I thought I would start the building of the guitar body with the pickup itself. As I have a magnet which I think is suitable I decided to 3D print a bobbin that fitted it to hold the winding coil. The magnet is 8 mm in diameter and 15 mm in length so I looked at making a bobbin with these dimensions. I also looked at what wood I might have available as that might have an impact. I found some pine plank that is 22 mm thick and 71 mm wide and about 750 mm long. I don't know how long a guitar should be but it seemed a good starting point. I could make the bobbin 15 mm thick but as the wood is 22 mm thick I decided to make the bobbin 22 mm thick as well. I used 1.5 mm thick walls for the centre of the bobbin which made it (8 + 1.5 +1.5) = 11 mm thick. I have a 15 mm and a 22 mm wood drill for making the hole in the wood to take the bobbin. If I use the 15 mm drill this only leaves (15 - 11) = 4 mm for the flanges that will hold the winding, which would be only 2 mm each side. I don't know if this would be enough (how many turns should the pickup have?) so I decided to go for the 22 mm drill as this provided more possibilities. So I made the bobbin outer diameter 22 mm as well. See video below:
I found a used steel guitar string which is 1.1 mm diameter - no idea what note that is and this has an eyelet at one end. I have some stainless steel pins left over from fixing my fence (which by the way didn't work as the wood shrank and the pins fell out so I had to buy new fence panels anyway) which I have used for numerous things. I'm going to get more when these run out as they are so useful. Fortunately the pin fits through the eyelet and the head doesn't so it can be used to fix the string at the bottom of the guitar. I decided to use black japaned slotted screws to form the tightening mechanism as I didn't want to purchase proper guitar string tighteners. To enable the string to be tightened I filed one side of the black japaned screw to a flat and drilled a 2 mm hole though it so that the string would go through. The screw is then fitted to the top end of the guitar, the string threaded through the hole and then tightened. I used two more slotted screws to lift the string away from the body. I don't know what height is best so these can be adjusted if needed. When the string is tightened I have effectively made a one string acoustic guitar - although it doesn't have a sound box. The bobbin fits into the hole drilled into the body of the wood. It is rather loose which I assume is just the extra width made by the drill bit so I will have to put some tape onto the bobbin once the coil has been wound in order to make a snug fit. Or I could hot glue it. See below for the completed guitar body.
All I have to do now is wind the bobbin to complete the pickup and the prototype guitar is finished. Assuming it works I will then consider how to incorporate a pre-amplifier and then paint it and smarten it up.