As I started to prepare the rim to receive the back, it became clear that I had taken to much off the bottom of the Spanish heel and in order for the entire surface to make contact with the back plate, it had to be build up a little.
I cut a slightly oversized 1/8" thick slice of mahogany and glued it to the heel, using the leftover as a caul against the slice and a small piece of 1/2" plywood underneath the heel. As it turned out, it was not as bad as I first thought. After the rim had been taken down to it's final height it became apparent that I could have gotten away with a slice of veneer for the last 1/2" of the tip of the heel, but it was good to be on the safe side.
Once the glued had dried I trimmed the sides and end flush with a chisel and took some of the bulk off the top with a block plane.
RADIUS SANDING THE SIDES TO FINAL WIDTH
For this I had to remove the support blocks on the solera, as they were protruding up over the rim. Instead I held the guitar in place in three places; With two clamps on the neck and with two low makeshift blocks clamped to each side of the lower bout. This provided amble stability and support for the sanding job while not getting the way.
I started by marking the final height of the sides at the heel and end block - 78.5mm and 83.5mm respectively. Two reference marks were also made on each side at the waist, not as final marks but as marks that would enable me to monitor that each side was taken down evenly.
Once all the marks were in place it was time to start the grunt work. First I sanded that entire rim with an 80 grit sanding disk and the 15' foot radius hollow form by rotating the disk and paper back and forth. The sanding left a lightly scrubbed up surface on the rim that provided a great visual reference for where the high spots were.
The disk has a selfadhering backing but I opted not to stick it in permanently, partly because I just learned that I had to ad some sort of finish to the hollow form in order for the adhesive to stick and I simply just wanted to get on with it and partly because the convenience of having the bare disc for a multitude of other purposes.
Once this was established, I continued to shave the rim down with a spokeshave and the little fence jig I used for the soundboard side of the rim. The spokeshave jig was set to about 2º, an angle that roughly fitted the sanded edge. When I had worked my way around the entire rim, which included planing the heelblock down with a blockplane, I switch to the sanding disk, sanded, measured and determined where more stock needed to be taken off and did so with the spokeshave. In this fashion the rim was slowly worked all the way down to its final dimension.
I had to be careful not to get carried away when using the sanding disk, and only use light pressure as the radiused hollow form itself was a little wobbly being only 5/8" thick. At times I resorted to holding the edge with one hand while exerting pressure down with the other hand over the center of the hollow form.
Last the rim was sanded lightly, first with 150 grit paper, then with 320 grit to remove the scratches left over from the sanding disc. A little piece of scrap spruce was used as a sanding block, and basically pressed against the rim with my thumb. This eliminated most of the danger of rounding the rim that I feared could have happened had a bigger block been used.
MARKING AND CUTTING THE BRACE NOTCHES AND FITTING THEM TO THE BACK
Fitting the back to the rim was very similar to fitting the soundboard. The main difference was that on the back I didn't have to make individual feet for the braces, but rather had to cut little notches in the linings to house the much shallower brace ends. Also, the back graft had to be trimmed to butt up against the heel and end block.
The back was laid on the rim and clamped to the end block, using a 6mm shim to raise it back above the rim at a height equal to the brace ends. The rim was then marked on each side of the protruding brace ends with a scalpel. I started by doing these marks in white pencil but found it difficult to do with precision and so switch to using a scalpel instead.
While I was at it I also scribes the braces ends to length up against the rim.
Once these marks were down, nine in total on each side, I laid a ruler on top of the assembly and aligned it with each two corresponding marks and scribed marks across on top of the linings with a scalpel. A mark was also done about 1/4" down the sides of the linings, to indicate the depth of the notches.
With a little razor saw I did two cuts for each notch on the inside of the mark, holding the saw approximately at 45º angle, ending the cut where the linings meet the sides and at the bottom of the notch. After that the waste was cleared away with a 1/8" chisel until the notch was all squared up.
Finally brace ends were trimmed to about 2.5mm inside the template, first with a razor saw and the cleaned up with a chisel and it was time to do the final fitting of the notches.
It proved to be quite a fiddly ordeal. Suffice to say that the notches didn't line up perfectly and I had a hard time determining which notches were cut slightly out of alignment, which were not, which were simply just too narrow and what not. Suffice to say, I was quite surprised to find out how tricky this part of the building process turned out to be.
