How to Draw a Hexagon or Bolt Circle in CAD (Polygon and Polar Array)

To draw a regular polygon in CAD, give the number of sides, pick the centre, then give a radius — or pick one edge and let the rest follow. To draw a bolt circle, draw one hole and repeat it round the centre with a polar array. This guide does both, with exact numbers, in a browser at app.kulmanlab.com — free, nothing to install, and the file never leaves your computer.

We build KulmanLab, so the steps below use its commands. The ideas — across-flats versus across-corners, pitch circle diameter, whether copies turn as they go round — are the same in any CAD program.

Draw a regular polygon

A regular polygon has equal sides and equal angles: a hexagon for a nut, an octagon for a sign, a pentagon for a decorative cut-out. In KulmanLab it is the Polygon command.

1. Type polygon in the terminal, or use the Polygon button in the Shapes panel.
2. Enter the number of sides — any whole number from 3 to 1024 — and press Enter. The prompt is pre-filled with the count you used last.
3. Click the centre, or type X,Y for an exact point.
4. Click the radius, or type it and press Enter.

The result is a single closed polyline, so everything you can do to a polyline — move, rotate, offset, scale — works on it.

Across flats or across corners?

This is the part that trips people up. “Radius” can mean two different distances, and a hexagon is specified by one of them depending on what you are drawing:

Press I at the radius prompt to switch. A hex nut is sold by its width across flats, so use Inside off and type half of it. For an M8 nut, 13 mm across flats:

1. polygon, then 6 for the sides, then click or type the centre.
2. Press I to turn Inside off.
3. Type 6.5 and press Enter.

The flats are exactly 13 mm apart; the corners reach 7.51 mm from the centre, about 15 mm across corners. Type the radius rather than clicking it and the polygon sits with its lowest edge level, flat on the bottom. Click it instead and the polygon takes its orientation from where you click.

From one edge

Sometimes you know a side length, not a radius — an octagonal tabletop with 20 mm sides, say. Press E at the first-point prompt to switch to Edge mode, then pick the two ends of one edge. The remaining corners are built counter-clockwise, to the left of that edge. Typing 0,0 and then 20,0 puts a 20 mm edge along the X axis with the polygon above it.

Draw a bolt circle

A bolt circle — or pitch circle, “PCD” on drawings — is a ring of holes equally spaced round a centre. You draw one hole, then repeat it. In KulmanLab that is ArrayPolar.

Take six 6.6 mm holes on a 50 mm pitch circle diameter, centred on the origin:

1. Draw the first hole. Run circle, type the centre as 25 , 0 — half the PCD along the X axis — press Enter, then type the radius 3.3 and press Enter.
2. Select it by clicking the circle.
3. Run the polar array. Type arraypolar, or use the ArrayPolar button in the Edit panel.
4. Pick the centre of the pattern — type 0,0.
5. The terminal shows the array as it stands — Change [Items=6] [Angle=60°] [Fill=360°] [Rotate=true] — and the five copies preview live. Press Enter to accept.

That is the whole bolt circle. For a different count, press I before confirming and type the number of items — the original counts as one, and the angle between them is worked out for you. Or press A and type the spacing in degrees instead; the fill angle is restated to match.

A few details that matter:

• Fill is the angle from the first item to the last. The default 360° spreads items round a full circle; a smaller number spreads them over an arc — a row of holes round a quarter turn, say. A negative angle runs clockwise.
• Rotate decides whether each copy turns as it goes round. For circular holes it makes no difference. For a slot, a tooth or a bracket it does: on, every copy faces the centre as the original did; off, every copy keeps the original’s orientation and is only moved into place. Press R to flip it before confirming.
• The array makes copies — the original stays where it is, and every item is an ordinary entity you can edit afterwards.

Put them together: a flange

Draw a hexagon for the outline, a circle in the middle for the bore, and a bolt circle for the mounting holes. Three commands, every dimension typed exactly, and nothing to measure off the screen.

If the part is going to a laser cutter, delete any construction circle you drew to find the pitch circle — it would be cut like everything else — and check the file against our guide to preparing a DXF for laser cutting. The polygon is a closed path by construction, which is the most common thing cutting services reject files for.

What this won’t do

• Regular polygons only. Every side is equal. An irregular outline — a shape with a few sides longer than others — is a polyline you draw point by point.
• 2D only. This draws flat outlines. It will not give you a modelled nut or a threaded bolt.
• Desktop browsers only — Chrome, Firefox, Safari and Edge. There is no mobile version.

Related: Polygon and ArrayPolar for every option and key, Circle for typing exact radii, and ArrayGrid for repeating objects in rows and columns instead of round a centre.