This document is part of my MRNet project.

Walk Around Cab Box Construction

There are two choices when it comes to the cab box:

Use a preassembled box, or
Build a box from the ground up

Preassembled boxes are nice, until the vendor decides to stop making them and then it is time to rearrange the board to deal with the next box. I would rather do everything once and be done with it. I willl build the box from the ground up.

Below is a rough drawing of the front view of the cab:

Below is the break down of the box parts:

Top Sheet: The top and bottom of the box are made out of sheet aluminum. The aluminum sheet with be of a thick enough gage to not flex too much. Holes are drilled into the top sheet for the buttons and the single LED's. A nibbling tool is used to nibble out slots for the linear potentiometers and the 7-segment displays. The controls are labeled by printing a reverse image on some overhead transparency, cutting it out, and wrapping the edges around the top sheet, and taping the edges to the buttom surface.
Bottom Sheet: The bottom sheet has the PC board attached to it. It also provides a place to attach the voltage regulator for a heat sink.
Printed Circuit Board: The current plans are to attempt to attach all or the components on one side of the board. The microcontoller and a few extra chips are at the top of the board. This results in a blank area at the top of the box. This provides some extra blank space to place a model railroad logo.
Box Sides: The box sides are made out of half round plastic rod and quarter inch (~6.25mm) thick sheet plastic. The half round plastic rod can be manufactured by taking a full round plastic rod and cutting it in half on a band saw. The quarter inch sheet is cut into long thin strips on a band saw. The strips thickness is such that they are slightly thinner than the flat surface of the half round stock -- by two pieces of aluminum thickness and one sheet of overlay plastic.
Attatchment: The cab has a 4-wire telephone connector on the bottom for attaching to the layout via a standard coiled telephone handset cord. The cab can be hung on the layout either by an eye and hook arrangement where the eye is at the top of the cab and the hook is on the layout or by Velcro (tm) attached to the bottom of the box.

Below is a cross-sectional diagram of the hand-held cab:

The box is assembled as follows:

Assemble the printed circuit board.
Top and bottom sheets of aluminum are cut to exactly the same size. This can be done on a band saw or by hand with tin snips.
(Optional) The aluminum surfaces are painted.
The control labels are printed in reverse on overhead transparency film, cut out and taped to the top surface. Care is taken to make sure that there are tabs that extend out over the edge of the top surface and are wrapped around the top surface edges.
A drill press is used to drill holes for the single LED's, the buttons, and the screws around the edge that will attach the front surface to the box sides. (Possible problem: the drill press might chew up the overhead transparency film; it may be necessary to print two, and replace the film after drilling.)
Use a nibbling tool to nibble out the slots for the linear slide pots. Use the nibbling tool to nibble out bit holes for the 7-segment LED displays.
Make sure that the single LED's, buttons, 7-segment LED's and the slide potentiometers all fit into their appropriate holes.
Take the long quarter inch plastic strips and place them under the attachment holes on the front panel. Mark where the holes are and drill them with a drill press. Use a tap to tap threads into the holes. Use pan head screws to attach the front surface to the side. Do the left and right sides first, then the top and botom sides second. Remember to drill a hole in the bottom side for the 4-wire connector; use a file to square off the hole.
Take the bottom surface and drill the holes around the outside edge for the attachement screws. Use an extra copy of the overhead transparaency to place the drill holes. Make sure that the holes line up with the holes in the long plastic strips. Do not screw the bottom on yet.
Mount the printed circuit board on spacers.
Put down the bottom surface first, the printed circuit board on spacers second, and the top surface with sides third. Everything should fit. Taking care not to jar the printed circuit board, carefully lift the top surface off. Using a felt tip marker, draw circles on the bottom surface around the spacers. Drill holes for the spacers. Attach the printed circuit board to the bottom surface using pan head screws. Re-verify that everything fits.
Unscrew the top surface from the sides. Attach the half round stock to the sides. Either use cynoacrylic glue or drill, tap and screw.
Screw everything together.