> > You can get away with using
>> just a taper tap for a through hole in relatively thin material.
>
>Through holes, use a gun tap. And don't back off. The gun tap pushes the
>chips forward, so you you tap in one pass.
That's a spiral fluted tap, right? They don't work as well in
non-ductile materials, which don't form such long chips.
>One instructor I had always used a gun tap in blind holes, also. He did
>half the hole with the gun tap (no backing off), then removed it, blew out
>the hole, and finished with a plug tap.
>
>> Good cutting fluid is a must when tapping.
>
>Except in cast iron. Always tap cast iron dry or the stuff can crumble on
>you.
Hmm. Many of the cutting fluids I've used claim to be suitable for
tapping cast iron. I don't tap many holes in cast iron, so I don't
have any experience.
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