New Machine Build- Cheap design idea with a few questions.

[greyroot]

I'm looking to make a new desktop CNC design, but I lack a lot of the mechanical know-how for it so I'm hoping a few of my questions can be answered here. As a programmer by profession, I'll be writing my own software for this, and would like to keep the interface to the device as USB so I was looking at this: http://www.robotshop.ca/phidgetstepp...tml?lang=en-us
Easy, no mess way for me to handle the motors. I'm not worried about the slight delay that I might experience between sending messages to each motor (since theres no way of doing simultaneous commands). It will still be more accurate than me doing it by hand.

I know this will be a weak machine but as I said its tabletop. I will most likely be making this about 18"x18" and cutting through relatively thing wood and plastic (if I can).

My questions are as follows:
When it says max 1A per coil, I assume per coil is basically per stepper motor? If thats the case, I was hoping for something along the lines of http://www.robotshop.ca/rbsoy13-soyo...per-motor.html as a 12V 0.6A motor. I don't know if a torque of 84 oz/inch is enough to do anything worthwhile though? Speed is no issue for me, it can take all day for all I care.

Is a regular threaded rod & nut good enough for a DIY setup that won't be moving a lot of weight? I see things like this: http://www.instructables.com/id/SE219C4F5FEQ16W/ that make me think it'll be easy from a mechanical standpoint but I don't know if these simple unipolar motors will be enough.

Any help is really appreciated! If I manage to pull this off, I'll have a desktop CNC with no soldering that cost a little over $200 Canadian (plus a dremel, and frame but those are minor)... so around $300 Canadian in total if I'm careful.

[ger21]

While everything you're asking should work, I can't advocate any of it.

First, why spend hundreds of hours writing control software, when there are several freely available ones that have been in development for years??

Second, if you don't mind soldering, you can get a HobbyCNC drive for only a little more money that will give you far better performance than the one you linked to. Much more powerful motors are available for about $30-$40 each.

While a lot of beginner machines have been built with threaded rod, for a few dollars more again, 1/2-10 acme can be found very cheaply and will give at least double the performance.

www.hobbycnc.com
www.kelinginc.net

The problem with the items you asked about, is this. Stepper motors are rated for holding torque, when they are not spinning. The faster they spin, the less torque they have. Increasing the voltage can increase torque (up to 15-20X the motors rated voltage), but since those drives are limited to 12V, that's not an option. And the motors are also rated at 12V, which means they'll spin very slowly at best. Couple that with regular threaded rod, which needs to spin fast to get any speed, and you're at strike 3.
You could very well end up with a machine that takes well over a minute (or 2) to travel you're 18" While you say you have all day, you'll quickly become frustrated.

Now, if you're budget has no extra room, than at least you'll get a learning experience, but I think you'll end up disappointed in the long run.

[greyroot]

I was looking for a simpler solution that didn't require GCode formatted data for parts. There seemed to be more steps than I wanted getting from CAD to the machine, and I could probably write the software I needed in under a week. That being said, looking at the Hobby CNC again it seems good. What software do most people use for it?

As for what I was looking at, is the biggest issue the voltage on the steppers I was looking at? What kind of voltage should I be looking at? And what about torque? Considering I'm looking for a cheap desktop solution, any suggestions for what stepper motors I should be looking at?

[FandZ]

I'd suggest you read this post by CR. It'll answer a lot of questions for you. http://cnczone.com/forums/showthread...709#post572709


Price wise, this is what my research has pointed out.
100 to 300.. Slow and lots of slop (not good for much of anything other than plotters)
300 to 600.. Faster and manageable slop. (doing good on wood and plastics as long as you don' push it too hard)
600 to 1200.. (the best place to be on your first build. Good speed, good cuts, a little soft metal work)

1200 to??? ( so many yummy options)