Acoustic Guitar Build – Day One
Joining the Soundboard and Back
Here we look to the putting the pieces together and seeing not only where it looks best when joined but – also where the grain is tightest.
This tight grain should be placed in the centre – tight grain is stiffer than loose grain and loose grain is better around the edges as it allows the board to flex, akin to a speaker.
Once decided, mark the top with a few pencil strokes across the join.
Now the pieces need to match exactly to be joined. On the left-hand piece, mark the right edge e.g. with a tick mark. Flip the right-hand piece over on top of the other one and mark its right side with a tick also. These are the edges which will be planed / sanded smooth for an exact match. The pieces are flipped so that if the fence against which we are sanding is not dead at 90 degrees, the fact that the pieces are flipped will still match exactly.
Using a piece of flat MDF, put one ticked side under the other so that the top piece has a slight overhang. Hold these boards down with your hand or a beam and use a straight sanding to sand the edge. Swap the boards and repeat, same number of sanding strokes on each one. It is always the tick side you will be sanding. Repeat until you can’t see the light through the join when you hold them up to the light.
Now we use a jointing jig. This consists of a flat board with a stop piece of wood either side and a groove down the middle for excess glue from the joint to run into. This means that the board will not stick to the base of the jig – important!!
Place the two pieces of wood so that the glue line will match up with the groove then take a stop piece and butt it against one side of the board, screw it into the base board of the jig. On the other side, leave about an inch and a half, then screw this to the base board as well.
Using a slat of wood on each board, clamp the first one onto the side of the board which is butted against a stop piece. With the other, apply the clamps but do not tighten yet. Use wedges to force the second piece up tight against the one already clamped – when good and tight, tighten the clamps on the board holding the second piece down.
That’s the dry run over – remove the wedges first (stops the boards from popping up in the middle) and then the clamps from the second side. Apply glue and re-clamp / wedge, leave to dry.
Once thicknessed, sand the inside of the back to remove all scratches from the sander to ensure that all subsequent braces have perfect surfaces to adhere to. Pencil in the centreline using the saw cuts previously made.
Draw the bracing positions on using the template – these are generally used measurements which are also referenced in “Guitar Making” by Cumpiano & Natelson.
Mark 42mm from the top and 20mm from the bottom and now cut out a “centre seam reinforcement strip” from spruce or mahogany offcuts for each large gap between lines allowing then strip to overhang by approximately 3mm. Whilst these are east to break lengthways, the grain runs across, making them incredibly strong and stable when glued across the glue line.
Now these need to be clamped: Using a jig if possible, Clamp a straightedge to the back board, 1/2 the width of the strip from the centreline – we can then align our strips up against the straightedge and be sure they are all in the middle of the centreline. Once aligned, apply glue and a thin strip of board across them all then clamp with 5 or 6 clamps. Make sure strips are flush against the straight edge once clamped as clamping tends to shift them.
Once dry and set, remove glue with a chisel.
Preparing the Back
Using a template, draw the shape onto the jointed board using the glue line as a centre line. Use a fine saw to mark the ends of the board where the glue (centre) line is as when this is sanded it will eventually disappear. Use the bandsaw to cut out the shape about 3mm from the line and then thickness the resulting cutout to approximately .110″.
Preparing the Back and Sides
Thickness the sides to approximately between 0.085″ and 0.090″ – remember to always run each side through twice as they come out more even.
As I am going to be having a cutaway, I marked roughly where the cutaway bending will start, ran this piece through the thicknesser then snatched it back out one it had reached the marked line. This makes it just slightly thinner for easier bending.