10 tips for scribing with the compass

Table of contents:

Marking and transferring dimensions
Draw parallels on curved edges
Approximating the centre of a circular surface
Halve the distance/determine a 90° angle
Determine 30°/60° and 45° angles
Transfer angles
Halve angle (determine mitre angle)
Mark the rounding of corners
Outline the largest possible hexagon
Construct a harmonious oval

Transferring and drawing measurements and angles is usually more accurate than measuring. For this reason, the "old masters" often used compasses and string to find the right measurement. In this blog post, we would like to introduce you to 10 possible uses for compasses.

First of all: Some compasses have a practical quick setting, but this is easily adjusted by applying pressure to the compass legs. Therefore, always hold the compass by the head when drawing and do not exert any pressure on its legs.

1. mark and transfer dimensions

You can do much more with a compass than just draw circles. A compass is also the best measuring tool for marking out regular measurements, e.g. for dowel holes, rows of holes for shelf supports and belt holes. It is also ideal for marking out and transferring dimensions (e.g. to transfer individual points from a true-to-scale drawing to the workpiece). You can also use a compass to take and check measurements from a workpiece that are difficult to measure with a ruler or metre rule.

2. marking parallels on curved edges

A compass is much more suitable than a moulding knife for marking parallel to the curved edge, for example for a profile or chamfer on signs, a juice channel on cutting boards or similar. Depending on the complexity of the shape, you can either simply run the compass along the edge, keeping it as perpendicular as possible to the edge, or you can make arcs at regular intervals or in corners and then join them. If the compass is fixed, the marking is always the maximum distance to the edge. If you deviate, always orientate yourself on the inner edge of the line. The compass can only deviate outwards, not inwards.

3. approximate the centre of a circular area

Determining a centre point works in the same way as with curved parallels, except that these are drawn as close as possible to the assumed centre point. Set the compass approximately to the assumed radius of the circular area and make several compass arcs from different points on the outer edge of the circle. In the centre, leave a free area that corresponds approximately to the centre of the circle. It does not matter whether the compass is set to a slightly larger or smaller radius than the actual radius of the circle. You can use this technique to find the centre of a turning blank, for example, or to drill a hole for hanging a wooden plate.

The following applies to the following compass constructions: Compasses always indicate the radius (r), i.e. if diameter (D) is given, then the radius corresponds to half the diameter (r=D/2). Points are indicated as follows: Centre point = M, other centre points = M1, M2 etc., auxiliary points = P or P1, P2... and determined (intersection) points = A, B, C... or A1, B1 etc.

4. halve distance/determine 90° angle

To exactly halve a distance between two points, proceed as follows:

Define two points (P1, P2) on a line (base).
Set the compass to radius P1-P2 or larger.
Starting from the two points, draw a circle base above and below the line. Two intersection points A and B are created.
Connect the two intersections A and B. The line drawn in this way intersects the base exactly in the centre between P1-P2. The line is exactly at right angles to the base (90°).

A 90° angle can also be drawn on an edge in a similar way:

Mark the point (M) on the edge where the "right angle" should be.
From point M, mark two points A/B on the edge using a circular arc.
Increase the radius r (ideally r = A-B) and make an arc from points A and B above point M to create intersection point C.
Connect intersection point C with point M. The line drawn in this way is exactly at right angles to the edge at point M.

5. Determine 30°/60° and 45° angles

To mark out 30° and/or 60° angles, first construct a 90° angle as above.

From point P, draw a ¼ arc over both legs (perpendicular and horizontal) and mark points A and B.
Pierce A and B with the same radius and draw two more arcs upwards. The intersection points C and D are obtained on the first arc. The point of intersection of the two new arcs is point E.
Connect C, D and E with P. C-P = 60°, D-P = 30° and E-P = 45°

6. transferring angles

If you want to transfer a specific angle to another workpiece, you can also do this without a bevelled bevel or protractor. Use the following method:

Make an arc around the apex P, resulting in points A and B on the legs.
Maintain the radius setting, pierce at the starting point of the new angle P1 and make an arc. The result is A1.
Now take the line A-B in the compass and use it to pierce A1 to mark B1.
Connect B1 with P1. The line drawn in this way is at the same angle as the starting line.

7. halve the angle (determine mitre angle)

You can also precisely determine a mitre angle using a compass, ruler and pencil. The principle is the same as when bisecting a line, except that the line has a "kink".

Make an arc around the vertex P over both legs. Intersection points A and B are created.
Pierce A and B and mark the intersection C with two arcs.
Connect intersection C with P to form the angle bisector.

8. scribe a rounded corner

Normally, a round object such as a plate or a tin is used to mark a curve in corners. However, if you want an exact radius, proceed as follows:

Set the desired radius r and make two marks A and B on the edges from the corner.
With the radius unchanged, make two compass strokes from A and B near the assumed centre of the corner radius. Their point of intersection is the exact centre of the corner rounding M.
Now insert the compass into M and mark the corner radius r.

9. mark out the largest possible hexagon

The largest possible hexagon can be marked on a board in the following way:

Draw a horizontal centre line.
Draw an arc with a slightly larger diameter than the height of the board (D = 2r1). The starting point P is on the centre line near the edge (the compass cannot be inserted well at the edge). Point P1 is at the intersection of the arc and the centre line.
Draw an arc from P1 with the same radius. This results in the intersection points A and B.
Connect points A (or B) with P and extend the line to the edge.
The distance P-edge determined in this way is the required radius r for the largest possible hexagon. The hexagon can now be drawn as usual.

10. construct a harmonic oval

A harmonic oval can be drawn in the following way:

Draw two circles next to each other (r = ¼ length of the oval) that are tangent to each other.
Now set the compass to the diameter (r2 = 2r) (distance between the two centres M1-M2). Use this to make two arcs. The intersection points A and B result.
Leave the compass in M1 and take the outer radius of the other circle from there (r3 = 3r).
Now make punctures in A and B and close the oval with two arcs.

A simple basket arch, i.e. half an oval, is constructed in the same way.

The compass can also be used to construct other geometric objects such as a hinged arc, a spiral or ellipses. However, their construction is somewhat more complex and there are better solutions than the compass for drawing ellipses, for example, so we will probably make separate contributions on this.