I have threaded internal NPT threads both on straight and on tapered holes. You
remove less metal with a hole that is tapered, so you wear your tap less and
also it's easier to turn the tap. But on 16mm aluminum (britspelled "-ium") it
wouldn't be that different. If I were doing this, I'd use kerosene for cutting
fluid.

GWE

Randy Replogle wrote:

On Thu, 23 Mar 2006 22:34:55 +1100, "Simon"
wrote:


Hi, I'm cutting a 1 1/4 NPT thread in some 16mm thick aluminium. My tapping
chart says 37.5mm hole, I'm wondering if I should use a tapered reamer on
the hole first? Or should I just cut the thread in the straight hole?

thanks

Simon




They tell me that there are tapered reamers for this but I've never
used one.
Randy Replogle