Introduction: A Simple Machine for Drilling Stand-offs
I make lots of electronic boards that require stand-offs for mounting. I like to make these out of Delrin rod, but drilling out the ends 1/4" rods by hand with a tiny drill bit for a #2 screw isn't easy, and using a drill press isn't much help either for a variety of reasons. After considerable contemplation on how to make this task easier, I came up with this machine, utilizing available parts at hand. I made it at TechShop over the course of an evening, scrounging almost all of the materials needed from scrap. In fact, the only thing I had to buy was some screws for mounting to the linear slide bearing block. It may not look fancy, but the final result works well, allowing me to do nearly 2 stand-offs per minute with minimal effort required.
Step 1: Take Apart an Old Cordless Drill
The first step for me was disassembling an old cheap cordless drill, and removing the trigger switch and motor/gearbox/chuck assembly. I was lucky enough to already have a 6" linear rail with a bearing block which I'd actually received for free as a sample. For this application, a single rail would suffice. My inspiration for the actual design was an old nut cracker I remember using as a kid. The concept is simple, the drill motor is mounted at one end and moving a lever causes the stage to slide, parallel to the axis of the drill: effectively a horizontal drill press with a stationary bit.
Step 2: Mounting the Drill
I carefully selected a base large enough, and then a block of wood which would raise the drill motor to a height which would allow me to mount the jig on top of the stage and line up with the dowel. I noticed a single protruding tab from the motor assembly which would be useful for assisting with locating the motor and preventing movement from motor torque. Rather than notch the block of wood, I decided to cut a notch in a piece of scrap 1/8" ply and glue that on top of the block for the mount.
I recommend starting off by drawing a centerline on your base to assist with locating the rest of the mounting points (something I didn't do).
I carefully glued and screwed the motor mount block to my base. and then mounted the motor with a short length of pipe-strapping tape and a couple screws on each side. This actually secured the motor quite well, but I later realized that the unsupported plastic gearbox assembly gave my drill bit at the end of the chuck way too much play. The bracket seen on the right gets added at a later step to address that problem.
Step 3: The Sliding Stage
With the motor mounted, I put my production bit in the chuck and selected a location for the slide mount along the center axis. The stage jig was made from a small base of 3/8" wood with a narrow block of wood mounted on top of that (so that the stage mounting screws could still be accessed).
The simplest way to make sure that everything ends up being aligned correctly is to basically machine the hole for the dowel in-place on the slide. I started with a 1/4" Forstener bit, which matched my dowels, and drilled a hole to the depth of the dowel length simply using my hand to push the stage/jig against the drill.
With the primary hole drilled, I removed the stage from the slide and moved over to a drill press where I used a 5/8" Forstener bit to drill a hole carefully located just above the first hole so that it intersected the first hole just above the lower hemisphere. I then used a saw to cut away the front top half of the block to reveal the carefully machined trough to hold the dowels and provide access for insertion/removal.
Step 4: The Handle and Linkage
I used a couple pieces of aluminum angle to create a bracket for the control lever which was made from a scrap of 12 gauge steel. I inadvertantly got lucky when installing the brackets and one turned making it narrower at the end. This had the effect of providing an automatic friction stop to prevent the handle from falling forward.
A piece of aluminum scrap from someone practicing a T-weld provided a bracket for the back of the stage to attach the actuating linkage, and also another bracket to stabilize the drill bit and possibly provide any fine adjustment needed. I simply held the bracket by hand, against the base, and then pressed it against the bit to drill a hole at the proper height. A couple small L brackets helped attach this to the base and aren't really visible in the pictures.
I little eyeball guess work and trial and error quickly derived the ideal linkage length and control arm mount position. I drilled a couple holes in the lever and mounted the trigger assembly from the original drill using a couple zip ties. This was wired up with some scrap to the motor and a terminal for connecting to a small 12v battery. A little bit of foam pipe insulation and duct tape finished up the lever with a comfortable handle. The MOSFET and heat sink for the speed control can be seen dangling a bit from the handle in the picture.
Step 5: Put It to Use
The final machine works by simply laying a dowel in the slot on the stage, and holding it down with one hand, while using the other hand to squeeze the trigger and move the lever, pushing the dowel into the drill bit and drilling out a nicely centered hole. Holding the dowel to prevent it spinning by hand is a bit challenging, but a pair of vice-grips can also be easily used. Once one end of the dowel is drilled out, the dowel is easily flipped around to drill out the other end.
A slightly more advanced version could feature a second linkage mounted higher on the control handle with a spring system that could be used to automatically hold the dowel and allow for single handed operation.