With my previous bass now complete, I've been making progress on the next 4 string build. This one will be fairly similar to the last bass (with some small tweaks to the design), only without the magnetic pickup.
I begin work on the English Walnut top by sanding each half on the drum sander, to remove the saw marks left from the bookmatching process, and to thickness them to the correct size.
It's important that the top is jointed precisely, particularly as the method I'm using relies only on tape to apply sideways pressure, so you can't 'cheat' by tightening a clamp to close up a small gap, etc.. the joint must be spot on.
To check for square, I use this fantastic little square, made by David Barron.
Once I'm happy with the fit, I carefully line up the grain and apply a couple of pieces of tape to temporarily hold the two halves in position.
The top is then flipped over, and with one half raised up slightly, I apply tape every couple of inches. To make this method work well the tape you use should have some degree of elasticity, as it helps to increase the clamping pressure (I'm using Stew Mac binding tape).
I stick one end down and then pull the tape as tight as possible before sticking the other end down to the wood. Because the tape has been applied with one half of the top raised up, when the top is placed flat the tape will tighten and apply sideways pressure.
Flipping it back over to the front face, I remove the two pieces of tape and while lifting the top up (this is why this method is often refereed to as the 'tape tent'), I apply a bead of glue into the join.
I then place the top onto a large offcut of worktop (covered in parcel tape to prevent glue sticking), and push it down flat, firmly pressing up and down the length of the join to make sure there's no high spots. It will naturally want to spring back up due to the pressure of the tape, so I attach three scrap wood cauls to keep it flat while the glue cures.
Once the glue has fully cured, I scrape off any squeeze out, and then give it a quick sand with a random orbit sander, to remove the coarse sanding marks left from the drum sander.
The grain matches up nicely, and there's no visible glue line.. success!
With the top joined, I cut some black veneer and attach it to the back of the top, using my vacuum press. The glue will continue to cure once the top is removed from the vacuum bag, so I clamp it to a flat surface, with some spacers underneath it to provide air flow to both sides of the wood. Keeping it clamped flat is necessary, as attaching veneer to just one side of a piece of wood tends to make it cup, especially when using water based glue.