Gore Medium Body 12 Steel String Guitar blog:
April 2nd 2016
A player I know asked me to build him a 12 string guitar. He really likes the Gore medium body Steel String I built. He likes the size, shape and the sound. This lead me to start a 12 string falcate braced guitar. The 12 string presents a number of issues including how to modify the braces to support the increased string load and a 12 pin bridge would not work with the falcate bracing pattern I use.
After asking for some suggestions on the Australian/New Zealand Luthiers Forum (the home of many Gore followers) a member (woodsy23) modified an existing Finite Element (FE) model he had for 12 strings load, both light and medium (EJ38s and EJ39s). He determined I would need to increase the height of the falcate braces from 7 mm to 10 mm for the EJ38s and 11 mm for the EJ39s. I will probably stick with 10 mm as I want to limit the monopole frequency of the top to keep it in the typical SS range.
Also from the anzlf I found a tutorial for making a 6 pin 12 string bridge by Craig Lawrence. Way cool!
I had been thinking of going pinless but the above bridge looked pretty cool.
My client selected a nice looking set of Zicicote. The wood is pretty, has a nice tap tone but it is very dense. Not as dense as Cocobolo but denser than EIW ro BRW. This choice may push me away from an active back as it is a lot of mass to get moving. Also the wood is supposedly real brittle and hard to bend.
Before going any farther I decided I was first going to see if I could bend the tight Venetian cut away this the guitar design has. To increase my chances I decided to use almost all the tricks to bend brittle wood.
The first was a new suggestion from some forum. Wash one side of teach side with naptha; turn the board over and mark where the naptha comes through. This seems to be a brilliant idea as it will highlight any existing cracks. Then on wax paper flood the marked areas with thin CA.
The sides were thinned to about 2 mm or .080" and then starting a bit above the waist I used a scraper to take the area in the Venetian cutaway to .070"
I spritzed the sides with super soft II and let them sit over night.
while warming the sides in my John Hall fox style bender to about 300 degrees I used a heat gun to warm the inside of the Venetian cutaway.
After all of that the bending was uneventful and I had very little spring back. In the last picture you can see it in the mold with no clamps.
Now I am just waiting for the regular side to cool and set.
April 3rd 2016
The second side bending went OK as well but I had a close call. On the cutaway the non-cutaway side goes about 29 mm beyond the center line. I thought my template had taken that into account, it probably did but I cut my prebent sides closer and closer to actual size as It gives me useful bits of wood. In any case when I put the side in the mode the upper bout was just exactly the right size. No trimming.
I glued up the heel block with the block of wood for the bolt on bolt off neck extension.
I also made a batch of heel blocks out of plywood.
I used my band saw and my belt sander to follow the template to shape the heel block
I then glued up the rims to the blocks
Lastly before I profile the sides I index off of the top and make a couple of parallel white lines that I can use to realign the rims in the mold. Also while profiling I can make sure that I am profiling the rims symmetrically.