I have no idea about the material, but I can tell you about one application method you may not have considered. I have mentioned it here before but maybe you have joined the list recently. Similar drums were made by ICT/ICL from 1962 to 1965 for the 1300 series, and probably for the 1200 series drum based computers in the 50s. They too had fixed heads with set screw adjustment, which was carried out by monitoring the pressure of compressed air blown through a venturi in each head while moving an Allen screw. The 1300 drums were 12000 48bit word capacity, driven by a 3/4 horsepower motor geared up to 5240rpm at the drum spindle for lower access times. After many experiments they found they could not beat the human hand applying a magnetisable compound like a potter making a pot. Sounds very low tech but apparently it works, and I have drums which have not been touched since manufacture and they still work 46 years on. Of course for you, low tech could be a bonus as it means low cost. Maybe your local educational establishment has a skilled potter who could do a great job for a reasonable price, or just for interest. > The drum is quite low density, and does not have air bearing heads. > The head heights are actually adjustable with a bunch of set screws. > The heads themselves are also pretty big. This is a late 1950s drum, > not a 1970s era hard disk - there is a world of difference. I would > bet the heads ride a few thousands above the surface. > The whole assembly is in a very rigid cast chassis, driven by a > relatively low-frills AC motor, apparently. > My thinking is that the drum could be recoated (this is assuming it is > indeed shot), and using the rigid cast chassis, ground down to a > smooth surface with a custom made tool. This is much like a "poor mans > wheel lathe" used on railroad wheels. As long as the bearings are > still pretty tight, there should be very little wobble between the > drum and chassis. With each head being adjustable for height, much > inaccuracy across the drum becomes fairly unimportant. Inaccuracy > around the drum is more of an issue, but I suspect it will not be too > bad if the correct tool material and magnetic coating is used, and the > drum ground down gently. I will ask my real machinist friends about > the tooling, as I doubt I (or any of us) could make it.