Angled-Side Spade Bits: Each Wing Bent Forwards Along a Diagonal Line, the Way the Bit Turns (Vasudeva, 2005)

"The longitudinal sides of the head portion are bent along a bend 9, in the direction of rotation of the spade drill bit during operation, so that the outer ends of the cutting edge are bent forwards in the rotating direction." "The shorter the bend 9, the larger the angle with the longitudinal direction is going to be, and the more abrupt is the chip break-up. Larger angles require more power for drilling."

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, 22 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 end of the cutting edges. Scribe the two bend lines through the paper onto both faces. Drill a 3 mm hole at the template's circle.

Heat the blade to a bright red. Grip it in the vice with one bend line exactly along the top of the jaws and the wing standing above them. With the face towards you and the point up, push the left wing towards you about 10 degrees with the flat-nose pliers or light hammer blows close to the jaws, so it bends on the line. Reheat, grip along the other line and push the right wing away from you the same amount. Look down the bit from the point: the two wings should lean opposite ways, like a shallow S, as in his Fig. 2D. Let it cool slowly in the air.

Bevel each cutting edge and each side of the blade so the edge that leads as the bit turns is sharp and the face behind it clears the wood. Sharpen the spurs' outer edges and the point's two leading edges the same way.

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.

**Kailash C. Vasudeva** of Waterloo, Canada, assignor to Maxtech Manufacturing Inc., US 6,957,937 B2, dated 25 October 2005, filed 20 February 2002. His head's sides are "bent along a bend 9, in the direction of rotation", the bend running from a position on the side nearer the bottom of the head to a position on the cutting edge between its outer end and the tip. He shows arced and straight cutting edges, serrated sides, chip-breaking reliefs on the tip, and a head made separately by powder metallurgy. We build the straight-edged form of his Figs. 2E to 2G with spurs, forged in one piece, without the reliefs. He gives no bend angle or sizes; 10 degrees and our sizes are ours, the bend line placed as measured off his Fig. 2B.