Case Construction

Pi-Amp Wood Case

Milling

Case Parts Description No. Supplier Stock No. USD ea. Total
Red Oak 10 board feet, 4/4 10 Local Lumber Yard NA 3.50 35.00
Total NA NA NA NA NA 35.00
  1. The inside dimensions of the case must be exactly 18" wide, 6-3/4" high, and 15-1/2" deep (before applying front and rear edge banding), as viewed from the front, to accommodate the chassis. When milling Case Top and Side pieces, it is essential that the width of each be exact or slightly wider (+1/32") than "theoretical". For example, if the 6 Case Top pieces are cut to 2-15/16", the Case Top will have a final width of 17-5/8". That dimension will not accommodate the chassis. It is best to cut the Case Top and Side pieces a "hair" wider. The Case Top and Sides will be trimmed on each edge, to final width, before final assembly.
    Case Front Layout
    Pi-Amp Wood Case Schematic Front Elevation
    Case Top Layout
    Pi-Amp Wood Case Schematic Top Elevation
    Case Side Layout
    Pi-Amp Wood Case Schematic Side Elevation
    Case Bottom Layout
    Pi-Amp Wood Case Schematic Bottom Elevation
  2. Mill the following Case pieces from 3/4" material. If a stop on the cross cut sled (table saw) or chop saw is not available, cut the case pieces 15-3/4" to allow final trim after glue up.
    • Top, 6 pieces, 15-1/2" x 3+"
    • Sides, 6 pieces 15-1/2" x 2-3/4+"
    • Bottom Rails, 2 pieces 18-1/4" x 3" (final length 18")
    • Bottom Spanner, 1 piece 9" x 3" (final length 8-3/4")
    • Top and Bottom Stiffeners, 4 pieces 18"+3/4"+3/4" x 1 3/4"
    • Case Trim, 3/4" x 1/8", length to cover front and rear edges (+108")
  3. Cut the ventilation slots in the Case Top and Side pieces using a router, a 1/2" flush trimming router bit, and shop made jig. The alternative is a 1/2" straight bit and router table. The jig produces a more accurate cut and is safer and faster.

    1/2" flush trimming router bit, 1/4" shank -

    Pi-Amp Flush Trimming Router Bit

    Shop made router jig -

    Pi-Amp Shop Made Router Jig
    • The jig base can be made from a scrap of plywood or MDF. The bit bearing rides on the front edge of the jig base and that edge must be flat. If there are bumps they will be transfered into the cut made by the router bit.
    • The thickness of the end and back stops must be less than or equal to that of the case pieces to ensure that the router base rides flat on the work piece.
    • The distance from the front edge of the jig base to the front edge of the piece (the overhang) is 1/4".
    • Each Case piece should fit snuggly between the end stops. Use masking tape as a shim to adjust the fit.
    • The jig base must be wide enough to be clamped on each end to the work table and not have the clamps interfere with the router.
    • The bit depth is set such that the bearing rides on the edge of the jig base and the bit's cutting surface completely straddles the edge of the work piece.
    • Begin cutting to the right of the red dashed line and cut in multiple passes. Never climb cut with a router. To complete the milling one edge, flip the piece over, end wise, and finish the remainder of the ventilation slot.
    • Clean the wood chips from the jig before reseting the piece for the next cut. The gaps between the back stop and the end stops make this easier.
    • Remember - there are six case pieces that have a ventilation slots milled on one edge only!

Initial Jointing

Pi-Amp Biscuit Jointer and Blade
  1. Each Case Top and Side piece is joined together with one #20 biscuit on each end. An alternate method that works just as well, and is possibly stronger, is a spline joint. The spline joint will take longer to prepare, however will not require anything more than a table saw and a brad point drill bit. I do not recommend skipping the joint work and simply face gluing for two reason. The biscuit or spline joint will add strength, and ensure that the glue up is flat, hence minimizing cleanup time.
  2. The illustration below shows the placement of the biscuit or spline joints.

