# How to draw perpendicular lines using trammel heads?

Like compasses, trammel heads can be used to construct perpendicular lines. This makes them suitable for use in the laying out stages of a range of woodworking tasks.

### Step 1 – Draw primary line

Draw a primary line of the desired length using a ruler or straightedge.

### Step 2 – Find midpoint

Half the length of the line to find the approximate midpoint. Mark this midpoint on the line.

This will be the point at which the secondary perpendicular line meets the primary line.

### Step 3 – Set up beam compass

The distance between the two trammels on the beam is not critical, although they should be slightly under half the length of the primary line apart.

### Step 4 – Draw reference marks

Using your trammels, scribe arcs “A” and “B” at each end of the line from the midpoint mark.

### Step 5 – Scribe two arcs

Reset your trammels so that they are slightly longer than half the length pf the primary line apart.
Scribe an arc from each of the reference marks “A” and “B”.

The point at which the arcs intersect one another is where the perpendicular line will start.

### Step 6 – Connect points

Connect the point where the arcs meet to the midpoint on the primary line.

### Step 7 – Erase marks

Using an eraser, rub out the arcs and the reference marks.

You will now have two lines perpendicular to one another.