How to draw a 'circle' with straight sides

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How to draw a 'circle' with straight sides

SouthernFellow
So, from the title of this post, you can probably tell I'm not an engineer and an utter newb with CAD!

What I want to draw is this:



My issue is, is that it has to be properly dimensioned and my trig is probably the weakest part of an already weak math's ability.  This means drawing two lines and a couple of curves is going to be tough for me to get absolutely right.

I was wondering if there's an easier way of doing this than getting out a calculator and pencil and paper!

Thanks in advance
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Re: How to draw a 'circle' with straight sides

dellus
Hmm. It's easier to do it with a calculator and pencil and paper.
But if you have the ambition to do it with CAD, you will have to challenge your brain.
Do you have an idea how to do it?
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Re: How to draw a 'circle' with straight sides

SouthernFellow
I did work it out in the end.

I ended up drawing two isosceles triangles each way from the centre point (I cheated and measured the length of the flat part on the actual component with digital calipers).  I knew the length of all three sides and so used cosine law (and yeah, you bet I had to look that up on the internet!) to work out the vertex angle.

One I'd done that, I used divide to mark the part of the arc between the intersections of the triangles sides and the circle.  Then I just selected the new 'arc' entities and just deleted them.  Then I just removed the sides of the triangle, leaving the bases there.

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Re: How to draw a 'circle' with straight sides

LordOfBikes
Administrator
My suggestion without calculator:
1. draw the vertical and horizontal center lines
2. with Parallel from Line tools draw 2 vertical lines, distance 10.8 / 2
3. draw the circle with Center, Radius tool, radius 6 and snap it to the center lines intersection point
4. divide the circle at the right and left intersection with the horizontal center line to get two semicircles
5. trim the lines and arcs at the intersection points using Trim two tool

Sometimes Trim two tool fails on arcs, then use single Trim tool and trim the line and arc one by one

There are a couple of other ways to construct this, with various tools, this is a matter of personal preferences at least.
It also depends on the given parameters. Maybe it's easier to start with the circle and snap the center lines to the circle's center then.

Like on paper, you can mostly draft construction elements to find distances or intersections to finally construct what you want.
The rules of geometry are your friend in CAD construction and often replace the calculator.
Draw the construction entities on separate layers, then you can keep them for further reference but switch them off for printing or drawing clarity.

Armin
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Re: How to draw a 'circle' with straight sides

dellus
In reply to this post by SouthernFellow
I hope you didn't take my answer seriously. I just wanted to challenge you a bit instead of giving a ready to use solution. As Lord of Bikes explained, it is better to solve it by geometrical means. You might follow his instructions and compare the result with yours.