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If they started with a no-signatures preproduction mould, adding embossed signatures wouldn't be terribly hard (relatively speaking). The lid was almost certai

If they started with a no-signatures preproduction mould, adding embossed signatures wouldn't be terribly hard (relatively speaking). The lid was almost certainly injection moulded - which means you have two mould halves which form a complete mould. In this case, one half for the "inside" of the case (with the screw bosses and sprues) and one for the "outside". The usual build process for these is to start out with the mould glossy, check the resulting parts for form and fit, make any adjustments needed. Once the mechanical aspects are settled, the final texture (like the matt surface effect that a lot of PC cases have) is added as the last step. The reason for starting out with a glossy finish is because it's easier to make changes when you don't have to match a texture with every change. The signatures were likely added to the inside mould by engraving or CNC cutting them at the same time the texture was added to the outside mould. I wouldn't expect it to be done by chemical etching, the process is too slow. There would have been a tooling cost, but that's an NRE. Amortised over the production run, it probably added pennies. Depending on CBM's relationship with their toolmaker, it might have been priced as part of the texturing (which would have needed to be done anyway).

metaphor 7y ago
Thanks for the technical perspective. > The signatures were likely added to the inside mould by engraving or CNC cutting them at the same time the texture was added to the outside mould. I'm also guessing that given the detail of each signature, this would have been digitally handled in RS-274 or a plotter language? The level of detail is so spot on that it's tempting to overlook the circa 1980s timeframe and what consumer manufacturing could do cost-effectively back in the day. Another observation is that none of the signatures overlap with the internal support ribs...almost as if the image was transferred in sections. I wonder if the original design team signed a silhouette of the rib pattern, or if the signatures were post-processed to eliminate collisions.
- birdman3131 7y ago
  Most likely standard gcode. We still run CNC machines from that era. At least one of our machines dates to 1979. While it would take a lot of tape there is nothing that I can see that makes those hard to do. (Ours no longer use tape but a drip feed from a parallel port.)
- philpem 7y ago
  They would have had a technical drawing of the top lid, which (if it was a mould drawing) would have shown the various ribs. Put a sheet of Vellum over the top, sign it, then use a graphics tablet (Summagraphics were around back then) to digitise it into a CAD workstation. Heck, if you're cheap, use two pots to make a two-piece digitiser arm and scan it that way (Mike Cook wrote an article in BBC Micro User back in the 80s about this). Measure the angles then do some geometry to figure out the Cartesian (X/Y) position of the arm. Create a point cloud, join the dots. Once you have the outline, creating GCode would be a relatively simple task (for a computer). Also I don't think the ribs are for support, though they will certainly do that. To me it looks like they're to allow the plastic to flow into the mould faster. Hunt down the "Engineer Guy" video on injection moulding if you're interested in the details. It's a fascinating process. Simple concept, but the devil is very much in the details.

metaphor 7y ago

Thanks for the technical perspective. > The signatures were likely added to the inside mould by engraving or CNC cutting them at the same time the texture was added to the outside mould. I'm also guessing that given the detail of each signature, this would have been digitally handled in RS-274 or a plotter language? The level of detail is so spot on that it's tempting to overlook the circa 1980s timeframe and what consumer manufacturing could do cost-effectively back in the day. Another observation is that none of the signatures overlap with the internal support ribs...almost as if the image was transferred in sections. I wonder if the original design team signed a silhouette of the rib pattern, or if the signatures were post-processed to eliminate collisions.

birdman3131 7y ago
Most likely standard gcode. We still run CNC machines from that era. At least one of our machines dates to 1979. While it would take a lot of tape there is nothing that I can see that makes those hard to do. (Ours no longer use tape but a drip feed from a parallel port.)
philpem 7y ago
They would have had a technical drawing of the top lid, which (if it was a mould drawing) would have shown the various ribs. Put a sheet of Vellum over the top, sign it, then use a graphics tablet (Summagraphics were around back then) to digitise it into a CAD workstation. Heck, if you're cheap, use two pots to make a two-piece digitiser arm and scan it that way (Mike Cook wrote an article in BBC Micro User back in the 80s about this). Measure the angles then do some geometry to figure out the Cartesian (X/Y) position of the arm. Create a point cloud, join the dots. Once you have the outline, creating GCode would be a relatively simple task (for a computer). Also I don't think the ribs are for support, though they will certainly do that. To me it looks like they're to allow the plastic to flow into the mould faster. Hunt down the "Engineer Guy" video on injection moulding if you're interested in the details. It's a fascinating process. Simple concept, but the devil is very much in the details.