok? The maximium travel is about 13x13x4".

Stepper 1:
http://www.halted.com/commerce/catal...=1119415781953
This is a big (~3" diamater), but seems to have ~5°/step
It says 9V 1.5 A.

Stepper 2:
This is the smallest of them
http://www.halted.com/commerce/catal...=1119415604062
5.7ohm 1.5A 1.8°/step
Cost: $14.95


Stepper 3:
Also at halted, but not listed on the webpage
should be a 1.42V 1.5A 1.8°/step (200 steps/rev) motor according to http://home.earthlink.net/~doncox/cnc/cnc.html
Cost: $6.95


Cost is a major factor in the design, and I am not sure which one to get. Pics to follow. Sorry for the low quality, they were taken with my cell phone.

P4

[2muchstuff]

Have you looked into pulling the motors out of an old HP LaserjetIII or IV. They are bigger than what you have pictured and they are 100 oz.in. motors. Check out thrift stores for old printers, they can be gotten cheap and you have parts left over.

[P-4]

What torque rating should I look for? Also, motors 2 and 3 NEMA23 size and 34 and 50 mm long respectievly. Arent those decent size for a 13x13x4?

Also, I looked at old junk printers, but none are avaible in my price range.

-P4

[H500]

I don't like the first one because it's stepping is too coarse.

Comparing the 2nd and 3rd, without having a torque curve to compare, I would choose the 3rd because it seems to have a lower voltage rating. This will allow you to get more speed out of it.

I'm guessing that you will get 100-200 in-oz of torque. This is plenty for a light duty machine.

[P-4]

Is that touque from steppers 2 and 3? I rember stepper 3 having a really stiff turn (the steps were vere present.)

More data on the motors:
Stepper 2:
Vexta PK264-01A
NEMA 23 (56x56x34mm) 6 wire

Stepper 3:
See above for data

Also I saw some others:

Stepper 4:
Portescap H425488010
3.3 ohm 4V 1.8°/step
42x42x47mm
8 Wire

Stepper 5:
Astrosyn 17PM-K401-T24V
No. 4311-01
42x42x45mm
1.8°/step

Are any of the others good?

-P4

P.S. Thanks for taking the time to respond to my questions!!!

[H500]

Both. I'm guessing at the torque from the current rating (1.5 amps). Without a torque curve, you don't really know for sure, but the current draw is and indication. In general,

-the higher the current draw, the greater the torque
-the lower the voltage and resistance, the higher the speed

choice 5 is unknown because there is not enough specs
choice 4 is versatile cuz of the 8 wires, so you can use a unipolar or bipolar drive, but seem to have a lower current draw than choice 3, so might also have a lower torque.

The other thing to consider, is how old the motors are. Magnets do demagnetize over time and lose their power, so new is better than old. Motor3 seems to be the best, but if it's really old, then who knows what condition they're in.

You should also make sure they're not one of those 3 phase motors, since they are oddball and you will have trouble finding a suitable driver.

If you're willing to pay $40, automationdirect has a ~280 oz-in bipolar motor (new). Also, take a look at hobbycnc and xylotex.

[P-4]

Is that per each motor? Also #3 is 8 wire!!

-P4

[H500]

Yes, $40 is per motor. That's actually quite cheap. It might seem like an overkill for your app, but once you have your first machine working, you will almost certainly want something bigger and stronger!

8 wires mean that you can use it with either a unipolar or bipolar drive.