What is grinding?

Grinding is machining with geometrically undefined cutting edges: the grains of a rotating abrasive wheel each remove a very small chip. It also works on hardened steel and other hard materials. The common forms are surface grinding for flat and parallel faces, external cylindrical grinding for shafts and diameters, internal grinding for bores, centreless grinding for pins and shafts in volume, and profile grinding. Depending on machine, wheel and process, grinding holds tighter size and form tolerances and a finer roughness than milling or turning.

What does the grinding result depend on?

The result depends on the wheel (abrasive, grit size, bond and grade), dressing, infeed and speeds, coolant and the stiffness of machine and setup. Too much heat can cause grinding burn: a thermally damaged layer with altered hardness and unfavourable residual stress that need not be visible. After hardening, grinding is a common route to remove heat-treatment distortion. Hard turning or hard milling with CBN or ceramic inserts can be an alternative for some of those requirements.

How does grinding work in practice?

Grinding usually adds a step to the route: at milling or turning you leave grinding allowance, the part often goes to the heat treater first, and then to the grinder or a grinding shop. That brings its own setup, its own price per piece and, when subcontracted, transport and lead time. Whether a requirement calls for grinding depends on the requirement, the material and what your own milling and turning can hold reliably. If such a requirement is only spotted after machining, the grinding allowance is missing.

What is grinding often confused with?

Grinding is not deburring with an angle grinder: that is hand work to break edges, with no size to hold. Honing and lapping are processes of their own: honing works with abrasive stones inside a bore, lapping with a loose abrasive between the part and a lap. Polishing mainly improves the surface and hardly changes size.

How do you see grinding in Blake?

Roughness and tolerances sit in Blake as proposals from the drawing, which you confirm or correct. If grinding goes outside, it is a subcontract operation in the estimate, priced from your subcontract library; if that price is missing, the line stays open instead of zero. More on estimating.