Dynamo screw threads

[Rex]

He does not take something simple like a screw thread and make it complex.
  Lee

That's one of those philosophical arguments that I've never really understood.
When I'm looking for, repairing, recutting, rethreading, drilling and tapping or any other operations involving BA threads,  why would I give two fecks over the included angle or mull over the chosen major diameter, etc? It's irrelevant.
So it's different to other screw threads.....so what? No-one's going to mistake it for anything else, but it works, and works well.
It's like complaining that a foot is made up of twelve inches and saying that it should be nine or fifteen to the foot.
It's the past and they did things which we wouldn't do now.

[BSA_54A10]

He does not take something simple like a screw thread and make it complex.
  Lee

That's one of those philosophical arguments that I've never really understood.
When I'm looking for, repairing, recutting, rethreading, drilling and tapping or any other operations involving BA threads,  why would I give two fecks over the included angle or mull over the chosen major diameter, etc? It's irrelevant.
So it's different to other screw threads.....so what? No-one's going to mistake it for anything else, but it works, and works well.
It's like complaining that a foot is made up of twelve inches and saying that it should be nine or fifteen to the foot.
It's the past and they did things which we wouldn't do now.

No it is EXACTLY the same as smashing a round peg into a square hole and is the reason why holes split,  small bolts corrode into place and snap off or just plain fall out
You can hammer a screwdriver into the key hole in your front door and turn it with a foot long spannar and that will work as well.
Back in the day, people worked with their hands and understood mechanical things, now days wea re soo much smarter and work with out brains so smashing something into a hole where it does not fit is a sure sign of a higher level of interlect.

IF understand it is difficult, draw a pair of lines 1" apart then pinch the kids, grandkids protractor and make a zig zag 60 deg and another 55 deg  between the two lines.
Cut them out and lay them on top of each other.
You will then see in place of the threads contacting full length they just touch each other at either the top or the bottom.
A bolt is held in place by friction and if the threads don't touch anywhere other than at a knife edge you dont get any friction.

Now because 1/4" is small it is well withing the strength of even the most imaciated brain dead to deform which ever is the softest material if they use a big enough lever.
The first time you do it you bend over the tips.
The 4th time you screw them together you brake off the tips of the threads and it strips.
Now because you have made the hole deeper when you try to put a helicoil into the buggered hole the helicoil dose not have enough material to crush so the helicoil then come out with the bolt and you have totally destroyed what ever you you were working on.
Now it is your bike so if you want to wreck it then fine because you own it thus you are entitled to destroy it.

[groily]

You kind of get used to it over this side Lee!

Nowadays it's all ISO metric and ISO metric fine for these things out this way. Good stuff I'm sure . . .  even if 'Metric' doesn't mean 'simples' and 'uniform' though. Far from it. 

Not sure what you guys use over there (metric too maybe these days?), but I get confused by the nomenclature of the tiny sizes in UNC and UNF to be honest, simply due to my lack of familiarity (although their sizings are a bit more transparent I do agree).

Come to that, the Brit imperial focus on shank diameters not spanner sizes doesn't make life easy for many people - my French friends struggle with non-across-the-flats measurements for wrenches. Can't figure why the US imperial system is different from the British. Think 55° is also an odd angle.  Can't understand why BSC and BSF would be 5° apart, all being 'anglais'. Think the near-interchangeability of some WW and UNC sizes was designed specifically to drive them, er, nuts . . .!  The only constant is change, indeed.

And as Rex says, the past is another country.

The fact that an inch is 25.4mm and that it only divides once before hitting a prime number just adds insult to injury for those wanting to lathe-cut perfect threads across the divide on small machine tools.  Even if the French mathematicians had got the earth's dimensions right when calculating the metre, the relationship would probably still have been uncomfortable or bizarre. As it is, couldn't have made things more awkward if they'd tried - and BA would still be near-impossible to lathe-cut at pitches other than 0!

Just have to accept the rich diversity of it all and tool up accordingly!

[BSA_54A10]

OK you two,

 Being an American I can safely say you two have drunk too much of the Cool-Aid.

 A good engineers can take something complicated and make it simple.

 He does not take something simple like a screw thread and make it complex.

 47.5 degree included angle, 31.36 threads per inch, and a .185 OD for a threaded screw form sounds to me like a paper tiger, some engineer developed this using nothing but a math calculation. Someone should have kicked his ass right then and there.

 Lee

A good engineer would not take something that was metric then complain it seems too complicated for them to comprehend when converted to inches.
Cutting a thread forming tool to 47.5 is no different to cutting a thread forming tool to 55, 60 or 45
And if you want stupid complication how about an inch thread form that goes down in 1/16" then for not good reason suddenly switches over to wire gauge for diameters.
And from memory BA thread count is  mm/ per 10 threads