Questions on an inside micrometer.

[mcostello]

I bought an 1-2" inside micrometer from one of Our favorite tool resellers. Mic is undoubtedly made from an way off shore company. They supply a ring gauge with the micrometer. Accuracy is said to be .00024". I use the size 1.1811" and the mic reads .0015" too low. I calibrated the mic with the ring setting gauge. The mic agrees with the ring and My Mitityoyo 1" gauge block. I sent the mic back and the company agrees with My findings. The description says the mics are checked at 10 datum points, evidentially not the one I use. They say I am expecting too much from this style mic. What does everyone here think about this?

 

[vtcnc]

A lot of questions, but I wonder if the issue here is repeatability not accuracy. When you state the accuracy is .00024" is that off a supplied certificate? The reason I say this is that you state the mic agrees with your Mitutoyo standard and the supplied ring gage. So, it is accurate to a standard. But if you travel the mic, that accuracy isn't repeatable? Am I understanding this correctly? If so, then I agree that you should have sent it back based on its inability to be repeatable. I can't see how a mic should be expected to be off by .0015" over a .1811" travel. That seems excessive and defective in my view and I think you did the right thing.

 

[Holescreek]

You realize that you calibrate the micrometer to your block by rotating the sleeve right? They are adjustable for a reason.

 

[vtcnc]

You realize that you calibrate the micrometer to your block by rotating the sleeve right? They are adjustable for a reason.

Good point...I'm assuming that is what he did after he gaged it to the Mitutoyo block. Need more info.

 

[mikey]

I use the size 1.1811" and the mic reads .0015" too low. I calibrated the mic with the ring setting gauge. The mic agrees with the ring and My Mitityoyo 1" gauge block. I sent the mic back and the company agrees with My findings. The description says the mics are checked at 10 datum points, evidentially not the one I use. They say I am expecting too much from this style mic. What does everyone here think about this?

Your post is a bit confusing. It sounds like you stuck the mic into the supplied ring gauge, which is 1.1811" ID?, and calibrated it to read 1.1811? If so, then it should be accurate throughout its length. I'm not sure how you used a gauge block to check this mic because the mic reads an ID and a gauge block is meant to check outside dimensions. Maybe give us more precise info.

Most inside mics read to 0.001". My Starrett and Mitutoyo inside mikes do, anyway.

 

[higgite]

...........What does everyone here think about this?

When, where, what, who and how is it reading .0015” too low? If you calibrated it with the ring gauge and it agrees with both the ring gauge and the 1” gauge block (?), what is it not agreeing with and how do you know it’s not agreeing?

I think we need some clarification before we can give you any meaningful thoughts.

Tom

 

[Holescreek]

I bought an 1-2" inside micrometer from one of Our favorite tool resellers. Mic is undoubtedly made from an way off shore company. They supply a ring gauge with the micrometer. Accuracy is said to be .00024". I use the size 1.1811" and the mic reads .0015" too low. I calibrated the mic with the ring setting gauge. The mic agrees with the ring and My Mitityoyo 1" gauge block. I sent the mic back and the company agrees with My findings. The description says the mics are checked at 10 datum points, evidentially not the one I use. They say I am expecting too much from this style mic. What does everyone here think about this?

I just read through the original posting again and now understand mcostello's point. He is setting the zero and verifying it with a gauge block but when he rolls the thimble back to measure a 30mm port (1.1811") the mic is inaccurate by .0015". That's really bad considering he only opened te mic a couple more turns.

The seller states that the manufacturer inspects the instrument at 10 places throughout the travel (extremely doubtful, as is their inspection certificate). The seller states that this mic is the wrong tool to expect that kind of accuracy from.

If I had read the post correctly the first time my first question would've been "what accuracy level is the seller claiming the instrument to be capable of?" If they are claiming +/-.002" then they are OK. providing that the .002" range is full scale. Anything less is a lie.

I use this style of inside micrometer at work (Mitutoyo) and they are quite capable of holding 20 microns ( .0007") throughout the scale. That said, I would use a tri-mic for anything I was measuring that required an accurate number in that range because a tri-mic will self center and adjust perpendicular to the bore whereas a 2 blade mic is easy to get cocked or twisted in the bore.

 

[mcostello]

Holescreek has it right. The 1.1811" dimension is a bearing race that I use to check things with. I took it to work and checked it against the gauge blocks there. It just happens to be the size I need for a repeating job that I have. On the lower end of measurements it is correct, it is just wrong at 1.1811". Am wondering if buying another one from another reseller might be accurate. I have looked at several sellers and They basically use the same picture. Sounds like buying a lottery ticket.

 

[Holescreek]

For the threads to be out that much within a couple of turns suggests that the thread pitch is off. Personally I wouldn't waste any more time on that brand if you're holding tolerances that tight. I get better results using Starrett telescoping gauges and a good micrometer.

 

[mcostello]

I use telescope gauges also, just trying to speed up the process. Company was not worried that the accuracy was 10X worse than the tolerance listed.