New RepStrap builder in need of help

Hi guys, my name's Tony... been wanting a Makerbot or RepRap for a while now, and can't afford one... so I was thinking I'd build a RepStrap so I could pay for materials in increments and learn something about how these things work in the process!

Toward that end, I started building a McWire cartesian bot, but I don't think it's going to work with the motors I bought from eBay because they're too big and heavy (thought I was getting NEMA 17's... turns out they're NEMA 23's).



Ebay link

They also came with these boards which have a driver chip on them, but someone over at CNCZone told me that the chips are probably useless for my purposes because they don't do microstepping...



So... here's where I'm at:

I was thinking about making an Eiffel-like device, but it'd be a gantry with a fairly large, stationary build area underneath. That way when I get the thing up and running I can print a whole set (or maybe 2 or 3 sets!!!) of Mendel parts all in one go. Does anyone see problems with this plan?

Also, it's much cheaper for me to try to build the thing with a leadscrew drive for the axes, but I'm told that I will have problems with them not being able to move as fast as the minimum speed of the extruder if I do that... can someone give me more info on that?

Third, and finally... I need to drive these big honkin' motors now... will the RepRap Gen3 motherboard be able to do so? Or some other easily obtainable off-the-shelf solution? Or am I stuck trying to cobble together some sort of custom gear?

Thanks! I hope to get this RepStrap up and running soon, use it to print out several sets of Mendel parts which I'll sell to recoup some of the cost of the machine, and then refit the machine to be a laser cutter or something and use my Mendel for printing.

Oh, and one more thing... these things are rated for 149 - 179 oz in of torque depending on how you set them up, and the folks over at CNCZone said that's mighty weak if I want to ever set it up to do any milling... is that true? I mean, I wasn't planning on milling metal (YET), but it'd be nice if I could cut my own furniture parts out of 1/2" MDF on this thing...

Edited 3 time(s). Last edit at 11/19/2010 02:32PM by IWorkInPixels.

IWorkInPixels Wrote:
-------------------------------------------------------
> Hi guys, my name's Tony... been wanting a Makerbot
> or RepRap for a while now, and can't afford one...
> so I was thinking I'd build a RepStrap so I could
> pay for materials in increments and learn
> something about how these things work in the
> process!
>
> Toward that end, I started building a McWire
> cartesian bot, but I don't think it's going to
> work with the motors I bought from eBay because
> they're too big and heavy (thought I was getting
> NEMA 17's... turns out they're NEMA 23's).
>
>
>
> Ebay link
>
> They also came with these boards which have a
> driver chip on them, but someone over at CNCZone
> told me that the chips are probably useless for my
> purposes because they don't do microstepping...

You don't need microstepping if you are using threaded rod as a leadscrew, you will have plenty of resolution. Reprap machines only need 0.1mm resolution. Milling machines need more but with a 200 step motor and a lead screw pitch of say 1mm for M6 studding that would give 5 um per step.

>
>
>
> So... here's where I'm at:
>
> I was thinking about making an Eiffel-like device,
> but it'd be a gantry with a fairly large,
> stationary build area underneath. That way when I
> get the thing up and running I can print a whole
> set (or maybe 2 or 3 sets!!!) of Mendel parts all
> in one go. Does anyone see problems with this
> plan?

Probably OK if you use PLA. If you ABS you would need a heated bed, which if it is large will need a lot of power. About 1kW per square meter just the maintain temp and several times that to warm up in a reasonable time.

>
> Also, it's much cheaper for me to try to build the
> thing with a leadscrew drive for the axes, but I'm
> told that I will have problems with them not being
> able to move as fast as the minimum speed of the
> extruder if I do that... can someone give me more
> info on that?

You will probably only get about 6mm/s which is very slow for a reprap machine. If you use a stepper based extruder you can extrude as slow as you want, but it will take a very long time to make anything. For example, a Mendel would take about 240 hours.

>
> Third, and finally... I need to drive these big
> honkin' motors now... will the RepRap Gen3
> motherboard be able to do so? Or some other
> easily obtainable off-the-shelf solution? Or am I
> stuck trying to cobble together some sort of
> custom gear?

The motherboard doesn't drive the motors directly so it can drive any size motors provided you have stepper drivers to match and they have step and direction inputs.

>
> Thanks! I hope to get this RepStrap up and
> running soon, use it to print out several sets of
> Mendel parts which I'll sell to recoup some of the
> cost of the machine, and then refit the machine to
> be a laser cutter or something and use my Mendel
> for printing.
>
> Oh, and one more thing... these things are rated
> for 149 - 179 oz in of torque depending on how you
> set them up, and the folks over at CNCZone said
> that's mighty weak if I want to ever set it up to
> do any milling... is that true? I mean, I wasn't
> planning on milling metal (YET), but it'd be nice
> if I could cut my own furniture parts out of 1/2"
> MDF on this thing...

That is typical torque from a NEMA23 and certainly enough to drive a fine pitch lead screw to do slow milling. Even with a large pitch leadscrew you will be able to mill wood and plastic but you will probably need more torque for metal.

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