Hence concludes the many months where I couldn’t get my act together to post about my projects!!
Here is a small one that I did a few weeks ago on my last visit to MIT. I spotted the chunk of aluminum (that makes up the base of this drill press) in a scrap bin. The only thing I did to it was drill two holes, so it already looked a lot like the base of something. I just had to make something to go on top of it.
This drill press is essentially a spring-loaded motor on a stick. Instead of the typical rack and pinion mechanism of larger drill presses, you just push the motor assembly down to drill, and let the spring push it back up when you’re done.
The shaft that the spring is on slides up and down through bushings that are potted with epoxy into the black plastic (I used delrin). Originally I intended to just drill and ream a nice hole through the delrin and use that as the bushing. But of course I did a sloppy job clamping things down, and the drill bit grabbed the plastic, creating a less than round hole. Instead, I over-sized the hole and potted some brass bushing with epoxy.
In general, I think that potting bushings is just a fantastic way to get well-aligned, accurate holes, without needing fancy machine shops filled with Nice Things.
The green thing in the photo below is a washer made of fleece (just happened to have a scrap), which cushions the motor assembly when the spring pulls it back up. Leather or rubber would probably work fine, too.
I drilled and tapped a hole on the end of the rod for a screw that holds the spring on. But a shaft collar might have been a nice way to constrain the spring and be able to vary its compression.
The motor is face mounted to a small plate with two screws. Its just a typical hobby motor, I’ll probably run it between 5V and 12 V. If I can’t find a wall wart, I could just power it off battery (or maybe USB!). I wish I had a tachometer to tell you how fast it runs, but probably you’ll want something that goes around 10k RPM or higher. The two round things on either side of the motor are spacers. The shaft with the spring on it is press-fit into the plate behind the motor (This is another place where you could drill an over-sized sloppy hole, and just pot with epoxy to make an accurate part). The co-linearity of the spring-loaded shaft and the motor spindle is not critical, since only the motor spindle spins.
The collet only takes 1/8″ shafts, since there are lots of micro drill bits available with 1/8″ diameter shafts. I didn’t look very hard for an off the shelf collet, since I could just make one on a lathe, but it certainly would have been nice.
There’s a slight bit of runout, but not too bad. I think I’ll try carefully cutting down the drill bit shanks so that the drill bits are shorter.