Thread: Metrology for Amateurs

Originally Posted by Stustoys

Hi Michael,

But by that definition my master height gage cant be used for measuring in absolute terms either? or my normal height gages for that matter.

Yes you could. If the DTI is set from check a 50mm dia part, if the run out was 0 but the DTI was reading 0.1mm you would know the actual diameter was 50.2mm. If the run out went from +0.2 to -0.1 the actual diameter would be 50.01mm

Stuart

Your height master can as it is graduated with numbered divisions - if the numbers were removed your heightmaster would be pretty much useless. If the numbers were removed from a DTI it would still be usable because you are comparing how much it is between 2 marks.
It is convention that an indicator is used with a heightmaster, but you could use it by standing a part next to it and eye balling it. Accuracy would suffer but it could be done.

Originally Posted by Bryan

At the risk of being obtuse... A micrometer reads relative to its anvil, a height gauge relative to the base plane, an indicator relative to whatever you zeroed the dial to. What's the difference?

The difference is that the micrometer etc will give a value. You could send me an email asking me to make up a certain diameter shaft with that value. There is a good chance I could give you what you want as my micrometer should read the same as yours (absolute value).
On the other hand an indicator will only give you a value that you then have to relate to something else. You can't measure a diameter in a lathe with a DTI. You can only use it to give me a diameter if you use the DTI to compare it to a known standard - that is the diameter of the standard +/- indicator reading (relative value).

Michael
(Sowing seeds of confusion where ever he goes)

• Accuracy - how close it was to the true value

Michael, the value is the value it "should be" over that distance, and doesn't need to be referenced to an absolute datum.

Pete

Originally Posted by cba_melbourne

Somethink to think about:

Yes, I believe it was the moebius site that did my head in. Different oils for just about every part of a watch/clock... I gave up lol

Stuart

Originally Posted by Pete F

Michael, the value is the value it "should be" over that distance, and doesn't need to be referenced to an absolute datum.

Pete

Perhaps I'm interpreting datum in the wrong sense, but I'm meaning to a standard and precision has to relate to a standard. Values being what they "should be" over a distance is repeatability - you don't necessarily care what the number is (because it is a relative value - you want the difference) provided that it is consistent.

Martin, try here - Micrometer Standards - Series 167

Michael

Values over a certain distance is accuracy if they conform to an accepted standard, obtaining a small deviation from that number is repeatability.

Pete

Edit: Hmm, perhaps an example is better. Say you have a 25 mm gauge block and accept that as a standard. You take your calipers and take the first reading, you read 26.00 mm, you take the next reading it's 26.01, the next 26.00, the next 26.01, the next 25.99, and so on. The calipers are in this case repeating well, but are clearly inaccurate.

The next calipers read 25.00, 25.01, 24.99, 25.00, 25.00, 25.01, etc. In this case the calipers are both accurate and repeatable.

The third calipers read 24.00, 26.00, 25.00, 24.05, 26.00, 24.98, 25.84, etc. in this case the results are not repeatable, by default they cannot therefore be accurate, as repeatability is a prerequisite for accuracy.

The third pair are also from Aldi.

Phil

Originally Posted by Steamwhisperer

The third pair are also from Aldi.

Phil

Yes I was tempted to write that at the time, but thought my example figures were a little too close for Aldi calipers!

I love the good old vernier calipers. Need no battery, always work, solid, accurate..... but I grew up with verniers. The young guys that grew up with electronic calculators find it hard to quickly and accurately read a vernier scale.

Here I like to compare one of the best vernier calipers, with an average low cost caliper. The Mitutoyo "diamond" I have bought in the late 80's, it is my most used caliper, and it is my favorite caliper (and I also have a mitutoyo absolute!). The other caliper is what I believe to be one of the better vernier calipers made in China, it is branded "Kincrome". I bought it specifically for use close to the bandsaw.

On the pictures, both calipers are set to read 10.00mm. The Mitutoyo "diamond" prismatic calipers are a joy to read..... no parallax error, no disturbing shades. I really trust it to read repeatably 1/20mm. The Kincrome I would at best trust to 1/10mm. But I let you decide which one you would rather use:

Calipers01.jpg


Calipers02.jpgCalipers03.jpg

Calipers04.jpgCalipers05.jpg

Calipers06.jpgCalipers07.jpg

Calipers09.jpgCalipers10.jpg

I have only heard about the diamond calipers Chris, never seen them before.
After years with an absolute i am now using 3 dial's for everyday stuff, a .02 Tesa, .001" Etalon and a .05 Mits. I find them easy to read, don't play up with a drop of coolant on the wrong spot and are very accurate considering they are calipers.

