I have followed the tutorials that Adrian did a few years ago with some success, thank you Adrian.
Thanks for the feedback - it's good to know they have been useful.
My question is how would one go about drawing coach turnunder as non of the drawings give a radius or radii for it and thus no centre(s).
I'm afraid I'll have to offer an alternative option as I don't think an arc with 3 points is suitable. The reason being that the top end of the arc needs to be tangential to the vertical side of the coach, the 3 point arc won't guarantee a tangential arc. If you play around with the points then you will get something close but in my experience it never quite works because you are trying to judge very fine angles with the Mk1 eyeball.
To a certain extent it depends on the drawing you are using to trace. If they are old blue prints then sometimes it is possible to work out the radius, the original draughtsman for the drawing would have used a compass to draw the arc, if you look carefully at the drawing there may well be some witness marks, just a small black dot, in the region of the centre of the arc. This is indication of where the draughtsman stuck the point of his compass into the paper to draw the arc. So even though the radius is not labelled it might be possible to work out the centre of the arc used.
If no marks suggest a centre then I would suggest trying the "Tangent, point, radius" option.
Start by selecting the vertical side as the line entity, set a smaller than anticipated radius, on first effort the arc might not meet the vertical side so go back a step an increase the radius until they meet as close as you want. This is too small and doesn't meet so I need to increase the radius used. I prefer this method because it allows me to type in a number for the radius which I find easier to fine tune rather than clicking a point on the drawing.
Finally extend or trim the 2 entities to each other to ensure the end points are co-incident and the shape can be enclosed for any fill.
This method should ensure that the arc is truly tangential to the vertical coach side.