Fluted-Shoulder Spade Bits With Spurs: Flutes Along the Shoulders, Stopped by Corner Spurs (Williams & Thackston, 1987)

"If the flutes are 'stopped', that is, if they do not extend or 'open' to the respective outer sides of the blade, and if cutting spurs are provided at the outer corners of the shoulders so that the spurs 'close' the flutes, then this splitting is virtually eliminated and cutting proceeds more smoothly."

Cut three 170 mm lengths of 10 mm octagonal tool steel. Heat 50 mm of one end to a bright orange in the forge and flatten it on the anvil to about 3 mm thick, centred on the bar. Hammer across it with the peen to spread it wider than the bit, about 2 mm over its size: 18, 24 and 27 mm. Draw the neck down smoothly where the blade meets the bar and keep the blade in line with it. Reheat as soon as the colour fades to red. Finally heat each one to a cherry red and let it cool slowly in the air, to soften it for filing.

Glue each bit's outline from the template on its blade, centred on the bar. Grind to the lines on the bench grinder, dipping the steel in water often: the two sides parallel, the shoulders square across, the point in the middle. Grind the blade's two faces flat and parallel to 2.5 mm. Grind three flats on the end of the shank, a third of the way round from each other, 20 mm long, for the chuck's jaws. Leave a spur 2 mm wide and 2 mm high at each outer corner of the shoulders. Drill a 3 mm hole at the template's circle.

Bevel the outer sides and the shoulders' cutting edges slightly, so each edge meets its leading face at about 86 degrees. On the face towards you, file the point flute along the point's left edge with the 3 mm round needle file, 0.3 mm deep. Then file the shoulder flute with the three-square needle file along the left shoulder, right behind its cutting edge and square to the bit's axis, from the point flute to the spur, and stop there. Bevel the spur's inner edge into the flute so the spur has a sharp outer edge. Turn the bit over and do the same along that face's left edge and shoulder.

Heat the blade and the neck evenly to a cherry red, until a magnet no longer sticks to it, and quench it straight down in water, moving it up and down. Rub the faces bright with a stone. Heat the shank gently 30 mm behind the blade and watch the colours run down; quench again as soon as a dark straw colour reaches the shoulders and the point. Do the other two.

Hone the cutting edges on the shoulders and the point with the stone, keeping their angles, and take the burr off. Chuck a bit by its flats and bore a scrap of hardwood: it should start on the point without wandering, cut two clean shavings from the shoulders and leave a round hole of its own size; check it with the caliper.

**A. Graves Williams III**, Wilmington, and **Ronald L. Thackston**, Hillsboro, Ohio, assignors to The Irwin Company, US 4,682,917, dated 28 July 1987, filed 24 January 1986. They claimed "cutting spurs projecting forwardly from the shoulders" with sharp outer edges, and shoulder flutes from the point flutes towards the spurs, "terminating at the spurs so that the shoulder flutes do not extend across the spurs to the outer sides of the blades". They prefer the flutes forged and the flute wall at about 68 degrees; we file them, with a three-square file at 60 degrees, inside their "less than about 78". Their shank has a hexagonal end; ours is octagonal tool steel with three ground flats. They give no heat treatment or spur size; those are ours.