not sure what window you are making as your sketch refer to weights and casement. This method is really for 90 and 45 degree bays with straight casements and although made a 45 degree box sash, it was as a whole unit. this jointing method suits site fixing. what stock are you using and have you done a workshop rod? Joiner by trade, always used rods, white hardboard, and always encourage the practice . Draw out the window full size, showing rebate lines. the rough sketch is based on a 90 degree bay, hence the 45 but the joining method will work on any angled bay, just adjust the tooling, I had a precise vari angle block for use on my spindle. The tongue is plywood and the groove mid way on the splay. From the rod the cheese can be seen and machined up. need a sketch really of your plan.