Grinding to the line, not past it

1. 1Water to the mark, sponge touching the bitThe sponge is what carries water up the bit. Dry grinding chips the glass edge, wrecks the diamond and throws dust you should not breathe. If the bit is not visibly wet while running, stop.
2. 2Change the water when it goes milkyThe slurry is ground glass. Once thick it polishes rather than cuts, and you will push harder to compensate, which is how edges get chipped.
3. 3Grid or face shield down, glasses onA wet grinder throws a fine spray of glass grit forwards. It is easy to forget because it does not feel like it is doing anything.

A clean break leaves a slightly flared edge: a small lip where the glass parted, sharp and marginally proud of where you wanted it. That lip is what the grinder is for. It is not a shaping tool, and a piece that needs shaping was cut wrong and should be recut.

• Hold the glass flat on the deck and bring it to the bit. Do not tilt: a tilted piece grinds a bevel, and bevelled edges do not foil evenly or sit square in came.
• Light pressure, keep it moving. Dwelling in one spot cuts a notch you will then have to grind the whole edge down to meet.
• Work in short passes and look. The bit removes more than you expect, and glass does not grow back.

Here is the arithmetic nobody does until it is too late. Grind each piece 1/64 inch (0.4 mm) small, an amount you cannot see, and a row of eight pieces comes out 1/8 inch (3 mm) short. A panel eight rows deep loses an inch overall, and every seam has to widen to swallow it.

The panel does not fail. It just ends up smaller than the frame, with fat wandering lead lines, and it takes people a long time to work out why their panels always look slightly loose.

1. 1Check against the pattern, not the neighborLay the ground piece on its paper pattern piece and look for paper showing. Fitting each piece to the last one is how error accumulates, because you never compare with the original.
2. 2Grind to fit, then stopThe moment a piece sits on its pattern with no overhang, it is done. There is always a temptation to make the edge “nicer”. Resist it.
3. 3Lay up as you goEvery few pieces, put them back on the intact cut line. Drift shows up as a widening gap long before it becomes a problem, and one recut piece fixes what ten shaved ones cannot.

• Chipped, flaky edges

  Usually

  Dry bit, worn bit, or pushing too hard.

  Fix

  Check the sponge and water first. If it is wet and still chipping, the diamond is worn. A bit is cheap and a panel is not.

• Edge is bevelled, not square

  Usually

  Lifting the back of the glass off the deck while grinding.

  Fix

  Flatten your hold and let the deck set the angle. Foil will not sit straight on a bevel and came will rock.

• Piece rocks in place after grinding

  Usually

  A notch ground into one edge.

  Fix

  Take the whole edge down to the notch in light even passes, then check the piece against its pattern: it may now be too small to keep.

• Panel is short but every piece fits its pattern

  Usually

  The gaps, not the pieces. Seams are eating the difference.

  Fix

  Tack the layout and measure. If the pieces are right, the fault is in how tightly you are pushing them together, not in the grinding.