How much oz-in my steppers need?

[Ivan.Kalafatic]

Hello people ,

My first post here

I'm building 50x30 cm work area CNC router (for PCB-s) made from MDF (1" thick)

Here is image how it looks in prealpha version (only construction, without sliders)

http://www.imagesforme.com/show.php/587368_IMG9144.jpg

Get to the point..

I'm aware that Y and Z axis motors needs to be more powerful than X axis.
But still I don't have any ideas how much oz-inches (Nm) my steppers need to have.

I was thinking to buy these - KL23H256-21-8B (127oz-in for unipolar drive (DIY from pminmo.com))

But, will it do the trick? X axis will be moving only light wooden table and workpiece.

Y axis is moving wooden piece and whole Z axis gantry (tool and stepper will be weighing approx 4 kg).. so stepper for Z axis is moving nearly 3 kilos and stepper for Y axis is moving 4-4.5 kilos.

I'm using threaded rods from local hardware store - 14 mm diameter with 2 mm pitch. For my first CNC, i'm not looking for some extreme rapids.. I'll be happy with speeds like 200-300 mm/min.

I hope that here is someone willing to help..

Thanks,

Ivan

[pminmo]

It really depends on have efficent your mechanics are. 127oz should suffice with respectable efficiency.

[Ivan.Kalafatic]

It really depends on have efficent your mechanics are. 127oz should suffice with respectable efficiency.

Thanks for answer Phil (you've helped me with current chopper ).. btw what is with site (pminmo.com)? It's kinda down..


Well.. I don't have idea how much efficient my mechanics are ..
I know that I'm using M14 threaded rods with 2 mm pitch.. that is similar to acme 1/2-10 if I'm correct.. I'm using sliders like in drawer, because at the store did not had 20 same bearings..
Steppers would be connected unipolar (full step), probably at 24V (9 times higher than nominal), chopped;

I'm student, so i don't want to spend 150$ and see that motors are weak..

TIA..


(EDIT: site works, it's DNS problem)

[pminmo]

Thanks for answer Phil (you've helped me with current chopper ).. btw what is with site (pminmo.com)? It's kinda down..


Well.. I don't have idea how much efficient my mechanics are ..
I know that I'm using M14 threaded rods with 2 mm pitch.. that is similar to acme 1/2-10 if I'm correct.. I'm using sliders like in drawer, because at the store did not had 20 same bearings..
Steppers would be connected unipolar (full step), probably at 24V (9 times higher than nominal), chopped;

I'm student, so i don't want to spend 150$ and see that motors are weak..

TIA..


(EDIT: site works, it's DNS problem)

DNS on your end? As I've not noticed anything.

[Ivan.Kalafatic]

DNS on your end? As I've not noticed anything.

Yup.. sorry for false alarm..

[Ivan.Kalafatic]

Uhm.. I know that patience is virtue.. But anyone has other opinions? I appreciate pminmo's answer, Phil is experienced machinist, but I want second thought..

TIA..

[pminmo]

BTW, the bipolar half coil and unipolar rating of the motor in this video is 126 ozin:
http://pminmo.com/which-stepper-motor

[Ivan.Kalafatic]

BTW, the bipolar half coil and unipolar rating of the motor in this video is 126 ozin:
http://pminmo.com/which-stepper-motor

Yeah.. i've seen that video already.. Very nice job.. Can you tell me how much weights drill and Z construction (what is load of Y axis.. at least approx)

thanks..

[pminmo]

spindle an z together probably 4 lbs

[Ivan.Kalafatic]

spindle an z together probably 4 lbs

Pretty easy.. I have noname-made-in-china "600W" drill (costs 23$) that has 4lbs itself.. and 1.5 pound on stepper.. pound on wood/rest of construction.. 6.5 pounds.. I hope that 127 oz-inches will be enough.. If not, 185 should be enough (new bipolar drive)

Thanks again Phil

[pminmo]

You have a lot of mechanical advantage so for the rapid speeds you described in your 1st post, you shouldn't have an issue. You can always go larger without much of an issue.

[Ivan.Kalafatic]

You have a lot of mechanical advantage so for the rapid speeds you described in your 1st post, you shouldn't have an issue. You can always go larger without much of an issue.

I guess then that i'll be ordering steppers from 1st post this week or so.... Again, Phil, thank you so much!.. And yeah, Tachus42 chopper is working.. despite few burned fets )