Minimum cost CNC/3D printer?

I am looking to make a 3D printer and I need a few questions answered.  A) How can I convert a sketchup or solidworks model to G-code
B) how can I feed that to an arduino uno line-by-line
C) how powerful does a laser have to be (when well focused) to burn wood or paper/thin plastic (black paper, of course)? Not cut the wood, just make a visable surface darkening, but cut the paper/plastic?
D) what is the simplest method to make a miniature extruder? my printer will have very little torque and size, not enough for the glue gun one, not my arduino enough IO outputs for a stepper.

Answers to any questions are appreciated. 

David971 year ago
I am actually trying to do somthing simmalar. I am trying to build a 3 axis CNC for $250 (without computer). I have found some things that may be usefull...

For the awnser to question A, I have found an instructable on how to convert sketchupfiles to g-code here.

I am also waiting for my grbl sheild to arrive. The grbl is a sheild that plugs ontop of an arduino board and converts it to a 3 axis cnc controller. You can get it here.

Another thing that may be usefull is the shapeoko plaform. It may be good if you dont want to desinge your own.

Hope this helps, David.
jduffy54 (author)  David971 year ago
Thanks for the converter, but I don't need a platform, nor an arduino shield. I already have some 2003 stepper drivers, and an H-bridge for the DC motor. For the platform, I'm using a scanner for the Y-axis, a printer for the X, and a disk reader carriage for the Z. It was REALLY easy to put together, and accurate enough for me. Anyway, the main two things I needed answers for were the G-code and laser, so thanks for that.
rickharris1 year ago
There is no real way to assess lowest cost as much depends on what you already have and what you can get.

I doubt you will be looking at less than 100usd even with a lot to select from.

There's a lot of software out there to convert to G code although I am not aware of any ‘ruin software most people buy commercial step per drivers.

Your results will be as good as your mechanical construction is.

jduffy54 (author)  rickharris1 year ago
I was mainly asking about the laser or extruder. The G code thing only needs to be able to feed it over serial one line at a time, and not sure what you mean by 'ruin.
Sorry sent from my tablet and the keyboard is a bit small.

'ruin = Arduino

A few watts will charr or mark wood and paper BUT the lower the wattage the longer it takes. In practical terms if all you want is to mark the surface in a reasonably quick time I would think your going to need 15 - 20 watts.

Have a look at the commercial lasers and you will see they are around 30 to 80 watts and that cuts wood and paper.

What do you want to extrude?

A ram, a heater able to get the tube up to 150 deg C minimum (if extruding thermoplastic) and a tube with a piston is all you need - these can be manufactured easily at home.

jduffy54 (author)  rickharris1 year ago
Wasn't quite expecting such high power for that... I know a well-focused 1W laser can mark wood slightly, (albeit slowly, but that's fine), so I doubt I need >2W, plus, for the most part the laser will then cost more that every other part X10, and this is really designed to be absolute minimum cost, Plus, I don't have very extensive manufacturing capability, so even an extruder wouldn't be easy.