Swing Away Guard : Caclulation

This document might help you to design your own guard. It summarises some needed methods to calculate required dimensions before getting started. The following elements presume that the sliding cover is made from 6 trapezes forming a 5° angle each giving a total of 30°. All measurements in millimetres and degrees.

Formulas :
• 2.5° is the half angle of every trapeze of the sliding cover.
• A dodecagon (12 sides) allows the trapezes to fold at a 30° angle maxi. 30 ÷ 2 = 15°.
• 7.5° is the angle the bending track need to move due to the width of the rotating arm.
• Sinus 2.5° angle = 0.0436194
• Sinus 7.5° angle = 0.130526
• Sinus 15° angle = 0.258819
• Isosceles triangle base from radius : Radius × Sin(half angle) × 2
• Radius from isosceles triangle base : (Side ÷ 2) ÷ Sin(half angle)

Needed Dimenions :
• 100 mm : the minimum sliding cover width define the inner circle of that one dividing by two and subtracting the outcome from the main radius.
• 430 mm : the main radius meaning from the mount guard axis to the cutter head block axis is the key dimension of the project.
• 550 mm : the outer circle radius of the sliding cover define the maximum sliding cover width and consequently the bending track width that extends the same dimension before and after the cutter head axis.
• 573 mm : the circle radius defining the length of the rotating arm. This one is not used in the following operations.
• 12.5 mm (5 + 7.5) : the sliding cover thickness, plywood plate plus pad. Calculation :
From there it is possible to calculate...
• The inner side of every trapeze of the sliding cover :
430 - (100 ÷ 2) = 380 which is the inner radius of the sliding cover.
380 × 0.0436194 × 2 = 33.15
• The length of the bending track :
550 - 430 = 120 which is the half length of the bending track.
120 × 2 = 240
• The end radius of the bending track :
550 × 0.0436194 × 2 = 47.98 which is the outer side of the sliding cover if not truncated.
12.5 × 0.258819 × 2 = 6.47 which is the reduction due to the sliding cover thickness.
47.98 - 6.47 = 41.51 which is one side of the dodecagon.
(41.51 ÷ 2) ÷ 0.258819 = 80.19 which is the ending circle radius of the bending track.
• The start radius of the bending track :
550 - 240 = 310 which the dimension between the main axis and the start of the bending track.
310 × 0.0436194 × 2 = 27.04 which is the starting radius if sliding cover thickness equals 0.
12.5 × 0.258819 × 2 = 6.47 which is the reduction due to the sliding cover thickness.
27.04 - 6.47 = 20.57 equals one side of the dodecagon.
(20.57 ÷ 2) ÷ 0.258819 = 39.74 which is the starting circle radius of the bending track.
• The spacer end side of the bending track :
550 × 0.130526 = 71.79
• The spacer start side of the bending track :
310 × 0.130526 = 40.46 Of course other arithmetic calculations will be required but they don't need trigonometry or will be explained trough the building work. You also may compute here.