WHY DESIGN A KNEELING CHAIR?
Back Pain is a huge problem and will effect 80% of the population at some point in their life. Chronic back pain is widespread and can last years or decades. Our increasingly sedentary lifestyles don’t help because most traditional chairs deform the base of the spine which throws the whole spine out of its correct alignment. The kneeling chair helps by making people sit autonomously in a position that maintains the correct curvature of the spine.
Some of the benefits of Correct Spinal Alignment.
What might a ‘Kneeling Easy Chair’ be like? How could I make it feel relaxing?
Group mindmapping my project with fellow students. (Sonia , Ross Crawford, Paula Grubb, Kirstie & Megan Stenhouse.)
Sorting some of the basics. How do you actually sit down on a kneeling chair?
EARLY SKETCH DESIGNS
Just thinking with a pencil in my hand, trying out various ideas and forms.
Taking into account how you could sit down easily and what might make it look more inviting.
Perhaps developing it into something solid but much more organic and sculptural?
Or taking on some of the curved shapes we played with in the ‘Mandala’ chair project?
Looking again at the simplicity of the Balans chair by Peter Opsvik.
I liked the idea of using curved forms for the seat, but splitting it and perhaps creating a large stylised pelvis shaped seat from which your own spine grows as the back.
But how to support of these two elements the seat and the knee pad? Runners that might get in the way for your feet?
I liked the idea of something that looks quite simple, perhaps based on a triangle because the seating area was developing into that shape.
Developing a seat shape
- Basing the under structure on a triangular form to keep feet space clearer.
- Stylised pelvis seat.
I Feel it would be better to;
- Relate the shapes of the seat and knee pad more.
- Try to create space free from structure at feet area.
More thinking … the under structure is whats going to give the chair its aesthetics.
- Playing with the idea of two separate elements; a bench like seat and a knee pad that could be swung out of the way if you preferred perching to kneeling.
- Simplifying the seat to a curved ellipse shape just to give a slight sense of enclosure (see early sketch).
- Continuing the structure through the seat to form arm rests for enclosure and psychological support
- Initially angled suports inwards towards the front.
- Tried it the opposite way because it gave a larger angle of swing for the knee pad
- Better framing of the Seat area.
- Tried similar arrangement but with curved support/arms
- Decided that I didn’t like this concept afterall and should return to my initial, simpler, idea of a single unit.
- Liked the idea of arms providing a sense of enclosure and support instead of a back, but it wasn’t working in these models.
- Tried several different to scale drawings to see if I could get something to look better
- Basic Concept – unmodelled form.
Some ideas how the understructure might look.
- Triangular base gives overall stability for the chair, but the seat is supported by only two of these supports so would need very secure fixing to be safe.
- Really like the overall form now its being modelled
- Cruciform base gives better stability overall and specifically to seat.
- Would like to move junction further back if possible to give more room for feet.
- Would like to continue to experiment with arms as these might be the key to making the chair look more inviting and secure.
- Wonder if there is a way to allow the kneeling pad to push backwards under the seat to allow ‘perching’ as well as ‘kneeling’, without compromising the stability of the whole chair? A Telescopic Connection perhaps?
- Or just keep it simple?
- Arrow shaped base pushes the structural junction slightly further back and less underfoot.
- Seat support meanwhile pushed slightly further forward giving more stability.
- I prefer the shapes made by these angled forms to those made by the cruciform.
- The cruciform would be easier to construct with the forward sloped seat, especially if I was to curve the seat slightly.
- I think I prefer the wider 100mm I used in Model 4 rather than the 75mm I’ve used since.
SO TO CAD!
As I’ve been doing CAD drawings I’ve been finalising the measurements of the chair and have decided to go with a forward seat slope of 10o (see Research), and reduce the depth of the knee pad to 275mm (removing 25mm from the rear) because a number of people who ‘tried out’ my current kneeling chair felt it cut ever so slightly on their lower shin.
In terms of styling I’m tending towards a softer more feminine look whilst still maintaining a simple structural form, and have taken inspiration from the ‘Bouquet Chair’ by Tokujin Yoshioka, Louboutin’s Red Soled Shoes and the ‘Orange Slice Chair’ by Pierre Paulin.
MATERIALS AND STYLING
Since the mid-project review, I’ve been thinking more about the materials and image I want to portray with the chair and have made some changes.
- Instead of beech, I intend to use plywood. Cutting the main elements from 18 mm plywood and gluing these together to make up the 90mm sections. This will both be structurally stronger and give an interesting stripy aesthetic along the legs and across the base that will emphasize that they are one piece.
- I’m still working on the central joint of the three main structural elements, but I like the idea of making this a distinctive feature. I am considering an arrow shaped joining fillet perhaps cut from a brightly coloured 12mm acrylic or nylon. I’m not sure how strong this will be so I will have to experiment.
- We’ve been enjoying the summer like temperatures this week and been having our lunches outside on the grass. This has led to me thinking about a fresher brighter sort of image rather than the overtly feminine look I’d been considering. I’m now thinking of maybe a grass-like upholstered seat complete with flowers!
