Pin gages - plus or minus?

RJSakowski said:
It is true that there is a tolerance associated with both minus and plus pins and there is no guaranty that a minus pin will measure in at nominal - .0002" or a plus pin at nominal + .0002".

I have to say though, I have never measured a pin that wasn't exactly .0002" under nominal for a minus pin or .0002" over for a plus pin based on a micrometer measurement. Just luck, I guess.
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In many instances, I just want to know if a hole is .250" rather than .249" or .251" and the tolerance band is good enough for that. For any critical dimensioning, I always measure the pin with a micrometer.

"Trust but verify."
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It will be interesting to spot check a few of the moderately priced pins that I ordered when I receive them in a few days to see how close they are. Of course they are the ZZ spec. and are minus sets. (+.0000", -.0002").
 
Alan,

Don't worry about what ezduzit said about the Shars gage pins. For your needs, they will last a lifetime. Keep them oiled down with LPS-1 or Starrett M-1 or Starrett gage & Instrument oil. DO NOT USE WD-40!. Doing so could/will turn them brown!

Ken
 
Thanks Ken, yes I believe they will be fine. Shars is certainly not Vermont, Meyer or one of the other top shelf manufacturers. I am looking forward to confirming their specs on tolerance, edge treatment, surface finish and hardness they claim. I have bought very few Shars items but what I have bought is okay.

I am fortunate that my shop is humidity controlled and I don't have problems with rust.

Your recommendations for surface treatment are appreciated and I have all of them in the shop. I added the LPS a few months back and haven't used it yet. I believe your recommendation against using WD40 is spot on too. It is a great cleaner because it's full of surfactants/detergents and I use it by the gallon but never for permanent lubrication or protection. I use it in my ultrasonic tank (in a beaker) from time to time and it makes a dandy cleaner.

One I might add to your list for a corrosion protectant is Boeshield. I've had great luck with it over the years. A flannel cloth saturated with it is an excellent tool to wipe down gages and the like.
 
The pin gages at work came with a sheet of paper giving the exact size of each pin.
 
The pin gages at work came with a sheet of paper giving the exact size of each pin.
 
Holescreek said:
Every place i've ever worked (including the QC lab I'm in now), and all the sets in my own shop, are minus sets. Minus gauges are .0002" undersized.

If you use a +pin to size a hole and it fits, it's already too big.

The sets at work are Meyer. The 3 sets in my shop are import (.011"~.5").
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I agree, If too small you may be able to remove some material to get an exact fit.

If too big you are stuck.
 
The diameter callout on the hole will dictate what size pins will be required.
As an example a diameter dimension of .500 -.000 +.001 will tell you that the intention of the engineer is a hole that is not LESS then .500 so buy a .5001 pin as a GO gauge that MUST go into the hole (a + pin) and a .5019 pin as a NO GO gauge which MUST NOT fit in the hole (a - pin).

This assures that the hole is larger then .500 but smaller then .502
You will notice that this example is 3 decimal places, there is no wiggle room with -.000 because at 4 decimals it is still 0, the + .001 is still within tolerance at .5019, if the call out is .5000 -.0000 +.0010 then buy a -.501 pin as a NO GO.

Much to your chagrin you will have to buy pins for each size hole in .0001 increments if you work that closely at all times.
.032 to .5 is .468 / .0001 = 4680 pins.
At .001 increments it is only 468 pins.

Good luck
 
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