Newbie- Stepping into the CNC world...Directions needed.

[Regalrip]

I have delved into the world of CNC and am planning my first CNC Milling machine. Read up on the various parts and build and would like some assistance on this matter.

The plan is to build a basic machine based on the Tom McWire CNC build that I want to use to with a dremmel to cut a wooden shape for vacuum molding and creating pc boards.

My machine construction is well on its way and I am planning on ordering,
Torque Nema 23 Stepper motors or Torque Nema 17 Stepper motors. Still deciding.

My main question is what electronics should I purchase to drive this.

The challenge is that I want to use this build as a stepping stone into cnc, and then upgrade or use this to build a 3d printer or at least try. Ie extruder working on a cnc model.
Based in the Uk, budget build (but thought it might be worth to get decent motors and electronics), so I would like to ensure that when I buy the electronics that this can be used further.
The other thing is that I would like to setup the basic machine as soon as possible.

ANY assistance in this matter would be greatly appreciated.
Thank you in advance.

;-)))

[Jesse B]

Did you want to purchase or build your drivers? How much were you looking to spend?

[Regalrip]

Thank you for the reply.

I ended up buying the following electronics.

1x Arduino Mega (always wanted to play with it, he he)
3x Stepper Motor Driver A4983 Carrier with Voltage Regulators (coolcomponents.co.uk)
3x M57STH76-2808S High Torque Nema 23 Stepper motors

Hopefully I can use this to run the machine for a start, then I can Create some new stepper drivers if need be. Will post my findings and hopefully a few completed pic's once all is up and running.

Although I will be attempting a bigger machine once I have the experience of this first learning build & playing with it. Would need a larger cutting size for my next project.

Thanks

[Regalrip]

Finally finished with the mechanical side of the the project, quite pleased with the outcome.

Now I am having a bit of trouble with the electronics.

Wired all 3 Pololu A4983 stepper motor driver, Carrier with voltage regulators to breadboards. Connected all the Step/Dir/EN to Digital outs on the Arduino.

Now I am unsure of the connections on the Stepper motor and would appreciate some guidance on this, don't want to fry it at my first attempt.

I have the M57STH76-2808S Nema 23.
http://www.motioncontrolproducts.co....TH76-2808S.pdf

From the Diagram I can see there are 4 coils. On the driver board we have 4 outputs. So do I connect 2 coils in Serial, don't think I can connect in Parrallel as the driver board can only produce 2A per coil?
http://www.pololu.com/file/0J199/a49...translator.pdf

Then the Voltage for the stepper is 4V, Can I connect this directly to a 5v supply from a ATX power supply? or would I need to add a component to lower the voltage. As the Stepper driver board runs on 5V I take I can connect all up to the same rail.

A quick breakdown of the connection or any help would be appreciated

[Jesse B]

You'll want to go Bipolar series. Wiring it as parallel would require a constant 4A per motor, which exceeds the limit of the chip, while Series only requires 2A. However, the problem with wiring in Series is that it shoots the Inductance wayyy up to 6.4mH. This means that for ideal operation, you'd need an 80v power supply. Mind you, running lower would work just fine. A 48v power supply I'm sure would run pretty well.

[Regalrip]

Originally Posted by Jesse B You'll want to go Bipolar series. Wiring it as parallel would require a constant 4A per motor, which exceeds the limit of the chip, while Series only requires 2A. However, the problem with wiring in Series is that it shoots the Inductance wayyy up to 6.4mH. This means that for ideal operation, you'd need an 80v power supply. Mind you, running lower would work just fine. A 48v power supply I'm sure would run pretty well.

Jesse, How would I calculate the required voltage, looking at the specs on the driver board the Vmot inputs rates (8 – 35 V)?

[Jesse B]

Originally Posted by Regalrip Jesse, How would I calculate the required voltage, looking at the specs on the driver board the Vmot inputs rates (8 – 35 V)?

To calculate the ideal voltage for your motors, you just need the Inductance of the motor:

32 * sqrt(Inductance).

If the inductance is 6.4mH...

32 * sqrt(6.4) = ~80.95V

However, if your driver board can only handle up to 35v, then you'll just want to feed them 35v. The motors should still perform just fine on that voltage. Note that power supplies can usually be adjusted +/- ~10%, so if you get a 36V power supply you could turn it down a little.

[RomanLini]

I'd like to make a point that that is only the "ideal" voltage for VERY HIGH SPEED USE.

If the machine is going to be used primarily for low to medium cutting speed then the "ideal" PSU voltage is much lower. I recently lowered my PSU voltage from 40.5v to 33v with significantly improved performance all round.

Provided that the machine does not miss steps when used at it's highest typical speeds then a lower PSU voltage offers the best performance because it will have much reduced motor resonance.

Be wary of some of the gung-ho attitudes of people thinking the highest possible PSU voltage is best, and the lowest possible motor inductance, then you find them on the "how to build resonance dampers" thread trying to fix their machines up...

[Jesse B]

Originally Posted by RomanLini I'd like to make a point that that is only the "ideal" voltage for VERY HIGH SPEED USE. If the machine is going to be used primarily for low to medium cutting speed then the "ideal" PSU voltage is much lower. I recently lowered my PSU voltage from 40.5v to 33v with significantly improved performance all round. Provided that the machine does not miss steps when used at it's highest typical speeds then a lower PSU voltage offers the best performance because it will have much reduced motor resonance. Be wary of some of the gung-ho attitudes of people thinking the highest possible PSU voltage is best, and the lowest possible motor inductance, then you find them on the "how to build resonance dampers" thread trying to fix their machines up...

I really should start mentioning that, thanks for reminding me.

I did say at the end 35v would work fine, however