CNC machine

I have 5 stepper motors to start with. I don't think they are very strong, but I should be able to get a functioning model built.

The head assembly should be interchangeable. In the long run I would like to have a mill-head, a plotter (pen) and a laser cutter. Concrete extruder may be interesting like this.

http://www.instructables.com/id/Make-Your-Own-DIY-CNC/

Goal is to make the first one simple, but able to handle 2x4 plywood. Then I can cut pieces for later versions.

V-Groove bearings are pretty cheap (can be). I should be able to build something very smooth with a few of those and some 90 angle metal.

To do a really nice one would require 2020 V-Rail, but that can be a little pricey.

https://www.youtube.com/watch?v=MlR-9Uiab60

https://www.youtube.com/watch?v=5siv7DM08bw&t=34s

Positioning

Threaded Rod

About $1 per foot (3/8" at Home Depot).

I really like the HomoFaciens technique of using an angle bracket to support the weight of the mechanism and a threaded rod to position it.

Timing Belt

Only about $0.70 per ft. But kind of flexible.

Lead Screws

Best option, about $3/ft, but it's hard to find longer lengths.

Motors

Stepper

84 oz/in NEMA 17 is about $9. This would also be an interesting area for DIY.

Worm Gear + Encoder

I'm finding a common worm gear for about $1.5, but I'm not sure it's strong enough.

There are KitchenAid replacement gears that might work.

It might be possible to cut one.