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

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




Srtraight is what it takes.

The tap takes care of the taper.

It's the thread depth which "tapers", not the hole.

HTH,

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."

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

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

On Thu, 23 Mar 2006 12:47:17 -0500, Jeff Wisnia
wrote:

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




Srtraight is what it takes.

The tap takes care of the taper.

It's the thread depth which "tapers", not the hole.

HTH,

Jeff

Both the major and minor diameters taper on my NPT taps, Jeff.

Don Foreman wrote:
On Thu, 23 Mar 2006 12:47:17 -0500, Jeff Wisnia
wrote:


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




Srtraight is what it takes.

The tap takes care of the taper.

It's the thread depth which "tapers", not the hole.

HTH,

Jeff


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.)


--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."