Opposed Piston Axial Engine

[Ken I]

What do you call a shape that has six sides, opposite sides parallel and equal distance apart; six corners with equal angles of 120 degrees. and yet no two edges equal in length?

I believe its a Hexafrustragon.

Your problem starts with having no point of reference to the centre - so start with it turned round or bore a hole (if there's going to be one anyway).
Obviously the RT is the way to go (but you still need your centre reference or its all going to go pear shaped).
On the RT you can otherwise "work your way in" to size after guessing the part to be approximately on center (the hex being your first desired outcome) by this method the center is an outcome rather than a starting point - you will also need to move the clamps at least once.
Clamped to the table (no RT ?) you can clock against a 30° wedge for each "index" - but you still need your centre reference.

After each "index" you have to refind the centre using an edge finder (whatever)

If you can't turn or bore a centre reference - superglue a button - use as reference and remove later. For non-RT use you could also glue a large hex nut to the plate and use that as both angular and radial dimension reference (of course your result will only be as good as the nut).

Ken

 

[Captain Jerry]

Ken

You are right that the center reference is the key. Where is it? Drawing diagonals produces a triangle that defines the center. Constructing a circle tangent to the three sides gives you the center. Then you can set the height of the cutter to twice the distance to the closest side. The angles are all good so the RT isn't needed. Just take the cut off of the three sides that the small triangle points to. (AS shown in the attached)

When I was actually doing this in the shop, I didn't have my computer so I had to sneak up on it. It is fairly easy to guess at the actual center of the small triangle but with only a digital caliper to get the dimension I couldn't really trust it so I went light on the first three cuts and followed the procedure again. The second time, the triangle was much smaller and the third time it was a point.

Jerry