One way to look at it is to make a hole the same size as the proper tap
drill for the 3/8NPT, which is 37/64, but that's a straight hole. What I do
is create a straight sided hole that is Ø37/64 to whatever depth I need.
Then I offset a plane from the surface to the depth of the thread, which is
the handtight engagement length plus the wrench makeup length given in
Machinery's Handbook as L1 + L3, in this case .240 + .1667 = .4067. Create
a sketch on that plane and subtract extrude the projected hole with a 1°47'
(1.79°) taper back to the surface. Add the thread to the tapered hole. Now
you have a properly tapered hole made by a proper tap drill. BTW I only do
this procedure when it is necessary to have a proper representation.
Normally I just subtract extrude a circle the same diameter as the OD of the
pipe with a -1°47' taper to the effective thread length.
I have a "Engineer's Quick Reference Calculator" Publication #5013 from
Media Marketing Associates (www.mma-engsupport.com) that is a slide chart
showing all kinds of design info for inch fasteners, wrench clearances, and
pipe threads. Much easier than Machinery's Handbook, but not as complete.
-Mike
"TAHDESIGN" wrote in message
news:31479651.1103031204285.JavaMail.jive@jiveforum1.autodesk.com...
> I have always wonder about the proper use of NPT thread in my models,
maybe someone can clear something's up for me.
>
> 1) When using the thread feature, a hole needs to have been already placed
(not a HOLE but and extrusion). IV selects the default size of the thread
presented to you by that hole size (which you just change to what you want).
What would be the nominal hole size for say 3/8 NPT? Have never found a good
source for that info.
>
> 2) Even though IV does represent the thread in the IDW, does it have to be
manually called out with just a leader? I know the hole note will not see
it.
>
> Thanks
> Todd