I read some where that a commercially available drill is capable to drill square holes. How is this possible ?
Could a drill be desinged to make triangluar or other shapes holes ?
It’s called a “mortise bit”. Basically a regular round drill bit surrounded by straight chisels. Usually used in a drill press. As you plunge the bit into the wood, it drills a round hole, but the chisels square up the sides.
I’ve never seen any other shape mortise bits…but I suppose it would be possible.
There is actually a rotary drill for drilling square holes that is different from the mortise bit. It has three flutes, and they are straight. The bit wanders around in the hole (regular bits sometimes do this a little making a hole that isn’t very round). As it wanders the flutes vibrate into the corners and chew them out. There is also a five sided version for drilling hexagonal holes. The bit needs a special holder to let it wander around.
Square holes in metal are frequently punched or broached if precision isn’t required.
A broach is a tool consisting of a succession of punches aligned as if on a mandrel. The broach for a square hole would start round and in succession get gradually more square as the tool is pulled through the hole.
The secret to that square-drilling drill is two-fold: the drill is derived from a constant width shape, and the chuck it is in allows it to float in two dimensions.
Draw an equilateral triangle. Then set your compass to the length of one side. Put the point on one corner of the triangle, then trace an arc between the other two corners. Repeat for the others. If you cut this triangle out, you will discover that it can be rolled, spirograph-fashion, in a square template.
Now image a drill with that cross section, but part of the arc ground away to make cutting edges. If you had a chuck that could roll it around in a square template, you could drill square holes…
You still won’t be able to put a square plug in that hole, the corners will have the radius of the drill bit.