Chassis Mechanical Drawings
- Chassis is made from 1/8", 5052 aluminum plate, 36" x 36". Cutting layout shown below.
- Chassis is joined using 3/4" x 1/8" angle brackets. Bracket layout shown below. Here is a printable version of the bracket layout.
- Main board tray extracted from salvaged ATX PC case. I/O bracket trimmed to 4 slot micro ATX. Tray is steel and cut with angle grinder using 1/16" thick cutting wheel.
- Chassis parts cut. -
- Ventilation slots -
- Begin laying out holes for brackets -
- Assemble chassis -
- Chassis assembled -
- Layout heat sink fins on face plate -
- I have been testing various methods of attaching the heat sink fins to the face plate and was surprised by how difficult this turned out to be.
Aluminum solder is not an option. Too much surface area to heat and aluminum solder works only when the solder joint is exposed allowing the surface under the wet solder to be scratched with solder rod in order to break through the infamous oxidized layer. That cannot be done with a lap joint.
My going in plan was to use Arctic Alumina Thermal Adhesive.
The first problem with Arctic Alumina is that the quantity in each kit is miniscule. To coat all heat fin surfaces would cost a fortune. The second problem is the 5 minute open time. This product is clearly intended for small heat sinks.
In order to minimize the quantity of thermal epoxy I decided to use a combination of thermal epoxy and thermal pad. I settled on Gino 400mm x 205mm x 0.5mm Silicone Thermal Pad. For about $15 US, one sheet will do the job with plenty left over.
The first sample was prepared using a piece of 6" angle, one piece of thermal pad, and two Arctic Alumina bond points. This resulted in flexing (due to compression of the thermal pad) and a failed glue joint (top of illustration below) even before applying heat.
The test was repeated, using Arctic Alumina, and three bond points as shown above. One additional sample was prepare using JB Weld (not known for good thermal conductivity).
After 24 hours of clamp time I heated the center of the plate gently with a propane torch until "warm".
Due to differential thermal expansion, both test samples failed.
The heat sink fin prepared with Arctic Alumina released from the surface of the aluminum plate.
The heat sink fin prepared with JB Weld bonded to the aluminum but the glue joint failed in shear.
On a positive note, the Gino thermal pad worked well.
The mechanical solution is effective but time consuming.
- Installed Plexiglass power transistor shields.
Chassis is complete. Continue to the amplifier power supply.