This is a difficult shape to draw in Carbide Create since one needs outside rounding (easy) and internal rounding (difficult). Having a program do the math reduces this to just specifying a couple of parameters:
With the variables specified, we add support for units and the attendant calculations and begin placing things:
As a check on this, drawing things up in parallel in Carbide Create will help us to see what is involved:
Note that the circle and rectangle need to be rotated as a unit, and a copy of the circle rotated in place as well so as to allow for snapping:
A bit of duplication and flipping (and rotating the circles) allows us to arrive at:
which when unioned yields:
and when zoomed in on, shows a very slight rounding is necessary:
Duplicating this geometry and subtracting the circle from the nascent bow-tie gives us a node we can snap against for measurement purposes:
Since Carbide Create only affords an option to draw from the center out this must necessarily be reduced in size by a scaling factor of 0.5 and repositioned.
But we are asking the wrong question — what needs to happen here is we need to inscribe a circle inside a figure which has angles of:
180 - 15 * 2
so, 150 degrees, so a 12-sided figure, so a dodecagon
Carbide Create makes it simple to draw a circle with an inscribed dodecagon (since it draws polygons using the radius to a point):
So the math should be:
- determine the length of the base of a right triangle which has a hypotenuse of radius and an apex angle of 15 degrees
- use that base distance of calculate the height of a right triangle which has opposing angle of 15 degrees
to determine the distance which the circle should be lowered from the point of the interior angle of the bow-tie.
This dimension of course gets re-used in a number of places, so we’ll start at the lower left corner we are using as an origin:
With those numbers worked out, it’s a simple matter to make a module to make half:
and then to mirror it and place the copy appropriately.
Next is exporting OpenSCAD, wiring up the customizer and adding the projection() command so as to be able to export a DXF or SVG.
Will you have encyclopedic knowledge.
Thanks, mostly I’m just stubborn and manage to look up the specifics I need.
Very interesting and complete solution. Designing the object with tooling geometry in mind allows for direct machining of both the bow tie and pocket on the machine.
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