TAPERED PIPE THREADS

Geoffrey Cox

unread,

Dec 18, 2001, 8:40:54 AM12/18/01

to

This is most likely a dumb question... Using the hole wizard I place a
1/8-27 npt threaded hole through a .120 thick surface. In this case I leave
cosmetic thread off. When I dimension the hole in the drawing view it shows
up as a .366 dia hole. When you really zoom up on it you see another circle
that is .374 dia. In the hole wizard dialogue box a .332 dia hole is called
out for. (which is correct according to my old fashioned drill/tap chart.)
Does anyone have any idea what is going on? I think it might be related to
the "tapered" thread, but you can not drill a tapered hole.

We laser cut these parts, so we need the correct diameter on the DXF file
for the CAM program to process. I don't like the idea of manually drawing a
circle in the drawing and then hiding the incorrect part edges. You might
say that I should just use the "legacy" tab and enter the diameter that I
want, but I like the idea of using the hole wizard to tell me the correct
diameter for a given tap size.

Any thoughts on this?

Thanks

Adam Reif

unread,

Dec 18, 2001, 7:22:36 PM12/18/01

to

> 1/8-27 npt threaded hole through a .120 thick surface.

Not a whole lot of material for the taper to work with, but I assume you
have your reasons :)

As far as deciding on a tap/drill size the best results will result from a
real world test, it is the sure fire way in the cases of tapered pipe
threads.

And - since your material is so thin, a small difference in taping depth
will make a huge difference on where the fitting sits.

Adam.

Jeff Cox

unread,

Dec 19, 2001, 4:49:09 AM12/19/01

to

Thanks for the info,but, the material thickness and thread size are dictated
by our customer. You did not address my question. Why doesn't the hole cut
through by the wizard match the hole size given in the wizard parameter
table?

"Adam Reif" <1adam12...@inforum.net> wrote in message
news:3c1fd...@news3.calweb.com...

Dave H

unread,

Dec 19, 2001, 10:08:14 AM12/19/01

to

Jeff,
Because the tap is tapered, it starts with a smaller tap drill diameter and
makes it larger as the tap gets deeper. The diameter at the surface where
you started will get much larger as the tap gets deeper. On a thin piece of
material you no longer see the smaller diameter since it no longer exists at
the tip of the tap.
Dave

"Jeff Cox" <geof...@home.com> wrote in message
news:poZT7.78783$py4.36...@news2.nash1.tn.home.com...

Geoffrey Cox

unread,

Dec 19, 2001, 10:14:40 AM12/19/01

to

Thanks Dave,

I thought that something like what you described is what was going on. I
just deal with it....

Jeff
"Dave H" <da...@millenniumautomation.com> wrote in message
news:9vqagu$q...@dispatch.concentric.net...

est3428

unread,

Dec 19, 2001, 12:44:29 PM12/19/01

to

Turn on the cosmetic threads and you will end up with the correct hole
size before tapping. Hide the cosmetic threads in your drawing before
converting to .dxf

If you have the threads turned off, you end up with the O.D. of the
threads. (The reason for you having two different edge diameters.)

"Jeff Cox" <geof...@home.com> wrote in message news:<poZT7.78783$py4.36...@news2.nash1.tn.home.com>...