Complaints about measurement
Where there is a client – supplier relation there are usually some issues with business performance, especially in leather world. You may have to argue with your suppliers, workers, or customers about the leather measurement. To settle the situation we need to present the measurement data and print provided by the measuring machine. Then, after comparing it with supplier’s information one can start negotiations. But what is the acceptable difference? Usually, the buyer will not accept any. Luckily, there is a document which in the leather market seems to be most useful as it gives a common ground for negotiations. The official “Code of Practise”.
Code of Practice for the area measurement of leather by the pinwheel measuring machine
1. Template storage and calibration
Leather market uses as accurate data as possible. An objective scientific body should verify the size of each new template. Each year used templates should be re-submitted for examination. And each machine should be given appropriate templates – depending on the measured leather size. The templates themselves should be kept away from light, at room temperature, and of the flat surface.
2. Calibration of machine with template
In all parties best interests is systematic calibration of the machine with templates. It is not only necessary, but also a convenient protection of accuracy and leather world is unforgiving in this regard. In order to be measured, the machine must be calibrated with a template of approximately the same area of the leather. All pinwheels should be tested and to achieve that the templates should be passed through the machine as many times as necessary. It is a good practice embrace by the leather market leaders to calibrate the machine at least twice a day and in addition - randomly from time to time.
3. Leather conditioning
In order to conduct an accurate leather measurements the material should be exposed to a standard atmosphere of 65% (+/-5%) relative humidity at 20°C +/-2 °C. Moreover, for at least 48 hours, each skin should be provided with free access to the air surrounding it. If for some reason above steps are hard to be performed, there should be a clear notation in the repost about given deviation from the method. One should remember though that the humidity is more important than atmospheric temperature.
4. Operation of the machine with leather
a. Before each measurement the dial-pointer must return to zero. It can be achieved by installation of a special damper or thanks to the supervision of operators.
b. Speed of the machines recommended by the manufacturer should not be changed.
c. The operator who reads the dial measurements should mark or record the area of a piece of leather. d. The operator has to make sure he faces the dial squarely and the distance between the pointer and the dial face is minimal in order to avoid errors (due to parallax).
e. The supervisory stuff should randomly run the re-measurements of samples of measured material.
5. Measurement method
Leather world is a world of strict rules to prevent from any mistakes and losses of valuable material. The machine should have set higher friction surface coming into contact with the pinwheels before the leather is fed to it. When it passes between pinwheels and the top of transporter roller, the material has to be totally flat. The soft leathers can be a hard case here, since it may need to be pulled from edge to edge to avoid the pins pushing the skin into the transport feed slots. This is why more than one operator may be needed to run the whole process.
An acceptable tolerance is +/-2% (on the whole order, not on each, individual hides). For softer leathers which stretch easier (like clothing, upholstery or gloving leathers) the acceptable tolerance is +/-3%.