More Finds and More Hawaiian Style Chairs

Around a year ago I posted a project, Hawaiian chair in Kona wood.  In that posting I noted that the bent wood forms took a lot of time to build, and ruminated that I would need to build some more of those chairs to retroactively justify the time spent on the forms.  But not having any more Kona, the plan seemed doomed.  Until …

 .… another Craig’s List find.  A noted woodworker in San Francisco, who specializes in restoring historical buildings while strictly adhering to the style of the era, was advertising a few slabs of monkeypod wood.  His intent was to make a desk from them, but he never got past planing the lumber, so the slabs were (mostly) flat and square to start. While not as exotic as Kona, it is in fact an island hardwood with many of the grain patterns and color that its better known cousin sports.  Admittedly, it is not as spectacular, but is attractive in its own way.  Monkeypod is a lot less dense than Kona though, and working it takes a lighter touch and sharper chisels than usual.  There was enough wood to make two full chairs.

Slabs for sale.  I bought them minutes after seeing this posting on line.  

The first step, as always, is to figure out where to cut each of the chair pieces from the slabs.  To do this, I take photos of each slab, move the photos into the computer design software, scale it to actual dimensions, then overlay the line drawing of each piece and move them around on the slab to get the most pleasing grain pattern while avoiding that nasty knot.  This screen shot image shows the red layout lines at final placement for the pieces on the large slab.  A similar layout is done on the smaller slabs.

 Large slab with parts placement.  Red lines outline the parts.  

Instead of laboriously transferring the outlines onto the actual board by hand, I made a large size “D” printout of only the outlines at 1:1 scale.  The drawing is then mounted on the slab using light tack spray-on adhesive.  I use a track saw to separate the parts I need into billet form, for example front legs and rails.  The square billets are trued up on the jointer enabling accurate mortise and tenon cutting.  Curved and oddly placed parts are rough cut on the band saw and worked to final dimensions with a spoke shave, spindle sander, and hand sanding, or in the case of the back legs, a templated routing operation.

  For the soaring 52” tall back legs, I first shape one to final dimensions with a combination of spindle sander, spoke shaves, and hand sanding.  That leg then serves as a router template for the other three legs.  These photos show the template leg on the bottom clamped and double-side taped to the work piece on top.  A 2” long bottom bearing trim bit chucked in a battery-powered hand held router mills out the final shape.

Two views of the back legs getting final milling to shape with a pattern router bit.  The pattern is on the bottom in this set up, dictated by the router bit available.  

I prefer this method over individually shaping each leg since all four legs turn out exactly the same. Cutting the mortices thus becomes more repeatable.  Plus, it is a lot less work.  After the mortices are cut, I round all four edges using a ½” radius bit on the router table.  The left photo below shows all four legs after morticing but prior to edge rounding. The right photo shows one full back leg assembly in clamps.

Left - all four back legs milled and mortised ready for edge round-over.  
Right - One pair of back legs with cross-ties in the clamps 

 The front legs are mostly straight sided, with a slight concave curve on the inner side.  After cutting the mortices while in square billet form, the leg tapers are cut on the table saw.  The single concave curved inner face is cut on the band saw.  The tenons on the rails are cut on the horizontal CNC while in billet form, and then shaped on the band saw.  Final shaping for the legs and rails was primarily by hand sanding from 80 grit on down to 220 grit.  The two front legs are joined with the top and bottom rails and the joints are sanded with 80 grit paper wrapped around a dowel to obtain the smooth transition from the front rails to the front legs, four joints in total.  The two photos below show a joint just after gluing, and after sanding.  This operation takes about an hour per joint.

Rail to Front Leg joint smoothing. 
Left photo is just after gluing. 
Right photo is after hand sanding. 

 With the back and front leg sub-assemblies complete, the two are joined with a pair of horizontal rails.  As the clamps are applied I make sure the measurement from the bottom of the front leg to the bottom of the rear leg is equal on each side, that the tenons are properly seated in their mortices, and that the cross diagonal measurements of the seat frame are equal as well, assuring the frame is not skewed.  In practice, if all the mortises and tenons are done well, there is (and was) no need of any adjustment at this step.

 

Basic frame with front and back leg assemblies joined by a pair of horizontal rails during glue up.

Two major elements of the chair design call for bent wood pieces, namely the back and the bottom ‘rail’.  The width of both pieces was larger than my 6” steam bending pipe, so once again I opted for bent laminations.  I re-used the CNC cut bending forms from the first edition of this chair design.  After all, that was the whole justification for making this pair in the first place.

The stock for the two bent pieces is re-sawn into five each pieces for the long back board, and four each pieces for the shorter rail.  Each laminate was left about 1/16 inch thicker than the final thickness, and run through the drum sander to get to 0.15” for the long boards (total thickness ¾ ” ) and 1/8” for the short boards (total thickness ½ “ ).  The stock board is run through the planer after each re-saw pass to get a smooth surface for the next laminate cut.  

The laminates are first soaked in water for a few minutes, and then assembled without glue and clamped in the forms overnight.  This minimized spring back later.  I use clear polyurethane glue (clear Gorilla Glue, non-foaming) to glue the laminates together prior to clamping in the bending forms for a second time.  The residual moisture in the wood helps cure the glue.  Polyurethane glue creeps far less than the traditional PVA glues, so the piece holds its shape better over the long run.    The monkeypod is a very porous wood, and some of the glue oozed through the pores to the outer surface.  To be clear, this is not edge squeeze, but rather penetration of the glue through the thickness of the outer laminate.  A good sanding removed most of the bleed through, but it would be better to seal the two outer surfaces prior to gluing to prevent ooze out altogether.

Curved back in the form under clamp pressure during final glue step
  

Cutting out the seat pan is done on the CNC from a ½” thick plywood board.  I saved the CNC file from the first edition of this chair, so cutting another pair was relatively straightforward. The seat pan is attached to the two rails which join the front and back legs.  I used tee nuts in the plywood and four each 10-24 machine screws fed up through holes in the rails.  Upholstery is a simple foam fill with the patterned denim cover wrapped and stapled from underneath.

CNC cutting the seat pan.  The slots create some flex in the seat as well as providing an exit for air when the foam is compressed.  

Final Assembly
The back and bottom ‘rails’ are joined to the frame with 3/8” dowels.  For the back, there are two dowels at the top crossbar, and two at the lower crossbar.  I arranged the backs to have the sap wood showing in a left hand and right hand pair to emphasize that these two chairs are a pair.  The bottom rail is pinned with two more dowels to the lower end of the back, but the front of the bent rail is shaped into a tenon that fits into a corresponding tenon in the front seat frame rail.

Finish
The final finish is one coat of shellac followed by four coats of Minwax Tung oil varnish gloss.  No stain is used.  Each coat is lightly sanded to knock off those pesky nibs and provide adhesion for the next coat.

At the end of the day it is all worth it.  Two views of the finished chairs and a close up of the front leg joinery.