Stock left on purpose is a plan; stock left by accident is a gamble.
Where allowances earn their keep
Ground faces typically carry a modest allowance so the grinder cleans up without multiple heavy passes. Hardened plates need allowances sized to expected distortion, which differs by steel and section.
Pockets and bores that will be finish-machined after heat treatment should be roughed with a planned over-stock agreed between design and machining.
FAQ
Who sets the allowance figure?
It is a joint call: the base supplier knows mill tolerances, the machinist knows process capability. Writing the number on the drawing removes the guessing.
Does allowance differ between pre-hardened and through-hardened plates?
Yes. Through-hardening distorts more, so those plates usually carry more grinding stock than pre-hardened ones.
What happens with zero-allowance plates?
Any mill or handling deviation passes straight through to the finished mold. Zero-allowance only works with verified suppliers and careful handling.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.