Eventually I got it to a point where the braces were seated fairly nice and firmly, with only the odd gap showing here and there. Hopefully not too big a deal and if my Alhambra Luthier Model is anything to go by it's not an uncommon feature.
The depth of the notches were a little easier to deal with, and more importantly, trim to a tight fit. Here I set my calipers to the height of each brace end and used that as a reference to pare the bottom of the corresponding notch to the proper depth.
Last I cut little bevels on the ends of the braces to make room for bits of waste that hadn't been cleaned out of corners of the notches and to give excess glue somewhere to go to, other than being squeezed out in the open.
CUTTING THE BACK GRAFT TO LENGTH
The back graft also needed to be trimmed in order to fit snuggly up against the heel and end block respectively. I started with the end block. A straight edge was laid on top of the assembly, aligned with the brace notches for the lower back brace. This way it was simply a matter of butting a ruler up against the end block and measuring the distance to the straightedge to establish the length needed for the back graft to fit up against the end block.
This was done while the assembly was lightly clamped to the solera, just enough to keep it flat and in contact with the cork shim all around. If I hadn't clamped it, the body would have been tilted upwards slightly because of the neck angle.
The back graft was trimmed using chisels only. I thought of sawing it first but decided to try just to make the cut with a chisel using the polished surface of the back as a mirror to monitor the squareness of the cut. If the chisel wasn't held perfectly square the mirrored image would not be in line.
This method worked rather well, but as the cut got deeper the chisel started to crunch the work a little creating a slight peek where the cut was done. Luckily I had to trim the back graft a little further which took care of the problem, not that is was really too a big deal.
The graft was trimmed at the heel end in the same manner.
GLUING THE BACK ONTO THE ASSEMBLY
With the back held in place I was able to turn the guitar around and see the fit through the soundhole and it looked like everything was in the right place. I did a dry run with clamps as I knew that was going to be a cumbersome ordeal, more on that later.
A long bead of glued was laid on the rim and spread out with a finger tip. I tried to be a little more generous than I've been in the past as I knew the kerfed linings would provide a lot of nooks for the glue to escape into. I spread the glue to a semi transparent film that covered the rim, heel and end block completely. Cumpiano suggests doing this with two fingertips forming the glue to a little peak in the center of the rim. I tried that too, but I don't know if it made much difference in my case. It was as if the glue tended to collect towards the center of the rim anyway.
While I was spreading the glue I suddenly realized I forgot to write a little inscription to my two sons that I'm making the guitar for. And so I stopped the glue spreading and grabbed a soft pencil and wrote: "Til Frederik og Albert, fra Far, 31. marts '08" in mirrored writing while my hands were shaking and the adrenalin was rushing. Being a one-man-band, I also had to take photographs all while the glue was slowly drying. Probably not the best way to go about things, but what is done is done.
Nevertheless, I eventually got the back placed on the rim and attached the first spool clamp on the end block, next up a big Bessey bar clamp was put on the heel with the 15' radius template doubling as a caul. Then spool clamps was added at the widest place of the lower bout, then the upper bout, the waist and slowly all the spool clamps was put in place covering the entire rim.
TRIMMING THE OVERHANG
After 2 hours all the clamps were removed and it was time to trim away the overhang. I tried to do this with a chisel as I did when I trimmed the overhang of the soundboard, but it was quite difficult to work the hard bubinga. Instead I resorted to my two spokeshaves, a flat bottomed one for the bouts and a curved bottomed one for the waist area.
The blade were set so it was fully detracted at the side that was on top if the guitar body, while on the other side the blade was protruding a little. This way I virtually eliminated the danger of accidentally taking material off the sides. I started using the deep cutting side of the spokeshave and slowly moved the tool over to a finer cutting part as the work progressed.
When I was done I took the guitar off the bench and just for fun tried to hum into the soundhole to find the natural resonance of the soundbox. It ended up being an A - 110Hz or perhaps a tad sharper than that. I have read some makers aim for somewhere between a F2 and F2# - about 90Hz, but since this is 3/4 sized instrument it is not surprising that it ended up a little higher.
OOPS - A FEW MISHAPS AND A NOTE ON THE SOLERA DESIGN
Just before I was going to glue the back on I decided to trim the overhang from a 1/4" down to, well, something less. As I still had the template line showing on the inside of the back plate I quickly took it to the bandsaw and trimmed it down about an 1/8".
