|The original chair|
I kept the middle three spindles in about the same locations as on the original chair. For the outside two, I wanted to space them out roughly equally along the back curve of the seat, and away from the curve of the back by about 5/8". Sketchup helped a lot with this.
Up top of the five spindles is a crest rail.
|Partial Sketchup model (stretcher rails in undercarriage not shown)|
To determine how far back the crest rail should be, I looked to the original chair. The top of the arch is set back about 1 1/2" from a line vertically perpendicular to the seat at its back edge. I used the same for my chair. For a crest rail about 13-15" higher than the seat, this gives a seat-back angle of about 10-11°.
For the undercarriage, I wanted to keep close to the original. But I thought the original's leg mortises were a little close to the edge of the seat.
|Underside of original seat|
|A 7/8" deep leg mortise on the original seat|
So I moved the tops of the front legs toward the center of the chair about 1/2" and towards the back by about 1/4". I kept the bottoms of the legs in the same position to give the chair the same stability as the original and then used my resultant and sightline calculator to figure out the new rake and splay angles. The original front legs had 2° rake and 4° splay and the new chair has 3.4° and 6.7°.
|Leg mortise locations on underside of the chair|
I ended up moving the tops of the rear legs 1" forward and 3/8" towards center (might have been 1-3/16" and 1/2" - didn't document it properly). The original rear legs had 14° rake and 6° splay and the new chair has 18.6° and 8.2°.
Next up: the chair build begins!