Folding Lounge Chair. Cherry

I needed a project to distract me from the boredom of retirement.  Approximately 45 years ago I designed and built my folding Fit Lounge Chair.  Other than one update to trim the legs and lower the seating height, that original made from red oak has survived the passage of time and still serves me as a nice place to relax.  I made a second one from redwood to help point out the value of folding it up to move easily in and out from my deck to indoors over winters. The first two were made before I even knew what a CNC was. This one exploited the capabilities of my CNC to make the best use of the material I had on hand. 

Folding Lounge Chair.  Cherry.

First came dimensioned drawings, My Aspire CNC Software had all the drafting features I needed. 

Side View

There are three main sections of this design.  They include the rear legs with a stretcher between them, the seat frame with one stretcher and two dowels between the sides, and the front frame with two stretchers between the sides. 

I had quite a bit of cherry wood hoping it was enough to make the parts for one chair from.  A check of the size of each part revealed I didn't have any Cherry boards long enough to make the front leg frame from.  This was not a project ending problem though as I can join boards end to end with CNC cut joinery.  

Rear leg frame.

I had two 24" long sections of 6/4 cherry already sliced 2" wide.  Those were enough for the rear legs. The two strips of cherry were planed down to 1.25" thick.  I drew up the toolpaths needed for them. and cut them out. They needed slots for the sliding pins, tapered mortises for the stretcher end tapered tenons, and holes for bolts.  I had to order the needed bolts for them.

Next came the rear stretcher. Boards in my garage yielded enough for the stretcher that goes between them. All the cherry I had was 6/4 thick,  I ripped three strips of 6/4 cherry 1" wide, then tipped them 90° and glued together them together to make one 1" thick rear leg stretcher from.

Seat frame.

The seat frame sides have a hook on their rear ends. These are the most complex/detailed parts of this design.  They needed threaded inserts for the cam levers that pull the canvas tight. They needed holes for bolts that join the seat to the front frame. Two tapered mortises were needed for the front stretcher end tenons. It also needed projecting bolts to slide in the slots in the rear leg sides. To cover the bolt ends I made two 1/2" long bushings from HDPE, 3/8" o.d. and 1/4" bore.  They slip over the bolt ends and slide in the slots. 

The stretcher for the seat front is the most complicated one.  It traps the canvas end and needed a slot to trap it into. The cover plate needed three threaded inserts for bolts to hold it down.  The seat frame doesn't need to come apart after it is glued up. 

I have my garage router table set up with a 1/2" round over bit to round over the stretchers and make the dowels.  I CNC cut the tenons on the ends of the stretchers.

Press-in threaded inserts/capped nuts were needed for the seat/front leg pivot.  Amazon didn't seem to have them. Lee Valley had them, so I ordered 10 of them. They arrived a few days later. 

Insert Nut

I cut a block of cherry large enough to make the two sides of the seat frame from. I  had to wait for the press in cap nuts to verify their size.   I needed all the hardware on hand to measure and finalize the CNC toolpath for the sides. I had to mirror the sides, and could only cut all the details on one side to optimize the layout of them. I had to set up a new toolpath layout for the second side details after cutting it out from the initial block. 

I made two 1" diameter cherry dowels for the seat. As I bought more 1" thick boards than needed for the stretchers I ripped one into 1" strips and rounded them over to make the dowels.  One dowel serves as the rear stretcher of the seat frame.  The second dowel is there to support the back canvas.  

Front leg frame

Last parts I made were for the outer long leg frame.  Two legs each 2" x 1.25" and 46.375" long, with two 1"x 3" stretchers between them. I didn't have any cherry long enough so some CNC joinery came to the rescue. One leg was made with twin tapered floating tenons between two halves.

Two Tapered Floating Tenons Hiding

The wood I used was salvaged from a past failed project. I'm hoping this will be a strong enough joint.  The other leg was also made from two sections. I ripped and planed the cherry for that leg from 6/4 cherry I still had. To join them I used an end--to-end finger joint.  

End-to End Finger Joint

I clamped the leg sections vertically in my CNC frame to cut the male and female sides of the finger joint. 

Next step after gluing up the legs was trimming them to length.  The ends were rounded off. Mortises for the two stretchers were cut, along with holes for the bolts that connect them to the rear leg plate and the seat sides.  

