Chassis Construction


Milling

Chassis Parts Description No. Supplier Stock No. USD ea. Total
Aluminum Plate, 5052 36" x 48" x 0.125 1 OnlineMetals 5052-H32 88.90 88.90
Aluminum Angle 3/4" x 3/4" x 0.125" x 14' 1 OnlineMetals 6061-T6 11.33 11.33
Aluminum Channel 3" x 1" x 0.125" x 3' 1 OnlineMetals 6063-T52 12.16 12.16
Machine Screw #6-32 x 1/2" Pan Head 50 NA NA 0.05 2.50
Machine Screws #6-32 x 1/2" Counter Sink Head 50 NA NA 0.05 2.50
Machine Screw Nuts w/ Integral Washers #6-32 Round and Counter Sink Head 100 NA NA 0.05 5.00
Total NA NA NA NA NA 122.39
  1. The aluminum used to build the chassis should be cut on a table saw with a non-ferrous blade. A non-ferrous blade is designed to cut metals that do not contain iron. The teeth are carbide set with zero degree rake. The kerf will be slightly narrower than the wood cutting blade (3/32" as opposed to 1/8") so you will need to keep this in mind when setting the fence if you use a fixed scale.

  2. Before cutting, lubricate the blade teeth using a candle stick. Touch the end of the candle stick to the teeth with the saw running. Always lubricate the blade between cuts. Cut with the blade set at minimum height to reduce vibration. The teeth should just break the surface as the cut is being made.

  3. Cuts must be made with a slow feed rate. Be sure to cut all pieces dead square. This may require cutting 1/16" over size and trimming to square with a second pass through the table saw.
  4. Mill the following pieces from 1/8" thick aluminum plate -
    • Base, 1 piece, 17-7/8" x 15-5/8"
    • Rear Panel, 1 piece, 17-7/8" x 11-1/8"
    • Top, 1 piece, 16 1/2" x 18 5/8"
    • Side, 2 pieces, 16 1/4" 11 1/8"
    • Drive Head Bridge, 1 piece, 5-3/4" x 5-3/4"
    • Drive Head Side, 2 pieces, 10-1/4" x 5-3/4"
    • Amplifier Fin, 2 pieces, 10-1/4" x 5-7/8"
    • Controls Panel, 1 piece, 8-1/2" x 5-3/4"
    • Toroid Cover, 1 piece, 5" x 4-1/2"
    • Toroid Bracket, 1 piece, 5 1/4" x 2-1/2"
    • PSDU Cap, 1 piece, 4-1/2" x 2-1/2"
  5. Mill the following brackets from 3/4" x 3/4" x 1/8" angle -
    • Base to Rear Panel, 1 piece, 16-3/8"
    • Base Front, 1 piece, 16-3/8"
    • Base to Side, 2 pieces, 15-1/2"
    • Side to Top, 2 pieces, 12-7/8"
    • Amplifier Fin to Base, 2 pieces, 5-7/8"
    • Controls Panel to Base, 1 piece, 5-3/4"
    • Drive Head Bridge, 2 pieces, 5"
    • Toroid Cover to Rear Panel, 1 piece, 4-1/2"
    • Drive Head Mount Top, 1 piece, 2-1/4"
    • Zobel Bridge, 1 piece, 2"
    • PSDU, 3 piece, 2"
    • Toroid Bracket, 2 pieces, 2"
    • Drive Head Mount Side, 2 pieces, 1"
    • PSDU to Base, 2 piece, 1/2"
  6. Make the Hard Disk Drive (HDD) mount brackets from 3" x 1" x 1/8" channel. Use the table saw to cut off one of the flanges to give one piece of angle 1" x 3" x 1/8". After trimming off one flange, cut the brackets to length as follows -
    • HDD mount brackets, 2 pieces, 5"
  7. Cut the Power Supply Distribution Unit (PSDU) post from 3" x 1" x 1/8" channel.
    • PSDU Post, 2 pieces, 9"
  8. Smooth all edges and corners of the pieces cut in steps 4 - 6 with a flat file or sanding block.
  9. Cut the ventilation slots in the side and top using the layout shown below.


