Sometimes it is necessary to drill a hole at an exact angle, for example when making a propeller or nose block. This is easy to do if you have access to a drill press, but many do not. I will show you how to make a drill guide using simple materials and tools.
Here you see the drill guide being set up to drill a 1/16″ diameter hole for a propeller hub. The hole must be exactly perpendicular to the face of the block. The guide consists of four right triangles glued together to form a 1/16″ hole perpendicular to the four base legs. You could use this guide placed on an angled plate to drill at other than a right angle, for example, to form side thrust or down thrust in a nose block.
My first drill guide of this type was made from sturdy cardboard from a large size cereal box. I took the pictures of that build that you see here. This proved to be very successful, but cardboard is somewhat soft and must be handled very carefully. Later I made another from 1/16″ plywood that is more robust. I used slightly different dimensions. The triangles were 3/4″ x 3/4″ instead of 3/4″ x 1″. I recommend that you use plywood or a similar hard material for your drill guide. You can start by cutting out a 3/4″ x 1 1/2″ piece, cut that into two 3/4″ x 3/4″ pieces and cut each of those on a diagonal to form the four triangles used. Sand the edges perfectly square. If you cut with a saw, make allowances for the width of the saw kerf.
There are several ways to mark out the triangles. This is the way I did my first one. There are better ways to do it, but I don’t have photos to show them. After you see this, you can figure out another way more to your liking. Cardboard is cheap, but you might want to avoid wasting plywood.
I started with a layout line.
I set up a perpendicular line with drafting triangles. Anything with a square corner will work here.
Next I drew the perpendicular line with a sharp pointed pencil.
I marked 1″ out both ways from the crossing on one line.
I marked 3/4″ out both ways from the crossing on the other line. On my plywood guide, I made all four edges 3/4″.
I cut out around the marked out area.
I cut along the lines to make four quadrants.
I cut between the marks on the lines to make four equal 3/4″ x 1″ right triangles.
I marked 1/16″ from the 3/4″ edge. Unlike what is shown here, all four triangles should be oriented so they will lie exactly on top of each other. I made it 1/16″ because this will determine the size of the hole in the center and I am going to use this to guide a 1/16″ diameter drill. For a 1/32″ drill, I put a length of brass or aluminum tube into the hole, with an outside diameter of 1/16″ and an inside diameter of 1/32″.
I drew a line through the mark parallel with the 3/4″ edge.
I put glue along the surface of the edge.
I glued it to one of the other triangles right behind the line so it was 1/16″ away from the edge.
I checked that all the angles were square and the bases were even.
I made another pair in exactly the same way and set them aside to let the glue dry completely.
I applied glue to the remaining edges on each piece.
I aligned the pieces and pressed them together.
I checked that everything was square and that all four bases would lie flat on a flat surface.
The dimensions were chosen to fit the length of my 1/16″ diameter drill. When the drill is mounted in the bit, it must project enough beyond the drill guide to make a good start into the wood. Once it is about 1/2″ into the wood, the hole itself will guide the drill the rest of the way through.