Also take a look at the Part #3 Update here.
The diagram below – you can call it a blueprint or whatever (I make no claims in that area) – shows the holes and necessary cut outs for the support struts I am going to fabricate from the steel I purchased recently.
Don’t forget that I am using some of the parts from my existing chair, and that explains some of the oddities (e.g. the 9mm holes, the hole spacings on the seat plate, and so on).
The plans above should make sense – the 9mm holes are in the sides of the A and B struts, and there are a set of 5mm holes in the top faces of the B struts for the knee-cushion to be fixed to. All the holes go through both faces of the struts.
At the bottom end of the A and B struts, in the side faces, there needs to be a cut out 30mm across (the width of the box section metal) and with a radius of curvature of ¾” (so it fits the 1½” diameter tube which forms the feet of the chair).
I’ve spent a few hours over each night of the last week sanding the parts to remove corrosion and oil coating, cutting out the curved notches, and drilling holes. I’m hoping to at least start the assembly over the weekend.
EDIT: If you came to this page from a search engine, don’t forget to look for Kneeling Chair Project parts (#1), #2, #3, and #4 (plus a couple of updates) using the site search facility. This project is now complete and there are drawing/blueprints in the other parts.