  10. Cut the slots using a 1/4" spiral "O" single flute solid carbide bit mounted in a plunge cutting router. Use a straight edge as a guide. The bit shown below is made by Amana (Number 51402) and will plunge and cut each slot in one pass. Be sure to use a scrap of plywood below the work as a spacer to protect the work bench.

  11. Cut slots in the amplifier fins as shown below using the router set up from the previous step. Smooth the edges with sand paper or small flat file. Particular attention should be given to these slots because wires from from the amplifier main circuit boards to the power transistors will pass through these slots. Why slots instead of holes? Easy installation and removal of the power amps. Drill 5/32" holes for mounting the power transistor heat sinks (out set of four holes, top and bottom) and amplifier PCB standoffs (inner set of four holes top and bottom). Counter sink the PCB standoff holes to accept #6-32 counter sink head machine screws. Note: The counter sinks are on the front side of the amplifier fins. To facilitate hole layout use this template.

  12. To facilitate drilling holes in the angle brackets, fashion a support jig using a 24" long scrap of wood as illustrated below. The slot is cut, 1/2" deep, using the the table saw. Place the angle in the jig, measure, mark and drill.

  13. Drill 5/32" holes in all mounting brackets as shown below. Unless specified, adjacent holes on opposite flanges are separated by 1/2". Use a scratch awl to make a starting mark each hole before drilling. Select here for a larger version of this layout.

  14. Drill 7/32" holes in the sides of the two HDD mounting brackets as shown below. All 3.5" form factor HDD have a standard side mounting hole spacing and use #6-32 machine screws. The 7/32" holes allow mounting tolerance. Note that there is a right and left bracket.
    • The right hand bracket, as viewed looking at the front of the drive head, is the top bracket shown in the illustration below.
    • The HDD mounting brackets function as heat sinks for two hard drives.
    • The HDD's are shown in silhouette by the green lines. The end connectors face toward the rear of the drive head.
    • Detailed 3.5" HDD layout dimensions can be found here (mm). Note: Limit screw penetration into hard drive case to 3/16".

  15. Drill 5/32" mounting holes in the top of the HDD mounting brackets as shown below -

  16. Drill 7/16" holes in the Drive Head sides as shown below. These holes provide screw driver access to the HDD mounting holes in the HDD mounting bracket. Drill 5/32" holes for the Drive Bridge mounting brackets. Cut the 2-1/2" x 5-1/2" wire ways in each Drive Head Side. This cutout gives clearance for routing wire between the Drive Head and Main Board.

  17. Drill 5 3/2" holes in the Drive Head Bridge as shown below (top view). Counter sink each hole from the top to accept a 5/32" countersink machine screw.

  18. Drill holes for the control hardware in the controls panel as shown below. Start each hole with a 1/8" pilot hole. This layout is suggested but not mandatory. If you are considering adding additional controls refer to the drive head assembly to for clearance restrictions between it and the controls panel. The hole sizes below are based on hardware called out in the Amplifier section. If you are using different hardware, check the mounting hole sizes. If unsure of exact hardware, drill only the pilot holes.

Assembly

Chassis
  1. Assemble the chassis by attaching the Rear Panel, Amplifier Fins and Controls Panel to the base. The two illustrations below show the chassis in elevation and plan view. The mount brackets are shown in blue. All screws are #6-32 x 1/2" machine screws.


  2. Align the Base to Side brackets with the left and right edge of the chassis. Mark, drill, and counter sink each hole from the top. Fasten the bracket with counter sink screws.
  3. Align the Rear Panel bracket to the under side of the chassis Base, flush with the rear edge. Mark, drill, and counter sink each hole from the top. Fasten the bracket with counter sink screws.
  4. Scribe three lines on the chassis base to position the Amplifier Fins and Controls Panel bracket. Position each bracket on the scribe lines. The fin brackets must be flush with the outside edges of the Base and the Controls Panel bracket must be dead center. This will ensure a 3/16" gap between the inside edges of the Amplifier Fins and the adjacent edges of the Controls Panel. Mark and drill. No counter sink is required for these holes.
  5. Align the Base to Front bracket to the underside of the chassis Base such that it is centered on the holes drilled for the Amp Fin brackets. Mark and drill the four holes in the bracket.

