[Methias]

Hi,

I'm going to get myself 3 steppers for a DIY CNC machine for PCB milling and light alu milling.

I have a choice of the following steppers:
Option 1)
Motor,stepper,hybrid,57mm frame,1.8deg. step angle,2.3V,101Ncm holding torque
Cost/item Brand Frame Size Step Size Holding Torque Num Wires Rated Volts Rated Current Shaft Size Length
R 652.19 ($83.61) RS 57mm 1.8° 1010mNm 4 2.3Vdc 2.8A 6.35mm 51mm

Option 2)
Motor,stepper,hybrid,57mm frame,1.8deg. step angle,2.5V,126Ncm holding torque
Cost/item Brand Frame Size Step Size Holding Torque Num Wires Rated Volts Rated Current Shaft Size Length
R 671.27 ($86.02) RS 57mm 1.8° 1260mNm 4 2.5Vdc 2.8A 6.35mm 56mm

Option 3)
Motor,stepper,hybrid,57mm frame,0.9deg. step angle,2.5V,126Ncm holding torque
Cost/item Brand Frame Size Step Size Holding Torque Num Wires Rated Volts Rated Current Shaft Size Length
R 742.92 ($95.12) RS 57mm 0.9° 1260mNm 4 2.5Vdc 2.8A 6.35mm 56mm

Option 4)
Motor,stepper,hybrid,57mm frame,1.8deg. step angle,3.2V, 189Ncm holding torque
Cost/item Brand Frame Size Step Size Holding Torque Num Wires Rated Volts Rated Current Shaft Size Length
R 982.30 ($125.93) RS 57mm 1.8° 1890mNm 4 3.2Vdc 2.8A 6.35mm 76mm

Option 5)
Motor,stepper,hybrid,57mm frame,0.9deg. step angle,3.2V,189Ncm holding torque
Cost/item Brand Frame Size Step Size Holding Torque Num Wires Rated Volts Rated Current Shaft Size Length
R 984.01 ($126.15) RS 57mm 0.9° 1890mNm 4 3.2Vdc 2.8A 6.35mm 76mm

Which of the above would be the best bet to get? And the difference between 1.8 and 0.9 deg steppers?

[pminmo]

It depends on the mechanics of the machine, rotary to mechanical conversion efficiency, cut footprint, gantry or table, etc. Here is a video on two different motors that might help get you a datapoint: http://pminmo.com/which-stepper-motor

Ncm to OZin is 1.416.

[Methias]

Okay so there is no simple answer .

The idea is to have a cut footprint of no greater than 12" x 12" (Maybe even smaller).

I would assume that the mechanical efficiency wont be amazing since I plan to use easily obtainable items (which rules out high quality lead screws), most likely a hardware store type design using skate bearings, alu angle, MDF and threaded rod (I still need to do more digging for reasonably priced lead screws and nuts to see if I can afford them). The spindle will be a Dremel 300. Every attempt will be made to get it as aligned and smooth running as possible. As for the gantry or table design. Not sure which option yet. While I am trying to build this machine as cheaply as possible I don't see the point in spending a hundred or so dollars less and getting something that wont do the jobs reasonably, in the end it would be a waste to skimp too much.

The purpose of the machine is to mill PCB's for me, engraving, and mill parts for robots from perspex and aluminum. The robots won't be large beasts so I shouldn't need a huge cutting area. A smaller cutting area should also mean I would have an easier time of getting the machine stiff and accurate (Please correct me if I am wrong on any of these points).

As for the other electronics (in case it makes a difference in the choice of the motors) I'll be using a chopper drive (with 1/2 step ability) with L297/L298N(The L298N will only run up to 2Amps per output, using them in parallel will let me get 3Amps continuous). There will be 3 of these boards and a breakout board with limit switches for each axis and support for home location. All this lot will be controlled via PC running EMC. The PSU I will need to build, prolly something like a 30v 15amp supply.

[timber_MG]

Another South African joins the fray ;-).

Forget about RS Components for Stepper motors. Kelling will ship in a flat rate box which comes out quite reasonably. Use the money saved on motors and rather spend it on a lead screw, nut and bearing end support kit off ebay (Widgetmaster for instance has a nice kit going at the moment though there are others that may suit your needs).

If you want, I have a built up and tested HobbyCNC 4 axis board and some Keling motors that would get you up and running very quickly. The low backlash and improved mechanical operation of the ACME screws and nuts will make the machine not only much more accurate, but would also be much less of a hassle, faster and perhaps stand a chance at cutting aluminium beyond just engraving.

[pminmo]

Keling has several motors that would run it nicely. Look at their 8 wire nema 23 motors.

[nessatse]

I have to agree with timer_MG, Keling is your best choice if you are shipping to SA. I paid around R1300 (inc shipping) for three of their 282oz-in steppers last year.

PS - Does anyone know a source for ACME/Trapezoidal screw in South Africa? Shipping costs plus the risk of getting bent rods make this a non viable import item for me.

[timber_MG]

I have some KL23-276 steppers surplus that I offered him with an assembled HCNC Pro.

I have been looking for trapezoidal screw as well, but only found some at pricing that makes me look straight to China for ballscrew. I once bought a 1m length with steel nut at Screwman here in Pretoria, but the backlash and poor alignment of the nut made me think twice. Cncdirect.co.za has decent pricing on rack and pinion and many other components, but I cannot help but envy the cnc builder in the states.