3 point micrometer

AlexO · Mar 25, 2018

I'm looking for 6-8 / 8-10 / 10-12 and 12-15 3 point micrometers, NOT digital.
I need to be sure of 4 microns. Also, I absolutely need carbide anvils and they must be replaceable and..available. I'd appreciate recommendations based on actual experience. Thank you in advance !

markz528 · Mar 25, 2018

AlexO said:
I need to be sure of 4 microns.

What does that mean? Are you looking for resolution of 4 microns or a measurement uncertainty of 4 microns? If measurement uncertainty of 4 microns then I think you are pushing a rope.

My Mitutoyos are 0.0002 inches resolution. I use several different sets. Not quite 4 microns - a little worse than 4 microns (5 microns). I don't believe the Mitutoyo non-digital come in 0.0001 inch resolution. Not sure if other manufacturers do. The only other one that I am familiar with (and used) are Starret but those are digital.

Sounds like you are familiar with 3 point mics. Are you sure that is what you want? They are not for the faint hearted and can't measure form factor.

Steven-Canada · Mar 25, 2018

I'm just curious, what't the use that you plan on having to wear out and replace carbide anvils ?

Gordon B. Clarke · Mar 25, 2018

Steven-Canada said:
I'm just curious, what't the use that you plan on having to wear out and replace carbide anvils ?

I was thinking the same thing. 3 points don't measure roundness so no need to "twist and turn".

3 point internal micrometers from reputable manufacturers have a specified accuracy of 4µm. Both mechanical and digital.

AlexO · Mar 25, 2018

Steven-Canada said:
I'm just curious, what't the use that you plan on having to wear out and replace carbide anvils ?

Internal lapping.

AlexO · Mar 25, 2018

markz528 said:
What does that mean? Are you looking for resolution of 4 microns or a measurement uncertainty of 4 microns?

Well, what could " I need to be sure of 4 microns" might mean ?

8-10 I used to have a Mitutoyo with 2 microns uncertainty. And I think Tesa ( or Mahr ? ) made one too.

Danny VanVoorn · Mar 25, 2018

I think the Brown and Sharpe/Tesa and the Mitutoyo are about as good as they get but not quite 4 microns. If you need that type of accuracy an air bore gage with the proper rings might be what you really need. The Federal brand comes to mind as to one I used in another life time.
Dan

markz528 · Mar 25, 2018

Remember that with a 3 point micrometer operator influence plays a much more significant part in measurement accuracy than in many other types of measuring equipment. If the instrument has a stated accuracy of 4 microns, that does not mean that your measurement tolerance is 4 microns.

The OP did not provide enough information on what his expectations really are for measurement accuracy. One needs to develop a control plan (my words) to define on paper what the tolerance of the part is and how accurately it needs to be measured. Whatever tool is chosen, you then need to conduct a Gage R&R study to determine the repeat-ability and reproducability of the the instrument and operator. 3 point micrometers tend to do poorly in Gage R&R studies - relatively speaking.

Remember - for the most critical parts, you need to subtract the measurement uncertainty from the part tolerance. Do these parts need this close measurement accuracy?

AlexO · Mar 25, 2018

markz528 said:
Remember that with a 3 point micrometer operator influence plays a much more significant part in measurement accuracy than in many other types of measuring equipment. If the instrument has a stated accuracy of 4 microns, that does not mean that your measurement tolerance is 4 microns.

The OP did not provide enough information on what his expectations really are for measurement accuracy. One needs to develop a control plan (my words) to define on paper what the tolerance of the part is and how accurately it needs to be measured. Whatever tool is chosen, you then need to conduct a Gage R&R study to determine the repeat-ability and reproducability of the the instrument and operator. 3 point micrometers tend to do poorly in Gage R&R studies - relatively speaking.

Remember - for the most critical parts, you need to subtract the measurement uncertainty from the part tolerance. Do these parts need this close measurement accuracy?

One of the problems I've noticed often here is how replies to the OP are written without reading the OP properly and ( ! ) under the apprehension that the OP is an imbecile. My need for the 3 point micrometer has no bearing on the final part dimension - it's not used to measure that. It's used to reduce the number of other measurements with a different tool, I make. The roundness of the part being measured is beyond the ability of any but the most sophisticated equipment. My original post contains everything needed in this context. It's not conversational, I agree there but then I don't like conversations.

