Other Dimensions: Buyer Beware
March 28, 2008
Many battles are waged over what someone buying equipment thought they would get compared to what is usually supplied by the industry. Most of the problems arise due to folks not reading the product specifications.
One key area for misunderstanding is “industry practice,” which usually means everyone in the industry knows it while those not in the industry don’t. The fact that a lot of what is normal in the industry is not written down in some sacred book somewhere adds fuel to the firestorm that can result.
The following notes may be of help to you when buying instruments or gages.
Thread Plug Gages. Unless you specify otherwise, they will be supplied to class X tolerance with a taperlock style handle. This also applies to setting plugs for adjustable thread ring gages, so if you want ‘W’ tolerance, specify it and be ready to pay more.
Thread Ring Gages. In North America, you will automatically be quoted for the adjustable type for parallel threads, not the solid type. The reverse applies to the rest of the world. The rings are usually supplied set and sealed by the maker and may not match your setting plugs or those of any outside laboratory you use for calibration but still be within tolerance.
Calibration Reports. Proper calibration reports are not automatically supplied with gages and instruments because most customers would not pay a higher price for the item if they were. Sometimes a gage supplier will include a ‘cert’ at low or no cost with a gage, but this is not a calibration report unless there is data and a lot of other details. That’s why it’s free or cheap.
Buyers of calibration services should be aware that there are no hard and fast rules as to how many measurements will be taken on a given feature. Similarly, there are variations in what features will be inspected on a gage or instrument. The American Measuring Tool Manufacturers Association (AMTMA) is preparing a paper dealing with this subject.
Special Gages. Orders for special gages are non-cancelable unless the buyer will pay for work already done on them. Some makers will not accept any cancellations.
Credit for Returns. If the supplier will accept a returned item, it must be complete with its original packaging and not marked up with your tool number. If it has been calibrated, you are unlikely to receive a credit for the calibration because it is no longer valid. Those items deemed returnable that are re-saleable will usually incur a re-stocking fee of up to 20% of the value.
Setting Masters. Policies vary between instrument suppliers so if you’re buying a 2-inch or 50-millimeter micrometer-or larger-or a long-range bore gage that requires a setting master, confirm that one will be included.
Special Thread Ring Gages. Like all other adjustable rings, specials require a setting master. You should buy the proper setting plug when you buy special thread rings so they can be verified later. If you don’t, the maker will use tooling to set the rings if a setting plug is not available. This type of tooling is not suitable for re-setting purposes, so even the maker of them can’t check them for you later.
Training. Some companies will provide on-site training in the use of products they supply while others won’t. So-called discount dealers or catalog houses are unlikely to provide training, so you may save a few dollars on the purchase price but spend it later if you have to hire someone to train your people.
Gage Tolerances. Standard practice in North America is to apply a plus tolerance on the go plug gage, and a minus tolerance to the no-go gage. The reverse applies to ring gages and these tolerances are inside the product size limits. In the rest of the world, gage tolerances are outside the product limits.
If you don’t have experience regarding these matters, you should list what you expect when buying gages or instruments and discuss them with your supplier or service provider. Reputable suppliers prefer you do so to avoid possible misunderstandings later.