4 Tips For Pattern Drafting with a Compass

Today I want to talk about using a compass. I don’t mean the magnetic thing that helps you point north, I mean the pointy one you used to carve your name into the desk during maths class (or someone else’s name if you’re smart). Pretty sure mine hasn’t seen the light of day since I left school, but this weekend it was just the thing I wanted while I was pattern drafting. Compass1

I don’t have one of those big fancy rulers with the squares on and I needed to get  perpendicular lines, which a compass does perfectly. For those of you who weren’t paying attention at school, I’m going to outline some of the useful things that you can do with a compass that I found came in really handy for pattern drafting.

Perpendicular lines

To get a perfectly perpendicular line, first draw a little mark on your original line where you want your new line to cross. Place the point of your compass on the mark and open the compass up – it doesn’t matter how much, but somewhere in the middle is easier than a very small or large distance, which are likely to cause the pen to slip. Draw an arc through your line on one side. Compass2Now, keeping the compass open exactly the same amount, pivot around the point and draw an arc on the other side of the line. I like to then go back and check the compass is still the length of the first arc. You could also just draw a circle, this is my way of keeping the guidelines minimal. Compass3Now take the compass off the paper and open it a little more. Again, it doesn’t matter how much as long as you keep it consistent. Put the point of the compass at the point where one of your arcs crossed the blue line and draw another arc above your mark. Compass4

Repeat this with the other side, making sure the compass stays open the same amount. This line should cross through the one you just marked.Compass5The point where the lines cross will be perfectly perpendicular to your original line at the point you marked, so draw a line between the cross and the mark and admire your right angle!Compass6

45 Degree Angle

Now we can do exactly the same thing to get a 45 degree angle, which I’ve shown in green. First, set the compass to an arbitrary length , put the point at the centre where the blue lines cross and draw an arc that intersects both the horizontal and vertical lines.Compass7Now, place the compass point at one of the points where the green line meets the blue and draw an arc between the two blue lines. This time it doesn’t matter if you open it up more, it will work fine staying at the same length. Compass8Repeat this step with the other green-blue intersection, keeping the compass open the same amount and you should have made a cross. Compass9Draw a line between the green cross and the crossing point of the blue lines and you have a perfect 45 degree angle. The camera angle I’ve used makes this look a bit off unfortunately, but it did look pretty perfect, I promise!Compass15For a longer perpendicular (or 45 degree line) I would sometimes do 2 crosses different lengths away from the line to give me another guide. Because it doesn’t matter which distance the compass is set at you can do this as much as you like and every cross will be perpendicular as long as you use the same length for the left and right arcs of each cross.

Specific Distance Between a Point and a Line

Sometimes a pattern drafting step will require you to measure a certain distance from a point to a line. This can be done by moving a ruler around until you’ve got the right distance, but a compass does it so much more quickly and accurately! Just set your compass at the desired length on a ruler…Compass11

…then place the compass point on your point and draw an arc that intersects your line. The point where they meet is the point you’re looking for. Eagle-eyed amongst you will have noticed that it could intersect at two points, but in most cases it will be obvious which one you need. Compass12

Adding Seam Allowances

One last thing I found a compass really handy for is adding seam allowances once you’ve finished pattern drafting. Set your compass to the desired seam allowance – here I’ve used the standard 1.5 cm – and move along the pattern piece marking small arcs all the way along the pattern piece. Once you’ve gone all the way round, join them all up and you have a perfectly added seam allowance. Woo!

Compass13At the corners you’ll need to extend your lines a bit to meet at a point because the compass would give a curved corner, which isn’t what you want. Compass14

So there you go! Do I have some compass converts? For the drafting itself I found that using a soft pencil for the lines and a harder pencil in the compass for the guidelines worked well, making the guidelines fainter and the main pattern lines more prominent.

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