Thickness Sanding Soundboard and Back of Guitar

So hopefully at this point you have now joined your pieces together for your soundboard and/or the back of your guitar. Also hopefully you did not leave the pieces overly thick but at least thick enough to make sure you could sand out any unevenness in the joint you made. Most likely your plans will have recommendations for thickness of your soundboard or back of your guitar. I’ve seen anywhere from 1.6mm to 2.5mm.

If you are loaded and a ton of money you wish to just invest in wood working tools, then now would be a great time to go by a really nice thickness sander. Here is a nice one, it costs about $1,229.99

Of course if you are like me you either don’t have the money or you have other better things that money could be spent on. So let me tell you what I came up with an alternate option that is a lot better than going at it with a sanding block. Specifically I went and bought myself an inline sander at Harbor Freight along with some wood sanding belts that I cut to fit on the inline sander. Typically and incline sander is meant for use for body work on a car, but it serves its purpose for thickness sanding wood as well. Now obviously if you don’t already have a good air compressor you will need to get a decent air compressor to run it as well. But in the end you still will spend a lot less than a thickness sander and the air compressor can obviously be reused for many things.

First you will need a way to hold your piece in place. I opted to lay it on my wood work bench and drill holes and stuck wooden dowels around it to hold it from moving around as I sanded it. Now you can use your inline sander to go back and forth over your board to thickness sand it. Because it has such a long sanding pad it is easier to keep everything even across the board. Another option that I have seen others do when hand sanding and trying to achieve a uniform thickness is to use a drill press with a stop to put holes to the exact depth they want all over the boards. 

Joining the Guitar Soundboard and Back

Assuming you didn't spend outrageous money for a single piece top and single piece back for your guitar, you will have to join your book matched pieces together in order to have a single piece for your top and/or back. For the professional with a full workshop including a joiner, this task is pretty easy and straightforward. For us amateur garage wood workers, we have o be a little more creative. You may come up with your own creative ways to get a good solid joined top or back, but here I will explain how I went about it. I tried a couple other ideas first but after finding this solution, it has proved consistent.

Step 1

First you have to decide which edges you are going to join. Obviously the joined edges will end up in the center of your guitar, so most of the time you will have a preference in the grain pattern. Once you do this fold the two pieces together so that the sides that are together are either both that should end up on the back of the guitar or both are those that will end up inside the final guitar.

Step 2

You will need two identical metal straight edges that are longer than your pieces as well as a piece of scrap wood as long as your pieces and at least 4-5 inches wide. . Align your board edges so they are even. Take your scrap wood and place it on top of your board pieces so that its edge lines up with the board edges you already aligned. Take one metal straight edge and lay it on top of your scrap piece and your two board pieces so that it’s edge also lines up with the edges of the boards. Clamp that sandwich together on both ends. Now take your other straight edge and lay it on top of the boards a couple inches behind the other straight edge. Now clamp that to the boards. The second straight edge is simply to help provide a flat surface for your router that you will be using in the next step. Now that you have that all clamped together clamp the whole thing to your workbench with the flat edge that needs to be joined facing out and hanging off the work bench slightly.

Your sandwich should resemble this

Step 3

In this step you will need a decent router with a good 1/4 inch or 3/8 inch straight router bit. Put the router bit in your router so that the shaft is sticking out far enough to run against your straight edge without catching it but not so far that your bit is past your scrap would in step two.  Basically you want to make sure the bit will be hitting your final board edges completely without hitting the metal straight edge. Now very carefully run your router on top of the flat straight edges with the router shaft guiding you against the straight edge. You will want to make sure you keep your router flat on top of the straight edges.

Step 4

Once you are sure the router has completely edged your pieces, you can unclamp the entire sandwich you made. If you unfold the pieces and put the freshly router’d edged together you should find that they match perfectly.

Step 5

Now that you have good edges on you boards it is time to make your joining jig. Yes we still have more to do before we can glue those nicely edged pieces together. To make the joining jog you will need two pieces of 3/4 inch cabinet grade plywood that are about as long as your pieces that you want to join and a little wider than your end joined top or back will be. You will draw an evening spaced 5x5 grid on those pieces and cut them out so they look similar to the picture below. You could use thinner plywood but you will then have to reinforce it since the purpose is to be rigid while your pieces are joined.

Step 6

Now that you have your joining jog ready you can join your pieces together by

1)      Placing one of the grid pieces on a flat surface.

2)      Place a strip of wax paper down the center of the grid

3)      Evenly spread glue on the two edges to be joined

4)      Lay down the pieces with edges to be joined in the center of the grid and line them up and pushed them together.

5)      Lay another piece of wax paper down over top of the glued edge

6)      Place other grid piece on the top.

7)      Place hand clamps on the 8 grid edges

8)      Use bungee cords to squeeze the glued pieces together by wrapping them around the top bottom and middle locations where the grid is indented.

Step 7

Now you just have to let them dry and you will end up with a nicely joined piece.  You will obviously need to sand them but I will cover sanding and thicknessing the front and back in another post.