[Amps] drill bits

[Peter Chadwick]

Bud asked:
 Can someone tell me how to drill small holes (for pots, 1/8-inch phone 
jacks, RCA phono jacks, etc.) in typical small aluminum chassis (plural) 
so that the holes aren't triangular?<
Firstly, start with a small pilot hole, and centre-pop the centre. Make sure the drills are sharp. If you're skilled, you can sharpen a drill on a grindstone by just holding it. I can't - I can't even guarantee getting it right with biggish drills and various patent fixtures! Clamp the material down on the work table of the drill, using some scrap wood as packing underneath the metal. Don't use too high a speed - figure on about 60 feet/minute as the peripheral speed of the drill. For very small drills (under 1/16th inch), this generally means that you can't go fast enough. I don't generally use lubricant on thin aluminium, but some people recommend it. I also find it useful to drill undersize and use a taper reamer. Generally, triangular holes come about as the result of 'chatter' when things aren't held firmly. Also, don't led the drill take charge and try to 'walk' into the hole. This can be a real problem with copper and brass, which is why it's recommended that you use drills with negative rake for those materials. I never bother, since I don't drill enough brass (except in the lathe) to make it worthwhile.
73
Peter W6/G3RZP this week