Eul's mathematical Achilles heel showing again, I was thinking in a muddled way,
60° to the horizontal (patibulum), 30° to the vertical (stipes) would be your recommendation?
Yes. That's what I used in all of my crucifixion pictures. Note that in this picture, where Sabina is about to have her left wrist nailed, her arm is bent maybe a bit more than 90 degrees at the elbow to get her wrist into position. If you were to swing her arm upward at the shoulder, her elbow would pass pretty close to where her wrist is now placed.
And you can see that she is pretty well centered with her neck about where the mortise is in the patibulum.
Her other wrist is positioned similarly for nailing.
A little trigonometry here: The length of your forearm and upper arm are close to equal. When Sabina is hanging by her wrists, as shown here:
Her arms form the hypotenuse of a right triangle, and the distance along the patibulum from a vertical line through her shoulder out to where her wrist is nailed is the length of her upper arm, because that's how the executioner measured it. Since her upper arm and forearm are about the same length, the hypotenuse is twice as long as the distance outward along the patibulum. Dividing that distance by the hypotenuse gives us a value of 1/2, which is the sine of 30 degrees, so her arms are about 30 degrees from the vertical - very rough measurement, nothing precise at all, good enough for the purpose.
And by the way, the nails for Sabina's cross are in precisely the same place in every scene. They are actually there all the time, even before she's nailed, they're just invisible in the renders. That's how I pose Sabina's arms, so that her wrists are on the nails, how I place the executioner's finger when he's probing her wrist, etc. I just make the nail invisible before I do the renders.
Another plus for doing it this way is that she can move pretty much through her entire vertical range from hanging to fully raised without twisting the nails in her wounds.
Although she can if she struggles:
The reason an executioner would care about that is it hurts a lot more, pain draws strength out of the victim, and if your goal is to prolong her suffering, that is counterproductive. Might have been a trick of the trade.
So for me, having her hang like this portrays what I saw in my imagination when I wrote this story. It's one way that an executioner from Roman times might have done his job.
