This is a protective base for the RC2014 Backplane Pro 12-slot main board for the RC2014 modular Z80 retro computer kit.
- designed for laser cutting
- adds a half-inch border around the board
- does not obstruct the top of the board
- provides maximum support beneath the board
I began with the idea of adapting davidbro's RC2014 Pro Backplane Tray, which was designed in three dimensions using Fusion 360 for 3D printing. I didn't find the sketch lines in the f3d file to be especially convenient for my laser-cutting purposes, so I ended up redrawing everything in CorelDraw from my own measurements of the RC2014 Backplane Pro board.
The pin headers used in RC2014 systems in place of real backplane connectors require substantial insertion force, so I was worried about supporting the backplane board. Rather than adding support features only where the six mounting screws go, I chose to start with a solid sheet of material and make cutouts only where necessary for clearance or access. This choice led to a two-layer design. The top layer has cutouts for component leads and holes for mounting screws, and provides support for the board. The bottom layer has holes only for access to the mounting screw heads, and is otherwise solid to protect the exposed leads on the bottom of the board.
Each layer can be almost any thickness you like, as long as the top layer is at least as thick as the tallest component lead sticking out from the bottom of the board. I chose a nice 1/4-inch solid walnut for the top layer, and an inexpensive 1/8-inch hardboard for the bottom layer. I made both layers the same size, glued them together with Titebond II wood glue, and sanded the edges to perfect the alignment and remove the darkened edge from the laser cutter. The light hardboard and the dark walnut gives the base a racy two-tone look.
To make it a little nicer to handle and more attractive, I used a router with a 1/8-inch radius roundover bit to soften the edges of the upper layer. To keep the surfaces nice and to seal in any residual laser-cutter odor, I gave the glued-up base three coats of polyurethane finish on the top and sides, with light sanding between coats.
Both layers are described by a single CorelDraw file (and I've provided an exported DXF file in case you don't have access to CorelDraw). The features are color-coded, and there are a number of build options available to you when you cut the two layers.
Yellow is the outline of the Backplane Pro board itself. You could use this to create a pocket for the board to sit down inside, either by engraving the top layer or by adding a layer above that to frame the board. In my build, I did not use the yellow line at all.
Blue is an outline 1/4 inch outside the board. I contemplated building the base with a stair step edge, with the top layer outlined by this line. That would have been better if the two layers had been made of materials that could not be sanded or finished together, such as acrylic and wood. In my build, with both layers made of wood, I didn't end up using this line.
Green is an outline 1/2 inch outside the board. I used this to cut out both layers in my build. I like having the base a little larger than the board, to help keep random clutter on the bench away from the circuitry. The border also makes the top layer much sturdier, since some of the cutouts would otherwise come very close to the edge of the material.
Red lines define the cutouts in the top layer for clearance around all the component leads. These are mandatory in the top layer, and shouldn't be used in the bottom layer. You could choose to treat these as areas to engrave and create a single-layer design. Because lasers are slow and not very repeatable in engraving large areas to substantial depth, I chose to use two layers and vector-cut these outlines all the way through the top layer. Note that the screw holes are also red, and they of course need to go all the way through in any case.
- Black areas create clearance around the screw heads. I chose to engrave these into the bottom of the top layer, to sink the screw heads into the top layer. I ended up also vector cutting these through the bottom layer, to provide access for a screwdriver, so I could have skipped the engraving step. As long as the thickness of the bottom layer plus the depth of the engraving exceeds the thickness of the screw head, the screws won't stick out below the bottom of the base.
Note that the drawing is looking at the bottom of the base. That made it easier to create from measurements of the bottom of the backplane board, and it also made it possible to engrave the screw head countersinks in the same operation as cutting the cutouts. If you choose a material for the top layer that has a good side and a bad side, you'll need to cut this design with the good side down. My walnut was good on both sides, or I would probably have learned this the hard way.
Build Plan Summary
To build this exactly the way I did:
- Top layer (1/4-inch walnut, good side down)
- engrave black areas to depth of screw heads
- vector cut red lines
- vector cut green line
- Bottom layer (1/8-inch hardboard)
- vector cut black areas
- vector cut green line
- Glue the two layers together
- Sand the edges clean
- Roundover the top edge
- Finish top and sides with polyurethane
- Insert six 1/2-inch 4-40 nylon machine screws from the bottom
- Place the Backplane Pro on top and fasten with 4-40 nylon washers and nuts