Step 1: Planning / Materials
The solution that we arrived at was to use a Harbor-Freight Pneumatic 1/8" Micro Die Grinder, and attach it in-plane with a precision linear slide rail. The Micro Die Grinder runs at 56,000 RPM and has the 1/8" collet that I needed for the PCB drill-bits.
The keep the die-grinder in-plane with the rail, we decided to mount the linear rail to a self-centering drill-press jig.
The parts list:
1.5" Square Steel Tubing - Scrap from Around the Shop
56K RPM Micro Die-Grinder Drill - Harbor Freight - $10.00
Self Centering Drill Press Jig - Harbor Freight - $6.00
THK Linear Slide Rail - $10.00
- Ebay, Search for "THK Slide" or "Linear Slide"
MDF for deck - Scrap from Around the Shop
MISC. Screws - Scrap from Around the Shop
Springs - Home Depot / Lowes - $5.00
Step 2: Build the Drill Mount and Attach it to the Slide
We removed the excess sides of the self-centering drill press jig, and sanded all the rough edges smooth. The THK rail mounts vertically along the center. We used the measurement between the holes to drill through the drill mount.
The holes are easily centered along the mount by drilling in the V in the center of the mount with a small bit, followed by a larger bit and finally using a tap and die set to tap out the threads from the back of the mount.
This is the most critical step of the process, the Drill-Mount MUST be in-plane and square with the Linear Slide.
We then attached the other side of the rail to a small section of angle-iron. We did this by drilling out four holes that I had previously marked. Get these as close as you can to square with the Linear Rail.
If your angle iron isn't square (ours wasn't), then use a square and a sander to square it up.
This piece of angle-iron will be used to mount our Linear Rail / Drill Mount to the Frame.
Step 3: Build the Frame
I won't go into exact dimensions, however you do want the drill to be forward enough from the back plate to allow for whatever size boards you would like to drill. It will also need to be high enough to accommodate the drill and have enough room to move at least 1/2" above the board to just below the boards surface.
We will also be attaching 3/4" MDF for the deck, so don't forget to allow for that in your vertical measurements.
After you cut the pieces you need (you can see how we did it below), you will need to weld them together. If you don't know how to weld see if you can get a friend to weld it for you. Failing that you can take it to a metal-shop and they should be able to do it for fairly cheap.
Step 4: Mount the Deck, Slide, and Drill
We started by cutting the Deck out of some MDF we had around the shop. We cut a notch out of it to fit around the back of the frame. We mounted the drill to the drill-mount/slide with some zip-ties that we had around the shop, and then attached the slide to the small piece of angle-iron that was welded to the frame.
We drilled and tapped a couple of holes near the middle of the upper arm and also in the drill mount and ran the springs between them. This provided the auto-return for the drill.
We also tapped and drilled to holes into the base of the frame to attach the deck to. The screws in the deck are counter-sunk (see finished pictures on next step) so that the PCB's can slide around the top of the deck easily.
End-caps were installed to keep everything looking neat.
Step 5: Finishing Thoughts
The only changes we may make is to add a handle to lower the drill. Currently you simply press down on the top of the drill which works great for now.
Our holes came out perfect, and there was absolutely NO noticeable wobble or tilt in the drill. Just straight, clean holes every time.