Using dial calipers and micrometers correctly
Discussion
Can someone with some experience clear this up for me please...
When measuring something with dial calipers, how much pressure (if any) should be applied once the measuring jaws have made contact with the piece being measured? I've noticed there's a big difference between just allowing the jaws to touch the piece compared with applying some pressure and 'squeezing' the jaws with the thumb wheel. Should a reading be taken in both states and then the average calculated, or should the jaws just come to rest?
Similar to the above, what approach should be used with a micrometer? Most mics have a ratchet mechanism that's supposed to limit the amount of torque applied in order to make consistent measurements but some don't and some mics have slightly different calibrations for the amount of torque applied through the ratchet.
When measuring something with dial calipers, how much pressure (if any) should be applied once the measuring jaws have made contact with the piece being measured? I've noticed there's a big difference between just allowing the jaws to touch the piece compared with applying some pressure and 'squeezing' the jaws with the thumb wheel. Should a reading be taken in both states and then the average calculated, or should the jaws just come to rest?
Similar to the above, what approach should be used with a micrometer? Most mics have a ratchet mechanism that's supposed to limit the amount of torque applied in order to make consistent measurements but some don't and some mics have slightly different calibrations for the amount of torque applied through the ratchet.
Both items are fine measuring instruments so no pressure is required for either.
As a new user your biggest issue will be making sure you have the instrument aligned correctly. If it is not square to the item being measured you will get a false reading. You would do well to spend some time measuring the same item over and over again. In this way you will learn the feel and what misalignment errors you can produce.
For the micrometer to main thing to learn is how to hold it. If you have the typical 1"/25mm size then learn to hold it (for example) in your right hand palm up, hook your little pinky up through the hoop of the body and grip. You can then adjust using thumb and first finger. Use the ratchet to start with but pretty soon you will get the feel.
Enjoy
Steve
As a new user your biggest issue will be making sure you have the instrument aligned correctly. If it is not square to the item being measured you will get a false reading. You would do well to spend some time measuring the same item over and over again. In this way you will learn the feel and what misalignment errors you can produce.
For the micrometer to main thing to learn is how to hold it. If you have the typical 1"/25mm size then learn to hold it (for example) in your right hand palm up, hook your little pinky up through the hoop of the body and grip. You can then adjust using thumb and first finger. Use the ratchet to start with but pretty soon you will get the feel.
Enjoy
Steve
I used to practice measuring "slip gauges" to get the right feel for the correct measurement. There not cheap but you can get individual ones to practice with.
The blocks are calibrated to within +/- a couple of hundredths of say 10mm so you can be confident that if you are getting say 9.95mm you are applying a bit to much pressure.
http://www.google.co.uk/url?sa=t&source=web&am...
The blocks are calibrated to within +/- a couple of hundredths of say 10mm so you can be confident that if you are getting say 9.95mm you are applying a bit to much pressure.
http://www.google.co.uk/url?sa=t&source=web&am...
rhysenna said:
I used to practice measuring "slip gauges" to get the right feel for the correct measurement. There not cheap but you can get individual ones to practice with.
The blocks are calibrated to within +/- a couple of hundredths of say 10mm so you can be confident that if you are getting say 9.95mm you are applying a bit to much pressure.
http://www.google.co.uk/url?sa=t&source=web&am...
The blocks are calibrated to within +/- a couple of hundredths of say 10mm so you can be confident that if you are getting say 9.95mm you are applying a bit to much pressure.
http://www.google.co.uk/url?sa=t&source=web&am...
The only way I think. When I was in engineering the squeeze technique came in handy for tolerances to make them fit the QA requirements 
on a vernier you can get a good couple of hundred microns out of them like that!
Using vernier and micrometers you should be able to remove the piece whilst still feeling a slight rub on the faces. Take 2 or three measurements to verify and make sure the faces are spotless, zeroed and true. It's all about feel, with experience you can tell the difference. I used to be able to tell the difference by hand between 1.9mm and 2.1mm when I was in engineering. I also used to calibrate machines to tell the difference in sheet plastic to a resolution of 10 microns and quantify that with really stupidly precise gauges.
on a vernier you can get a good couple of hundred microns out of them like that! Using vernier and micrometers you should be able to remove the piece whilst still feeling a slight rub on the faces. Take 2 or three measurements to verify and make sure the faces are spotless, zeroed and true. It's all about feel, with experience you can tell the difference. I used to be able to tell the difference by hand between 1.9mm and 2.1mm when I was in engineering. I also used to calibrate machines to tell the difference in sheet plastic to a resolution of 10 microns and quantify that with really stupidly precise gauges.
Edited by Fireblade69 on Monday 3rd January 09:14
Silver steel is supplied to a good tolerance so if you can get some it will give a good "practice" piece.
depende on the tolerances you are working with too.
best technique is to rotate the diameter being measured and take several readings
This will show up any ovality. If no ovality then average the readings taken.
ALWAYS zero the gauge before use so you are at least not introducing an error in that way.
Best bet is to get hold of calibration standars if cost permits, but silver steel may be a cheaper substitute for general use
depende on the tolerances you are working with too.
best technique is to rotate the diameter being measured and take several readings
This will show up any ovality. If no ovality then average the readings taken.
ALWAYS zero the gauge before use so you are at least not introducing an error in that way.
Best bet is to get hold of calibration standars if cost permits, but silver steel may be a cheaper substitute for general use
sospan said:
Silver steel is supplied to a good tolerance so if you can get some it will give a good "practice" piece.
depende on the tolerances you are working with too.
best technique is to rotate the diameter being measured and take several readings
This will show up any ovality. If no ovality then average the readings taken.
ALWAYS zero the gauge before use so you are at least not introducing an error in that way.
Best bet is to get hold of calibration standars if cost permits, but silver steel may be a cheaper substitute for general use
Good advice. depende on the tolerances you are working with too.
best technique is to rotate the diameter being measured and take several readings
This will show up any ovality. If no ovality then average the readings taken.
ALWAYS zero the gauge before use so you are at least not introducing an error in that way.
Best bet is to get hold of calibration standars if cost permits, but silver steel may be a cheaper substitute for general use
Also, if checking clearances, make sure your external mic's and internal mic's are reading the same by setting your external mic's to 0 and then placing your internal mic's inside and see what reading you get. Can sometimes get a +/- 100th difference. You then know what your working with.
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