Once all the bolt holes, stretchers, etc., were all done the frame was dry assembled to verify it works. 

Dry Assembled

To deal with the canvas and straps I had to take apart my initial prototype done 4.5 decades ago to see how I trapped the straps into the frame sides.  

Details:  

On  the bottom of the seat front stretcher there is a slot. The canvas wraps around a dowel and is held in that slot securely. A cover plate traps the canvas in the slot:  

Cover plate

Under the cover plate there are 3 threaded inserts for screws. The cover plate was made from 6mm plywood.  I used some flat head nylon screws to hold it down.  

Cam levers to pull the seat canvas tight I cut from 6mm plywood. These will likely be replaced by metal levers. 

Cam levers

Lumbar straps needed slots in the sides of the long frame. I cut mirrored files, one for each side.    The cover plates and pockets for them were cut using the same perimeter vector to make sure they fit. 

Back strap slots and cover plates.

One side of the chair frame needs to be removable for assembly ease. The stretchers have embedded square nuts on one end for bolts to draw the tenons tight into the mortises in the side parts.  I cut pockets for square nuts near one end of each back frame and long frame tenon.

Pockets for Square Nuts.

 

Hole for the bolts to intersect them.

Two 1.75" long bolts for each stretcher end draw them tight.  I ordered the bolts from the jungle store.  They arrived 2 days later. 

The recess over the nuts needed plugs to cover the nuts and keep them from falling out.  I used the same vector that made the pocket, array copied it, and cut 6 plugs out using my CNC.

Six Plugs

I cut the plugs free using my bandsaw.

Plugs cut free from the scrap.

A little glue in the pockets before I pressed a plug into each one.

Plug glued in.

Once the glue dried I sanded them flush.

Sanded flush.

I  used Teak oil to seal the wood.  It nicely darkens the cherry.  Canvas and lumbar support back straps, as well as the red cushion were also ordered from the jungle store. 

The straps were cut to length, then wrapped around a short section of wood dowel. A couple staples keep the ends from pulling out.   

Lumbar Support Straps

To pull the seat canvas support tight I needed a 1/2" metal rod with 1/4" diameter ends.  I clamped the rod vertically in a v-block between the jaws of my CNC bridge vise. 

1/4 inch end

Using a milling bit rather than a router bit I then stepped in 1/64" at a time until the center was just under 1/4" in diameter.

Milling Bit

I am pleased with how well the ends turned out. The rod fits perfectly between the cam levers on the inside of the seat frame.

For the canvas seat and back supports I used iron-on fusing tape to hem the edges.  I wanted to avoid needing to sew.  The canvas is one long strip, with  both ends trapped under the front stretcher. They wrap forward and back over stretcher, over the rear dowel, then around the metal rod. That took twice as much canvas, but simplified the work needed. 

The inner width of the seat frame is 19.25".  Between the cam lever the width is 18.75".  As such the canvas strip is 19.25" wide, then tapers down to 18.75 after it rolls over the rear dowel.   The canvas doubles back after wrapping over the metal rod. I kept it narrower when returning so the hemmed edges of one layer rest inside the hemmed edges of the other layer.  

Once hemmed it was time to see if it worked as designed.

View from below the seat frame.

The canvas was installed with the side cam levers loose.  Once the ends under the front stretcher were trapped down, a flip of the cam levers pulled the canvas drum tight. 

To support the seat cushion. 

The last build step was the canvas back support. I cut it out and hemmed the sides.  The back canvas snaps onto the front of the top stretcher, wraps down and over the stretcher and over the snaps to the lumbar straps, over the rear dowel of the seat frame, around the rear leg stretcher, then snap it to itself.  

The top edge of the canvas has 4 snaps, each 5" apart.  The mating part of the snaps were  screwed into shallow pockets on the front face of the top stretcher   A snap kit bought from the jungle store made it easy installing the snaps on the canvas. 

Back support Canvas

The canvas was the last detail to solve.   Finding a cushion took two tries, but I like the fit and color of this one made for rocking chairs. 

Job Done.

I don't remember much about making my first prototype of this design.  My sense of that time when I was in my early 20s is that nothing was impossible and making this chair was a quick effort done in my limited garage shop space.  Making this cherry version was also not impossible, but seems to have taken twice the effort and time.   Such is life.

4D