The oil seller's oils are all the same, is anyone else interested? I have Dean and Bryan so far.

Cheers,
Ew

Originally Posted by cba_melbourne

I love the good old vernier calipers. Need no battery, always work, solid, accurate..... but I grew up with verniers.

Me too. I have a pair of Kingchrome electronic digital calipers that rarely get used as I prefer my Mitutoyos.

However one comment on your Kingchrome ones - they epitomise the lack of attention to detail that drives me nuts with a lot of Chinese tooling. Note where the locking screw is WRT the Mitutoyo. You can't use the inside measuring jaws without that screw fouling, for an awful lot of operations. With the Mits, you can.

I have 2 cheap Chinese calipers with the screw in the same place. I've tossed it in the rubbish and use the calipers without the locking screw. My guiding principle being, if the hole size was really important to get right, I'd be using the Mits calipers anyway. The Chinese ones live on the workbench for general use.

PDW

Originally Posted by Ueee

I have only heard about the diamond calipers Chris, never seen them before.
After years with an absolute i am now using 3 dial's for everyday stuff, a .02 Tesa, .001" Etalon and a .05 Mits. I find them easy to read, don't play up with a drop of coolant on the wrong spot and are very accurate considering they are calipers.

The oil seller's oils are all the same, is anyone else interested? I have Dean and Bryan so far.

Cheers,
Ew

Ew,

Add "Diamond Master" , "Quadri" and "prismatic" to your saved searches along with diamond.

Mitutoyo used those terms when describing their 522 series calipers. I'd seen them in my Mit catalogue collection but it wasn't until now and Chris' photos, that I realised how nifty they were.

I have a vial of Koch watch oil that I reckon will see me out hence the lack of hand raising. Thanks for the kind offer though.

BT

Another vote for the Mitutoyo Absolute calipers. I have a bunch of calipers ranging from Aldi specials I keep meaning to take a hammer to and recovering any useful parts from, to some Tesa calipers I bought brand new. Although the Tesa is the most accurate (partly I expect due to no wear), I always use the Mitutoyo calipers as they're by far my preferred. I find calipers normally provide all the accuracy I normally need and would suggest anyone starting out to not waste money on buying crap, grit their teeth and wait until they can afford some good calipers as if they're looked after, they'll possibly last the rest of their life in an amateur's workshop.

Pete

Hi Chris,
While I'm not so sure I'm that upset about parallax error issues* the shading issue alone would make them worth it.... though my unassisted eyes are getting beyond verniers. I'd think about adding a magnifier like one of my mics has, but I dont have a vernier caliper worth the trouble

Thanks for the pictures. Like Bob I'd seen them but never had my sticky fingers on them.

The next guy selling one on ebay might do better than he thought lol do they make one in decimal inches?

*though it could well be one of those things you dont think you need until you have it and then its "how did I get by this far without it?" lol

Hi Ray,
Bad luck on the dial indicator side of things. I dont think I can get them on my master.

Hi Michael,
I've been struggling to put a post together that even makes sense to me

Originally Posted by Michael G

Your height master can as it is graduated with numbered divisions - if the numbers were removed your heightmaster would be pretty much useless.

But the same goes for a micrometer? The "marks" on a DTI are no good to you if you dont know what they mean, Even for zeroing you need some idea of what the marks mean.

How would you measure runout with a micrometer without a fixed reference point?


Stuart

Originally Posted by Pete F

.....Aldi specials I keep meaning to take a hammer to and recovering any useful parts from.....Pete

Pete, do not bother. I already tried to save the circuit board and use as spare for the better made but otherwise very similar chinese calipers and chinese scales. The thing is that the Aldi calipers have a modified circuit board that is made to fit the part I did post the awful picture from. That part determines the distance between the beam and the circuit board. This distance is critical for reliable reading. The Aldi board has two milled recesses, which makes it bind if installed in any other chinese caliper make. If you look at the board, it becomes instantly clear what I mean: "normal" chinese scale boards have a flat bottom surface, the correct distance to the beam is set by two bronze strips. The Aldi scale boards have a bottom surface that is recessed on both long sides. Sorry about that. Just bin them when they stop working. With calipers, you get exactly what you pay for.

PS: the other way around does not work either: you cannot take a circuit board from another chinese caliper, to repair an Aldi caliper - unless you spend the time to mill two recesses into it. It's definitely not worth the time.