#Offset

A contour or a chain standing off the selected one at a given distance.

#How to do it

1. Choose a contour, a chain of lines and arcs or a circle (by clicks, with Shift for several) and press Offset. Or the other way round - the button first, then clicks on the curves.
2. Point to the side the copy should go to - the preview is drawn there.
3. Click on that side, off the curves. The side is fixed, the preview changes colour, and the Distance box opens beside the copy. The pointer can now go to the box - the copy stays where it is.
4. Type the distance - the preview follows the number. Enter or the tick makes the copy.

Enter without a click makes the copy at once, on the side of the pointer, with the distance of the bar above.

After a copy the tool stays in hand: choose the next curves and go on. Esc in the box frees the side - the copy follows the pointer again; one more Esc puts the tool down.

A negative distance lays the copy on the side away from the pointer.

#An open chain

A polyline or a chain of lines and arcs is offset to one side. A corner between two lines stays a sharp corner in the copy - the lines of the copy run on to where they meet. Where an arc meets a line, a convex joint is rounded. The ends of the copy stand opposite the ends of the chain. A closed contour of lines keeps sharp corners in its copy too.

#The copy holds to its source

The copy is tied to the source contour: its segments run parallel to their own at the given distance, its arcs from the same centres. Change a size of the source — the copy follows. The offset of a circle is a concentric circle with a radius larger or smaller by the distance.

#Where it is used

• A wall: the outer contour exists, the inner one is an offset inwards by the thickness.
• An allowance: the outline of the part and the outline of the blank around it.
• A slot along a path: a centreline and two offsets at half the width.

For an even wall over a whole body, Shell in the part is better: it works on the body, not on a flat contour.

#If it did not work

• Inwards does not work — the distance is more than the contour holds: going inwards the sharp corners close in. Make the distance smaller.
• The copy did not follow the source — where the offset dropped or merged segments (a narrow ledge inside), the copy lies free. Make the distance smaller or split the contour into parts.
• The status says "Offset takes lines, arcs and circles" — nothing chosen is a curve (points only, or construction lines). Choose a contour, a chain or a circle.
• The copy went to the wrong side — press Esc to free the side, and click nearer the one you want.
• The click added a curve instead of fixing the side — it landed on a line. Click on an empty place beside the copy; take the extra curve off with another click on it.