Reference Section > Shape Library > Other Shapes

The Chain guard shape is a plate made of two circular ends joined by straight sides. The two ends can have different radii, and the straight sides are tangent to both ends, so the plate tapers from one end to the other. Each end has a round hole on the same centre as the end. Use it for chain guard plates, links, lever arms and similar two-hole brackets.

It appears in the shapes library under Other Shapes.

Insert point and direction

The centre of the bottom end (and of the bottom hole) is the insert point (Base X, Base Y). The top end is centred Center Dist directly above it, on the +Y axis. Use Rotation (see Transform) to lay the plate at another angle.

The outline is one closed path, built anticlockwise: it starts where the left side meets the top end, runs down the left side, round the bottom end, up the right side and round the top end back to the start. The two holes are separate full circles, not part of the outline.

The Bottom R and Top R dimensions are drawn as radii, the Bottom ID and Top ID dimensions as diameters, and the Center Dist dimension as a linear dimension between the two centres.

Properties

Property	Description	Default
Center Dist	Distance from the centre of the bottom end (the insert point) to the centre of the top end, measured along +Y (length). Must be greater than the difference between Top R and Bottom R, taken as an absolute value (see Limits).	100 mm (4 in)
Top R	Outside radius of the top end (length).	25 mm (1 in)
Top ID	Diameter of the hole in the top end, on the same centre as Top R (length). 0 leaves no hole; a point is placed at the centre instead.	25 mm (1 in)
Bottom R	Outside radius of the bottom end, centred on the insert point (length).	50 mm (2 in)
Bottom ID	Diameter of the hole in the bottom end, centred on the insert point (length). 0 leaves no hole; a point is placed at the centre instead.	40 mm (1.6 in)

Limits

•Either end can be the larger one. With the defaults the bottom end is the larger; make Top R larger than Bottom R to taper the other way.

•The hole sizes are not checked against the end radii. A Top ID larger than twice Top R (or a Bottom ID larger than twice Bottom R) gives a hole that breaks through the outline, and the shape is still drawn.

•Center Dist is the +Y distance from the bottom centre to the top centre. A negative value is not checked by the shape and puts the top end below the insert point; use Rotation to point the plate in another direction instead.

•Center Dist of 0 is not checked by the shape, and the angle calculation divides by it. Keep it above 0.

•Negative values for Top R, Bottom R, Top ID and Bottom ID are not range-checked by the shape. Enter positive values.

When the shape cannot be built

If the values cannot make a valid shape, the shape is not drawn, a broken-shape marker is shown at the insert point, and the property page shows Warning: Cannot build shape from these parameters. This happens when:

•the difference between Top R and Bottom R, taken as an absolute value, is equal to Center Dist: the top arc then has a zero swept angle and is rejected;

•the difference between Top R and Bottom R is greater than Center Dist: the shape does not check for this case, so do not rely on the result (see Limits);

•Top R or Bottom R is 0, or within the drawing tolerance of 0;

•Top ID or Bottom ID is greater than 0 but within the drawing tolerance of 0 – set it to exactly 0 for no hole, or to a real diameter.

Every 2D shape also has the Transform properties (Base X, Base Y, Rotation, Scale, Mirroring X) and the Polar Array properties, listed after the shape's own properties.