Spindle Back Repair

I've had this old spindle back rocking chair cluttering the place up which you can't really sit in because the main spindle on one side broke off the top and the back won't support anything. Since I'm now retired, I obviously need to get it repaired since retirees are supposed to sit in rocking chairs, right? I've been meaning to figure out how to repair it for years, but now I can use my 3D printer to help by printing a gadget to clamp the end of the broken spindle in place on the bottom and guide a drill dead center on the top:

There is a 1/4" hole in the top of the left piece as a drill guide that doesn't show up due to the shadows, but it really is there. The pieces fit together like this:

and fit on the chair like this:

I've successfully drilled a deep hole down through the top and well into the broken spindle. (Using an extra long 1/4" drill bill I got from amazon). Didn't punch out the side anywhere, so it looks like it worked well as a drill guide.

The 1/4" dowel stock I have is really too large to get all the way into the hole (size is apparently just a suggestion at Home Depot), so I'm planning on slathering a piece of 1/4" allthread (which does fit) with epoxy and shoving it in (then putting a dowel in the top of the hole).

OK. Allthread and epoxy inserted in hole, and wooden dowel plugs the 3/4 inch at the top:

Epoxy given time to dry, dowel cut off, top sanded, and some black acrylic craft paint I had covers it reasonably well:

I can even sit in the rocker and lean back and rock and the back no longer flexes, it actually supports me. Job done.