NPT Thread Depth

[Anonymous]

I didn't see any posts about this so I will throw this out there.

The hole function seems to place the wrong NPT thread depth when creating holes.  I've checked the thread.xls and all the values seem to be correct.  Please have a look at the inserted pics...

Sorry if this is hard to read, but the arrow is pointing to the Useful Thread Length column of thead NPT tab on the thread.xls. For 3" NPT holes, the thread length value is 1.016".

The hole feature also reports this value

But when I complete the feature, this is what is returned:

This happens with my 3" and 4" NPT holes.  All other holes smaller than these sizes report back the correct value.  Am I misunderstanding how larger NPT holes are drilled?  Any help is much appreciated

[Anonymous]

Same thing here.

Appears that any size above 2-1/2" NPT is incorrect.

Only use the small sizes here.

[Anonymous]

Thanks for the confirmation John.  I'll try logging with support...

[karthur1]

The whole NPT thread thing is hosed in my opinion.  I edited the original spreadsheet for all sizes NPT sizes thru 4in so the tap drill size would be called out correctly on the drawing.  With these values, the holes do not look right in the models... especially for  NPT 1/8 and 1/2.

If I use the stock values for the tap drill the holes "look" correct, but the call out on the idw is wrong.  I have to produce correct idws, so I just live with the hosed up views.  Its been like this for a very very long time and it will probably NEVER be fixed.... aint worth ADs time.

[dan_inv09]

The tap drill is to big. (Or the I.D. at the big end of the taper is to small.)

Have you tried changing  in your Document Settings?

(I don't know if that affects the tapered threads.)

How does it look on the drawing?

[Anonymous]

So I played with the tapped hole diameter a little, but it didn't change anything on the model or the drawing.

Here's what my coupling looks like sectioned on a drawing.  It shows the thread depth correctly, but it doesn't place the threads at the full depth?  Wonder if this is as designed...

[dan_inv09 · Accepted solution]

The thread graphic is applied to the tapered face.

If the taper were to continue to the 1.094 depth the i.d. would be 4.2190

but the hole (the tap drill diameter) is 4.25 so the taper runs out at .5980

If you adjust the Document Settings Tapped Hole Diameter to anything but Minor the thread texture will go all the way to 1.094

You would have to consult ANSI/ASME standard B1.20.1 to see if this is "as designed"

Inventor is probably using the correct Minor Diameter, Major Diameter, Taper Angle, Thread Depth, Tap Drill, etc., etc. but maybe there is some sort of mention of the actual amount of perfect threads you should get in a hole using those numbers.

[Anonymous]

Dan, thanks much for that.

Previously, the model or drawing didn't update when I changed the Tapped Hole Diameter.  I wasn't updating my model correctly.  I now see where changing it to Tap Drill, the model and threads update correctly.  Seems like I'll be taking a look at that standard to get a better understanding.

Thanks again for your help...

[dan_inv09]

And if you want to get picky, according to the Machinery Handbook:

"Straight Pipe Threads in Pipe Couplings, NPSC.—Threads in pipe couplings made in accordance with the ANSI B1.20.1 specifications are straight (parallel) threads of the same thread form as the ANSI Standard Taper Pipe Thread. They are used to form pressuretight joints when assembled with an ANSI Standard external taper pipe thread and made up with lubricant or sealant. These joints are recommended for comparatively low pressures only."

so now I don't know if there is supposed any taper at all on internal pipe threads on stuff rated for 300 psi or less.