My husband is making my daughter an adjustable pikler climbing frame and we are trying to work out the joins.
I think the best way would be to do 8-dowel joins then with a bolt and nut through the middle but we don't know how to go about doing it. I find it hard to explain so I've included a picture.
I would really appreciate any help or suggestions.
If I had to do this and didn't have cnc access, I'd make a drilling template that indexed on the previous hole, so even if it was slightly inaccurate, it would be consistent. I'll try and sketch a 3d version later today, but it's a chunk of plywood with an index pin, a drilling hole, and a center hole. Critical aspects: the index pin (dowel) has to come out both sides so you can mirror image the drilling, dead perpendicular is important for the index hole, the drilling guide hole, and the center hole, so take exceptional care with these. When drilling the rest of the holes, perpendicular is also important.
There's a chance that there's a simpler solution to the problem, but it's early in the morning and I might not have had enough coffee.
Edit to say that all my attempts at drawing this were utterly terrible. That said, @Graphus has a very good point about multiple drillings causing the template to get sloppy. Perhaps what I called the 'drilling hole' above should just be a 1/8" 'marking hole', where you thump it with a nail to establish the center of the drilling. Remove the guide; drill with the dowel sized bit, spin and repeat. And I should have been explicit earlier; the distance from the center to the index pin and the marking hole has to be absolutely exact, or the first time you try to spin the index, you'll be off.
Edit again don't forget to make left and right sides match exactly. The easiest way I can imagine is to do both the arms of one side, then use those to mark (or even drill) the corresponding other side.
That type of constructions lends itself to a CNC router, in order to get the precision required, but a DIY approach isn't completely impossible.
Consider to create a graphic image using a vector editor such as Inkscape (free, multi-platform) or Illustrator or CorelDraw (both pay) to represent the holes of the join. Ensure that your graphic also includes a dot or cross-hair for each hole (see below). Cut out the printed version and attach to the work piece with suitable adhesive.
Wood is an organic material and it's going to be challenging to ensure the hole placement. The drill bit will wander from the desired location. Usually, one prepares for drilling metal by using a center punch, and rarely does so for drilling wood, but for this project, it would be a good idea to very carefully center punch the appropriate locations from the template.
Use a small diameter drill (1/8" or 3 mm) on the punched locations. This will serve as the guide for the subsequent drilling process. After your pilot holes are complete, use the final drill size to match your dowel pins. For best results, clamp the work piece to a scrap to prevent the drill bit from splintering on the exit. Using a forstner bit or a spade bit rather than a twist drill will reduce splintering as well.
It's unlikely that you'll have perfect results if the drilling is done using a hand drill. A drill press will provide the best chance to keep the holes parallel to each other and perpendicular to the face of the work.
If you have a makerspace nearby, they may have a CNC router or a laser cutter/engraver. I can envision using the laser cutter software to create the circular array, also called a polar array to create the shapes. Using high power would create the centering holes as well as the perimeter lines, reducing splintering and enabling precise drilling. Most hobby grade laser cutters will not cut through such thick material, but that's not required to accomplish the task.
