chair rail tenon broken off at back leg ,,repair?

[laska santino]

hi, i am restoring 6 dining chairs.. all were in good condition but one.. this one,,the chair crest rail attaching to the back legs had a tenon that broke off inside of the mortise.. i have chiseled the old tenon out of the mortise and cleaned out all the glue. and cut off the crest rail tenon at the shoulder so it will attach smoothly to the back leg.. because of the way the crest rail attaches to the side of the back leg rather than into the front of the leg..i can no cut into the crest rail arm to add another tenon.. so i've filled the old mortise with a block of wood and am hoping for help in how to proceed.. i have been told various things.. can i use two screws? now that the wood in the leg that i would ber screwing into is solid,, i was hoping this would work.. however, i've read several places that screws dont work.. what about doing through dowels.?? i have posted pictures..the first two are of a completed chair,, then a close up of the joint in question,,then a picture of the back legs assembly mortise filled in,,then a picture of the front leg and rail assembly that i need to attach,, then a close up of one of the rails with the tenon cut off at the shoulder...

[Jim Matthews]

I would route a new mortise into each side of the joint, and insert a floating tenon of hardwood.

Screws concentrate force in a small area, when the chair racks and will eventually fail.
You might further stablize the joint by attaching more gussets as shown between the legs and rails.

This design, without a lower stretcher puts all the lateral and vertical load on this joint.

I would guess that this was "Daddy's" chair, and carried more weight than the others in the set.