Many calibration customers become frustrated with their calibration sources because of price changes after they’ve sent a purchase order and the gages to the lab. Often it looks like the lab may be playing some games in this regard, i.e. quote a low price to get the order, then the real price once the order has been received. Changes to an already approved and issued order become a real hassle in many companies and reflect badly on the person requisitioning the service.
This situation is usually the result of a misunderstanding that can be avoided once you know how things work from the lab’s point of view. Hopefully the following notes will give that insight and ways to prevent the problem in the first place.
It all starts with a request for pricing to calibrate a list of gages. The lab will respond using prices from an established list but that list is based on the assumption that the gages in question are worth calibrating. In many cases their actual physical condition would make calibration meaningless. By this I mean, they appear to have been a casualty of war and are so damaged a simple visual inspection indicates they are unlikely to meet any known specification. More commonly, gages are left unprotected and by the time they are next needed, they’ve rusted or pitted to such an extent they are not worth calibrating.
That standard lab price list also assumes the gages on your list are standard gages. If you forget to mention that the 1/2-13 UNC plug gage has a plain diameter ahead of the threaded portion for a special requirement, get ready for a revised quotation.
In North America, threads are considered to be right-handed unless otherwise specified. If the 1/4-20 UNC gage you want a quotation for is left-handed, the calibration cost is unlikely to change if it’s a thread plug gage. But if it’s an adjustable thread ring gage, the lab may not have the special setting plug that will be needed for the calibration. The same thing applies for ‘standard’ threads that have special pitch diameters. If the gage has a thread designated as NS or UNS it’s a special and this should be noted when asking for a quotation. You can prevent this causing a revised quotation by clearly stating all the details off the gage including the pitch diameters.
Typically, any thread gage over 1.1/2 inch in diameter will be considered a special even though it has been made to an N or UN thread series specification. The same applies to gages with freaky nominal sizes finer than 1/16 inch increments.
Gages of any kind made to a specific drawing usually means one or more elements of it may be special otherwise a special drawing would not be required. Similarly, threads that appear to be standard in every respect become special if they are marked ‘Pre-plate’ and/or have a US or OS designation along with a plating thickness amount.
Fixed limit gages are not the only items that get complicated at times when they appear to be fairly simple. Calibration laboratories are often forced to re-quote their services when measuring instruments are involved.
One example is the lowly micrometer. Specifying it as a 0-1 inch or 0-25mm outside micrometer may not be enough if it’s a thread mike with interchangeable anvils. Or a v-anvil or one that has an indicator incorporated that requires calibration in addition to the micrometer head. A 0-6 inch or 0-150 mm outside micrometer using interchangeable or adjustable rear anvils will have a standard calibration cost attached to it but if you don’t stipulate there are setting rods with it (and their sizes) expect a new quotation from the lab when they receive it.
When instruments from well-known manufacturers are involved it is always wise to quote the model number so the lab can ensure their standard prices apply. If it’s an unknown maker or private label model you can note that it’s similar to a model from a well-known manufacturer.
If you don’t want to get wound up in details of this nature but still want an accurate quotation for calibration, send the items involved to your lab with a “request for quotation only.” Your calibration people will be able to see exactly what they have to deal with and can issue a firm quotation. When you do this everyone will be happy—depending on the calibration results.