TL-1: NPT pipe threads, tips needed.

Tonight I was helping a buddy with a custom fitting which required a 3/4-in NPT male thread. I used the "Chamfer" screen to cut the major diameter taper, and the "Taper" field on the "Threading" screen. Both were set to 1.783-degrees. The problem was that the flats on the crests of the threads were not constant. At the narrow end they thinned out, which seems to indicate the thread taper was steeper than the initial major diameter taper. Or does it? I double checked and both numbers were the same value: 1.783-deg. Am I missing something? Is the a better procedure for doing this?

Thanks!

You could always add an "I" to the G76 code to create a taper. Just need to know the difference in dia. from start to finish and divide by 2.

I am trying to puzzle this out using the conversational screens.

Anyone?

We had to cut some 3" pipe tread awhile back on out TL-2 and had the same difficulties. Never did figure out how to do it "right", so we started cheating the thread taper to make it come out.
Aggravating as hell.

Charlie

Hmmm..... So I'm not crazy?

OK, time for some test cuts and careful measurements.

Will report.

First of all the taper function in the control isn't designed for that.
The taper really should be programmed, as it's length depends on the the diameter. Fudging it will take way too much time and effort.
Same for the thread itself. The pitch is given, the angle is given, but the starting min diameter, end min. diameter depends on where you start and finish in Z, so you really need to calculate it. Same goes for the I value.

Don't know how smart the conversational programming is, but 2 mins in CAD will surely beats it.
For figuring the specifics of the threads I'd recommend ThreadPal, which gives you every single detail you need.

When calculated properly, the only measurement necessary is the pitch dia with the NPT gage. No fudging or trial and error.

Today I think I found the discrepancy. The "Chamfer" screen takes its input in degrees of taper from centerline. The "Threading" screen takes its taper as inches per foot. It was a miracle that it came out close.

Will make chips tomorrow and verify.

OK... I finally figured it all out. Correcting the units of taper on the two pages, AND getting the pitch diameter sorted out did it. We created excellent NPT threads, using the Haas conversational programming.

.75 taper per foot, right?