When I welded on my stock Renesis exhaust manifold the end I welded the 270 deg bend on got warped.

It's about 0.04" bent away from completely flat at the top flange at flywheel  end.

Doesn't seem to have been an issue during the 100+ hours the engine has run.

But for peace of mind I'm wondering if I should mill the three flanges flat.

Is it true that I'll need a carbide end mill to do this? Even a 1/2" carbide end mill is close to $30.

Finn