Oak gazebo joint query

[JonCamo]

Dear all
I have a query about my oak gazebo project. New member so please forgive any inaccurate terminology and general newbie errors!
My gazebo will have a pair of parrallel tie beams joined to the four posts by mortice and tenon joints (100mm deep mortices, 1.5 inch thick tenons). The beams and posts are 150mm. I plan to place two more beams perpendicular on top of these beams and join using a mid lap joint similair to the images attached below.
Bearing in mind the mortice in the lower beam is 100mm and the beams are 150mm, how much depth can I cut into each beam to create the joint without the lower beam being weakened too much?
I hope this makes sense and forgive if my terminology is not quite accurate

Regards

Jon

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[johnnyb]

I would not half lap this at all just mortice through both of them and skewer them with a long tenon. otherwise you'd need to devise joints that don't weaken the shear line. patently a gazebo is carrying zero weight though so some lap won't weaken it excessively. though half seems excessive but 3 by 6 oak is unlikely to shear tbh.

 

[JonCamo]

Thank you

 

[JBaz]

If this is the kind of thing you have in mind, I'm happy to share how we cut the corner joints (or anything else you'd like to know).

(It is square in reality, it's just the lens making it look to be leaning.)

 

[JonCamo]

Thanks Jbaz

What dimensions are the rafters?

Regards

Jon