Storm proof casement windows

[JFC]

Why do storm proof casement windows have a through mortice and tenon rather than a haunched mortice and tenon ? Is it just because the factory can knock these out quicker or am i missing an important design issue ?

 

[lugo35]

its pretty much as you say its for speed. they usually use comb joints.
we used to use hunch M+T with a star dowel through the joint, but when the second rebate is cut most of the haunch is removed. so becomes a though M+T.

 

[JFC]

I was looking at the two i have to copy tomorrow and it would need to be a very small tenon to leave any sort of haunch on it . I spose ill just do the comb or double M&T as thats the joint on it and it will be quick this way .
I was just wondering if i could do a better joint than the original .