I dunno if anyone else has been bothered by this, but I have found it hard to be able to layout good looking and consistent 5 star knobs in the shop. I mean who has that kind of trigonometry in their head right, I remember basically nothing about trig from school. So I went researching and came up with a way I could reduce the process into a few steps that are easier to remember and doesn't require a lot of math. This requires a compass, a ruler and a calculator (phone basically).
1. Draw a circle of the diameter you want the knob to be.
2. Draw a bigger concentric circle, about 7/8" or 2 cm bigger in diameter (this is important to get the right look on the cutouts).
3. Divide the bigger circle into 5 parts, set your compass to the radius * 1.1756.
4. Now set your compass to 5/8" - 7/8" (15-20mm) place it on the intersections you have made on the bigger circle and make a semi-circle that intersects the smaller circle, now you'll see the familiar shape! By varying the size of this measurement you change the look of the knob. There's a certain geometric beauty or consistency to using 2 cm or 7/8" as it's how much bigger the outer circle is, to me anyway.
Now you could just bandsaw this shape out, or use a 7/8 forstner bit to drill out the holes before cutting the inner circle on the bandsaw or using a drill press hole cutter.
And the number 1.1756? It's the result of the trigonometry I won't be going into, it's what you can use to divide any circle into five equal parts if you know its radius. TabLeft Workshop had a great video on it here:
https://www.youtube.com/watch?v=8Rg2DT7BOE0
So hopefully it wasn't just me who was wondering about how to get about this and hopefully it'll be of use to others.
1. Draw a circle of the diameter you want the knob to be.
2. Draw a bigger concentric circle, about 7/8" or 2 cm bigger in diameter (this is important to get the right look on the cutouts).
3. Divide the bigger circle into 5 parts, set your compass to the radius * 1.1756.
4. Now set your compass to 5/8" - 7/8" (15-20mm) place it on the intersections you have made on the bigger circle and make a semi-circle that intersects the smaller circle, now you'll see the familiar shape! By varying the size of this measurement you change the look of the knob. There's a certain geometric beauty or consistency to using 2 cm or 7/8" as it's how much bigger the outer circle is, to me anyway.
Now you could just bandsaw this shape out, or use a 7/8 forstner bit to drill out the holes before cutting the inner circle on the bandsaw or using a drill press hole cutter.
And the number 1.1756? It's the result of the trigonometry I won't be going into, it's what you can use to divide any circle into five equal parts if you know its radius. TabLeft Workshop had a great video on it here:
https://www.youtube.com/watch?v=8Rg2DT7BOE0
So hopefully it wasn't just me who was wondering about how to get about this and hopefully it'll be of use to others.