  6. Fasten the Amp Fins and Controls Panel to the Base. Only the bottom center hole of the Amp Fin should be used to secure to the bracket (the other two holes will be used later when securing the bottom edge of the bottom heat sinks to the Amp Fins). Check the the outside edge of each Amp Fin to ensure that it is square to the base.

  7. Align the Rear Panel to the rear panel bracket. The bottom of the rear panel must be flush with the bottom edge of the bracket. Mark and drill. No counter sink is required for these holes. Fasten the Rear Panel to the chassis Base.
  8. Attach the rear panel to the bracket with pan head machine screws.
  9. Assemble the chassis cover by aligning the Side to Top brackets to the top edge of each Side as shown below. The brackets must be positioned to fit exactly between the Amp Fin and Rear Panel. Mark, drill, and counter sink each hole from the outside of the Side. Fasten the brackets to the sides with counter sink screws.

  10. Place the Top upside down on the work bench. Stand the sides up on the Top, align the rear edges of the Sides to the rear edge of the Top. Adjust the spacing between the sides to 17-7/8" (the width of the chassis) as measured next to the Top. Mark, drill, and counter sink each hole from the outside of the Top. Fasten the brackets to the Top with counter sink screws.


  11. With the chassis sitting on a flat surface, fit the cover and carefully mark the holes from the Base to Side brackets on to the side pieces. Mark, drill, and counter sink each hole from the outside of the Sides. Fasten the Sides to the Base to Side brackets with counter sink screws.

Drive Head
  1. The function of the drive head is to mount two HDD's and one optical drive, serve as a heat sink for the drives and provide easy access to the drives. The optical drive defines the width of the drive head so care must be taken during assembly to ensure that the optical drive fits snugly in the slot. The width of the slot is fixed by the width of the drive head bridge. All 5.25" optical drives have an enclosure width of 5-3/4", the same width as the drive head bridge. Sufficient adjustment can be made through the drive head brackets to ensure that optical drive fits properly.

  2. The drive head is shown below in front and side elevation. The Drive Head Bridge and HDD Mount Brackets are shown in blue, the drives are shown in green. The clearance between the the Controls Panel and the HDD's is 3/4". The Drive Head is fixed to the Controls Panel by the three Drive Head Mount brackets and three self taping sheet metal screws. The drive head is removed by removing the screws and lifting straight up (Controls Panel stays in place). The bottom rear corners of the drive head sides are angled to allow passage of wiring. Note that mounting holes are shown on the Drive Head Mount brackets in the front elevation view. This is for illustration only. These holes will be match drilled to the controls panel after the drive head is assembled and fitted in place.


  3. Assemble the Drive Head Bridge by match drilling the Drive Head Bridge and HDD Mount brackets as shown in the illustration below. Notice that the width of the drive bridge (5-3/4") is equal to twice the thickness of the HDD brackets (1/4") plus twice the width of the bridge brackets (1-1/2") plus the width of the HDD (4"). With this fact in mind, begin by match drilling the first bridge bracket followed by the adjacent HDD bracket. Make a 4" wide spacer from a scrap of wood and use it to position and match drill the next HDD bracket. Position and match drill the other bridge bracket.
  4. Attach the four brackets to the Drive Head bridge using #6-32 x 1/2" counter sink machine screws.

  5. Join the Drive Head Bridge to the sides using #6-32 x 1/2" machine screws. Check the fit the optical and HDD'(s).
  6. Fit the drive head to the chassis. The controls panel should fit snugly in its recess and the bottom edge of the drive head sides should fit flush with the chassis base. Transfer an outline of the drive head mount holes on the controls panel to the Drive Head Mount brackets. Drill these holes with a 1/8" bit to accept a #6 machine screw. Final fit the drive head to the chassis.

PSDU and Toroid Mount
  1. The post (two - 1" x 3" channels), cap, mounting brackets, and ground clip join to form the power supply distribution unit (PSDU). The PSDU serves as a mount point for the bridge rectifiers, reservoir capacitors, fuse buses, terminal strip and central ground. The capacitors are attached to the post with one wire tie. The fuse buses are attached to the post with #6-32 machine screws. The rectifiers are attached to the post with one 1/4" machine screw. Assemble per illustration below.

