Sink and Cooktop Cutouts
Datasheets Are Not Reliable
Published cutout dimensions are frequently generic across a product family, and manufacturing tolerance on a pressed steel sink is wider than the tolerance a fabricator is working to. Shops ask for the physical fixture because measuring it removes an entire class of error that would only be discovered at installation.
Undermount Costs More for a Reason
On a top mount the sink rim covers the cut edge, so the aperture only has to be roughly right. On an undermount the cut edge is visible, so it has to be accurate, smooth and polished all the way round. That is a separate machining and polishing operation on an internal curve, which is slower than any external edge.
The Reveal Is a Choice
Positive reveal leaves a little of the sink rim visible, zero reveal aligns the stone edge with the bowl, and negative reveal sets the stone slightly inside the bowl. Zero reveal looks the cleanest and is the least forgiving of any error. Decide it deliberately, because the shop will otherwise pick a default.
Radiused Internal Corners
Every internal corner of an aperture is cut with a radius rather than a point. A square internal corner concentrates stress and is the origin of most cracks that appear across a worktop months after installation. A radius of a few millimetres removes that, and it is invisible once a sink or hob sits over it.
Hobs Need Clearance and Ventilation
Induction and gas units both specify a gap around the aperture and, for many models, a ventilation route. A cutout made to the exact appliance footprint with no allowance traps heat against the stone and against the cabinet. This is in the appliance instructions and it is routinely missed.
Support Under the Sink
A cast iron or fireclay sink hanging from an undermount fixing is a substantial load carried by adhesive and a few clips. Heavy sinks need a supporting frame or a cradle in the cabinet below, fitted before the top goes on. Establish who is supplying that, because it falls between two trades.