    Pi-Amp Biscuit and Spline Joints
  3. Notes on cutting biscuit joints -
    • Lay out Case and Side pieces across the work table from left to right, in order of assembly (3 left Side pieces, 6 Top pieces, 3 right Side pieces). You will be looking at the "outside" of the case.
    • Match the grain by flipping and swapping pieces around.
    • Number each piece in pencil to aid in keeping the sequence straight.
    • Make a mark 2" from each end for biscuit jointer alignment.
    • Do not cut the biscuit joints for joining the Case Top to Case sides or the bottom at this time.
    • Set the depth of cut on the jointer for a #20 biscuit and adjust the guide fence to center the blade on the face of the joint (3/8" for 3/4" thick material).
    • Begin jointing by clamping one end of a piece to the work table. The face to be jointed should overhang the table by about 1/4". Cut the joint on the end opposite to the clamp, move the clamp to the end just jointed and joint the other end. Continue jointing as required until all joints are cut.
    • If you have not used a biscuit jointer, make a practice cuts on a scrap.
    • Be sure that all joints are cut with the "outside" facing up. Flipping the piece over to cut the next joint may result in misalignment.
  4. Notes on cutting spline joints -
    • Lay out Case and Side pieces across the work table from left to right, in order of assembly (3 left Side pieces, 6 Top pieces, 3 right Side pieces). You will be looking at the "outside" of the case.
    • Match the grain by flipping and swapping pieces around.
    • Number each piece in pencil to aid in keeping the sequence straight.
    • Do not cut the spline joints for joining the Case Top to Case sides or the bottom at this time.
    • Set the depth of cut on the table saw blade to slightly less than the depth of the ventilation slots cut in the previous section. Adjust the table saw fence to center the blade on the face of the joint (3/8" for 3/4" thick material).
    • Begin jointing by placing the first piece against the fence with the joint face down and "outside" face toward the blade. Feed the piece through cutting both joints in one pass. Continue jointing as required until all joints are cut.
    • Be sure that all joints are cut with the "outside" facing toward the saw blade. Placing the other face toward the saw blade when cutting the opposite pair of joints can result in misalignment.
    • Cut the splines to fit the joints. A typical carbide table saw blade has a 1/8" kerf. Rip the spline material to a hair less than 1/8". If the spline material does not slide in and out easily, it is too thick. The splines should be 5" long. The excess will protrude into the ventilation slot. The protrusion will be drilled out later with a 1/2" brad point bit. If the ventilation slots came out less than 1/2" wide, a smaller bit will be required. A brad point bit will center and cut smoother than a conventional bit.

Initial Glue Up

Pi-Amp Glue and Clamp Tools
  1. Assemble the Case Side and Top pieces and dry clamp (no glue). Use two bar or pipe clamps spaced about 11" apart to center on both joints. Do not use a clamp in the center. Check square by comparing corner to corner measurements. Ensure the ends and faces are flush. If the spline method was used, check the spline fit to ensure that compression of the spline is not required to close the joint. The Case Top will be glued up in two halves (3 + 3). Do not attempt to glue the Case Top pieces together all at one time because it will bow. Another reason to glue it together in halves is that most home shop planers will face up to 12".
  2. Remove the clamps and apply glue with a pipe fitters brush to the face and inside the mortise of each joint on three of the Side pieces. Coat the biscuits or splines with glue and insert into the joint. Have a small hammer and pliers handy to tap or pull as needed. Use plenty of glue. The glue should ooze out of each joint during clamping.
  3. Assemble the Case Side and place it in the clamps and tighten. As the joints begin to close, check square and ensure the ends and faces are flush. Tap the ends of each piece to adjust square and flush. Continue tightening both clamps until the joints are closed. Do not over tighten the clamps.
    • Depending on the accuracy of the milling, a compromise between flush ends and overall square may have to be made. Overall, square is the most important.
    • Misalignment between the face of adjacent pieces can be corrected by placing a C-clamp across the joint to pinch the faces flush.
    • The Illustration below shows the two types of joints as the clamps are closing.

    Pi-Amp Wood Case Glue Clamp Top Elevation
  4. When satisfied with the clamp job, quickly clean the glue out of each end of the ventilation slots with a Q-Tip or rag and screwdriver. Wipe the glue off the ends with a damp sponge or rag. The glue on the faces is best left alone until after the clamps are removed.

    Wiping glue off surfaces that are visible will force glue into the pours of some types of wood. Later, when finish is applied to the wood, the glue, in the pours, will prevent the wood from absorbing the finish resulting in a light spots.
  5. Continue gluing up the other Case Side and two Case Top sections.
  6. Allow 24 hours camp time. I know most glue manufactures say considerably less is required, however my experience pulling clamps before 24 hours has been mixed.
  7. After the clamps have been removed, cut away as much of the the excess glue as practical with a sharp chisel, bevel facing down. Remember to remove excess glue from the ends.
  8. If 4/4 boards were used, run the Case Sides and two sections of the Case Top through the planer to produce a final thickness of 3/4". Remember to plane the three Case Bottom pieces to ensure they are the same final thickness as the Sides and Top.
  9. Without the use of a planer, the remaining glue and any slight unevenness at the glue lines can be removed with a card scraper and / or a sander with 100 or 150 grit paper. Card scrapers are cheap and extremely efficient.
  10. If Case Side and Top pieces were cut slightly longer than 15 1/2", then cross cut the Case Sides and two Top halves to a depth 15 1/2". It is important that the cuts are square and the same length. A good method for doing this is with table saw. Ensure the rip fence is parallel to the saw blade. Set the rip fence at 15-5/8". With the miter gauge in the track between the blade and the rip fence, use a framing square to align the miter gauge square to the rip fence. Cross cut one edge, check square and adjust setup of necessary. Cross cut the remaining pieces on one end only. Adjust the rip fence to 15-1/2" and cross cut the other ends.
  11. Test fit, glue and clamp and clean up the two Case Top sections as described above.

