Tolerance of Shop Grade Plus Size Pins?

B

Bob_M

#1
Alright I was shown the basics on how to perform certain in-house calibrations/verifications when I took over my job...

We measure/verify our pin gage set (rarely used) in-house with a Digital Micrometer (flat/flat) 0.00005" resolution.

What SHOULD the tolerance be for shop grade plus size pins (generic brand)?

I'm getting numbers similar to last year's results (previous QA mgr verified them), but I don't know what the tolerance SHOULD be. None have been over 0.00050 beyond their stated sizes yet...

We have two sets:
.061 - .250
.251 - .500

We/I currently verify them annually, is anyone waiting longer?
 
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Mike S.

Happy to be Alive
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#2
Bob_M said:
Alright I was shown the basics on how to perform certain in-house calibrations/verifications when I took over my job...

We measure/verify our pin gage set (rarely used) in-house with a Digital Micrometer (flat/flat) 0.00005" resolution.

What SHOULD the tolerance be for shop grade plus size pins (generic brand)?

I'm getting numbers similar to last year's results (previous QA mgr verified them), but I don't know what the tolerance SHOULD be. None have been over 0.00050 beyond their stated sizes yet...

We have two sets:
.061 - .250
.251 - .500

We/I currently verify them annually, is anyone waiting longer?
I'm not an expert on this, but I have never had a set of + gage pins that were more than + .0002". If they are .0005" over I'd be suspect of them -- maybe there is rust or contamination on them?

How specific does your measurement need to be ?

Cal interval should take into consideration their usage level, previous cal history, and mfr. recommendations. For pins we use often we do them every 3 months, of less often used pins we go annually, but you gotta watch for rust/corrosion.

We have some really good cal experts on the Cove who may be able to answer better.
 
J

Jimmy Olson

#3
Most likely the gages you have are class ZZ, in which case the tolerance is 0.0002. If you are running into gages that are 0.0005 I would recomend cleaning them and remeasuring.

If 0.0005 is acceptable for what you are using them for then you could special cal them at that tolerance as long as you state that on the cert.
 
B

Bob_M

#4
Richard Olson said:
Most likely the gages you have are class ZZ, in which case the tolerance is 0.0002. If you are running into gages that are 0.0005 I would recomend cleaning them and remeasuring.

If 0.0005 is acceptable for what you are using them for then you could special cal them at that tolerance as long as you state that on the cert.
At the moment we're rarely using them (that I know of). I think our die maintainance uses them more often than production.

We have no current products with tolerances beyond 3 places, and the majority of our "manufactured" holes are in thin sheet metal at right around the nominal sizes. Larger holes, even using a caliper are within spec for all current parts. (Smaller Punched holes for our parts are not typcially critical dimensions).

I think we just have the pin as "just in case" or to help verify a hole size during setup...
----------
Most of what i'm reading is between +.00000 and +.00025 with a few as high as .00040.
At the moment its not a major concern...
Should it be? Or should I spend more time on the pins when we actually start using them on a regular basis?
----------
 

Mike S.

Happy to be Alive
Trusted Information Resource
#5
If a pin .0004" oversize is still okay for the accuracy you need, that's fine, just state this in the cal paperwork.

You might also consider, if you rarely use them, to save you lots of work, make them "calibrate before each use". Teach the users how to calibrate them when they use them. If the users will follow instructions, this can make your cal workload much lighter so you can concentrate on value-added work.
 
B

Bob_M

#6
Mike S. said:
If a pin .0004" oversize is still okay for the accuracy you need, that's fine, just state this in the cal paperwork.

You might also consider, if you rarely use them, to save you lots of work, make them "calibrate before each use". Teach the users how to calibrate them when they use them. If the users will follow instructions, this can make your cal workload much lighter so you can concentrate on value-added work.
Like I said we barely use the pins and our tolerances are not very tight, so I assume .0004 is OK for NOW.

The calibrate before use not going to happen right now.
 

CarolX

Super Moderator
Super Moderator
#7
same business

Bob,
You and I are in the same business. I have a full set of gages and I don't calibrate them in the classic sense, we put a micrometer with 4 place resolution on them before each use. We, too, do not use them very frequently, we use our calipers more often. They do get a bit of use when we run a part with pressed in hardware, since those tolerances are usually +.003/.000 (and can give you a real headache if you are out of tolerance...LOL).

Just another way to skin the cat....in other words....if they are not used...why check them????

Can they be marked "for reference only" and removed from the system?

CarolX
 
B

Bob_M

#8
CarolX said:
Bob,
You and I are in the same business. I have a full set of gages and I don't calibrate them in the classic sense, we put a micrometer with 4 place resolution on them before each use. We, too, do not use them very frequently, we use our calipers more often. They do get a bit of use when we run a part with pressed in hardware, since those tolerances are usually +.003/.000 (and can give you a real headache if you are out of tolerance...LOL).

Just another way to skin the cat....in other words....if they are not used...why check them????

Can they be marked "for reference only" and removed from the system?

CarolX
At the moment I'm keeping them in the calibration loop so they can be used without on the spot calibration. Switching to operator-based calibration is not practical at the moment. At times I barely know how to calibrate certain things. I'm not about to try to teach others how to calibrate. The only exception might be the tool maintenance guy.

Since its only a few hours per year "wasted" its not a big deal yet... I was more worried about what the tolerance should be. *shrug*

So much to learn, too little time, too little money...
 
R

Ryan Wilde

#9
Hi all,

Calibrating little things like these is what I used to do for a living (now I do electronics more), so I'll chime in.

The tolerance of Class ZZ Plus pin gages is -0 / + 0.0002". You cannot adequately prove that tolerance with a micrometer, but then again, with your stated use, you really shouldn't need to hold that tolerance.

The basic tolerance that you CAN adequately prove is -0.0001 / +0.0003. To prove that tolerance, you will have to hold firm on -0 / +0.0002 on your measurement tolerance. The reason being is that 0.00005" resolution micrometers have a possible error of 0.0001" (0.00005" linearity error + 1 count quantizing error).

I'd go with a wider tolerance for my pins if I were you. It's safe, and it makes sense for your use.


Ryan
 
B

Bob_M

#10
Ryan Wilde said:
Hi all,

Calibrating little things like these is what I used to do for a living (now I do electronics more), so I'll chime in.

The tolerance of Class ZZ Plus pin gages is -0 / + 0.0002". You cannot adequately prove that tolerance with a micrometer, but then again, with your stated use, you really shouldn't need to hold that tolerance.

The basic tolerance that you CAN adequately prove is -0.0001 / +0.0003. To prove that tolerance, you will have to hold firm on -0 / +0.0002 on your measurement tolerance. The reason being is that 0.00005" resolution micrometers have a possible error of 0.0001" (0.00005" linearity error + 1 count quantizing error).

I'd go with a wider tolerance for my pins if I were you. It's safe, and it makes sense for your use.

Ryan
Thanks for the very technical answer :D
I've already finished check all of them. The highest I got was +.00040
using our .00005 resolution digital mic.
At the moment that is not a big concern.

Althought people have assumed Class ZZ (which at the moment is Greek to me), but looking at the set, they look very generic, no brand name, no serial number, just a wooden box and numbered + pins...
I have no idea what quality other than
"shop grade +" they really are...

Thanks for the info.
 
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