Upper Back Rest - Office Chair Component
This is a step-by-step tutorial to construct the upper back rest cushion component that will be attached (and designed accordingly) to the skeleton piece. Some of the curvatures and features are made based on those present in the skeleton piece.
Visualization and Modelling
M. Said Jiddan Walta
2106718256
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Step 1: Base Sketch
Begin by drawing the general shape or curvature of the seat, without having to create elaborate curves. Simple straight lines with sharp edges will do, the curves are made by filleting later.
It is ideal that the skeleton piece is already made first, as the dimensions for the drawing are based on the skeleton piece. In the sketch above, an additional extension was made for both sides as the part to be attached to the side of the skeleton. The shorter end is the part for the soft cushion (making contact with the back).
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Step 2: Spine Curvature Sketch
Since we want to create the cushion following the ergonomic shape as designed by the skeleton, we draw an arc that has the same dimensions as those in the upper part of the skeleton.
Draw a sketch of the curvature on the XY-plane (perpendicular to the existing base sketch). We will use this as a reference for lofting the parts later.
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Step 3: Creating Duplicates of the Sketch
We want to create the seat by lofting multiple sketches of the base design along the curvature direction. To do so, begin with creating a plane offset from the XZ-plane.
Copy the sketch we already made from the side board and paste when we begin the 2D sketch on the plane.
When we paste it, it wouldn't be aligned with the curvature we made. To adjust, use the 'Move' function. Select all lines of the sketch, change to the 'Base Point' feature and select a random point outside of the sketch. Move the sketch accordingly based on the curvature that is already drawn.
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Step 4: Multiple Steps
If we want the Loft to have an accurate direction based on the curvature we desire, we need to create multiple sketches that direct the loft.
Create multiple planes offset from the ones already created and set them to be roughly an equal distance apart. The more sketches, the more accurate the loft will be later (but more work is necessary).
Copy the sketches and move them in the same way to ensure that each sketch is aligned to the curvature.
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Step 5: Lofting
To produce a single solid from the numerous sketches we made, use the 'Loft' 3D function and select the sketches in order from the top to bottom or bottom to top.
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Step 6: Filleting
Since this part will make contact with the human body, it is important to fillet the edges to minimize the chance for injury.
Some parts may need to be filleted earlier than the other due to the topography of the shape, which may require trial and error.
As shown above, the outer part needs to be filleted first for the inner part to be successfully filleted. Otherwise, an error may occur. This is where some trial and error may be necessary.
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Step 7: Corresponding Holes
As this cushion will be screwed to the holes already made in the upper section of the seat back rest skeleton, we need to create corresponding holes at the same positions.
To do so, it may require some precise measurement and comparison with the skeleton piece beforehand, which makes it ideal to have the skeleton file also opened along side the working file.
Since we want to make a hole on a curved surface, we need to create a guiding axis (for direction) and a working point (for entry point of the hole) as the 'Hole' function would not work.
Create a plane offset from the XY-plane and set it at about the line where the point should be, and sketch on this plane the direction of the hole that is desired.
Once the sketch is done, use the 'Axis' feature on the ribbon to select the sketch line and turn it into a working axis.
Create a working point by selecting the surface and the working axis next.
Once both the axis and point are created, we can use the 'Hole' feature by selecting the point first and the axis next.
Repeat this step for as many holes necessary.
