First the side of seat had to be drawn, I use AutoCAD LT from 1993. This photo was used to draw the outline of the seat casting by enlarging it to A4 . Using measurements off the full size allowed me to scale from the photo. Before going near AutoCAD I started by drawing a vertical line along the front of the casting on the photo copy, a second horizontal line along the bottom of the casting .A number of lines were then drawn by placing a ruler on the photocopy and drawing an extended line to pass through straight sections on the copy to intersect the base line,even the shortest sections were drawn in this way. The next step was to measure the actual distances from the front of the casting to the intersections of all the lines previously draw. The drawing can now commence in AutoCAD drawing the front vertical line and using the offset command to place all the other lines at the predetermined distances ( seven lines in this case ). The top of arm rest is parallel to the base line and can be placed in position, the casting has no right angles so it is necessary to measure each angle that all eight lines ( including the angle the front of the casting makes to the baseline). Using the rotation command the parallel array of lines can be made to run along the straight sections of our model casting. The curved sections of the drawing are completed using the fillet command, adjusting the radius by scaling off the photo copy and a little trial and error. The mounts were added to give the final outline.
This is a 1928 model Sixty showing the front detail of the driver's seat.
This is the screen showing the code to machine pocket.The model has a 1mm rib following the outline of the casting. This was achieved using the offset command which results in the outline of the pocket.
The tool path for the second casting was mirrored in SheetCAM.
The pocket was machined first.
Cutting the outer profile. Each casting took about half an hour to cut. I mention this as there is a reluctance for some to embrace this technology. From starting the drawing to the first completed casting took a day.
The finished seat still needs upholstering and arm rests.
Here is a comparison between full size and scale
