Building my first CNC!

[IWorkInPixels]

Hey guys, my first post here, so I'll introduce myself... my name's Tony.

I have been following the DIY scene for a while and really want a mill, laser cutter, and 3D printer, but can't afford any of the above, so I decided to build a machine that can, at intervals, be all three.

I was originally going to design it after the McWire machine and just use it long enough to print out a RepRap Mendel, but then I ordered some motors off of eBay that I thought were NEMA17 and turned out to be NEMA23.

So, now I have some huge motors with a lot more torque than I had counted on, and I guess I'll be building a much bigger mill/printer. Oh, darn...

Anyway, I was thinking about making a gantry-type mill, maybe out of MDF.

I had a couple of questions for people who have built these things before:

1: My motors are rated for 179 oz in of torque... is that enough for me to mill metal if I should decide down the line to mill metal with this thing?
2: Since this will be a mill other than a brief period up front where it will be a 3D printer, will I be able to reach a high enough speed with leadscrews instead of belts to be able to print out a RepRap?
3: I was thinking that the benefit to having a large flat stationary bed during the 3D printer stage would be that I could print out all of my parts in one go. Does anybody see any problems with that plan?
4: There were some circuit boards shipped with the motors, and I've attached pictures of them... what are these things? I know the chips are the control chips for these motors, but what's all the rest of the circuitry for? Are they the driver boards, and all I have to do is send them logic signals from my arduino, or are they something else?

Thanks for your help!

[doorknob]

Can you post a link to the specific eBay auction that you won?

[IWorkInPixels]

The eBay auction that I won

[doorknob]

The auction description states: " I will include plans for a DIY controller card based on a similar STK672-120 IC."

Did they send the plans along with the motors and the IC boards?

A quick look at the datasheet reveals that the IC can probably be used to do what you want, however it does not appear to be a microstepping driver like some of the ones that are commonly used by DIY CNC'ers.

BTW, the other components on the board look like they're probably bypass capacitors (intended to prevent voltage glitches from affecting the operation of the driver IC), and possibly also a capacitor on the IC's reset line (to stretch out the duration of a reset pulse or to activate reset after power is applied to the board). There are also a few surface-mount resistors and at least one diode - the spec sheet for the IC has a sample application circuit that shows components such as those.

[IWorkInPixels]

Yes, attached is the schematic I was sent with the motors...

And what I think I'm hearing here is that these might be what originally drove the boards, but it's a no-go for me because they don't microstep and therefore aren't accurate enough for 3D printing work?

Basically the other option I was considering was buying some RepRap Gen 3 electronics to run the thing, but I didn't know if that'd be capable of running these big motors...

So, does that seem feasible, or am I looking at desoldering these chips off of their current board and building a whole new controller for each motor?

[doorknob]

Don't read too much into my comments - while I have read about the RepRap, I haven't investigated its requirements in detail.

As far as microstepping is concerned, the combination of steps per revolution out of your motor and the pitch (turns per inch) of your leadscrew will determine the linear distance that your tool travels with each step, and so that needs to be coordinated with your intended application.

As far as the motor goes, 179 oz in is on the lower end of the motor rating range that I have seen people use with DIY CNC machines.

[IWorkInPixels]

Ok cool this is confirming some stuff for me... 179 oz in isn't going to let me mill metal with this thing (I had hoped it would because that'd be cool ), and I'll probably be strapping a dremel to it rather than a full-size router for the toolhead.

For a 3D printer, though, it's extreme overkill. I think the requirements to build a RepRap Mendel is like 50 oz in.

All a 3D printer has to do is be able to move the extruder in 3 dimensions to a specified point, and there's no resistance from the piece because you aren't actually touching the piece.

There is, however, a limit to how slow the extruder can reliably extrude an even amount of filament. Therefore, there is a low end on how fast your machine needs to get that extruder from A to B, and I'm told that most RepStrap makers have used belt drives for this reason. That's not to say that it won't work just fine with direct drive, but it's something to take into account.

So I think my next plan of attack is to get a suitable driver board, and see if I can make these motors turn at all. Toward that end... does anyone know if I can use RepRap electronics (or some other inexpensive off-the-shelf or kit driver boards) with these?

[MrWild]

The driver ICs sent are unipolar motor drivers. You have even less torque using them. The data on the sale says 149 inoz unipolar and 177 inoz bi-polar. No, there will not be enough power to do much of anything. Someone probably has cut metal with motors this weak, but it was probably a slow and tedious multiple light cut process.