Microns ...

When I worked in a tool drawing office for a teleprinter manufacturer (remember those?) the rule was that in Metric drawing dimensions the decimal point was to be denoted with a comma. The display itself violates that.

I am unable to vouch for that as when I got it out of the envelope David sent it to me in I dropped it onto the large box of 567BA machine screws I was slitting the heads of in the 3 jaw of my Drummond Roundbed lathe.

More seriously Drummonds proudly advertised that their Roundbed lathe beds were ground to a tolerance of 1/1000" so what does that suggest the tolerance of parts made on them would be in reality? 10x that??

Also John Stevenson in another forum a few years ago noted that the latest Myford connoisseur lathe bed was ground on the same surface grinder as his 40 year old one!

I'm with what John S wrote on this subject I'm afraid, silly tolerances are not necessary for our hobby - but as it IS a hobby, if you get pleasure from working to them, you are doing exactly what is right for you.

Nick

PS As someone diagnosed with autism late in life, if you say you have to work to them I can see where you are with that as well

Edited By Nick Clarke 3 on 05/07/2019 12:58:10

I've cracked this one before, but it might run again here:-

I was on a chair-bodging course using pole lathes, and when we were turning the location spigots on the legs we were supposed to turn them to a tight hand-fit in the jaws of a spanner that was being handed round (22mm A/F IIRC).

One of the punters snorted loudly: "Hah! I've worked to microns!".

Quick as a flash the instructor came back: "Maybe, but I've worked with morons..."

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I don't anticipate making any further posts on this thread ... but, having chucked my pebble in the pond, I will happily continue to observe the ripples.

May I just point out though ...

a) There is a subtitle

b) The topic is 'Related Hobbies'

"Many other hobbies go hand in hand with model engineering. Use this topic to discuss anything from astronomy to robotics."

MichaelG.

Resolution, precision, accuracy...

From Michael's photo and the context, this is a controller for a microscope focuser. I can well imagine that at very high magnification it would be necessary to move the lens very precisely, for example to focus on various layers of the object. By having calibrated Z you could estimate the distance between layers. Absolute accuracy will not be crucial; small, repeatable, precise movements will be; good resolution critical. Somewhere it says this is a piezo positioner - make small movements by changing the volts across a ceramic element probably.

With regard to the decimal point delimiter, though the "continental" system still uses that in principle anything made for a world market will probably use a full-stop.

Personally, I only work in zeptoparsecs (zpc), which saves a lot of argument.

My son uses the Metric Beardsmore, which is the length of his boss's forearm.

George B.

I have micrometers capable of measuring microns, but it is extremely difficult to get repeatable results at this scale. When I was working in a firm making parts for aircraft, there was rarely any requirement for drawings to call up tolerances of less than +- 10 microns, that is less than +- half a thou.

Those people who like to boast and have deep wallets can buy themselves a Mitutoyo digital micrometer with a tenth micron scale.

A digital micrometer reading tenths of a micron would be worth boasting about! But I think Old Mart has his Microns confused. A micron is much, much smaller than a thou.

In this picture the horizontal line represents half a thou (0.0005" ), and on the same scale the circle on the end is 1000µm in diameter:

The horizontal line actually ends in a ±10µm vertical line, 20µm in total. It's too small to see. Zooming in on the circle reveals:

Putting it another way, if flying Brisbane to London Heathrow represented half a thou, then 10 microns would be within walking distance of the airport.

Dave

Edited By SillyOldDuffer on 05/07/2019 16:49:42

[This posting has been removed]

Read my post again. 10 microns is less than 0.0005". 0.0005" is equal to 12.7 microns exactly.

One micron is a millionth of a metre, or one thousandth of a millimetre.

One thousandth of an inch is 25.4 microns.

Oh dear, we seem to have a CAD catastrophe. If the line is half a thou long then the circle at the end cannot be 1000 microns, as that is one millimetre, which is definitely bigger than half a thou. The scaling factor is 25.4, so more, but not much, much more?

Andrew

Microns !!! theres millions of them in an inch.

Don’t forget to add a temperature controlled room when shopping for your micron micrometer.

Mike

That non-temperature-controlled apparatus thinks it can resolve 1nm repeatably enough to justify the scale's resolution? Delusional, surely. It reminds me of a friend tickled pink by his small bench-top oriental CNC mill. He discovered that his CAD software could work to microns, and sincerely told me that he could now machine things 'accurate to a few microns'. Hmm. But then he also thinks that scraping has been made obsolete by modern CNC machinery. Hmm again.

When fitting pistons for race engines where between good and worn out engine is 2um on diameter , being able to turn and fit a new piston without lapping it, shows a performance edge with the stop watch. The other option is to turn a lot of pistons at slightly difference sizes and then find the best one that fitted. In realty, making 4 different pistons of different sizes and then finding the best fitting one, takes the same amount of time, but you have 3 spares that may never be used.

If I could have something that allowed me to turn a piston to 0.1 um, and be round to that tolerance, I think would be really great.

Of course the real biggest issue is having the material that can be stable enough to be sized to 1um or better. Until powder metallurgy arrived, pistons for model engines could not be sized to 1um at all.

Pistons fitted to petrol and diesel engines are never turned round, and are also tapered and if anybody tried to measure one to a 2 micron tolerance they would get a different reading each time.

Edited By old mart on 07/07/2019 11:44:25

So do they make it that way as a joke? It may well resolve to a nm, If it could do it repeatedly it would be precise to a nm, and if it could be calibrated (e.g. w.r.t. wavelength) it might be accurate to a nm. But for its probably purpose, making comparisons, it's probably fine.

Gentlemen, of course you are right. 1 thou = 25.4microns. How do these mistakes happen? Perhaps Nurse will explain after my afternoon nap...

Dave

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The specification sheet [*] makes clear what it can do, in terms of resolution and repeatability.

@ most contributors to this thread: Please bear in mind that the overall travel is only 0.5mm ... and temperature effects are proportional to the relevant dimensions.

Scale everything up to suit [say] a 500mm long milling table and you may appreciate that Marzhauser is far from delusional.

MichaelG.

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[*] see my opening post

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Would you care to recalculate that ^^^