Laying out and cutting f-holes

Using a few straight lines -- down the center, across the stop length (where the bridge will sit), and across at the low point of the c-bout purfling -- and circles of 32- and 64-mm, I'm trying to make the f-holes look right.

I'm using the lay-out scheme featured on Michael Darnton's website, as well as an image of a Brothers Amati f-hole he likes.  Even with all that, I still end up adjusting it a bit by eye.  And in doing so, hope to train my eye in the long-run.  Finally, say 'good enough' and cut the holes.

At this point they've got something of the shape, but still a little too thin.  How to decide that?  I make them wide enough to get the soundpost through.  I'm sure there must be a better criterion, but that works for now.

After a bit of clean-up work, I think I have them ok.

The poster below is of a 1666 Nicolo Amati, son of one of the Brothers Amati, and what I used as a model for my eye.  Again, not a perfect copy by any means, but something I hope works and looks decent.