Hi Joel,

I will do my best, and I am sure others that have built Hammer Trusses will join in...

Quote:
Are the arches typically cut/milled from a single timber, or are they constructed by joining two or more timbers to create the arch.
Yes... confused

This is tricky one to answer at it depends on the truss design, and how it is facilitated. I usually try "book matching" both side of the truss assembly, but that is more out of traditions and aesthetics that engineering, though I believe the symmetry does add strength.

Quote:
If multiple timbers are used, what type of joinery connects them? - scarf joint?
Scarfs, and splines are probably the most common, will see what others have to say on that.

Quote:
When the hammer post joins to the hammer beam what is the typical connection?
I prefer a housed joint with through tenon and wedge.

Example:
http://www.logandtimberschool.com/courses/frame-bents.php

Quote:
would most simply do a mortise and tenon, or would you use a through tenon for decorative proposes?
See Above.

Regards,

jay