Seat Back Rest Skeleton - Office Chair Component

This is a step-by-step tutorial for constructing the seat / backrest skeleton structure which functions to provide structural strength for the back rest of the seat, to be added with related cushion pieces.

Visualization and Modelling
M. Said Jiddan Walta

  1. Step 1: Sketching Base

    Note that the way that I personally began with this structure was by making the vertical base that extends from the chair base connector first. Starting with the chair base connector first is also favorable and interchangeable with this step.

    Start by sketching a curved or straight rectangular closed loop. The shape is arbitrary, and the image above was remnants of an attempt to manipulate the width of the sketch by moving the vertical line between the two arcs.

  2. Step 2: Extruding the Base Feature

    Continue by extruding the sketch upwards by a moderate height. This feature of the component functions to extend a decent height from the base seat cushion so that the upper cushion's planned ergonomic features does not collide with the cushioning of the lower seat.

    Depending on the needs, this part can be unnecessary or requires a lower height of extrusion.

  3. Step 3: Mirroring for Convenience

    For the convenience of all our work for this component, we take advantage of the symmetry that the part will have.

    Begin by creating a mirroring plane tangent to the lateral surface of the base feature we made.

    Using the 'Mirror' pattern feature, select the mirrored feature and the mirroring plane to produce a symmetrical structure.

  4. Step 4: Creating Connector Base

    This step is interchangeable with step 1, depending on where you begin from.

    Sketch a protrusion from the base with considerable length and width lesser than the combined mirror features. The length and width should match the connected piece on the base of the seat, if already created or designed.

    Extrude this extension downward to keep the base feature untouched.

  5. Step 5: Screw Protrusions (Optional)

    We want to create the protrusions on this connector base to attach to the screw holes already present on the seat/chair. To do so, we can choose to create physical protrusions or simple holes to attach screws to.

    Sketch circular features based on the holes designed on the existing seat component. We can use guidance sketch lines to keep note of dimensions and make it easier to match distances.

    Extrude these protrusions upwards equal to the maximum depth of the screw holes on the chair component.

    Add an additional minor chamfer on the top of each protrusion for additional feature and to prevent skidding or dents on contact with other surfaces.

  6. Step 6: Adding Fillets

    As this part is likely to make contact with users, it is necessary to minimize sharp corners to prevent injury.

    Add fillets where necessary and on edges that are possible to be filleted.

  7. Step 7: Ergonomic Back Rest

    The main component of the skeleton is the upper component to provide the ergonomic (following the human spine) shape of the back rest.

    Sketch the ergonomic shape on the existing mirror plane or on a plane offset from the XY-plane (perpendicular to the base pieces). The shape is drawn to the best of the user's abilities.

    Extrude the sketch of the ergonomic shape outwards to a length equal to about half of a normal chair's width, which is around 40 to 60 cm. We can now take advantage of the existing mirror plane to produce a mirrored feature.

    Select the solid part of this extrusion and the mirror plane to do so.

  8. Step 8: Creating Connective Holes

    Keep in mind that there are multiple ways to attach a cushion piece to the skeleton piece. The method that I personally chose for this component is creating screw holes on the side of the skeleton, along with corresponding screw holes on the cushion pieces and attach them together using screws.

    Create approximately equally spaced holes on the lower spine section of the ergonomic back piece. Using the 'Hole' feature, we can thread the holes based on the screw type we intend to use in the feature. Make sure to utilize the same screw type for making the cushion pieces.

    Do the same for the upper part. The number of holes is up to the user, though more holes can create more secure connections, it can also be difficult to make sure that the connected cushion pieces also have the same position of holes.