NPT Pipe Thread in Model Usage

[Anonymous]

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

[Anonymous]

Todd: FWIW, I choose a countersunk hole when specifying NPT. The hole is the minor diameter at the bottom of the threads, the countersink diameter is the minor diameter at the surface and the countersink angle is 3.57982° (twice the arctan of 1/32). The information needed to determine these diameters can be found in Machinery's Handbook and several other references, but they take a bit of math to get into the format you want. I then apply the thread to the countersink. The thread feature recognizes that I want a pipe thread and defaults to NPT, but it doesn't decipher the size so I have to manually select that. On the idw, the hole notes tool brings up the NPT thread designation. Viewed from the side, the idw shows the tapered thread properly. It's actually much easier to do than to describe. Richard TAHDESIGN wrote: > 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

[Anonymous]

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

[Anonymous]

" 'Engineer's Quick Reference Calculator' Publication #5013 from Media Marketing Associates..."

I have the Alvin version of this selector, which seems to have most of the same info, but is $12 rather than $19

http://www.alvinco.com/detail.asp?f=&FamilyID=5810&cat1=Templates&cat2=Mechanical&cat3=&cat4=&cat5=

[Anonymous]

Just to clarify, you can place a HOLE (unthreaded) in a part and then add a THREAD (NPT) to that hole. Since I call out the thread size and expect the machine shop to handle the issue of tap drill sizes, I don't worry about tapers on the thread representations. Machinery's Handbook is the source I use for sizing. You could also call a local wholesale plumbing supply and see if they have a copy of the Pipefitter's Handbook. TAHDESIGN wrote: > 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 -- Hal Gwin Mechanical Designer Xenogen W2K SP4 Dell Precision 650 Dual 2.66 GHz Xeon 1.5 GB DDR Quadro4 900 XGL nVidia 6.14.10.6085 w/registry update Dell UltraSharp 19" LCD