Slanting plates template...
Some descriptive geometry.
Let’s first draw a circle with a 1.5” radius (Ø 3” column). Divide the circle in four by drawing two orthogonal diameters.
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Now divide the circle into twelve equal parts. From each letter A, B, C, D, draw a circle (radius 1.5”) that cuts the directrix ( not a relative to Asterix and Obelix though) of the cylinder. Number those points from 1 to 12.
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Now draw a generatrix from each of those 12 points. You’ll have 7 lines perpendicular to AB.
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Draw your slanted plates at 30°.
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You can see that a line starts from each point where the slant plate cuts a dirtrix.
On the right, draw a line parallel to AB. Length = 23.9cm (3x2.54X3.14159).
From the origin of this line draw a line and mark every 2cm from 1 to 24. We are using Thales theorem to divide our 23.9cm in twelve equal parts. Draw a line between the mark 24cm and the end of your 23.9cm line. From each division of the 24-centimetre line (every two cm) draw a parallel to that line and mark the sections on the 23.9cm line. You have now divided it into 12 equal segments. Mark them from 1 to 1. Draw lines from each point parallel to your generatrixes.
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Now draw lines from each point where the slant plate cuts a generatrix, you will get the shape of your grooves. That's why it's iportant to number the 12 points on your circle. Mark stop points from the point you marked on the slanted plates (1cm overlap)
Use a cobra ruler to draw your curves.
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two curves
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The big picture...
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Next step, see how it works on a piece of Ø 3” pipe. I had to buy 6m, so there’s some available for testing the method first.
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