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

[spaceman_spiff]

I wanted something to measure ID's in tenths so I could analyze and improve my lathe skills.

This Shars micrometer is one of those irresistible deals..$50 for an ID micrometer that measures in tenths!!

http://www.ebay.com/itm/SHARS-PRECI...642?pt=LH_DefaultDomain_0&hash=item5197ff4f92

Opening the box: no instructions. Looks like it comes with a 0.20000" standard (yes thats FOUR zeros), a wrench, and the micrometer.

Not shown was the oiled bags the micrometer and standard were in, nor the "certificate" or silica gel.

The certificate just says that they made it on traceable machinery, its got no real numbers on it, not even an operators stamp.

The micrometer has a nice weight and appears fairly high quality. I would not say I was blown away by how great its appearance is.

There are pits on the end of the thimble which do not affect function. But overall Im happy with how it looks.

There is a bit of grittiness to the turning of the thimble, seems to be right at the 0.2" area. I tried popping the cap off using the wrench to see if I could take it apart. All I found is the calibration screw..and a bunch of grit under the cap but at least not inside the mic that I can see. I'm not sure how to take this micrometer apart. If anyone has any suggestions I'm all ears. I'll post up whatever I discover attempting to clean it. NOTE: After doing the measurements below I dont really feel the grittiness anymore. Hmm.

I calibrated it using the included standard, and adjusting the screw under the end cap very slightly.

After calibrating:

1st- 0.2000
2nd- 0.2000
3rd- 0.20005
4th- 0.20005
5th- 0.2000

Measurement method:

Standard held in plastic jaws of small panavise.

Micrometer held horizontal and ratcheted three times while very gently wiggling inside bore.

I made sure not to look at the vernier while measuring so it was "blind".

Temperature: somewhere between 70F and 80F

After calibrating I tried measuring something.

I have an ABEC 1 ball bearing laying around (EZ0 SR8 2RS) which should have a 0.5" ID with a +0 / 0.0003" tolerance.

1st- 0.49985
2nd- 0.49985
3rd- 0.49970
4th- 0.49985
5th- 0.49985

The accuracy of the micrometer is stated as 0.0002" and the bearing bore should be between 0.4997 and 0.5000". Looks like the measurements are in spec.

For comparison I tried measuring the standard and the bearing using my old ways:

5+ year old $10 horror freight 6" digital calipers, heavily used and worn, dropped, beat up, etc...

0.2" using ID jaws: 0.200"
0.5" using ID jaws: 0.5005"
0.5" using TELESCOPE and OD jaws: 0.5005"

New $30 hardly freight 0-1" digital micrometer, 0.00005" resolution

0.5" using TELESCOPE: 0.5001"

Lukin 1911 0-1" 0.001" mic

0.5" using TELESCOPE: 0.4998"

The "TELESCOPE" is a unknown age (probably VERY old) Starrett 229 telescoping bore gauge.

Not too bad either but not good enough for tenths work. Looks like you can probably measure within 1 thou using the very cheapest tools.

So what else can I do to put this micrometer through a gauntlet of doom? I'd like to prove its mettle (or disprove it).

I should say that I'm happy so far but measurements in tenths are the kind of thing that need frequent and careful verification so until I get my hands on a couple more bearings with something like 0.75" and 1" and then check the mic throughout its range I'll withhold being too overjoyed. But it looks good so far!

 

[JimDawson]

That's pretty durn close. I would say that you can't get better than that unless you were in a temperature controlled inspection room.

 

[chuckorlando]

For what you got in them, I would say you can be happy. Longevity is a whole nother concern though. But aint much to go wrong with analog. Only thing you can really do is test it at a range of sizes, but I suspect the results will be the same.

Nice score

 

[spaceman_spiff]

For what you got in them, I would say you can be happy. Longevity is a whole nother concern though. But aint much to go wrong with analog. Only thing you can really do is test it at a range of sizes, but I suspect the results will be the same.

Nice score

Im thinking I'm going to need a range of precision rings/bearings in order to truly work in tenths with these. Its not enough to just have the mic, it has to have standards to be a tool. That could help both with short term and long term accuracy..if I know the error I can account for it. But not knowing becomes a problem...

So where to get some precision rings..it'd be great to have a set every 100 thou that are +/-0.0001 lol but I'm guessing that aint cheap..

 

[spaceman_spiff]

I have an idea for a test..I could measure the temperature of the standard, then measure it, then put it in the freezer for 30 minutes, measure the temperature again and then measure it again. I should be able to measure the relative change in diameter with extreme accuracy no?

Problem is I dont know how much the diameter should change with temperature...its a steel ring I would think..unless its cast iron and then its not steel lol

 

[spaceman_spiff]

well it looks like there are actually quite a few ring gages with XX tolerance (20 millionths) on ebay for around $15 each with best offer..I bet $35 would get you a set of 3, say 0.5, 0.75, 1.0" roughly..

 

[chuckorlando]

Ton of them on ebay


http://www.ebay.com/sch/i.html?_odk...ring&_nkw=bore+gage+setting+ring&_sacat=11804

 

[spaceman_spiff]

wow I'm really drawing a blank on google finding anything precise and official about calculating the ID growth of a master ring gage versus temperature...am I looking this up wrong?

I did find some "ballpark" values that seem to suggest that my little chinese 0.2" ID standard is not going to measurably change even with a 100F difference...so I guess the idea of the freezer thing is out

 

[Holescreek]

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.

 

[spaceman_spiff]

so in my eagerness I decided to measure some more things! yes its a slow night

I had this little bearing block and shaft thing sitting around for a year that Ive never used for anything. Basically a block of aluminum, two bearings, and a shaft..not sure how tight the tolerances were it was machined to...

The shaft is a pretty easy sliding fit into the bearing..I would not call it super precise.

Lets see what the numbers say:

Bearing ID: 0.3749"

Shaft OD: 0.3744"

Block bore: 0.8755"

Bearing OD: 0.8747"


well isnt that neat...


hmm what else do I have around here...