A locking tenon joint?

[Charlie__V]

@tig said:

To force the final [purple?] tenon to lock firmly into the mortise...

Make it with a central small tapering horizontal cut along its length, make it widest at the visible end.
Make the tenon-mortise's cross-section so that its external end is slightly bigger that its start size.
After the joint whole is assembled, you can then drive a glued wedge into the tenon's exposed cut.
Over size the wedge's length so that after its firmly in and all is set, you can trim off the excess exposed end of that wedge and finish everything neatly.

Now all of these connections are locked in all directions ?

TIG,
Thanks....& Aha....much like an Axe handle wedge, to keep the axe head from flying off.

And also goes to dh's thinking on butterfly joint as final "lock".

I only tapered the tenon's mortise 1° which actually seems like a bit too much? (maybe not)

Please see GIF
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EDIT: I should have properly thanked Fredo for his Animator plug-in used to create the GIF’s in this thread ......so Thank you Fredo, for all the magic you have done with the Animator plug-in!
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SKP file

[davidheim1]

I think that does it. Thanks to TIG for suggesting the wedged tenon and to Charlie for producing yet another version of the joint.
Best,
dh