Cooktop and Downdraft Cutouts in a Stone Top
A cooktop opening is the one part of a stone countertop that cannot be adjusted after the fact. Cabinets can be shimmed, a sink can be re-clipped, an edge can be repolished on site. A rectangle cut through the middle of a slab is permanent, and if it is wrong by a quarter inch in the wrong direction the piece is scrap.
The Installation Sheet, Not the Box
Every cooktop ships with a manual carrying a dimensioned cutout drawing, and that drawing is the only source a fabricator should work from. It is not the appliance's overall width and depth. The visible glass or steel top overhangs the body that drops through the counter, sometimes by an inch a side, so cutting to the outside dimension leaves a gap you can see down into. Retailer listings and the carton itself quote rounded shipping sizes and are not cut dimensions. Sizes also move within a product family: a thirty inch unit and its thirty six inch sibling rarely share a cutout depth, and a model year change can shift the numbers without changing the name.
Radius Corners and Why Square Ones Crack
Cutout drawings almost always specify a corner radius, commonly a quarter inch to half an inch. That radius is structural, not decorative. A sharp internal corner concentrates stress at a single point, and stone is strong in compression but weak in tension at a notch. Heat cycling from the burners, the small flex a counter takes when someone leans on it, and ordinary vibration all load that corner. A square corner gives a crack somewhere to start, and once it starts it runs diagonally toward the front edge. A radius spreads the same load around a curve, which is why the cut edges get polished rather than left rough off the saw.
Clearance to the Front Edge and to the Wall
The manual also states a minimum distance from the front of the cutout to the front edge of the counter, and a minimum to any combustible surface behind or beside it. The front dimension protects the strip of stone between the opening and the edge. Too narrow and that strip becomes a weak rail that breaks when a heavy pan lands on it. In a shallow base cabinet, and many original 1950s Lakewood runs are shallower than current standards, front and rear clearance can conflict, and the answer is a different cooktop rather than a smaller margin.
Gas and Induction Do Not Cut the Same
Gas units drop a deep burner box and a manifold below the counter and usually want clearance to the cabinet sides as well as depth for a gas line and a shutoff. Induction units are shallower but they breathe: the electronics under the glass need an air path, so the manual will call for a ventilation gap at the front or rear and sometimes a minimum air space below. A drawer that cleared the old gas top can foul an induction unit's cooling, and induction models frequently ask for a different opening even when the visible glass matches the gas model they replaced.
Downdraft Units Need a Second Opening
A downdraft is not a variation on a cooktop cutout, it is an additional slot behind it, with its own dimensions and its own required distance from the cooktop opening. That leaves a narrow bridge of stone between two parallel cuts, the most fragile geometry a countertop can be asked to hold. It has to be cut, moved and set without flexing, and it may need a rod set into the underside. Downdrafts also carry a blower and ducting under the counter that dictate cabinet modifications, so cabinet work and stone work have to be coordinated.
The Appliance Has to Be On Site
Templating from a paper spec assumes the unit that arrives is the unit that was specified. Substitutions happen constantly: backordered models get swapped, a floor model in a different finish carries a different part number, and the wrong box gets delivered. Having the actual appliance in the house lets the template technician verify the drawing against the unit and check the trim overhang by hand. It costs a few square feet of garage space for a couple of weeks, and it is the cheapest insurance available against a cut that cannot be undone.