  2. The PSDU and toroid mount are located on the chassis base as shown in the illustrations below (the second picture shows the PSDU without the cap installed). Fasten to the chassis Base and Rear Panel with #6-32 x 1/2" machine screws. Counter sink the holes through the Toroid Cover and the Toroid Bracket.



Main Board Tray
  1. Obtain a micro ATX or ATX form factor PC case. These two form factors are the the most common in the industry. Do not use the less common low profile case.
  2. Identify the main board tray with expansion card and I/O bracket. Depending on the case construction, they may be integral to the PC chassis, attached with rivets or removable. In most cases the tray and bracket will be riveted to the PC chassis. The rivets are easily drilled out with a 1/8" bit. The two pictures below show two common tray arrangements. The dashed lines show the portion of the tray needed for this project. The ATX form factor is shown to illustrate additional required cutting. A micro ATX main board will fit in an ATX tray. The micro ATX form factor has four expansion card slots and the ATX has six. A micro ATX main board is 9.6" x 9.6". An ATX main board is 12.6" x 9.6". The 3" difference accounts for two additional expansion slots in the ATX board.

  3. Carefully remove the main board tray and bracket. Trim off the "ATX portion" using snips or jig saw and retain the "micro ATX portion". Notice the main board tray in the picture above on the left. The PC power supply is set precisely where it is needed so the portion of the tray that extends below the supply should be retained. The tray in the picture on the left does not support the power supply. That will not be a problem because the supply will sit next to the tray at a slightly lower elevation. Be sure to smooth the cut edges with a flat file.
  4. Determine the position of the expansion card and I/O cut out by placing the main board tray inside of the chassis snugly against the rear panel. The tray should sit 1/8" back from the left edge (as viewed from the front) of the chassis base. Check to ensure that there is enough space between the tray and the toroid bracket to fit the ATX power supply. If the tray was cut properly in the previous step this should not be a problem. The illustration below is the plan elevation of the main board, power supply and toroid transformer.

  5. Mark the location of the main board expansion card and I/O bracket on the chassis rear panel. Fit the main board tray to the chassis and hold it in place temporarily with tape. Transfer the position of the six corners of the bracket to the inside of chassis rear panel using a fine tip marker.
  6. Fit the ATX power supply to the chassis and make an outline the top and side edges on the chassis rear panel.
  7. Remove the main board tray and power supply from the chassis and remove the rear panel from from the chassis base. Use the measurements in the illustration below to finish making the outline of the bracket for cut out (blue lines). The dashed red circles mark the location of saw blade starter holes.

  8. Use the template shown below to mark the ATX power supply mount and vent holes. A template for holes can be found here. Measure the template to ensure that the scale has not been altered. Cut out the template on the 3-1/2" x 6" square that defines the outline of the power supply. Place the template on the reference lines and tape in place. Use a sharp center punch to mark the corners of the cut out and the mount holes. Remove the template and connect the corners of the cut out using a marker or scribe line.

  9. Cut out the access holes for the expansion card and I/O bracket and ATX power supply. Begin by drilling saw blade starter holes at the positions shown by the dashed red circles. Carefully cut between starter holes, along the outline, using a jig saw. Remove the remaining metal with a flat file. Ensure that the cut out is smooth and free of any burrs.
  10. Drill the four ATX power supply holes with a 5/32" bit for #6-32 x 3/8" machine screws. If the mount holes do not line up exactly with the power supply they can be enlarged to allow additional play.
  11. Drill holes for the speaker binding posts and cut out the hole for the IEC C14 socket.

  12. Attach the main board tray to the chassis. Fit the main board tray in place and ensure that the expansion-I/O bracket is centered over the rear panel access hole. Fasten the expansion-I/O bracket flange to rear panel by match drilling 1/8" holes through existing flange holes and using #4-40 x 3/8" machine screws. Fasten the main board tray to the chassis by drilling two, evenly spaced, 5/32" holes near the front edge of the tray (opposite of the expansion-I/O bracket). Place spacer washers between the tray and chassis to prevent deforming the tray when the screws are tightened.

    This image is slightly ahead in the build sequence but shows the position of the mainboard in relation to PSDU and the I/O and ATX12V power supply cutouts.