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High-back Chair

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Project by MJCD posted 03-22-2019 02:57 PM 367 views 2 times favorited 9 comments Add to Favorites Watch

High-back Chair

Woods: Rhodensian Teak, Hard Maple
Joinery: Pegged and floating (Domino) tenons; Trestle Wedges

General Comments
This is a ground-up design, 1st-prototype high-back chair. The intent is to create a stationary chair that flexibly supports the sitter regardless of their seated position. To this end, the chair’s back flexes to fully support your back at all times.

This chair is sized for a tall adult – accommodating up to a 6’6” and approximately 220 lbs. frame – with a 20” wide and 42” high overall dimension. The Hard Maple Frame is 5/4×6/4 (finished) is secured using both pegged and floating mortises; with two Trestle Wedges used to further secure the middle Back Braces. No screws or metal fasteners are used.

Re-sizing the chair should be straight-forward… with the most significant consideration being the Arms/Back Brace locus – as the Back Braces splay-out from the Transition Block, they can interfere with the back of the Arms. I designed-in a cove, toward the Arm-end, to accommodate this.

Design Elements
Initially, I wanted a set of continuous laminations forming both the back and the seat – the Teak resisted so many of my efforts to achieve this, that I opted for separate Back Braces and Seat Slats, with a Transition Block accommodating the mediating space. The Transition Block serves to a) hold the Back Braces, via a 2” (20 degree angled) mortise; b) provide a slotted-terminus for the back of the Seat Slats (this is angled to smooth the sitting position); and, c) bear the primary downward force of the sitter. Structurally, the Transition Block is mortised and tenoned to both under-support blocks, as well as directly to the Frame side.

As mentioned, the Back Braces are secured via an angled (20 degrees) mortise in the Transition Block – Trestle Wedges are used to take-up slack, where needed, at the base of the Back Braces. At their top, the Back Braces slip through a Back Brace Support, that both affords a degree of freedom and constrain them, such that they support each other. As the Back Braces splay-out from the Transition Block, and a sitter presses backwards, the Back Braces flex away from each other. If the BB are held rigid, uneven torsional forces could eventually undermine the laminations – colleagues have noted this with some of their work. For example, Hal Taylor created a flexible, free-moving Back Brace design for his classic rocker chairs; while others have moved away from fixed bent lamination offerings, due to their inherent flexing.

The Transition Block is sized to handle significant stress – starting as a 4” x 6” block; whose sections are then processed for Back Brace, Front Slats and Back Stretcher roles.

The Front Stretcher has (8) 1/8” slots to accept the front portion of the individual Seat Slats.
The chair’s width has a -4 degree taper front-to-back.

Prototype Issues
Prototypes serve many purposes, especially when incorporating bent lamination – these require precise contours and robust clamping. You start with an idea for a curve, make the jig, make the lamination strips, glue and clamp for 12 to 24 hours. Then, if the curve isn’t what you want, you start over…
The prototype issues aside… this is a very buildable chair… now that I’ve settled-in on dimensions and specific curve and structural forms.

Final Thoughts
Don’t use Rhodesian Teak for bent lamination projects!

This project started as a personal challenge; if I were to build another one, I would choose a more flexible dark wood, and try again to build a continuous Back Brace/Seat bent lamination chair. That said, I really enjoyed devising the Transition Block – its execution was a bear – it max’d-out my design and woodworking skills – as this is a 1st-prototype, I was designing and processing the Transition Block as I needed – with this experience behind me, I would choose more-repeatable, more precise methodologies that would yield a more professionally satisfying result.

Again – this is a very buildable chair; and I encourage those who see something they like within the design to create their own version – and then tell us about their experience.

Everyone, Do Take Care.
MJCD





9 comments so far

View pottz's profile

pottz

4711 posts in 1313 days


#1 posted 03-22-2019 03:18 PM

wow thats a gorgeous chair and beautiful design,a real nice flow to it,very graceful.it would be better to look at though if the pics were straight.i looked at some of your stuff and your work is outstanding.going in my fav’s.

-- sawdust the bigger the pile the bigger my smile-larry,so cal.

View WayneC's profile

WayneC

14349 posts in 4426 days


#2 posted 03-22-2019 03:26 PM

I really like this. It’s a lovely build.

-- We must guard our enthusiasm as we would our life - James Krenov

View MJCD's profile

MJCD

589 posts in 2700 days


#3 posted 03-22-2019 03:37 PM

Not sure why the picture became posted landscape… the original is portrait.
MJCD

View majuvla's profile

majuvla

14166 posts in 3196 days


#4 posted 03-22-2019 06:03 PM

Nice design and looks very ergonomic.

-- Ivan, Croatia, Wooddicted

View Kaleb the Swede's profile

Kaleb the Swede

1896 posts in 2298 days


#5 posted 03-23-2019 02:23 PM

This is very cool

-- Just trying to build something beautiful

View Lazyman's profile

Lazyman

3225 posts in 1716 days


#6 posted 03-23-2019 03:42 PM

I really love the design. Nicely done.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View therealSteveN's profile

therealSteveN

2362 posts in 903 days


#7 posted 03-23-2019 10:28 PM

“Prototype Issues
Prototypes serve many purposes, especially when incorporating bent lamination – these require precise contours and robust clamping. You start with an idea for a curve, make the jig, make the lamination strips, glue and clamp for 12 to 24 hours. Then, if the curve isn’t what you want, you start over…
The prototype issues aside… this is a very buildable chair… now that I’ve settled-in on dimensions and specific curve and structural forms.”

How many chairs did you end up making to get the “one?”

Nothing like sticking a clear goal out there, and seeing if you can do that. As good a way to learn wood as any other.

Thanks for posting.

-- Think safe, be safe

View MJCD's profile

MJCD

589 posts in 2700 days


#8 posted 03-24-2019 02:23 AM

SteveN:

4 or 5 different forms: each took about a day to make; and each took more than that time to test-out. The initial forms created unreliable glue-ups, due to the Teak not being able to uniformly bend to form a structurally sound composite (a single Back Brace or Seat Slate).
The original form – that created a continuous Seat & Back lamination – I glued-up (6) 7-pieces composites (1 Back Brace), with only 3 being acceptable – that is 50% of the effort was successful, the rest was trash. I decided that even the ‘successful’ ones were at their stress limit, and might fail under load. In all, I wasted the better part of three weeks getting the laminations correct. Couple this with the associated expense… Rhodesian Teak is expensive; you lose about 50% when you rip each lamination (a 1/8” blade creating a 1/12th to 1/10” strip); the waste accumulates along with the associated cost.

The rest of the chair – another than the Transition Block – I got right the first time around. I usually start with a 1:1 scale drawing on brown kraft paper, a large eraser, and several pots of hot coffee.

Also, the fact remains that I would change the Back Brace form, again, to pull the upper portion 2” closer to the sitter’s head, and make the Adult chair 1” wider.

All of that said… it is what we do… as woodworkers… while I really dislike wasted time, you can’t begrudge the process and still muster the enthusiasm for the craft.

Finally:

To each of the commenters – I appreciate the kind words – each of us spend personal time and effort; often, our most creative energies eventing something. At the end of the day, you hope it demonstrates the good effor.

Everyone, Do Take Care.
MJCD

View Terry O's profile

Terry O

159 posts in 1593 days


#9 posted 03-24-2019 09:49 AM

Very nice looking chair!

-- Terry O, Stonewall, MB, Canada

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