Drawing large circles may seem very simple, but sometimes it can be a headache if you don’t have the right tool. Making a beam compass is a fairly easy task, so simple that sometimes instead of making one we improvise something similar when we need it. And I’m sure you already know how difficult it is to hold the pencil in position with your fingers while trying to turn a wooden strip with a nail at the other end to make it turn and draw a large circle.
How to make a beam compass
To make an useful and easy to use beam compass, it is only necessary to ensure that its trammel points remain in position during the use of the compass. But it is also important that it is still easy to regulate the radius of the circles we want to draw. Basically we need three elements to make the beam compass: a wood rod to make the beam, a trammel point to make it rotate, and a trammel point to hold the pencil to draw the circle.
And after drawing it we can also cut the circle with a simple circle cutting jig.
The wooden rod is 15 millimeters in diameter, and I cut it 50 centimeters long to make the beam of the compass. At one end, at 2cm from the end, I drill a hole into which the pencil will fit. That hole is about 8mm in diameter. Now I cut the groove I show in the pictures up to a few mm beyond the hole for the pencil. I drill a pilot hole for the screw at 90 degrees to the slot and at about 8mm from the end of the rod. And with a slightly thicker drill bit I drill into the same pilot hole, but only going as far as the slot.
This way, when the screw is driven in and tightened, the groove closes and squeezes the wood around the pencil, clamping it in place.
I regulate the distance (the radius of the circles) between the pencil and the pivot point of the beam compass by using a wooden block inside which the beam (the wooden rod) slides. In this rectangle of wood I drill a hole with the same diameter as the rod (although I had to use a 16 millimeter spade bit). On the sides drill pilot holes for the screws 4 and a half centimeters long. I cut the dowel in the middle and then re-drill the top of the holes with a bit slightly thicker than the screws.
Thus, when the screws are tightened, both parts close tightly around the rod, holding it in the desired position. As a compass point I use a screw, for which I drill a guide hole in the lower part. On the inside I countersink the guide hole to accommodate the screw head so that it does not rub against the wood rod. I use my table jigsaw and the drill press to make this compass.
Surely even with a hand saw and the help of a pair of clamps, the necessary cuts could be made. And the holes can be drilled by hand with a drill, but the holes will hardly be vertical. Care should be taken especially when drilling the hole for the pencil, so that it is centered and does not damage the end of the rod.
It is also important to take into account the direction of the grain before drilling, because as I explain in the video we could find that the wood cracks when the tightening screw is inserted.