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
Srtraight is what it takes.
The tap takes care of the taper.
It's the thread depth which "tapers", not the hole.
HTH,
Jeff
They tell me that there are tapered reamers for this but I've never used one. Randy Replogle
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:
Both the major and minor diameters taper on my NPT taps, Jeff.
Argh! I'll fall on my sword. I didn't say what I meant.
I was remembering having worked in a place where we tapped 1-1/4" and
1-1/2" female pipe threads in big runs of cast iron fittings and always just used straight drills to size the holes before tapping.But, Machinery's Handbook does say, "To secure the best results the hole should be reamed before tapping with a reamer having a taper of 1/4 inch per foot."
Jeff (Never too old to learn something.)
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.