- I would like to still bow the seat slightly because I think it adds an overall elegance to the design. Malcolm is not so keen because of the added complexity this will add. We will have to see!
- I’m still intending to make the actual upholstered section easily removable, giving a crisp edge and extending the life of the chair because it could be easily re-upholstered or replaced. I was considering that it might be possible to purchase a number of differently upholstered elements so you could update your chair easily with the season or a change in fashion.
- Although I’m undecided whether to go for the flat packed idea or not, the intention is that the chair construction be kept fairly simple, so that at the end of it (hopefully long) life it can be deconstructed and the elements recycled.
WORKSHOP & PROTOTYPING
I am now building a full scale mockup of the present design in chipboard, to test out the idea overall and later this week intend using plywood/acrylic to evaluate what different joints look like and test their strength.
Marking out the pieces from cardboard templates.
Even allowing plenty of space between elements they will easily fit on one sheet of plywood, as this wasn’t a full sheet.
Drilling holes where I will need to turn the bandsaw really did make the initial rough cut much easier. Great tip from Jason!
Cutting the elements from the chipboard on the bandsaw.
Removing as much excess as possible before thinning the sections down to their final size was important because the chipboard is not very strong.
Nibbling away at the rounded inner corners.
The cut elements were glued and clamped together in groups of 5, to create sections 90mm thick.
The sections were then sanded back to the pencil lines to smooth. In the final piece I think I should cut slightly further from the lines to give extra leeway in the lining up, to ensure the finish is spot on.
The side leg sections were then sawn to the correct angles where they meet the seat and the long central section. Need to pay special attention to make sure I get the right lengths in the right places! If I were to make a bowed seat this will add slightly more complexity to the top angles. The end were sanded smooth.
An initial template for the joining element was cut from 12mm plywood on the bandsaw. Joints were then cut in the side legs and central section to take the plywood joining fillet, using a handsaw and chisels.
Cutting joint in side legs with saw.
Cross cutting area to clear with saw.
Cutting out waste with chisel.
Fitting the elements together. Glued and clamped whilst drying.
Kneeling Pad element screwed and glued to centre section.
Seat element screwed to legs. I have for simplicity in this prototype made the seat element flat to see what this will look like. I’m still of the opinion that a slightly bowed seat will look more elegant. This will be made of laminated plywood in the final design. The upholstery section will be added after and bolted to this from underneath.
EVALUATION OF PROTOTYPE
A couple of concerns have been raised by making this full scale prototype and a few others I had laid to rest.
I was concerned that the joint between the kneeling pad and support would not be strong enough to cope with the stress caused by eccentric loading as someone kneels down because the bearing area is small. This proved unfounded. However that same eccentric loading caused the whole front member to twist alarmingly. Imagine the shape as an allen key, with force applied, it acts as a lever increasing the torque. Also when weight is imposed on the seat there is again bending in this long front member.
The extent of this twist in the prototype is partially because it is only made of chipboard, however is clearly showed where and how forces were acting in the design and what would be needed to be addressed in the final design: the strength of the materials, the design of the central junction and the overall design itself.
The causes of the problem . . . and possible design solutions.
Testing how simply altering the material or its orientation might affect the overall strength.
Plywood used as proposed still showed a lot of twist when put under pressure using a long clamp as a lever.
The same test using a piece of Oak showed hardly any deflection.
I am also concerned about the strength of the central joint under these stresses. Malcolm assures me that these will be unfounded if I use Oak, and well, don’t tell him I said so, but he’s usually right!
Proposals for the central joint.
Working through the consequences of the using of a central band of Oak for the base and lower leg bend, with just a strip of plywood either side, and then change this to just plywood on the higher portion of the seat legs and its effect on the central joint.
I decided that visually it would look better if the Oak was on the outside and the plywood sandwiched inthe middle. I also intend to slightly deepen the bottom members from 25mm to 30mm to add a little more strength in this way too.
I was also concerned about the shape of the seat and knee pads and experimented with different forms.
FEEDFORWARD – FUTURE DEVELOPMENT
- I like the overall concept and design but it could be refined further.
- I think that the problem of the supporting frame being in the way has been resolved.
- There is still too much give in the kneeling pad for my liking. In hindsight perhaps I should have altered the design slightly in the other ways I was considering when this problem became apparent instead of taking Malcolm’s word that it was just the material and that using Oak would solve the problem. As a remedial measure I intend to strengthen this front member by routing a section underneath and embedding a steel plate.
If I were to develop this design further
- I would prefer to use 1 to 2mm veneers laminated along the curves, with either shaped hardwood or bright recycled plastic inserts (eg smileplastics) to give width to the upper legs. This would be much stronger and with the plastic possibly much lighter.
- I would also make each leg separately and use a steel or bright recycled plastic jointing plate.
- Laminated in this direction I would be able to sculpt the legs more which I think would add to the aesthetics of the design.
- I would like to develop this as a flat pack design, because I think the design could be developed along this line.