Degrees, in 0.5° steps.
Bar surface to stone surface, along the line toward the axle — use a caliper depth rod or a spacer block.
Measure across the stone with calipers. A new wheel is 200 mm.
From the support bar surface to the cutting edge, tool clamped in the jig. The 6 mm bar radius is added automatically.
Set the bar-to-stone gap to
— mm
—
K projection · R stone radius · G bar-to-stone gap
How to Measure
Projection: bar to cutting edge
Clamp the tool in the jig, rest the jig on the support bar, and measure from the near surface of the bar to the cutting edge. Enter that number as is: the 6 mm to the bar's centre is added automatically.
Shop tip: cut a notch of your favourite projection into a scrap block and set every tool against it. Same projection every time, no measuring.
Gap: bar to stone
Measure the closest distance between the bar's surface and the stone's surface, along the imaginary line from the bar toward the wheel's axle (the green dashed line in the picture). A caliper's depth rod works well, and a spacer block cut to the target size works even better at the machine.
Stone diameter
Measure straight across the wheel with calipers. The wheel wears smaller with use and truing, so a remembered bar setting slowly drifts to a different angle as the stone shrinks. That drift is exactly what this calculator corrects for, so remeasure whenever you true the stone.
Checking a setup: the marker method
Colour the bevel with a felt marker, set the tool on the bar, and turn the wheel a little by hand with the machine off. Where the ink rubs off shows where the stone is cutting: rubbed only at the edge means the angle is too steep, only at the heel means too shallow, and evenly across the bevel means you're set right. Trust the marker over any calculator, including this one.
Jig calibration: seat offset
The basic model assumes the blade's back passes through the centre of the support bar. On a square edge jig the blade rests on a seat, so its back usually sits a few millimetres away from that centre, and every result tilts by a few degrees. Calibrate once per jig and the calculator corrects for it everywhere.
Millimetres from the bar's centre to the blade's back. Positive when the back sits farther from the wheel than the bar's centre (the usual case). Leave at 0 for the plain model.
To find yours: set up at a computed gap, grind lightly, and measure the actual bevel with an angle gauge, or check with the marker method. If the true angle comes out steeper than the target, increase the offset; if shallower, decrease it. Each half millimetre moves the result by roughly half a degree.
Notes for plane irons
Camber (a slightly curved edge) comes from varying finger pressure across the edge while grinding, not from the bar setting. Flattening the back is a separate job for a flat stone: the jig and this calculator only handle the bevel side.