I have fabricated a vacuum formed case for my replica Softy 2, having not done this before I thought it would be useful to record how I did it.
I should add that this would not have been possible without the loan of a real Softy 2 from Tim Gilberts.
Stage 1: Mold Fabrication
The original SOFTY 2 case parts were setup on a bench carefully leveled having been 'painted' inside with a turpentine diluted Vaseline solution to act as a mold release.
For the top part thin slivers of sanded down plywood were inserted into the thin ridges at the top, being so thin they would have snapped off if attempted to be filled with plaster.
A mix of Plaster of Paris was then poured into each half of the mold. This was allowed to start setting for a few minutes before being leveled off by 'pulling' a steel rule across the surface.
Next day the molds could be removed.
The plaster molds were then glued to two pieces of MDF for added strength and to create the lip, an important step is to bevel the edges of the MDF otherwise its difficult to remove the finished part.
The small hole in the center of the top part is to allow compressed air to be blown in to help release the formed part.
Vacuum Forming
The case parts were formed on a commercial Vacuum Forming machine using black 1.5mm ABS taking about 70 seconds to be heated and then pulled over the mold, a very quick process once warmed-up. A light dusting of talcum powder was applied to the molds to help in releasing the formed parts.
Vacuum Formed Parts Finishing
This was the time consuming part !
The two halves were roughly cut to size in a band saw.
I then cut the bottom half first leaving an approximate 10mm lip, then carefully sanding to straighten the edges and round the corners.
The PCB was then put in place and the four corner mounting holes drilled, 3.0mm diameter. The board was then attached temporarily with M2.5 screws.
The top half was then cut a few mm over size to fit over the bottom half.
Then the very fiddly bit, making the rear holes for the connectors, the only way to do this is with careful measuring (twice !) and marking one hole at a time starting with the longest - phono sockets.
I started each hole with a small drill, say 3mm, and then opened it up with a combination of files and tapered reamers, 'drilling' any larger is risky as the plastic is likely to tear away.
Its worth taking your time over this bit, keep trying for fit and adjusting as you go to make sure each hole lines up with its connector.
Once the connector holes were finished I drilled the four case holes, two at the rear corners and one on each side, 2.1mm diameter for the Heyco fittings. I then temporarily joined the two halves together with M2 screws for final finishing.
I used a sheet of abrasive paper on a flat surface and carefully sanded the top side edges down to meet the bottom and rounded off the rear corners.
Dismantle the two parts then a quick tidy of the edges with some fine abrasive and ready for a clean before final fitting of the PCB.
Final Construction
The original SOFTY 2 was not fitted with IC sockets, they are not a problem other than for one IC at the front - IC23 which has to be soldered in directly, also the resistor network next to it (R34-40 needs to be fitted as flat as possible towards IC23.
The top part of the case then just about fits ! (Ideally the molds would be adjusted to make the top slightly higher).
The keyboard overlay is attached to the PCB using 3off M1.6 x 4mm countersunk screws with washers, don't fit a screw in the bottom right corner.
The PCB is then attached with 3 off black Nylon M2.5 x 6mm pan head screws and nuts, leaving the bottom right corner which is fitted with an M1.6 x 6mm pan head screw which goes into the keyboard overlay
The top part of the case can then be fitted, held in place using 4 off Heyco 9302 Snap Rivets (available from Mouser).
The last bit is to cut out a piece of anti-static foam for the insert on the top !