Micrometer Blues

[Simon Williams 3Participant @simonwilliams3]

Calibrating a Starrett Mic’

[Simon Williams 3Participant @simonwilliams3]

Good evening everyone, after some advice please.

x

I find this quite difficult to read, as the fiducial line is inside the thimble. This presently reads 7.50 mm, but the 0.5 line is obscured by the thimble sleeve. It can be quite confusing particularly at intermediate settings.

So is it possible to move the thimble about 0.2 mm to the right on the spindle? How is the spindle held in the RHS of the thimble?

How many heart attacks would I be responsible for if I took the angle grinder and took 0.2 mm off the left end (scale end) of the thimble, heretic that I am?

Thanks as ever in anticipation of The Knowledge!

Simon

[Simon CollierParticipant @simoncollier74340]

Looks perfectly normal and correct to me. If you really hate it, get a digital one.

[EmgeeParticipant @emgee]

Hi Simon

With your picture viewed full size in your album it is clearly seen reading as 7.50mm, don't forget you only see halve of the line width. I sometimes have to turn the thimble a bit to check exactly before turning back to the measured position.

Emgee

[John ReeseParticipant @johnreese12848]

I can just see the line peeking out from under the thimble. You might try disassembling the mike to see if the graduated skeeve can be slid toward the frame. On some mikes the sleeve is just a friction fit. It might also be possible to stone off the end of the sleeve to allow it to slide to the left (according to the picture). I like the Brown and Sharpe mikes with the slant line graduations.

[David George 1Participant @davidgeorge1]

Hi Simon it is possible that the sleeve has worked is way to the right and using the adjustment C spanner rotate it and pull further to the right clean the gap then twist and push it back and adjust and calibrate to check size. It is tight fitting sleeve but only use the correct spanner.

David

[AJWParticipant @ajw]

All my mics look like that!
Always thought it was correct.

Alan

[duncan webster 1Participant @duncanwebster1]

Looks perfectly normal to me too, you can see daylight after the 7mm mark, so it's obviously not 7.0mm. Having said that, I hate metric mics, I've lost count of the number of times I've made something exactly 0.5mm wrong. Eventually you'll get used to it. I''ve bought a digital mic, but I hardly ever use it.

[I.M. OUTAHEREParticipant @i-m-outahere]

Hi Simon,

While i have to agree with the other replies in regards to it reading correctly i i also understand where you are coming from !

Take a look at the youtube channel mrpete222 Shop tips #302 he stripped down a mic and lightly skimmed the end of the barrel opposite the thimble so more of the line was showing as he had troubles seeing it when most of the line was under the thimble .

Ian

[jimmy bParticipant @jimmyb]

If it makes it easier for you, just skim the barrel.

[John HaineParticipant @johnhaine32865]

I agree with others, this is normal. I have found over the years that it takes practice and a basic knowledge of how the things work to use instruments consistently, just keep using it and thinking about the reading until it becomes second nature.

[Jon GibbsParticipant @jongibbs59756]

Hi Simon,

MrPete222 on YouTube has a video on rectifying this issue here… **LINK**

[Edit: Sorry Ian seems to have beaten me to it.]

HTH

Jon

Edited By Jon Gibbs on 13/04/2017 08:35:25

[Speedy Builder5Participant @speedybuilder5]

Go back to IMPERIAL, You don't get the same problem!
BobH

[not done it yetParticipant @notdoneityet]

Looks spot on to me.

Send it to me and I will replace it with something which would be easier for you to read. I think I may have something that reads to the nearest 0.1mm with an accuracy of about one digit.

As there appears to be only one reading among so many that troubles you, I think there is no reason whatsoever to consider potentially destroying such a precision device. Live with it and learn how to use it, is my advice. You clearly know where the 7.50 reading occurs, so what is the real problem?

[Nick HulmeParticipant @nickhulme30114]

If you can find one at a decent price the Mitutoyo Combimike is worth a punt, the white numbers on a black background are very clear, variants were available with an imperial spindle combined with a metric mechanical digital readout and vice-versa. Mitutoyo also did all metric and all imperial spindle/mechanical digital combination micrometers, other brands did them too.

[Tony Pratt 1Participant @tonypratt1]

I have had mikes worse than this but it is annoying, skimming the barrel end is about the best option if it bothers you that much.

