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Hertel is a quality tap but you need to use lubricant when tapping. WD40 is just deodorized kerosene so it's fine for aluminum. Using something is far more important than exactly what you use.Haven't you yet built some small tap holders according to the design shown here...http://www.homemadetools.net/forum/tap-holders-26298To make things easier you can safely go to 65% depth-of-thread in aluminum. [Probably in almost anything else on a model engine; very few model threads are stressed to the point of stripping.]
So Marv, lets see if I'm understanding this right. For example: My tap drill size chart shows using a #38 (.1015) drill for the hole for a 5-40 tap. Does that give me a 100% depth-of -thread? Some % other than 100%? Then if I wanted 65% depth-of -thread I'd use a larger drill? Would I just take the called for normal size drill (.1015 in my example here)and increase that size by some percentage? And what percentage might that be? Also would this work in other materials like brass and steel?Lots of questions.
IIRC Alum only works with carbon steel taps. I've never had success with HSS taps and alum. Could be me, though. I'm sure I've said this before but, form taps. (I've been happy with Balax)Yes, you need a lubricant when tapping anything (perhaps not with Delrin)
Stan,Love it. Trouble is, if Starrett sold crayons, they'd cost $20 apiece. Mitutoyo crayons would cost $1 and last three times as long.