Hello folks,

I want to build a small desktop CNC mainly for PCB prototyping. Now, the biggest thing is "not" to spend a lot of money, since you can get 3 piece two layer 2"x3" PCBs for $50 nowadays. I am hoping to spend less than $75 (not including motors and software). The overall size of the CNC can be ~18"x12"x15". I am not looking for a lot of power, but rather accuracy on the order of 0.01" for small circuit components.

Now, I am brewing a design for a ">90% home depot" based solution for the mechanicals. The design involves drawer slides and allthread screws. I have tested the ball bearing full-extension drawer slides in the store, and they don't have any play in the vertical direction, but have a lot of play out of the plane (which can easily be constrained):

Liberty 22-1/100 in. Full Extension Drawer Slides (2-Pack) - D80622C-ZP-W at The Home Depot


Home depot also sells pure steel ball-bearings under the disguise of door rollers:

Prime-Line Products 1-1/4 in. Steel Ball Bearing Rollers (2-Pack) - D 1502 at The Home Depot


On top of it, melamine coated particle board shelves seemed very flat and straight in the store, and you don't need to paint it:

3/4 In. x 11-3/4 In. x 97 In. White Melamine Shelf - 1605509 at The Home Depot


I hope you are following where I am going with this.

My initial trial with a 1/4 rod and a coupling nut and hardwood ended in the realization that i need a thicker diameter rod, and a different base material to make sure warping is minimum. The first stage whipped slightly as it was moving due to the 10"-cut threaded rod being bent. However, the screw/nut combination was very smooth without any lubrication. Next, I will try 3/8-16 screws.


Now, my question is , what is a realistic precision expectation for home-depot non-acme screws with coupling nuts? Can I achieve 0.01"? If necessary i can put two cascaded plastic nuts to compensate for some backlash. For 3/8-16, and 200 turn motors, the minimum step calculates as 0.00032" movement.


Thanks