I downloaded a plugin called ‘Get Center Point’ to find the centre of the circle. Then I drew a line to the edge. There’s a problem at this point - the distance from the centre to the edge varies even though its supposed to be a circle. ie. I drew a circle with a radius of 51mm but the actual radius fluctuates between 51 and 50.56mm. The centre line therefore potentially fails to cut the circle down the exact centre.
After doing this, the two halves of the circle are recognised as two shapes, so I selected just one. This should be exactly half. Now when I drag the edge out, the line in the middle of the circle, as well as the centre point dot hugely impact the new shape and cause a mess. It doesn’t seem possible to keep the semi circle highlighted while deleting these graphical markers. If I use the Ruler instead of the line tool, the semi circle is not recognised anymore, and its back to figuring out the exact half way point manually again, which is so painstaking that I inevitably make mistakes and need to restart all the time.
Is it essential that EXACTLY half the circle is dragged?
In relation to offsetting, justcheckinm8 seems correct in saying that the resulting image should be duplicated, resized along two axes and centred, although failing to adjust the third axis will result in warping. If three axes were resized, then there would be blade edges later on, but this would probably be easier to fix. I assume the gap would be filled by placing two lines between the gaps along the edges and sketchup would colour in the gap, then I would delete the two lines.
The other thing is that when I want to scale the curved rectangle to specific dimensions during resizing, I’m not sure how to input the correct scale in mm. The resize tool appears to be measure in factors rather than mm, and even if I try to calculate the correct size in factors rather than mm with an equation that takes the existing length x height and see what I need to divide by to calculate the end result length x height (this also requires pre-planning the amount I need to drag the semi circles out by multiplied what I will later divide by), I cannot centre the resizing because the alt key that is usually used to keep resizing centred is disabled if a numerical value is given for resizing. This also means that no changes to the length values of the wrist can ever be made unless I start again each time. Is there no way to simply draw a wrist hole with a 3mm offset, then the elbow hole with a 3mm offset and connect the two smoothly? This method seems uneditable and extremely difficult to calculate.