[Zouave]

So, a little background is in order...

I have not built a CNC machine before, I am very much a newbie in this field, so please bear with me if I ask what may be obvious questions to more experienced people. However, I love reading, so if there are extensive tutorials that you found particularly useful when starting out, please, please, PLEASE link me to them, it'll help me ask better questions in the future.

My project: A CNC router, cutting primarily wood or plastic, with a working surface area of just over 4' x 8'. I am strongly considering the MechMate design, but am not yet completely sold on the linear motion setup. I don't want to reinvent the wheel, I want some honest feedback on what people's experiences have been.

My considerations: I started out my adventures in a high school machine shop, so I have a bit of a fetish for being overly accurate. Sometimes I have to remind myself that I'm doing woodworking, not precision metalworking. That said, accuracy for what I'm doing will be fairly important, repeatability as well. Speed, as always, will be a major factor in my final decision, as will cost (isn't that always the biggest part?)...

My questions:

For a project of my size (8'x4' table), are there major drawbacks to any of the primary systems people are using for linear motion (ballscrews, leadscrews, rack & pinion, etc)?

For a fairly heavy gantry, as it will be primarily steel, in line with MechMate's design, are there specific bearing systems that I should avoid or gravitate towards for something of that length? (Vee-groove, supported shaft ball bearings, supported shaft plain bearings, linear rails/guide blocks, etc.) I am assuming that over an 8' length, unsupported linear bearings will have too much flex to be even considered for my application.

For a system that is highly repeatable, what drive systems work best, and are they worth the increase in cost? As I understand it, ground ball screws have the lowest backlash and depending on the quality, the highest accuracy, but are rather pricey, rack and pinion appears to be fairly repeatable, but not as accurate, and has more problems with backlash typically, and Acme style leadscrews are somewhere in the middle. Am I fairly on the ball in that regard?

Now, while I like to keep my shop clean, I am under no illusions that this machine will not accumulate its share of dust, grime and grit. I will be taking whatever precautions I can to prevent that, but if one of those systems breaks down significantly in that environment, that would be a consideration as well.

If you've made it this far, thank you very much for reading through my lengthy questions, and any help you can offer would be very much appreciated. Thanks!

(Back to my reading...)