Final Jointing

  1. Check the final width of the Case Top. If it is wider than 18", rip an equal amount off each edge to achieve an 18" width.
  2. Check the final height of the Case Sides. Case Side height less Case Top thickness, less case bottom thickness must equal 6-3/4". If the Sides are higher, rip an equal amount off each edge to achieve the required height.
  3. If spline joints were used, drill out the waste protruding into the ventilation slots using a brad point bit.
  4. Cut the two Case Rail pieces to the exact width of the case top (ideally 18").
  5. Cut the Case Spanner piece to a length equal to Case Side depth, less the combined width of the two Case Bottom pieces, less 3/4" (ideally 8-3/4"). The object is to ensure that the rear Rail is inset by 3/4" as shown below in the illustration of the Case Bottom.
  6. Take extra care to ensure that the ends of the Rails and Spanner are dead square.
  7. Cut double #20 biscuit joints or spline joints as shown in the illustration below. The double biscuit mortises should be on 1/4" centers. Spline mortises should be cut 3/8" deep by 1/4" wide to accept a 1/4" x 3/4" spline. The entire mortise should be filled with spline for stability, except the 3/4" gap shown at the rear of the case. The excess spline beyond the actual joints can be left protruding.

    Pi-Amp Wood Case Glue Clamp Biscuit and Spline

Final Glue Up

  1. Test fit, glue and clamp, and clean up the bottom frame, composed of two Rails and Spanner, using the techniques described in section above. Check square by comparing corner to corner measurements. Also check for unwanted twist, between the two rails, along the axis of the spanner. The exact lateral position of the spanner is not critical.

    Pi-Amp Wood Case Glue Clamp Bottom Frame
  2. Test fit, glue and clamp, and clean up the top, sides and bottom frame. Five clamps are required as shown in the illustration below. After the clamps are in place, the front and rear edges should be flush. Check overall square and adjust as necessary. If the case is not square the chassis will fit poorly. Wipe the excess glue from the joints on the inside of the case.

    Pi-Amp Wood Case Glue Clamp Sides to Top
  3. Attach the edge banding to the front and rear of the case. Begin by cutting the edge banding for the sides to length. The banding can be cross cut cleanly with a sharp chisel and hammer. Prepare several pieces of masking tape about 6" long. Apply a thin, even coat of glue on the concave side of the banding and center the banding on the case edge. The banding will slip around at first. Wait a couple of minutes until the glue soaks in before making final adjustments and applying the tape. Three to five pieces of tape across the banding will do a good job holding it in place until the glue takes a firm set.
  4. Cut the edge banding, for the front and rear of the case top and front bottom rail, to length. Put a 45 degree bevel on the outside edge of each end to create a shadow line where the ends butt against the banding on the case sides. Attach the banding as discussed above.
  5. Attach the four Top and Bottom Stiffeners. The bottom rear stiffener is inset 3/4" to make room for the chassis hardware. It may be tempting to leave the stiffeners off. I have found that over time that the top will develop a slight bow towards the inside of the case. Four pieces of flat cork can be glued to the bottom stiffeners as feet.
Pi-Amp Wood Case Bottom View

Sand and Finish

  1. Cut any remaining glue from the joints using a sharp chisel.
  2. Sand the case to satisfaction. Due to the relatively small size, a power sander is not required. The job can be accomplished with a card scraper and a sanding block. If a power planer was used, sand enough to remove any ripples left by the cutting knives.
  3. Finish the case with a wipe on polyurethane or 50/50 mixture of tung oil and polyurethane. Begin by removing the dust from the case with a rag dampened with paint thinner. Apply finish with a lint free cloth and buff lightly between coats with 600 grit sand paper or fine steel wool. It is important to finish the entire case with a minimum of three coats. The object is to seal the wood from moisture to prevent warping. Add additional coats to the outside to build depth as desired.
Pi-Amp Wood Case Front View