Special folding chair

Project  / Project number: 11\17-09  /  Status:

Chair ready for use

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The challenge

At the initial visit, no satisfactory commercial chair seemed to be available; it was decided to attempt to modify one of the chairs already tried by the client and found to be satisfactory except for the lack of the folding capability.
The client’s preferred chair took the form of an extra large version of the baby bouncer often used for very young children. In this enlarged implementation the base and seat frames of the bouncer were each made from steel tubing (approx 20mm o/d) bent into a horseshoe shape. The open ends of the horseshoes, were connected together by springs. The springs were captive in the seat frame but retained in the base frame by means of plastic conduit glands. This enabled the two horseshoe frames to be separated presumably to allow flat packing for easy delivery.
It was hoped to use this feature to achieve a simple means of “foldability”. However, it became apparent that this would not work. The two horseshoe frames were both slightly twisted and the springs although captive were allowed to move back and forth in the tube ends and also rotate around the tube axes.
It was found that all these degrees of freedom made the chair very cumbersome to assemble (like wrestling an octopus) and caused considerable wear and tear to the plastic conduit glands. A set of brass conduit glands and a alignment jig for the springs were tried but because of the twists in the frame they didn’t help enough to make this a going concern on a regular basis.

The solution

It was thus decided to abandon this approach and design a custom built chair based on a deck chair type frame but borrowing from the seat cover design of the bouncer which provided the required side support for the occupant.
The deck chair style chair frame was largely built from 25mm x 50mm ( nom.) prepared timber. It consists of 3 frames – a base frame, a seat frame and a prop frame. As shown in the photographs below the foot of the seat frame is hinged to the front of the base frame using M8 bolts and spacers. The prop frame is hinged to the seat frame approximately one third down from its head end using M6 furniture bolts.

The foot end of the prop frame is formed by a chromed plated steel tube, the length of which defines the width of the prop frame foot and is secured in place between the side members of the prop frame by a 8mm rod. The very ends of this 8mm rod have been reduced down to take a M6 thread and these threads protrude beyond end of the prop frame side rails and take M6 Nylock hold the foot together. When the chair is in use the chromed steel tube fits into a retaining housing to the rear of the base frame.
All hinge joints are secured by Nylock type nuts to minimise risk of the hinges working loose and allowing the chair frame to fail. Fixed wood to wood joints are glued and screwed.
The cover is made from heavy weight cotton twill. The head part of the back rest is a boxed envelope which fits over the head end of the seat frame.
The lower part of the back rest extends down almost to the seat/front of seat support and has “wings” on each side which pass under the back of Seat Frame and are Velcroed together loosely thus allowing the back rest to take up a natural shape.
The back rest is sewn to a separate piece of material shaped so as to allow a seating surface and leg rest to be formed. The leg rest also has a set of “wings” which are used to tension the leg rest laterally. These pass under the Seat Frame and are Velcroed together quite tightly.
The whole seat cover is tensioned longitudinally by two webbing straps which each pass around the lower cross member of the seat frame, are pulled tight and Velcroed together.
A five point webbing harness is provided with the chair. The shoulder straps are fixed to the cross member at the head of the Seat Frame and are prevented from slipping off the child’s shoulders by webbing loops sewn onto the back of the seat cover. The waist straps are fixed to the side members of the Seat Frame and the inter-leg strap is sewn to the seat cover leg rest. Plastic buckles at these fixing points allow the harness to be removed for washing. The cover can also be removed for washing but it is first necessary to remove the shoulder and waist harness anchors from the frame using a screw driver.

The benefit

The carer can now be confident that the client is comfortable and protected in the limited space available

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