Gordon B. Clarke · Mar 25, 2018

markz528 said:
If the instrument has a stated accuracy of 4 microns, that does not mean that your measurement tolerance is 4 microns.

What it does mean is that any measurement should be no more wrong than 4µm. It should be possible to obtain a greater accuracy if calibrated to see how much any possible deviation is. "Specified accuracy" is simply what the manufacturer "guarantees" the accuracy is when used "as is" from the factory.

In theory more than 50% of all measuring instruments should be accurate to half the specified accuracy.

triumph406 · Mar 25, 2018

AlexO said:
One of the problems I've noticed often here is how replies to the OP are written without reading the OP properly and ( ! ) under the apprehension that the OP is an imbecile.

Not entirely sure why you post here sometimes, most of the time your trying to wind people up.

Gordon B. Clarke · Mar 25, 2018

markz528 said:
Remember that with a 3 point micrometer operator influence plays a much more significant part in measurement accuracy than in many other types of measuring equipment.

Care to explain that? What to you is "operator influence" with a 3 point micrometer?

AlexO · Mar 25, 2018

triumph406 said:
Not entirely sure why you post here sometimes, most of the time your trying to wind people up.

You're winding up yourself because you think I'm here to chat. Which I am not. For example, I have no inclination to dissolve your "not entirely sure". I just don't care.

AlexO · Mar 25, 2018

Gordon B. Clarke said:
What it does mean is that any measurement should be no more wrong than 4µm. It should be possible to obtain a greater accuracy if calibrated to see how much any possible deviation is. "Specified accuracy" is simply what the manufacturer "guarantees" the accuracy is when used "as is" from the factory.

In theory more than 50% of all measuring instruments should be accurate to half the specified accuracy.

Thank you. Your patience here is appreciated.

AlexO · Mar 25, 2018

Gordon B. Clarke said:
Care to explain that? What to you is "operator influence" with a 3 point micrometer?

Operator doesn't know how to use it or which end goes in the hole, I suppose.

triumph406 · Mar 25, 2018

AlexO said:
Operator doesn't know how to use it or which end goes in the hole, I suppose.

Apparently a complaint your partner has had.

edelsailor · Mar 25, 2018

Gordon B. Clarke said:
Care to explain that? What to you is "operator influence" with a 3 point micrometer?

The error introduced by the operator: not ensuring that all 3 points of the micrometer maintain perpendicularity to the work in "plane" to all 3 points of contact. If you are needing 4 micron accuracy, you need to fixture (a reference guide) your micrometer and the workpiece being measured.

Sent from my SM-P550 using Tapatalk

Gordon B. Clarke · Mar 26, 2018

edelsailor said:
The error introduced by the operator: not ensuring that all 3 points of the micrometer maintain perpendicularity to the work in "plane" to all 3 points of contact. If you are needing 4 micron accuracy, you need to fixture (a reference guide) your micrometer and the workpiece being measured.

Meanwhile, in the real world ..............!

Rigor · Mar 26, 2018

AlexO said:
I'm looking for 6-8 / 8-10 / 10-12 and 12-15 3 point micrometers, NOT digital.
I need to be sure of 4 microns. Also, I absolutely need carbide anvils and they must be replaceable and..available. I'd appreciate recommendations based on actual experience. Thank you in advance !

OK, with all the flap being passed around here I'm hesitant to reply.............
In our shop we use Mahr "Micromar" 44AS self centering bore gauges. They work well and parts( consumables ) such as anvils, are readily available.

Made in Germany and 4 micron error limit over the entire length of the anvils. This according to their spec sheet. They are as expensive as TESA and other reputables. I hope this is the info you're looking for......

Here is their link.Micromar 44 AS - Self-centering inside micrometer set - Mahr Metrology

Rigor · Mar 26, 2018

And another link for pricing of set of 4 ( around $1300 U.S.)

Self-Centering Inside Micrometer Set 44AS 6mm - Mahr UK PLC

3 point micrometer

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