# Drilling square holes **URL:** \ **Category:** Factual Questions\ **Created:** [November 16, 2003, 12:08pm UTC](https://boards.straightdope.com/t/drilling-square-holes/213541 "2003-11-16T12:08:18Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Zweistein](https://avatars.discourse-cdn.com/v4/letter/z/54ee81/32.png) [@Zweistein](https://boards.straightdope.com/u/Zweistein)\ **Post date:** [November 16, 2003, 12:08pm UTC](https://boards.straightdope.com/t/drilling-square-holes/213541/1 "2003-11-16T12:08:18Z")
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 ? ---
**Author:** ![lucky\_henry](https://avatars.discourse-cdn.com/v4/letter/l/bc8723/32.png) [@lucky\_henry](https://boards.straightdope.com/u/lucky_henry)\ **Post date:** [November 16, 2003, 12:24pm UTC](https://boards.straightdope.com/t/drilling-square-holes/213541/2 "2003-11-16T12:24:43Z")
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. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [November 16, 2003, 12:29pm UTC](https://boards.straightdope.com/t/drilling-square-holes/213541/3 "2003-11-16T12:29:52Z")
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. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [November 16, 2003, 12:35pm UTC](https://boards.straightdope.com/t/drilling-square-holes/213541/4 "2003-11-16T12:35:45Z")
Look here: [http://upper.us.edu/faculty/smith/reuleaux.htm](http://upper.us.edu/faculty/smith/reuleaux.htm) > [@](#): > > So the Reuleaux triangle’s centroid does not follow a circular path. How then is the Reuleaux bit contained within the square outline it’s to cut? Harry Watts designed a drill in 1914 with a patented “full floating chuck” to accommodate his irregular bits. Bits for square, pentagonal, hexagonal and octagonal holes are still sold by the Watts Brothers Tool Works in Wilmerding PA. The actual drill bit for the square is a Reuleaux triangle made concave in three spots to allow for unobstructed corner-cutting and the discharge of shavings ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [November 16, 2003, 1:59pm UTC](https://boards.straightdope.com/t/drilling-square-holes/213541/5 "2003-11-16T13:59:49Z")
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. ---
**Author:** ![hammerbach](https://avatars.discourse-cdn.com/v4/letter/h/73ab20/32.png) [@hammerbach](https://boards.straightdope.com/u/hammerbach)\ **Post date:** [November 16, 2003, 2:46pm UTC](https://boards.straightdope.com/t/drilling-square-holes/213541/6 "2003-11-16T14:46:44Z")
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… ---
**Author:** ![herman\_and\_bill](https://avatars.discourse-cdn.com/v4/letter/h/f1d935/32.png) [@herman\_and\_bill](https://boards.straightdope.com/u/herman_and_bill)\ **Post date:** [November 16, 2003, 3:21pm UTC](https://boards.straightdope.com/t/drilling-square-holes/213541/7 "2003-11-16T15:21:00Z")
You still won’t be able to put a square plug in that hole, the corners will have the radius of the drill bit.