I thought I'd have a go at starting the cylinder block tonight from a sash weight.
I picked on the square one of my 3 that I have

Scored all four sides with the disk cutter, inc the end as suggested by Bogs


Took it outside and threw it against the concrete floor, nothing happened, tried again, and again, and again. By now I was really belting it.
I resorted to finding a granite rock in the garden and whacking it against a sharp edge along the score marks. It took several goes but finally it gave in.
I then tried to knock the end off with a sharp cold chisel and a lump hammer. I gave up in the end, I just couldn't hit it hard enough.
I was suprised just how tough this cast iron is, didn't seem very brittle to me


I then decided that to remove the hard abrasive crust I would lathe it off with a half beaten carbide tip. After all I have enough of them and better that than ruin a milling cutter I thought. Managed it too with just the one tip....

It was very uneaven and the surface slightly porus so took a bit of doing.

Off to the miller for a tidy up


Alas, it looks as if it's going to be a tad too small in height, ended up at 29mm and the plans call for 32mm, not much in it but 3mm is 3mm.
Not sure what to do now, I don't currently have any other suitable material.......
