I continue to be surprised when the subject of calibration costs comes up. Why? Because so many folks think they are getting a bargain when someone offers a calibration report for $10 when the rest of the industry charges somewhere around $35 for the same thing. Or is it the same thing?
Like many of my colleagues in the gage making business, I am astounded at how many manufacturers blaze away making parts to iffy or unknown specifications. Often the parts are made to a drawing with fuzzy details, and this lack of information is only brought to attention when a truckload of rejected parts hits the receiving dock.
Being in the calibration business for such a long time means we’ve had our share of weird requests, as have many of our customers. While providing a laugh from time to time, lately we seem to be getting more of them and that’s downright scary.
An uncertainty budget is similar to a financial budget in the type of information it can provide. But unlike a financial budget where every element is in dollar terms, the uncertainty budget has to deal with various elements and convert them into linear terms, such as millionths of an inch or microns, when doing gage calibration.
Nothing provokes heated discussion like uncertainty. We see it in the global warming-now relabeled as climate change-debate and scores of other issues. We demand precise yet simple answers to complex matters, as politicians know only too well. And if we can find someone else to blame, that’s even better.
In dimensional measurement, we use numbers rather than fear to make a point. But sometimes the irrational does creep in. For example: “I paid a gazillion dollars for that thing and you’re telling me it’s not accurate enough to measure these parts,” or “we can put a man on the moon but we can’t measure this better than ...”
Those of you who have been following this series of columns know the caveats
that apply so I won’t repeat them this time around. If you don’t know them,
buy, borrow, beg or steal the previous issues for an update.
I noted in last month’s column, this will be an overview of the most popular
hardware used for calibrating gages. In case you are wondering why I didn’t
mention the use of coordinate measuring machines for this work, and won’t, the
answer is quite simple. Few of them are accurate enough for the tolerances
involved, and those that are rarely exist outside of national measuring
Editor’s note: This is the first in a three-part series on gage calibration.
Part 1: Plain Plug Gages
This is not a how-to column but rather an overview of what is required in the way of hardware used for gage calibration. As with any measuring process, several types of equipment can be used; I will only deal with the most commonly used equipment. It is assumed that you have a proper environment, your equipment and masters are calibrated, and you have a skilled person to use the equipment.
I recently wrote about calibration reports and outlined some of the basics involved with them. This month, I thought it would be worthwhile to deal with documents that are often provided in lieu of calibration reports: certificates of compliance.
The original intent of certificates of compliance was to make sure that process steps were not overlooked if they could not be verified later. An example of this might be a product that has to be dipped in a specified solution at a specified temperature for a specified period of time before painting or plating. Usually, there is no way to verify that these steps were taken once the product has been coated. Testing after-the-fact can reveal that the correct thickness of paint or plating has been applied but not that all specified process steps were followed.