Microfinishing Film – the ideal filing material for piano hammers. This is an industrial abrasive with some very interesting characteristics and applications for us piano technicians. The backing material is a fairly stiff and very durable mylar film. It has the advantage that it will only bend in one plane at a time. This helps to maintain flat filing surfaces and crisp and defined edges on hammers.
The grit itself is aluminum oxide – a sharp and durable abrasive. The grains are micro-sorted by size to a high degree of precision; this results in an aggressive cut, yet a smooth finish. The Microfinishing film is denoted by the grain size in microns e.g. 100µ, 60µ etc. The smaller the number, the finer the grit and the finer the finish. I currently carry this material in 100µ, 60µ, and 40µ, which corresponds to roughly 100, 200 and 320 grit. While this material is a lot more expensive than hardware store sandpaper, its good performance and durability makes it an abrasive of choice for hammer shaping. It is ultimately very cheap to use, costing only pennies per set of hammers filed. This material will outlast any sandpaper; one university technician recently reported having filed 200 (!) sets of hammers over two years with one set of strips which were still going strong.
The Microfinishing Film is sold in the Hammer Filing Kit, consisting of three 2″ strips of different grits plus one Plexiglass file for mating hammers to individual strings as shown in André Oorebeek’s book “The Voice of the Piano”.
- # 130315 Microfinishing Film Filing Kit
Video showing master voicer Boaz Kirschenbaum using the hammer filing kit