The stock washer you gave me to analyse is made from a sintered material – most likely an iron/copper alloy. They do it this way at the factory because 1, it’s cheap and near net shape. 2, the sintered material is porous so lubrication is never a problem even if it doesn’t get oil all the time. The down side to the sintered material is it is extremely weak, with typical tensile strengths of around 300Mpa and it has very little fatigue properties.
The stock washer has been carbonitrided (a hardening process) about 0.2mm deep and has a surface hardness of about 52HRc.
My plan is to use a high strength carburising steel called EN39B (similar to the American grade 9310 but slightly better). This stuff is a 4.5%Ni Cr Mo steel and when carburised is extremely strong. Tensile strength will be up around 1300Mpa so it will take a lot more load than the stocker. The surface hardness will be 62HRc so wear resistance should be comparable to the sintered part. Carburising leaves a high compressive residual stress on the surface so fatigue life will be high and crack initiation difficult. The idea with carburising is you have a hard wear resistant skin on a tough high strength core so the part is not brittle.
Pretty much all of the parts inside the good transmissions (Hollinger, liberty, G-Force etc) are made from 9310 and heat treated this way, including the gears, shafts, thrust components and bearing races so I’m not reinventing the wheel.
Someone on the forum commented about a D2 washer breaking – that is because D2 is a high carbon/chrome tool steel. When it’s hardened it is full of huge chrome carbides and is very wear resistant but also very weak. It can only be through hardened so has no tough core to hold it all together, basically like a piece of glass.
On the subject of machining the nose off first gear… This is also a carburised part, the depth of carburising would be approx 0.6mm so you can't machine much off without breaking into soft metal – probably not the best option unless you want to try re-carburising etc, which whilst not impossible, will probably cause all sorts of distortion issues and noisy gears.
If I'm making a few of these I will probably CNC machine the majority of it so cost will come down a bit. All of the external stuff like material, heat treatment, surface grinding etc is a good part of the cost and something I don't have much control over so without going into too much detail I think we will be looking at about NZD$110 a piece.
If there is international interest shipping cost would be minimal because it could just be air-mailed in a small envelope.
Hopefully that will cover most of the enquiries until I'm back from holiday.
Regards,
Adam Walmsley
