Primus NRV M8 thread ?

I don't mind grinding it down if there's no other takers ! , though if we're removing the lead, we should maybe incorporate the modified die into some sort of fixture that aligns the NRV's into the die
Otherwise we'll be at risk of recutting/cross threading


Would be good to work with these threads instead of today's work !

1 1/2" O/D Square thread 3tpi , Internal and left hand thread
The steel piece in my hand is a 'gauge' to give me a 'go/no go' guide for the female threads

 

@Longilily You have made nice parts!

I don't have spare M8×0,75 dies. I would need to see which other thread tools I need and make order for them.

Some fixture could be good to drive die on right angle to the NRV threads. Or maybe two NRV chasing dies would be needed; one with 'very small' lead in and other one without lead in. Specially if no fixture is used.

Brierley style/type drill sharpening grinder should be good for well controlled die grinding. I was thinking to grind surface of die to few degree angle that cutters of the die have better access to the NRV up to the bottom of the flange.

 

On this thread we had discussion about NRV pitch: https://classiccampstoves.com/threads/warning-nrv.29083/ But there was not so clear decision what is 'the right pitch'.

Maybe I dig all my NRV's and measure with microscope what pitch they have.

 

Hello friends use this tool,
its cheaper than a measure microcope

https://www.hoffmann-group.com/DE/d...annungsprüfer/Gewindeschablone/p/477000-M@2FG

https://www.hoffmann-group.com/GB/e...,-voltage-testers/Thread-gauge/p/477000-M@2FG

With this tool I check all my pitches I dont know safe

Do you have ever this cheap tool at home near the fettling room:-)??

https://www.hoffmann-group.com/GB/e...ph-with-screen-⌀-315-mm-and-10×-lens/p/493510

RJ

 

@Russenjesus I have 5 or 6 those 'thread leaf gauges' for various thread types. They are quite useful but when you need to check if thread has 55° or 60° angle with 32tpi, 34tpi, 36tpi, 0.70mm or 0.75mm pitch or vice versa the are very difficult to use specially if measurement needs to be done from a very short thread.

Once I had an opportunity to get a Mitutoyo Shadowgraph/Profile projector (old floor standing type) for free when they cleaned un-used old stuff out from our work shop. I didn't had room for it. Instead of that Shadowgraph/Profile projector I took an old measurement/werkstatt microscope that gives same functionality but takes less space. Here NRV thread profile picture with that 'werkstatt microscope' :



From this thread: https://classiccampstoves.com/threads/warning-nrv.29083/page-4

 

I'll buy one

 

Well, an interesting discussion at last night's quiz, and a reminder that describing a problem to someone who has little previous knowledge of the issue is very useful to examine everything at a basic level.

My toolmaking friend also suggested grinding down the die to eliminate any lead in, even on a finishing type.

Discussion then wandered off into machine tool digital controller circuitboard back plane problems.

While explaining the problem in general terms it occurred to me that the thread profile up to the shoulder may not be particularly critical as there has to be a washer for the seal. Either lead or plastic.

I've not visually checked but are the NRV's cut back at the shoulder?

This would make a full cutting die a bit redundant, and reprofilling is all that's required.

The identification of original profile is a different question, and is clearly an ongoing discussion.

 

@Longilily Thanks think that is pretty conclusive.

Again a memory jogger as the washers are quite loose so there has to be a cut back there. So a clearance tap or thread profiler should be adequate without having to grind down one, or am I missing something.

The actual thread selected when they were designed is therefore an academic exercise then to obtain the correct tap or die to do the fettlng of the damaged pump tube end or NRV.

 

Lead washer is squeezed around the NRV to be tight so from new a NRV you don't want to remove the washer for thread cleaning. If you remove lead washer for thread cleaning and put it back lead washer will be (too) loose. Too loose lead washer will (in most cases partly) come out when you tighten NRV onto pump and NRV to pump joint is not air tight.

 

I tried two local tool shop to get that M8×0,75 die. Not available. Only ones that they had were with 1,25mm and 1,0mm pitch.

 

No problem Kari, I'll sort it, got a few Stovie related jobs to do in the next few weeks, once Crimbo is out of the way