# outside micrometers



## bedwards (Mar 9, 2013)

I bought a set of outside micrometers off of Craigslist. I couldn't resist the price but they didn't come with standards. Now for the dumb question. I have standards that will get me up to 3" but is there a way to set the 4-5 and 5-6 using things in the home shop, or am I going to have to buy the standards? 


thanks,
bedwards


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## Ray C (Mar 9, 2013)

Short answer:  Buy them.

Long answer:   Standards and Gauge Blocks are made under extremely high quality-control conditions on some really high-end equipment.  The quality control standards may even be traceable to NIST procedures and have NIST certification.  (NIST = National Institute of Standards and Technology.  BTW:  I used to work across the street from the main offices and was approached about a job there).  In a home shop environment, you'll struggle to keep something within a half thou -much less two orders of magnitude higher precision.  Certified standards are individually checked on a very expensive piece of equipment that bounces laser light off the surface and measures how long it takes to reflect back.  There are other ways too but this is a popular method now.

Anyhow, when you're calibrating your new mics (and congratulations by the way, contratulations on your new instruments) put them at room temperature for at least several hours.  Try to handle the standard as little as possible as the warmth from your hand will expand them.  As I recall, for true testing, it's usually done at 68 degrees F and the blocks and instruments to be tested have to sit for a full 12 or 24 hours.  This is probably overkill for HS work but, I have noticed differences in readings from the colder shop to the warm kitchen area.

Ray





bedwards said:


> I bought a set of outside micrometers off of Craigslist. I couldn't resist the price but they didn't come with standards. Now for the dumb question. I have standards that will get me up to 3" but is there a way to set the 4-5 and 5-6 using things in the home shop, or am I going to have to buy the standards?
> 
> 
> thanks,
> bedwards


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## bedwards (Mar 9, 2013)

Thanks Ray. They are not as represented when I bought them but didn't catch it till after I got home. (to many family and dogs tagged along on the trip)
They seem well made but don't have a brand name or where made on them, just a serial number on each one. They are somewhat more substantial than the HF set I have.
I see Enco has standards so another 30 bucks will get me where I need to be.


thanks again
bedwards


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