Chassis Mechanical Drawings

Front Elevation

Pi-Amp Rev 5 Front Elevation Mechanical Drawing

Side Elevation

Pi-Amp Rev 5 Side Elevation Mechanical Drawing
Chassis Assembly
  1. Chassis is made from 1/8", 5052 aluminum plate, 36" x 36". Cutting layout shown below.

    Pi-Amp Rev 5 Aluminum Plate Layout
  2. Chassis is joined using 3/4" x 1/8" angle brackets. Bracket layout shown below. Here is a printable version of the bracket layout.

    Pi-Amp Rev 5 Angle Bracket Layout
  3. 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.

    Pi-Amp Rev 5 Micro ATX Mainboard Tray
  4. Chassis parts cut. -

    Alumunum Chassis Plate
  5. Ventilation slots -

    Pi-Amp Rev 5 Side Ventilation Slot Mechanical Drawing

    Pi-Amp Rev 5 Top Ventilation Slot Mechanical Drawing
  6. Begin laying out holes for brackets -

    Pi-Amp Rev 5 Laying Out Holes for Angle Brackets
  7. Assemble chassis -

    Pi-Amp Rev 5 Assembling Chassis
  8. Chassis assembled -

    Pi-Amp Rev 5 Chassis Assembled 1

    Pi-Amp Rev 5 Chassis Assembled 2

    Pi-Amp Rev 5 Chassis Assembled 3

    Pi-Amp Rev 5 Chassis Assembled 4

    Pi-Amp Rev 5 Chassis Assembled 5

    Pi-Amp Rev 5 Chassis Assembled 6
  9. Layout heat sink fins on face plate -

    Pi-Amp Rev 5 Heat Fin Lay Out
  10. 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.

    Pi-Amp Rev 5 Arctic Alumina Failed

    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.

    Pi-Amp Rev 5 Gino Thermal Pad

    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.

    Pi-Amp Rev 5 Heat Sink Fin Showing Arctic Alumina Failure

    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".

    Pi-Amp Rev 5 Heat Sink Fin Test Clamp

    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.

    Pi-Amp Rev 5 Heat Sink Fins Instaled
  11. Installed Plexiglass power transistor shields.

    Chassis is complete. Continue to the amplifier power supply.