Thursday, May 23, 2013

Purlin Rafter with Claw Tip

Purlin Rafter miter & bevel angle development.
The points B1, B2, B3 and B4 develop the miter angles on each side of the purlin rafter. The bevel angle on the top of the purlin rafter is automatically developed from drawing a line across the top of the purlin rafter material from points B1 to B2.

Purlin Rafter Claw Angle development. (purlin lip cut angle)
The claw angle is developed from the H3 dimension on the hip rafter in elevation.  The hip rafter in elevation is drawn with the same depth as the profile rafter and purlin rafter. The H3 dimension line on the hip rafter is the purlin rafter housing angle. The H3 dimension is from the edge bevel line on the hip rafter to the bottom of the hip rafter. The purlin housing angled is developed the same way we develop the witches cut for the hip rafter tail when the common rafters are square tailed . Mark off the H3 dimension along the B1- B4 line on the purlin rafter. The claw angle is developed by drawing a line through points H3A and C4. The uphill side of the purlin rafter will use the same claw angle, but drawn thru point H3A that is on the line the B2-B4.

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