The first reinforcements made for string instruments were wooden props, the manufacturing process of which was relatively simple. The purpose of these props was to counteract the tension of the strings when their number increased, such as in the harpsichord. As the tonal range and number and tension of strings increased, additional wooden reinforcements were added, as in the case of the fortepiano. Later, metal props were also introduced. The next step was to equip the instruments with metal frames with pins where the strings were fixed. However, the number of strings and their tension continued to increase, and solid wooden reinforcements were not sufficient to counter their force and keep the pins in place.

So, after props and metal reinforcements, the idea of a single metal plate was finally reached. The first metal frame in an instrument dates back to 1825 and was built by Alpheus Babcock for a table piano. In 1855, a frame for crossed strings was patented (also intended for a table piano). In 1843, Chickering grand pianos were fitted with a cast iron plate, and in 1859, the same happened for Steinway pianos. The metal frame allows the strings to have very strong tension, while the wooden bracing at the back counteracts the tension of the soundboard. From the early 1930s, it was possible to build metal frames that were so robust that the wooden bracing at the back began to be no longer necessary. By mounting slimmer bracing, pianos became less bulky and lighter. Different materials were also experimented with as alternatives to cast iron. In the 1960s, a Dutch factory built lightweight metal frames, with the advantage that the instrument became much lighter. There were also welded steel plates, which were too elastic, and it became impossible for the instrument to remain in tune. Such instruments still needed very robust wooden bracing at the back.

The plate must be made of cast iron. The fractures of cast iron have a gray surface. Slow cooling is allowed so that the carbon forms graphite spots. Cast iron is dead from a sound perspective, and in fact, every vibration is dampened. Cast iron has minimal elasticity. All of these properties are important for the piano's ability to stay in tune. Cast iron is made from raw iron and scrap iron. Carbon is used to complete the process. The furnace is filled with layers of carbon, raw iron, and limestone. The production of cast iron involves the use of raw iron and scrap iron, completed by carbon during the process. The furnace is filled in layers with carbon, raw iron, and limestone. Limestone forms slag that increases the fluidity of the cast iron. The composition of cast iron includes 2-3?rbon, 1-3% silicon, little manganese, and phosphorus. The melting point of cast iron is 1290°C.
The plate project is calculated and designed, then transferred into the control computer of an automatic milling machine. This machine creates a model, a mold, made of alder or Delignit, which is made slightly larger than the finished plate, by 1%. During the cooling of the iron, it shrinks, but thanks to the precision of the process, the final plate will be exactly as designed, down to the hundredth of a millimeter. The plate is cast using a two-part mold. The bottom part is laid on a flat surface inside a containment box (frame) with the bottom facing up. The box is then filled with a mixture of sand, soot, clay, and water which, after a certain period, solidifies around the casting mold.

Subsequently, the box is flipped and the other half of the mold is positioned on top. Guide pins ensure that the two parts fit together properly. The other half of the containment box is placed on top and filled with the same mixture. Rods are inserted into the mixture, which will form channels through which the molten iron will later be poured. After the mixture has set, the box is removed and the mold and rods for the channels are removed.

Now there is a mold for the plate. The two halves are joined and the molten iron is poured into the mold. When the iron has cooled, the mold is removed. The plate is freed from the pouring channels, cleaned with compressed air, and is ready for further processing. Modern foundries use a method called vacuum casting, in which air is sucked out of the mold while the molten iron is sucked in. The next phase involves drilling holes for the pins, holes for the attachment points, compressors or staples, and all the rest. These holes are now drilled with CNC machines, which complete the task in a very short time. The machines automatically change drill bits, drilling exactly where necessary, and can be isolated to avoid disturbing with their noise. There are about 500 holes to be drilled in each plate. When the plate is drilled, it must be sanded, puttied, and painted.