I used a dremel this time instead of a router, since the router was pretty much overkill for engraving anything. I made a mount for the dremel by cutting up the little plastic guide that comes with it. It has an approximate O.D. of 1″ and acts as a nut that you can clamp with a shaft collar, and still unscrew the dremel from the mount if you need to get it out. I welded the shaft collar to a stainless steel bracket.

I haven’t made any boards yet to see if the dremel has much z-axis play.

There’s nothing special about this machine electronics-wise. Since I have NEMA23 steppers and 16TPI lead screws I don’t need a really high voltage drive or anything special. I’m using a 24VDC linear power supply with two automation direct stepper drives and one from Schneider. I didn’t connect the home and limit switches as I don’t think they have much value on machines this small. It’s a lot of work to do proper limit switches that disable the drive and signal the controller that a limit has been reached. Also to have home and limit switches on each axis you need two parallel ports. TurboCNC, being run in DOS, can only use the onboard parallel port so you can’t use PCI parallel port cards with TurboCNC. Only Mach3 can recognize inputs on the extra card since it’s address will map outside of the legacy range.

I used a NUD4001 constant-current LED driver from ON Semiconductor and some OSRAM SideLEDs. The NUD4001 is really quick and easy to implement as it only requires an external resistor to set the current level. The unit is fused, and powered by a 9V AC/DC wall wart. I tried a couple different colors, but this amber looked the best.

As a side note, I really like using ON semiconductor parts. They have excellent datasheets that usually have really good examples.

I found some mechanical engraving bits at Think & Tinker which is actually here in Colorado at Palmer Lake. Their URL descriptor says they offer “Instrument and PCB prototyping equipment”. They also sell carbide engraving bits, and the particular one I selected was the 60° cutter, part number #EM2E8-0625-60V. The bits came in a nice container and are labelled as having a 0.005″ tip. The shipping was also wicked fast. Granted, it’s only a few hours away from my location but I ordered them and got them in the next day.

I’ve only cut one board, but I’m really happy with the results. I successfully achieved 0.008″ isolation between the pads of the devices, and now I can finally route traces inbetween the pads of 0.1″ headers. I couldn’t do that before.

Most of the machine is made out of either aluminum or acrylic. These materials are both easy to work with when all you have available is various hand tools and a drill press with a cross slide vise. The motors are NEMA 23 high torque, the threaded rods are 1/2-10 precision ACME and the nuts are anti-backlash. This results in pretty decent X-Y movement. I made the slides from extruded aluminum profiles available at the hardware store and some strips of Teflon.

I made all of the electronics that support the machine. I made the optical home and limit switches, as well as both parallel port interface boards. I also assembled the stepper motor drivers and built power filters/regulators for the input to the stepper motor drives on all three axes. This prevents inductive feedback spikes from the motors ruining the stepper motor control ICs. I need this because I’m running the motors at 48VDC and the controller IC has an absolute maximum voltage rating of 60VDC. I also wanted to keep any switching noise and voltage dips from the switch-mode power supply out of the stepper drives. Each filter has a FET-regulated output that clamps the voltage and then sends it out to some big capacitors to prevent the voltage from dropping.

The parallel interface boards completely isolate the controlling PC from the drives and other electronics. Buffers handle all the appropriate levels and opto-isolators keep the ports safe.

I’ve run it extensively with TurboCNC, but I don’t get any of the limit and home functionality because TurboCNC only supports legacy port addresses, and most parallel port PCI cards can’t map to legacy addresses. This leaves me with only the one on-board parallel port, which is mostly used up by the 3 axis step and direction signals. It works in Mach3 CNC, but I can’t afford to buy that program right now. So I’ve used it in evaluation mode for doing simple text engraving on plastics and acrylic. Oddly enough I couldn’t get it to work at all in Mach2. The pulse train output to the stepper drives was inconsistent enough that the motors would stall. I even tried it on a few different computers, one of which was a brand new XP install.

The machine mostly cranks out PC boards thanks to Eagle CAD and PCB2GCode. I’ve made quite a few since the machine was finished. It does a pretty good job, and holds flatness to a couple thousandths. It’s enough to get routine 0.020″ isolation on traces and pads, and clean 0.012″ trace widths. It’s a bit slow because of the low-buck slides, the motors stall if I speed it up much. It’s not exactly a high precision machine, so I can live with slow.

I’ve got some better parts since I built this one, and I’m planning on building another one with much better accuracy in the near future. This machine won’t handle the fine traces necessary to make boards with the newer components.

Here’s a video of the machine in action:

You can see more videos at youtube: imsolidstate’s CNC machine