1.7*0.74*0.4m Mill / Router building...

[blackburn mark]

Could you use a timing belt inside the harmonic gearbox as the flexible gear thingy? Milling the inside out pulley would be fun. Probably do it in two semicircles...

haaha!!!! you read my mind this time :) iv already considered it, not really explored it deeply though, you would need a clever way to output the torque from your inside-out timing belt to your output shaft
the beautful thing about using a belt for the strain wave gear is its so flexble you could use two simple bearings or rollers for your wave generator and use a slightly larger timing belt for the outer gear and pre-load it with your simple two bearing wave generator....
im thinking it would take quite a bit of elegance to make it work... backlash might well be very small but with heavy cuts im thinking it will have quite a bit of give
errrrr..... i dunno ??? youve got me thinking on the issue again.... if i try to fit any more in my head i think one of my eyes might pop out :)

Edit: not sure why you would need to cut the internal in two halfs ?? i dont think you would need sharp corners at the root end of the pitch