small accurate holes

dcaster · 2005-03-11T06:57:19+00:00

A fair bit back, Jim Rozen described a drill press for Printed CircuitBoards that sounded like a good design. A microscope with a cross hairto align the board, and a drill that comes up from the other side todrill the hole.So the first step was to figure out what to use for a spindle for thedrill press and how to drive it. My choice was a small trim routerthat HF sells as low as $20. The second thing was to make a new colletto hold carbide PCB drills.Measured the angle of the existing collet as 30 degrees ( 15 degrees onthe lathe compound ). But how to get an accurate hole with very littlerun out.Well the first problem was to get an accurate diameter hole. A 1/8inch bit makes a hole that is too large. And the next size down was toosmall. So googled on this group for ideas and tried to make a smallboring bar out of a broken drill. The drill was about a 3/16 drill andI never did manage to make a decent boring bar.Okay a D drill will do it and I had several broken PCB drills. Andfortunately a small ( about 4 inch )diamond wheel. Much better luckthan I had trying to make a boring bar. Got one collet drilled out,but had guessed at the outside diameter. Bad idea. Made anothercollet and nearly got it right. I left a little straight bit at thesmall end of the taper that was just a little too big in diameter. Sopushed a broken PCB drill in and then chucked it in the drill press andfiled that to fit. Also smoothed up the tapered part with the file.It seemed to be true before I did that, but it couldn't hurt.So now I more or less have a collet. I will have to buy a slitting sawto put a slit in it, but the hole is tight enough to hold a PCB drillnow. Can't see any run out. I think that part will work. Dan