Gage Pin Quality - Buying new pin sets cheaper than calibrating our current sets

J

Jeff McBroom

#1
We are going through our yearly budgeting process and the question of whether to yearly have our gage pins calibrated or simple purchase a new set? Which brings in the 2nd question of what, if any, are the differences between a $80 (import)and $120 set from a more known brand? These are prices for a.061" to .250", 190pcs sets of ZZ grade. It's costing us nearly identical amounts for calibration as it is for the know brand name pins.

Is the only difference between a ZZ set and a X set the tolerance they are checked against (.0002" vs. .00004")?
 
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CarolX

Super Moderator
Super Moderator
#2
Jeff,
Remeber, much depends on the accuracy you need. What are you pinning? Holes with tolerane of +/-.0001 or +/-.005??
Our calibration procedure is very simple. We calibrate before each use. That is, we check each pin with a micrometer before we use it. Now I am only concerned with mearsuring to the thousdandth, and the micrometer measure to ten-thousanth (no guarantee on my spelling here!!! LOL....how about a spell checker, Marc??)
So don't specd the money if you don't have to.
 
S

Steven Truchon

#3
Jeff, Im not sure what your business is, but in many machine or mfg shops I have worked in, we would purchase the new sets of .001 increment pins from .011 to .500, and rotate the old pins out to the shop for reference use only, thus replacing the Quality Dept pins with the new ones. We still had to go through the sets and verify and certify the new pins against a known standard as the pins were not received with any kind certification. It was annually inevitable that many pins from all sets would come up missing or damaged, so this little method that cost the same as replace and certify worked well.

As for tolerances, I always got the inexpensive Chinese versions with a .0002 tolerance and I never had a problem. If I needed better accuracy I always wound up getting .0001 increment pins like Deltronics in a set that ranged +/-.0012 from a nominal size, or simply a high and a low size for limit applications. These pins (sets) would be then annually certfied in-house usually with a SuperMic or LaserMic and appropriate standards.

Steve
 
W

wmhray

#4
The typical problems with gage pins are misidentified pins and larger out-of-tolerance pins. We have found wrong pins in new sets and a reject rate of 25-35% in over .500 inch sets. The costs are smal compared to misuse. Do people really check before use?

The heat treat process of standard pins is suspect, with residual grinding stresses the most likely problem. No problems with Deltronic.

Bill Ray
 
A

artstauff

#5
Jeff,
The comments of the other contributors are all valid. We are a calibration house that does the calbration of tons of plug gage sets. We have several recommendations to our customers regarding plain plug gages. First, when we do a calibration we offer the service of "dip sealing" the pins after the calibration. The customer would then modify their procedures and label the boxes that the rule is to remove the dipseal before use. We find that most companies use roughly 30 % of the pins in a set, therefore making the calibration of all of them yearly, redundant and costly. With reference to using a micrometer to calibrate a .0002 tolerance plug, this does not meet the 4 times rule of calibration. The tool being measured must be calibrated by a tool at least 4 times more accurate. Manufacturers specifications for micrometers are typically +/- .0001, giving a range of .0002 to the mic's accuracy defeating the validity of the calibration. There are several ways to address this. If the work you are producing does not truly require .0002 accuracy pins, if your tolerance is more wide open, you may want to open the acceptable tollerance of the pins to say .0004 or .0008 thus making calibration by a micrometer valid. Or, obviously you can procure a more accurate measuring tool such as a calibration center. The quality of .0002 pins in general is often in question. They are manufactured from 52100 steel that does through harden, but the hardening process does not cause the complete transition of austenite to martensite. Without complete transformation, steel will grow with time as the transition occurs naturally. Gage manufacturers solve this process by cold stablizing the gages multiple times to complete the transition. The question of if Import gages are treated in this manner is often in doubt. Further .0002 gages are typically not round. The are manufactured by Cylindrical Grinding which leaves lobbing in the gages. Higher quality gages are typically Cylindrically Lapped, which produces a round pin. Several good american manufacturers produce pins in this manner including Glastonbury Southern Gage. Finally, many of the import sets are shipped with paper wrapped around each pin with a cosmoline type substance that is time consuming to remove. Good American sets like those manufactured by Van Keuren are not packaged that way. I hope this information helps. If you would like more info please feel free to call. Art Stauff, Angrave Metrology & Supply 203-574-1316


------------------
Art Stauff
Angrave Metrology & Supply
 
R

Ryan Wilde

#6
Originally posted by Jeff McBroom:
Is the only difference between a ZZ set and a X set the tolerance they are checked against (.0002" vs. .00004")?
Size tolerance, surface finish, and cylidrical form are all much tighter on Class X than Class ZZ.

Ryan
 
M

matech

#7
Can someone please recommend a good text on the basics of calibration for a QC Dept in a machining shop? Appreciate any suggestions.
 
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