|Power Feed Prototype on a Bread Board|
Power feed is generally pretty useful, and a Mini Mill model can be had for about $150 from LittleMachineShop.com, but as usual, I want more than an off-the-shelf model could provide. I'm making some part for my CNC router and will have to do repeated passes to a specific position. Initially I was going to rig-up some sort of adjustable limit switch, but after some experiments discovered that they are not very repeatable (at the leas the ones I had). A stepper motor, on the other hand, could be programmed to stop after a predefined number of steps. I didn't want to do a full CNC conversion, so I decided to go with a simple microcontroller-driven driver that would let me set 0-position and then jog the table to that position multiple times.
|NEMA32 Stepper Motor and Driver|
Two evenings later i ended up with a working prototype (shown in the first picture). At the core of the power feed is Texas Instruments MSP430 microcontroller (MSP430F2132), NEMA 32 stepper motor and an inexpensive stepper driver off eBay. So far I think the whole things costs about $80-$90 (without enclosure, hardware etc.)
Although the prototype works slightly different (I didn't have the right switches), in the final version the potentiometer will set the speed (the MCU reads the value and maps it to a specific step frequency); the large black switch starts the movement in the direction it was pressed. Short press will start "auto jog" and holding it for more than about 1 second will go into manual mode (i.e. the table stops when the switch is released). The little red button is used to stop the table (if pressed briefly) or to set the "home" position when held for more than 1 second.
I've tested the current version on the mill and it worked pretty good at low speeds but the motor missed a steps at a anything larger than 200 RPM. This gives me speeds of up to 10 IPM (I have 20 TPI screws), but I imagine that with at better driver the stepper will do much better. This weekend I am planning to make the motor mount/enclosure and build a more permanent circuit on a proto board. I will post the schematic and the source code on the final design is debugged.