I have been struggling with the final arm rest/leg design of a redwood patio chair, so I thought I would document the process and the progress thus far and as it moves forward (at a snails pace).
First off, when I originally sketched this chair I fell in love. I couldn’t wait to get into the shop and get started. The need was for a set of deck chairs but i really wanted to avoid a straight Adirondack design. I was trying to get a comfortable contemporary look with both a minimal yet substantial feel. As you can see in my sketch, the integral seat/backrest thickness would have required bent ply to achieve the super thin profile. And that isn’t yet in my skill bag. I’d have to work carefully to ensure the thin design was not compromised in the final version. Here is my initial sketch. Crude but a good start.
Here’s an image showing how I resolved some of the scale issues. This process, as rudimentary as it is, helps me envision the piece in it’s actual size. By no means is it a full mockup, but it allows me to quickly make adjustments to the design and get some real dimensional information before taking it to CAD.
After working the design out in sketch form, I worked it up in AutoCAD. As an architect, this is the program most familiar to me and the accuracy keeps me honest. I have started working with SketchUp more, but am still drawn back to AutoCAD mainly for familiarity sake. As I developed the design further in CAD, I eliminated the height adjustment and pivoting mechanisms (shown in the sketch), forcing me to really work through the ergonomics and (more honestly perhaps) make the fabrication more feasible and bullet proof. Here are the further developed Cad drawings.
Once I had the CAD work close I created a part list and cutting diagrams. For the curved back/seat support rails I printed out full size outline drawings to transfer (with good old carbon paper) to the final workpieces for cutting on the bandsaw. Here is a photo showing the full size printout (yep, that’s 8 ½ x 11 paper taped together). Unfortunately you can’t make out the printed lines in this image, but trust me, they are there.
And here are the rough cut rails.
Then a bunch of other boring milling took place to produce the 23 slats needed for the seat and backrest. Then it was on to assembly. Yes, that is my dining room table, but the work’s gotta get done and I have no home shop. I was so excited to get this started that I didn’t even bother taking the candle holders off the table….. This picture clearly shows the relationship between the curved support rails (only one of them shown here) , the stretchers locking them together and the slats. I used a bridle joint to connect the back and seat rails into one continuous rail, more on this possible weak link later. Underneath the precarious mock up is the full size printout of the original arm/leg design, more on that in a second.
Here you can see how the rail supports, stretchers and slats relate in the actual piece. Also, this is a good image to show how I dealt with the visual “thinness” or the edge. By centering the 9” wide support rail structure all you will perceive is the thickness of the slats. Pretty much in keeping with my original sketch.
Lots of screwin’ and gluin’ plugs goin’ on here.
Now onto the arm design, the big stumbling block. I don’t have any process photos of the arm fabrication but they are each composed of 5 pieces of ¾” redwood sandwiched and glued together to achieve the thickness. At the connecting ends, the laminated layers are held short or let run long to interlock with eachother to form a multilayer bridle joint (I’m sure there’s a more proper name than that but I don’t know it). In the photo you can see one leg/arm assembled and one disassembled.
Here is a plan view photo where I’m trying to resolve the location that the chair body will be positioned on the leg/arm.
Alright, so here’s the dilemma…… I hate the wood legs! In elevation view they looked like a good compromise between aesthetically right and buildable and structurally sound. Well, the structurally sound part is workin’ but they aren’t real pleasing to the eye. They look like two heavy, clunky, unrefined appendages! So as you can see below, it has literally been shelved. The bad part is I’m super pumped about seeing this thing finished.
So here is what I’ve come up with to get the Patio Lounger back on track. I sketched out a few idea and then put it into CAD to refine it and give it some real dimensions.
The material will be powder coated aluminum with welded fittings to receive cross bars that will both support the chair body and give the two legs lateral rigidity. That’s my thought anyway…..
So, in summary thus far, I’ve designed and built a chair body that is quite comfortable and meets my design concept I was going for.
As I mentioned earlier, there is a weak link with the chair body. After gluing up the seat and back support rails with a bridle joint, I wanted to test its strength so I put a moderate amount of pressure on it, and whamo, it blew apart. At the time, I was only testing one individual rail, so I figured that once the two rails were joined with the stretchers and the load was spread more evenly via the slats, it would be stronger. This has worked out so far, but because I have only tested the seat while it is on the ground and leaning against a wall, I haven’t yet given it a full, real world test. If it does fail, the easy solution will be to consider this a mock up and make the final version(s) with hardwood rails.
I will update when I’ve taken the next steps.
Thanks for reading.
-- Fritz Oakland, Ca http://www.muegenburg.com (dedicated to my other hobby)