How do I make a pattern meet up cleanly at the seam of a rotary job?

How the flat view maps to the cylinder

The flat 2D view is the cylinder surface unrolled. One side of the job is the length of the blank. The other side (the wrapped axis) is the circumference, which is 3.14159 times the diameter. A 3.5 inch cylinder is about 11 inches around, and a 5 inch cylinder is 15.708 inches.

The two edges of the job on the wrapped axis are the same line on the real part. The official guide calls them the wrapped boundaries. That shared line is the seam.

Steps for a seamless repeat

1. Decide how many repeats you want. The spacing is the circumference divided by that number.
2. Draw one element (a flute line, a motif).
3. Draw a guide line along the wrapped axis from one wrapped boundary to the other, with snapping on.
4. Select the element, hold Shift, select the guide, and use Copy Along Vectors with one more copy than you need. For 8 flutes ask for 9.
5. Delete the original, then delete one of the two end copies. The first and last copies sit on the two wrapped boundaries, which are the same place, so keeping both cuts that spot twice.
6. Toggle Auto Wrapping in the 3D view to check the result on the cylinder.

Designing across the seam

• Vectors may run past the job edge. The official spiral example draws lines far outside the job (a length of y * 3 for three turns) and the toolpath simply wraps around.
• In length boxes, y stands for the wrapped dimension when Y is the wrapped axis (use x when X is wrapped). y / 8 gives a one-eighth spacing without a calculator.
• A motif that straddles the seam works if the part cut off at one boundary is repeated at the other boundary.

Pro tips

• Circumference depends on the diameter you entered. If the real blank is a different size, the pattern will overlap or gap at the seam, so measure after rounding.
• If you change the diameter in Job Setup, Design Scaling decides whether the artwork resizes with the job.
• For ready-made flute layouts see the entry on the Wrapped Fluting Layout gadget.