Review: $50 0.0001" inside micrometer from Shars 303-2101

Holescreek said:
If you trust your micrometers, just set them for a size and lock them in place to check the width with the new mics throughout its range. When your talking tenths, temperature and surface finish are everything. Steel changes .0001 for every 5 degrees of temp change. Surface finish effects size every time the jaws close on non-ground parts.
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ahh that is an interesting idea..measure the ID mic with the OD mic

btw temperature expansion isnt measured in inches per degree its inches per inch per degree, i.e. relative change not an absolute change, unless you are specifying a specific starting geometry. It depends on the size of the object...otherwise if you had a 1 tenth cubed sized object it would essentially increase in size by 800% if you used 1 tenth / 5 degree and it went up 5 degrees, which is certainly not the case.

Steel is 0.00000645 inch per inch per deg F. So a 1 inch long object would become 1.00000645" long when heated by 1 F.

Anyone reading this should fact check what I just wrote BTW, this is the internet.
 
spaceman_spiff said:
ahh that is an interesting idea..measure the ID mic with the OD mic

btw temperature expansion isnt measured in inches per degree its inches per inch per degree, i.e. relative change not an absolute change, unless you are specifying a specific starting geometry. It depends on the size of the object...otherwise if you had a 1 tenth cubed sized object it would essentially increase in size by 800% if you used 1 tenth / 5 degree and it went up 5 degrees, which is certainly not the case.

Steel is 0.00000645 inch per inch per deg F. So a 1 inch long object would become 1.00000645" long when heated by 1 F.

Anyone reading this should fact check what I just wrote BTW, this is the internet.
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6.45 ppm/degree F is correct for ordinary steel. Your standard might be invar, though.

Can you borrow some traceable standards for long enough to calibrate some of your own?
 
John Hasler said:
Can you borrow some traceable standards for long enough to calibrate some of your own?
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is that what you would recommend? I dont think I can borrow any (dont know any machinists)...wouldnt it be better to buy some used ring gauges off flea bay so I could re-check periodically? Or is that for some reason no bueno

How much we talking for a set of NIST ring gauges brand new (why do I even bother asking)

EDIT: okay I get what you mean..you mean calibrate the used ring gauges I buy with known good NIST ring gauges I borrow..ahhh

so maybe I can buy the NIST gauges then sell them after I calibrate..
 
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spaceman_spiff said:
ahh that is an interesting idea..measure the ID mic with the OD mic

btw temperature expansion isnt measured in inches per degree its inches per inch per degree, i.e. relative change not an absolute change, unless you are specifying a specific starting geometry. It depends on the size of the object...otherwise if you had a 1 tenth cubed sized object it would essentially increase in size by 800% if you used 1 tenth / 5 degree and it went up 5 degrees, which is certainly not the case.

Steel is 0.00000645 inch per inch per deg F. So a 1 inch long object would become 1.00000645" long when heated by 1 F.

Anyone reading this should fact check what I just wrote BTW, this is the internet.
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I was going from memory on the placard mounted on the front left of a Moore Jig Grinder.
 
spaceman_spiff said:
is that what you would recommend?
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I'm not qualified to recommend.

I dont think I can borrow any (dont know any machinists)...wouldnt it be better to buy some used ring gauges off flea bay so I could re-check periodically?
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Seems to me that should be good enough for your purposes. You just need repeatability so that you can know for sure that you hit your target dimension, right? If you aren't making parts that need to interoperate with ones made in another shop it doesn't really matter if you are always a tenth off as long your measurements are consistent.

How much we talking for a set of NIST ring gauges brand new (why do I even bother asking)
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I'd rather not know. Finding a usable micrometer at a price I can afford would make me happy.
 
spaceman_spiff said:
is that what you would recommend? I dont think I can borrow any (dont know any machinists)...wouldnt it be better to buy some used ring gauges off flea bay so I could re-check periodically? Or is that for some reason no bueno

How much we talking for a set of NIST ring gauges brand new (why do I even bother asking)

EDIT: okay I get what you mean..you mean calibrate the used ring gauges I buy with known good NIST ring gauges I borrow..ahhh
Click to expand...

Or use borrowed gauges to calibrate set of bearing races of various sizes. A standard doesn't need to be an exact multiple of .10000". You just have to know that it is exactly .7492" or whatever.
 
I don't follow the desire for ring gauges (they're nice, but limited). Inside mics are good for anything the anvils fit inside. I calibrate them monthly using a master gauge made up of a series of discs with gaps between the discs. You can use your gauge block to check your mics too, both thickness and distance between.
 
I just picked up an identical mic, except branded Moore and Wright, and metric. 5-30mm. I'm experiencing the grittiness in the thread also,
 
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