Newly manufactured infills are probably machined from the solid as the low
volume would make it more economical. Old ones, when they were in
production, were cast same as any metal body plane. If you start out with a
piece of metal thick enough to make an infill and machine it to shape, it
WILL warp. It can, of course be stress relieved and machined strait. Cast
iron will warp, unless stress relieved and machined strait. Cast iron, when
treated correctly, is extremely stable. The bedways of precision machine
tools are now, and always have been, made of cast iron.

"RicodJour" wrote in message
oups.com...

It's how it's made that's the major advantage. Infills start out as
flat plates and are machined prior to assembly, as opposed to starting
out as a casting. Castings shrink as they cool and it can be a fair
amount of work to get the sole dead flat. Infills start out that way.
The weight is another advantage. There's also more hand work involved
in making an infill, so each one is closer to a custom creation.

R