My Homemade CNC Machine.

I am designing and building a homemade CNC machine. It will be a "Proof-of-Concept" project, and I will be using it as a learning tool, first and foremost.

I will attempt to use this blog will track my progress throughout the project.

Projected specifications as follows.

I will be using a stationary gantry frame comprising Y and Z axis motion systems, that straddles a 12X16 inch X axis table. The frame will be constructed from HDPE and Aluminum.

The machine will have a 16"x12x6" (X.Y.Z) cutting envelope. A 4th axis (A) will be considered as a future upgrade if I can find a really bitchin rotary head somewhere really cheap.

The spindle will be powered with a Dremel through a 225-01 flex shaft. The 225-01 flex shaft used to be a straight aluminum 10mm tubes with knurling near the ends, but recently, Dremel changed it to add a plastic housing and soft fingergrips. I have two of the old style which should mount much better than the newer style.

I am actively searching for a good encoded DC motor to use in a true closed loop speed circuit.

The X and Y axises will be driven with NMB Minebea PM55L-048 unipolar Stepper Motor, and the Z axis will be driven with a NMB Minebea PM42L-048 unipolar Stepper Motor.

The motion control system will use ACME screws on all three axises. I will use urethane nuts and spring tension assemblies to attempt to reduce backlash.

I am currently using ExpressPCB and ExpressSCH to design and develop the circuit boards and schematics. I will be doing my own etching and drilling, and plan to add solder mask and silkscreen layers to the boards. Nearly all passive components have been salvaged from old circuit boards.

The preliminary schematic design is nearly complete, after about a billion revisions. Nothing is in stone yet, so I keep altering the design.

I'm pretty sure I'll be using the StepGenie IC. It's a dedicated PIC, sold online, that is supposed to be a replacement for the Alego UCN5804B, which is a hobbyist favorite.

The StepGenie is slightly better than the 5804B, because they took the driver section outside the chip, allowing the use of much larger motors. I'll be using IRF540 HEXFET Transistors, which is good up to 100V@33A with a proper heat sink. Plenty for my application.

The control section will be isolated from the printer port with Opto-Isolators.


More later...