Questions about standards (measuring rods) for micrometers

How square is square and how do you know ? :grin: ( somebody had to ask ) :laughing:
 
Here’s an story about an eBay purchase I made for a 100mm measuring rod.

I bought a used Starrett 100mm measuring rod for $19. A couple of days later, the Seller sent me a message saying that it was mismarked “100mm” at the Starrett factory, and that it actually measured 125mm. He asked if I still wanted it, but I already have a 125mm standard.

Anyway, I don’t believe that Starrett would have mismarked it at the factory. I looked for another one for a good price, but there are none out there at this point.
 
erikmannie said:
Maybe I am wasting time by using a measuring rod to check the zero each day.
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Checking your mics daily?!!! How often do you have to re-zero them?

I continue to be amazed at how far down in the weeds hobbyists will get about precision for which there is no need. I guess it comes from not knowing what is reasonably expected in the real world. If you have to hit .001 or less, by all means get out the standard and be sure of your zero. Otherwise, you're just being EC. (That's Excessive Compulsive, the next step beyond Obsessive Compulsive.)
 
MrWhoopee said:
Checking your mics daily?!!! How often do you have to re-zero them?

I continue to be amazed at how far down in the weeds hobbyists will get about precision for which there is no need. I guess it comes from not knowing what is reasonably expected in the real world. If you have to hit .001 or less, by all means get out the standard and be sure of your zero. Otherwise, you're just being EC. (That's Excessive Compulsive, the next step beyond Obsessive Compulsive.)
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I have never had to rezero a Starrett. The Shars appear to be hopeless just about every time.

This is the first I’ve heard that practice machining to .001” may be excessive attention to detail. I took machining classes in Oakland, CA, and the turning and milling was to .001”. They also said if the drawing doesn’t list a tolerance, then you can assume .005”.
 
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erikmannie said:
Regarding measuring rods for outside micrometers, my questions are:

(1) to what degree do you trust import measuring rods?,
2) do you zero your micrometer before using it?, and
(3) should I be concerned about buying used measuring rods?

For my imperial mikes, I have Shars standards and Shars gage blocks.

For my metric mikes, I bought used Starrett and Mitutoyo standards.

As far as what tolerance I am shooting for, it doesn’t actually matter, BUT I do take my hobby seriously and I shoot for .001” or better. I fail more often than I succeed. I am striving to be able to work to .0003” one day; like I said, it will probably never have any practical application because most of what I do is just an exercise.

I make no effort for temperature control, but I do make an effort to clean the surfaces of oil before I take measurements. That should give you an idea of what precision I am aiming for. For myself, I consider anything much over a thou out to be a failure (or should I say a learning experience?).
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i check all mearuring tools by my starrett standards, I bough a set of mics from ebay, they were far out
 
erikmannie said:
This is the first I’ve heard that practice machining to .001” may be excessive attention to detail. I took machining classes in Oakland, CA, and the turning and milling was to .001”. They also said if the drawing doesn’t list a tolerance, then you can assume .005”.
Click to expand...

On most of the drawings we worked from (including the ones I drew), the titleblock (default) tolerances were
1/x=+/-.015
.xx=+/-.01
.xxx=+/-.005

These applied to dimensions without a specified tolerance. A specified tolerance of +/- .001 (or less) would not be unusual, but certainly not prevalent.

It is certainly important to be able to achieve tight tolerances, which is why you were taught that way. I would never discourage someone who is learning from trying to do the best he can. It is equally important to understand when close tolerances are unnecessary and not waste time (money) taking the extra cut(s) when the part is already within tolerance. The most valuable machinists are not the ones who hit every number right on the nominal, they are the ones who can produce a good looking part with all of the dimensions within tolerance in the least amount of time. When Fred would find someone worrying a dimension unnecessarily, he would yell "IT FITS AIR!!!"
 
MrWhoopee said:
On most of the drawings we worked from (including the ones I drew), the titleblock (default) tolerances were
1/x=+/-.015
.xx=+/-.01
.xxx=+/-.005

These applied to dimensions without a specified tolerance. A specified tolerance of +/- .001 (or less) would not be unusual, but certainly not prevalent.

It is certainly important to be able to achieve tight tolerances, which is why you were taught that way. I would never discourage someone who is learning from trying to do the best he can. It is equally important to understand when close tolerances are unnecessary and not waste time (money) taking the extra cut(s) when the part is already within tolerance. The most valuable machinists are not the ones who hit every number right on the nominal, they are the ones who can produce a good looking part with all of the dimensions within tolerance in the least amount of time. When Fred would find someone worrying a dimension unnecessarily, he would yell "IT FITS AIR!!!"
Click to expand...
true nuff, when it comes to shrink fot, or you are working in a tool room, close is close enough, but if you aim for 001 and get it,you feel good
 
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