Mic standards or gauge blocks

[John Evans]

Harold brought up a good point in my for sale add . I commented the mic set was missing the standards And his comment was if work was to be measured by different mics on the same part to fit other parts gauge blocks were preferred so all tools were set to the same standard. Looks like a hot afternoon project in the AC in the house correcting all my mics to one standard .

[Harold_V]

In reality, it likely doesn't make much difference, but I can still remember the standard that came with my 2"micrometer-----.0002" undersized, but without such a notation. A great deal of the work I used to do had only .0002" tolerance. Can't do that kind of work (successfully) when the mic isn't set properly.

H

[John Evans]

Well I have several of each Mic size and depending where I am in shop [zoo] I may measure the same area of the same part with several different Mics. Sooo I think I will use one standard [gauge block] to set all Mics of each size . Curious to what I will find as to variance in a size groop .

[Harold_V]

I'll be interested in reading what you discover, so be sure to post accordingly.
H

[John Evans]

Well spent some constructive time this afternoon at the kitchen table with a bunch of mics and gauge blocks. Bottom line was most mics were reading about 2 tenths to big on adverage . Closer than I expected that's for sure ! Wish I could remember what set of standards I used to originally to check these when I acquired them , the NSK odometer style one I've had the longest so that is the set of standards I probably used to check the rest. I think the worst one was about 3 tenths+ over .

[Harold_V]

More or less proves my point.

A standard need not be a given size, for any size can be used so long as it is known. One sets the instrument accordingly, but if it's marked with a size that isn't correct (as mine was), it should not be a part of anyone's tool arsenal (I discarded the standard the moment I realized it was not accurately marked). It's hard enough to do tight tolerance work without being undermined by lying tools.

H

[pete]

I forget what the industry standard + - tolerence is for micrometer standards, but there way looser than gage block limits are. Used, worn or offshore built mike standards may or may not be even further out if there not checked. I started my working career in a coal testing lab and one life lesson I learned from that job was when it comes to getting accurate and dependable results then consistency and double checks are everything. If it were me I think I'd check my mike standards as well as possible with whatever equipment I had or could borrow and only use and have available one of each size and store any extras marked with what they measure where they'd not be used without a decision to do so and knowing they weren't my accuracy standards. Likely + - .001" for most of us is probably about average for general and fairly tight non paying work until someday it isn't like a bearing press fit. That's when that consistency and double checking instantly pays for itself. Having to use locktite when you were shooting for a nice press fit is a bit hard on one's ego.

Many might see little need for them and I didn't myself for years. But I now consider a gage block set, small surface plate and a cylindrical square as my shops standards that allow me to check most other items against those known reference surfaces. It's tough enough to reliably measure down to a couple of 10ths without having to second guess if the tools providing accurate results or not. There was also a hell of a lot of very accurate and tight tolerence work turned out using little more than a good machinist's scale, toolmaker buttons, inside, outside, and hemaphrodite old school friction calipers and maybe one or two mikes if they were lucky before the more modern metrology equipment was invented. I'm not nearly as good with those tools as they were so I need to cheat.