Tony

[Bob StevensonParticipant @bobstevenson13909]

………So, if I have got the gist of this, you want to make an accurate micrometer 'inaccurate' in the interests of increased accuracy…(?)

[Tony Pratt 1Participant @tonypratt1]

Posted by Bob Stevenson on 13/04/2017 10:04:17:

………So, if I have got the gist of this, you want to make an accurate micrometer 'inaccurate' in the interests of increased accuracy…(?)

The gist is that the OP wants to see more of the spindle lines, no mods suggested will affect the 'accuracy' of the micrometer.

Tony

[Bob StevensonParticipant @bobstevenson13909]

If you shorten the thimble to make the line more visible you have built in an inaccuracy becasue the line placing will no longer by true (accurate)…especially with the OP's main problem of "intermediate settings"

…..unless the OP is planning to measure exactly how much he is going to remove from the thimble and then adds this number to any measurements he makes in future (to 'correct' the measurement and keep things 'accurate&#39

[mechman48Participant @mechman48]

… 'How many heart attacks would I be responsible for if I took the angle grinder and took 0.2 mm off the left end (scale end) of the thimble, heretic that I am'?

​I guess you're speaking metaphorically… If you think can take off 0.2 mm with an angle grinder you're a better man than I am Gunga Din, steer well clear of any 'adjustment', get a loupe or magnifier to view the line better, or better still get a digi mic, ( Mitutoyo if you can afford it )… leave well alone it's fine as it is.

​George.

[Jon GibbsParticipant @jongibbs59756]

Posted by Tony Pratt 1 on 13/04/2017 10:29:29:

The gist is that the OP wants to see more of the spindle lines, no mods suggested will affect the 'accuracy' of the micrometer.

Tony

+1

Few people seem to understand how a micrometer works.

Jon

[Rick Kirkland 1Participant @rickkirkland1]

From what I’ve seen on here few people seem to understand how a great deal else works as well. There really must be a massive dose of “Dumb Ass” medicine being put into the (fast? ) food chain these days.

[Neil WyattModerator @neilwyatt]

It will work fine, but seems a bit pointless, if the thimble is close to zero, then it's close to a fiducial line, even if you can't see it.

If you move it 'right' to show when it's creeping up on a line from the left better, won't it have the opposite effect and make it harder to judge when approaching a line from the right?

[Mike PooleParticipant @mikepoole82104]

This style of construction has no adjustment for positioning the thimble on the screw, it may be preferable to alter the sleeve rather than the thimble but I would be disinclined to do either. Reading the mic in the position shown the line is partially obscured but I tend to hold a small mic with my little finger through the c frame and third finger clamping it in my hand, thumb and forefinger to turn the thimble. In this position you tend to have the thimble vertical and looking into the joint between thimble and sleeve and the lines are much more visable. Moore and Wright mics can adjust the position of the thimble as it is clamped between a nut and locking screw so you can choose where the lines show.

Mike

[Simon Williams 3Participant @simonwilliams3]

Well, many thanks as always to all those who took the trouble to reply, it's been hugely entertaining watching this develop over the course of the last 24 hours or so.

There seem to be three schools of thought –

1- don't fix what aint broke,

2 – you're going to make it a whole worse

3 – I've been there too.

The back story is that I bought this mic' back in the late 70's, and have hardy used it since, because I've never learnt to read it reliably. I'm not sure I understand why the same is not true of almost all of the imperial mic's in my toolbox, but this one seems particularly obnoxious. To me.

I was sorting twist drills yesterday, and took to this one to see if I could get on with it, and decided the answer was no. So I might as well modify it as throw it away. Yes, I completed the job using a digital mic', but there are times when a tidy little thing like this is easier to use.

Tubal Cain's video gives me some hope that I'm not going doolally – well probably I am but it's nice to have company – so thanks for that link, and particular thanks to Mike Poole who seems to have dismantled a perfectly good identical mic' just to show me what the internal arrangement is, which was my original question. I'm still humming and hawing over whether the game's worth the candle – but I've just worked out how to get the sleeve off so that gives me the option of taking a lick off the heel of this instead of the thimble. Less likely to get grinding dust in the measuring thread.

I'm keeping schtum about whether my metaphorical angle grinder is the way to do the job. I never said I was going to plug it in!

I've been chuckling all afternoon about the debate between accuracy and legibility. My warped sense of humour finds in this a direct analogue of the inability of the newspapers to resolve the same.

Regards to all

Simon

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