The micrometer fairy cometh!

[steamer]

OK
Sometime ago I made mention that I was waiting for the micrometer fairly to bring me a metric micrometer.....well the fairy came!

An inexpensive 0-25mm micrometer showed up at my door just after Christmas.....had me completely befuddled!

Because ......I DIDN"T BUY IT!


OK fess up who sent it? ;D


I'm guessing it was you Bez!

Dave

 

[steamer]

Thanks anyway! It will be used,,,,at least I can measure microns now... ;D

Dave

 

[bezalel2000]

Hi Dave

Maaaaaaate ! ;D Are you calling me a Fairy ? *knuppel2*

I prefer the term "Father Christmas". It's a little more masculine, don't you think, 8)

How did you figure it out - Columbo?

It was supposed to be post marked from Hong Kong.

by the way that's a guilty plea Your Honour.

Merry Christmas Dave

Bez

 

[steamer]

"Just one more question Mr Christmas....Im not that good with the Christmas kinda stuff..Ya know.Mr's Columbo usually does all that shopping and stuff ...want's to keep me out of it....." ;D

Thanks BEZ! It WAS post marked from HONG KONG......but the penny dropped eventually after I checked my accounts and realized that I hadn't bought this nor was it a "buy now and get a micrometer free!" deal....then I looked carefully and realized it was metric.......BEZ!

;D


Thanks Mate!....I'll use it in good health......even though that silly metric stuff will never catch on.... : ;D

Dave

 

[rleete]

A karma point to you, sir, for your generosity.

 

[bezalel2000]

Thanks Mate!....I'll use it in good health......even though that silly metric stuff will never catch on.... : ;D

Dave

Metric can't be that hard to use, the US military have figured it out. ;D

I hear even their compasses are metric now too, where 6400 units equals a full circle ??? Figure that one out.

Bez

 

[bezalel2000]

Hi rleete

And a thank you to you too Sir.

Cheers

Bez

 

[Ken I]

Metric can't be that hard to use, the US military have figured it out. ;D

I hear even their compasses are metric now too, where 6400 units equals a full circle ??? Figure that one out.

Bez

You know the military - everythings gotta be bigger and better - so why not "bigger circles" ?

Ken

 

[mklotz]

Ah, yes, the can't-deal-with-irrational-numbers-Army. I had a lot of trouble with this while writing fire director software for high energy laser weapons.

BTW, this 1/6400 th of a circle is known in the artillery trade as a 'mil'. It always made me wonder just how confused things could get if you were a machinist in an artillery service depot.

Just to make things more confusing, other countries use other fractions "close to" 1/6400. I guess that's so their artillery misses will fill in the gaps left by our misses.

 

[steamer]

I was wondering what math that was Marv.

Dave

 

[raggle]

Marv, I'd hoped for some expansion to help the class here assembled.

They're called mils (one 'l') which is short for milliradian. There are 2*pi radians in a full circle. (Calculators out lads) that should be 6.2831854 or thereabouts.

Faced with the problem of finding a worm and wheel with that number of teeth, "they" considered a near-enough solution using 64 teeth to be ok.

1 mil is the angle subtended by a 1 yard object at 1000 yard range (or 1 metre object at 1 km, or one thou at one inch)

I've got the remains of a signalling lamp made in Canada in 1942 whose base has this arrangement, the worm being disengageable for quick initial setup. I've been looking for a sensible use for it, maybe in a dividing head, though 64 only has number 2 as its primes. So it's not that new, being from the year of my birth in WWII.

Hope I didn't hijack the thread.

Ray

 

[mklotz]

Since pi is an irrational number, you'll never get a gear to define a milliradian exactly. However, 6300 is a lot closer to 6283 then 6400. In fact 6200 is closer than 6400. And then there's the glaring problem that other countries use numbers other than 6400.

This is exactly the sort of confused, muddy, that-looks-about-right "thinking" that led to the abomination we call the Inferial system - a mishmash of unrelated units of convenience loosely defined with no regard for accuracy and used by a populace who doesn't understand them.

 

[steamer]

I too was wondering why they didn't just use a 63 tooth gear....

Curious.....

Dave

 

[raggle]

yeah, but I've got the gear - what do I do with it? :big:

 

[mklotz]

yeah, but I've got the gear - what do I do with it? :big:

Make a clock? After all, 64 is close to 60 for large values of 60.

 

[bezalel2000]

I too was wondering why they didn't just use a 63 tooth gear....

Curious.....

Dave

There is a very practical reason for selecting 6400 mils in preference to 6300 or 6283

that is the number of times it can be bisected to a whole number

i.e 8 times to arrive at 25 mils or
( 25 * 28= 6400) which is equivilant to 1.4o

compared to 360o

which can be bisected to a whole number only 3 times to arrive at 45o or
(45* 23 =360)