Saturday, October 8, 2016

Nana's Dining Chair Rebuild, Part 2: Some Joinery and Build Considerations

The chair I'm duplicating was the "head chair" (for lack of a better term) of the set of six and differed from the rest in that it had arms.  I got one of the other chairs out of storage to get more information on layout and joinery details.
"Head chair" at left (arms are not currently installed) and one of the others
It turns out that there are more differences between these chairs than just having or not having arms.  The head chair's front seat rail and side seat rails are about an inch longer than those for the armless version.  And the same applies for the lower rails.

I used the second chair to check out the backward lean of the chair.  It turns out that if I put a 1/2" shim under the back legs ...
Shim under back leg
... I get the seat rails parallel to the floor.
Seat leveled with 1/2" shim under back legs
This is important in the layout of the mortises in front and back legs.  In the drawings that follow, the bottoms of the front legs are set down 1/2" lower than those of the back legs.

I'll get to the drawings in a minute.  I'm not certain what wood was used for these chairs.  I scraped some finish off of one of the back legs to see the wood.
Not sure what wood this is
Another area of that leg showed definite evidence of poplar.  The curves on the upper leg required wider stock and you can see that a piece was glued on to provide the extra width.
The greenish wood is most likely poplar
I'm going to use poplar for this project, but I'm going to make the the back legs from a single piece.  You can see where a crack had formed in the above picture.  I hope the use of a single piece of wood will make it stronger.

Before I made the Sellers dining chairs I bought a flip chart like those used in businesses for presentations or meeting.  While expensive (over $30!), it has been nice to have paper this size for full scale drawings.  It's got vertical and horizontal lines at 1" spacing.  This first drawing is a cross section through the seat rails and legs at seat height.
Seat rail layout with legs
I hope you can see enough when you make the photo larger.  It is really invaluable to make full scale drawings to play with joinery.  Here's a closeup of the lower right corner of the above picture.
Front left leg joinery detail
Gotta stop to ask a question of anyone good enough to respond: do you name the left and right parts of a chair (or table, or cabinet, etc.) from the perspective of someone looking at it from in front of it?  Or do you name the sides from the perspective of someone sitting in the chair?  For example, sitting in the chair, my right leg would be near the right leg of the chair.  That's how I'm naming it.

In the above picture, some of the leg blank with be cut away during shaping.  In the picture above, the bit at the right and bottom will be cut away - that's why the reveal is measured from the dotted line.  To maximize the tenon length I show them mitered.

The rear leg joinery is much more interesting.  Remember the original chair was doweled together.  If I try to use M&T, I run into crossing tenons.
Rear left leg joinery detail
This shows why the original builder did something that I thought was interesting.  Here is a picture of the rear right leg, rear seat rail (to the right in the picture) and right side seat rail (coming toward the camera).  You can see that the the rear rail is higher then the side rail by about 1/2".
Right rear leg and seat rail joinery
This was so they could use dowels without the dowels for the rear rail intersecting with the dowels for the side rail.
Rear leg showing offset dowel holes
Here's how I'm going to handle it with M&T joints.  The following picture is a side view of the chair.  The red lines show the tenon of the side rail.  The rectangle that the tenon intersects is the rear seat rail (end view) and its tenon is shown in pencil dotted line.
Side view of chair
  My two tenons will not extend the usual width of a tenon.  I'm also going to make my short shoulders just 1/8" to add a little tenon width.  Here's a close-up photo.
Close-up of side view of rear leg and seat rail joints
I'll still get 1 1/4" width tenons (rather than the 1 3/4" I normally would have gotten) and they will not interfere with each other.

Another area that will be tricky is the lower rails, which will be joined to the front and rear legs in areas where the legs have a curved shape.  Here's the back leg / lower rail detail.
Back leg to lower rail joint
I'm planning to first plane a flat section (see the slanted dotted line) tangent to the curve at the joint location.  After the joint has been cut and fitted, I'll complete the shaping, leaving a small flat where the joint is.

The front leg is a different story.
Front leg to lower rail joinery

It would be tough to plane a flat spot at the location of the joint.  I think I'll just use the full scale drawing to determine the angle to use for the vertical shoulder of that rail.  This should be a real challenge.

It's really interesting how just a bit of experience has made me think of these things BEFORE I start cutting.  A great lesson to learn!

Finally, I got the wood for the project: some 5/4 poplar for rails, arms and backrest and some 8/4 poplar for the legs.  Mini rant: I can't seem to get full 4/4 wood from the local hardwood dealer.  It's planed to about 7/8" and I need 7/8" for my final thickness.  I was luck they had 5/4 thickness.  Arrgh!
Poplar for the project
I've already started cutting rough blanks for the project pieces.  The front legs, all rails and backrest pieces are stickered.
Most parts cut to rough dimensions
Still need to cut another back leg blank and the arm pieces.  I'll do that Monday and let them sit for a week.

I'm off Tuesday to southeastern Utah for a week of R&R - probably a lot more recreation than rest.  Catch you all on the flip-flop.