Threads begin where?

[dwlnson]

I have a customer whose valve must be orientated to an exact position based on the start of the threads. Is there some standard that would help me determine this where it is supposed to be? I can see it visually, but is there a thread requirement as to where the start of a thread is to begin? Is there a measurement techniques? Thread size is 2-7/8 - 8

Thanks,

[Kelly_Bramble]

Can you clarify? Thread start depth and end?

[PinkertonD]

This is a fairly big ask with pipe threads especially as I assume you mean tapered pipe threads. Their "seal" is largely dependent on the joint tightness. If a register for the valve/pipe is critical then tapered threads would be useless as I see it.

With CNC machines it might be possible by machining the exact start points on both pipe and valve even with tapered threads. BUT - I would suggest you look at an alternative to pipe threads if registration is that critical.

[jboggs]

I agree with Dave. I have seen younger engineers try to create some registration to threads (either start of parallel threads or tightness of tapered threads) on several occasions. I have NEVER in over 35 years EVER seen it work reliably and repeatably. Not ever. I would strongly suggest they look for some other method of achieving their goal. There is always a better way than that.

[dalecyr]

"I have a customer whose valve must be orientated to an exact position based on the start of the threads."

Is that really the requirement?
Or is this maybe the real requirement:
"I have a customer whose valve must be orientated to an exact position."?