Vectors, Logos and Things That Get PrintedLesson 14 of 73

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Vectors, Logos and Things That Get Printed

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Module 2 · Drawing curves people will pay for

Offsets, and the spike that appears at a sharp corner

8 min read

Where a 5 mm offset puts a sharp corner0255015120Corner angle, degreesDistance from the original point, mm—— Mitre join– – Round joinA mitred tip lands at the offset divided by the sine of half the angle, so it runs away as the cornersharpens. A round join stays at the offset distance whatever the angle, which is why it is the safedefault on anything you cannot inspect.
A mitred tip lands at the offset divided by the sine of half the angle, so it runs away as the corner sharpens. A round join stays at the offset distance whatever the angle, which is why it is the safe default on anything you cannot inspect.

Figure

Offset is not the same as a thicker stroke

Two operations look similar and behave completely differently.

  • Outline stroke / stroke to path takes a 2 mm stroke and turns it into a closed shape 2 mm wide, straddling the original path. The centreline is where your path was.
  • Offset path / contour takes a path and produces a new path a fixed distance away from it, on one side. The original stays where it was.

You want the first when preparing artwork for a cutter. You want the second for a sticker border, a keyline around a logo, a bleed contour, a CNC toolpath, or an embroidery underlay.

Where they live: Illustrator has Object ▸ Path ▸ Offset Path and Object ▸ Path ▸ Outline Stroke. Inkscape has Path ▸ Outset / Inset (fixed 2 px steps), Path ▸ Dynamic Offset (Ctrl+J, draggable and live), Path ▸ Linked Offset, and the Offset Live Path Effect for a numeric value. CorelDRAW has the interactive Contour tool, which does the same thing with a step count.

Why a sharp corner grows a spike

Offset a rectangle outwards by 5 mm and every corner is still a right angle, 5 mm further out. Now offset a shape with a 20° point: the tip of a star, the point of an arrow, an italic serif.

The two offset edges run parallel to their originals. Extended outwards, they do not meet 5 mm from the tip. They meet much further out. At angle θ, the mitred tip sits at a distance of offset ÷ sin(θ/2) from the original point. At 20°, sin(10°) is 0.174, so a 5 mm offset puts the new tip 28.8 mm away. At 10° it is 57 mm.

That is the spike. It is not a bug; it is what a parallel offset means.

Every implementation therefore offers a join setting with three options:

  • Miter: extend to the true intersection. Correct, and produces the spike.
  • Round: arc across at the offset radius. Always safe, slightly softens every corner.
  • Bevel: cut straight across. Flat corners.

And a miter limit: the ratio of spike length to offset distance at which the program gives up and bevels instead. SVG and PDF default to 4, which switches over at roughly 29°.

Set joins to round on any offset you cannot inspect, and set them deliberately on the ones you can.

Inner offsets eat themselves

Offset inwards far enough and thin parts of the shape vanish, then reappear inside out. A 2 mm-wide bar offset inwards by 1.5 mm leaves a 0 mm bar; at 2 mm it self-intersects and most solvers produce a small backwards loop rather than nothing.

This matters for three real jobs:

  • Embroidery underlay, which is an inset of the shape. A thin serif with too much inset produces a loop the machine stitches as a knot.
  • Screen-print underbase choke, typically 0.3 to 0.5 mm inset.
  • Laser kerf compensation, where an interior cut-out must be offset inwards by half the kerf.

Check thin features explicitly after every inward offset. Measure the narrowest part of your shape before you choose the distance.

Corner rounding is a different tool again

“Round the corners of this rectangle by 4 mm” is not an offset. Illustrator’s Live Corners (drag the small circle widgets with the Direct Selection tool), Inkscape’s rounded-rectangle handles and the Corners Live Path Effect, and CorelDRAW’s Fillet/Scallop/Chamfer docker all do this properly, and all of them refuse when the requested radius is larger than the shorter adjacent edge.

Do not fake a rounded corner by offsetting out and back in. It works, and it costs you nodes and precision each way.

One habit

After any offset, zoom to 400% on the sharpest corner in the shape and look. The spike is either there or it is not, and it takes three seconds.

And measure the result rather than trusting the dialog. Offset implementations differ: Inkscape’s Inset and Outset move by a preference value in pixels, not by the number you had in mind, and CorelDRAW’s Contour tool offsets by step × offset, so a 2-step contour at 1 mm reaches 2 mm. Draw a 50 mm square, offset it by 5 mm, and measure the result once in whatever program you use. You will know for the rest of your career which number that field means.

Every lesson here is open. Your progress is recorded once you pass the Editing an Image exam.

Check your understanding

A 5 mm keyline is added around a star-shaped logo using Offset Path with mitre joins. The five outer points now extend nearly 30 mm past where the designer expected. What determines that distance?

Pick the one you would defend. Your answer stays private.

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How to cite: Addaly (2026) ‘Offsets, and the spike that appears at a sharp corner’, in Vectors, Logos and Things That Get Printed. Edited by M. Mun. Addaly. Available at: https://addaly.com/learn/vector-and-print/offsets-and-the-miter-spike (Accessed: 13 October 2026).