MYP Design Cutting and Shaping Notes

Cut to the Waste Side: The Line Has to Survive

1. Every blade has thickness, and the slot it leaves behind, the kerf, is usually 1 to 2 mm wide on a hand saw.
2. Saw down the middle of your line and half that kerf comes out of the part you wanted to keep, so the piece finishes about 1 mm short.
3. Cut just outside the line on the waste side instead, and the pencil line is still there on the finished part when the saw stops.
4. That leaves a sliver of maybe 0.5 mm to plane, file or sand back, which is how you land exactly on size rather than near it.
5. Shade the waste with light diagonal pencil strokes first, because on a symmetrical part it takes about four seconds to forget which half is scrap.

Saws: Match the Blade to the Cut

1. A tenon saw has a stiff brass or steel spine along the top and roughly 13 to 15 teeth per inch, which keeps it straight for accurate joint cuts in timber.
2. A coping saw stretches a thin blade in a springy steel frame, and because the blade can be rotated in its pins it follows curves and can be threaded through a drilled hole to cut waste out of the middle.
3. A hacksaw takes a hardened blade of 24 or 32 teeth per inch and cuts metal and rigid polymer, with the teeth pointing forward so it cuts on the push.
   1. Keep at least three teeth touching the material at all times, so 1 mm aluminium sheet needs the 32 tpi blade and 10 mm steel bar can take the 24.
4. A bandsaw runs a continuous loop of blade downwards through a table and rips thick timber or gentle curves far faster than any hand saw.
5. A scroll saw uses a short blade moving up and down, and its tight turning circle suits fretwork and internal cutouts in 6 mm plywood or 3 mm acrylic.

Chisels: The Bevel Steers the Cut

1. A bevel edge chisel has its sides ground away so the blade reaches into the acute corners of a dovetail, while a firmer chisel is thicker and survives heavier mallet work.
2. Held bevel down the chisel rides up out of the wood for a shallow paring cut, and held bevel up it drives the edge downwards into the timber.
3. Chop straight down across the grain first to sever the fibres, then pare along the grain to lift the waste out in slices.
   1. Skip the cross grain cut and the chisel follows the grain, splitting off a chunk well past your line.
4. Clamp the work and keep both hands behind the cutting edge, because a chisel that slips is travelling at the speed you were pushing it.
5. A blunt chisel needs more force and is more dangerous than a sharp one, so hone the 30 degree secondary bevel on an oilstone before a fine job, not after.

Files and Rasps Finish What the Saw Left Rough

1. A file cuts on the forward stroke only, so lift it clear on the way back rather than dragging the teeth over the work.
2. Cross filing pushes the file diagonally across an edge to shift metal quickly, and draw filing, with the file held sideways in both hands, leaves a smooth flat surface.
3. Cuts run from bastard through second cut to smooth, and you work down the grades in order because a smooth file cannot fix a surface that a coarse one left wavy.
4. Section shape decides where a file can reach: flat for edges, half round for inside curves, round for opening out a hole, square for the corner of a slot.
5. A rasp carries individual raised teeth rather than rows of ridges, which clears wood shavings instead of clogging with them and shapes timber far faster.
6. Rub chalk into the file before working aluminium, or soft chips jam between the teeth and score deep lines into the surface you just flattened.

Drilling: The Bit Decides What Kind of Hole You Get

1. A twist bit has helical flutes that lift swarf up out of the hole, and a set from 1 to 13 mm covers most holes in wood, metal and polymer.
2. A forstner bit has a flat cutting face with a small centre spur and a rim that slices the edge of the hole, so it leaves a flat bottom and clean walls.
   1. That is the bit for a 35 mm hinge cup in a cabinet door, where the hole must stop 12 mm down with a flat floor.
3. Clamp a scrap board under the work so the bit breaks through into the scrap, which stops the fibres tearing out around the exit hole.
4. Drill a 3 mm pilot hole before any bit over about 8 mm, since the flat chisel edge at the tip of a large twist bit pushes rather than cuts.
5. Two things pull the speed down: a harder material and a bigger diameter, because the rim of a wide bit travels much further per revolution than the rim of a narrow one.

Pillar Drill or Hand Drill: Accuracy Against Access

1. A pillar drill holds the bit square to the table by construction, so the hole comes out perpendicular without you judging anything.
2. Its depth stop lets you drill twenty holes all exactly 12 mm deep, which is what makes repeat parts in a batch match each other.
3. Work must be held in a machine vice or clamped to the table, because a bit that grabs a loose sheet of 1 mm aluminium turns it into a spinning blade.
4. A cordless hand drill goes to the work instead of the work going to it, which is the only option once a frame is assembled or a fixing is going into a wall.
5. A hand drilled hole is only as square as your wrist, and being two degrees off over 40 mm of depth puts the exit point about 1.4 mm away from where you wanted it.
6. A drill stand sits between the two, clamping a hand drill vertically to give most of the accuracy without taking up bench space permanently.