But when I dry fitted the back I realized that somewhere along the line (probably when I marked for the notches) things had gone a little out of whack and the back was sitting 'low' on the assembly, sticking out at the end block and being about 1/16" short at the heel.
In retrospect I should either have left the back alone or marked a new saw line while having the back in place on the rim. In itself it is not to big a deal as the mishap will eventually get evened out by the binding and purfling, though that is not really the point. I must remember that one for next time.
As I took the clamps off after the gluing I also noticed that the back had slid a 1/32" to left at the end block, something I didn't pay any attention to as I thought the fit was tight enough to hold the plate in place. Obviously not! This will have some impact on whole look of the guitar as I now have to inlay the end graft a little off center in order to align it with the back center. I just hope it won't so much that it will be noticeable to the naked eye.
I really liked the spool clamps, however, it is now apparent that I would have been much better of cutting slots for them all the way around the solera instead of just doing it for the support blocks and drilling holes for the rest. Unscrewing and screwing wingnuts on 36 spool clamps takes considerable time in context of a gluing procedure and inserting the clamps into holes from underneath the solera is no laughing matter either. Sliding them through slots, preset in size, would have made the whole process so much easier.
I think I'll have to rethink my solera for the next one.
I cut a slightly oversized 1/8" thick slice of mahogany and glued it to the heel, using the leftover as a caul against the slice and a small piece of 1/2" plywood underneath the heel. As it turned out, it was not as bad as I first thought. After the rim had been taken down to it's final height it became apparent that I could have gotten away with a slice of veneer for the last 1/2" of the tip of the heel, but it was good to be on the safe side.
Once the glued had dried I trimmed the sides and end flush with a chisel and took some of the bulk off the top with a block plane.
RADIUS SANDING THE SIDES TO FINAL WIDTH
For this I had to remove the support blocks on the solera, as they were protruding up over the rim. Instead I held the guitar in place in three places; With two clamps on the neck and with two low makeshift blocks clamped to each side of the lower bout. This provided amble stability and support for the sanding job while not getting the way.
I started by marking the final height of the sides at the heel and end block - 78.5mm and 83.5mm respectively. Two reference marks were also made on each side at the waist, not as final marks but as marks that would enable me to monitor that each side was taken down evenly.
Once all the marks were in place it was time to start the grunt work. First I sanded that entire rim with an 80 grit sanding disk and the 15' foot radius hollow form by rotating the disk and paper back and forth. The sanding left a lightly scrubbed up surface on the rim that provided a great visual reference for where the high spots were.
The disk has a selfadhering backing but I opted not to stick it in permanently, partly because I just learned that I had to ad some sort of finish to the hollow form in order for the adhesive to stick and I simply just wanted to get on with it and partly because the convenience of having the bare disc for a multitude of other purposes.
Once this was established, I continued to shave the rim down with a spokeshave and the little fence jig I used for the soundboard side of the rim. The spokeshave jig was set to about 2º, an angle that roughly fitted the sanded edge. When I had worked my way around the entire rim, which included planing the heelblock down with a blockplane, I switch to the sanding disk, sanded, measured and determined where more stock needed to be taken off and did so with the spokeshave. In this fashion the rim was slowly worked all the way down to its final dimension.
I had to be careful not to get carried away when using the sanding disk, and only use light pressure as the radiused hollow form itself was a little wobbly being only 5/8" thick. At times I resorted to holding the edge with one hand while exerting pressure down with the other hand over the center of the hollow form.
Last the rim was sanded lightly, first with 150 grit paper, then with 320 grit to remove the scratches left over from the sanding disc. A little piece of scrap spruce was used as a sanding block, and basically pressed against the rim with my thumb. This eliminated most of the danger of rounding the rim that I feared could have happened had a bigger block been used.
MARKING AND CUTTING THE BRACE NOTCHES AND FITTING THEM TO THE BACK
Fitting the back to the rim was very similar to fitting the soundboard. The main difference was that on the back I didn't have to make individual feet for the braces, but rather had to cut little notches in the linings to house the much shallower brace ends. Also, the back graft had to be trimmed to butt up against the heel and end block.
The back was laid on the rim and clamped to the end block, using a 6mm shim to raise it back above the rim at a height equal to the brace ends. The rim was then marked on each side of the protruding brace ends with a scalpel. I started by doing these marks in white pencil but found it difficult to do with precision and so switch to using a scalpel instead.
While I was at it I also scribes the braces ends to length up against the rim.
Once these marks were down, nine in total on each side, I laid a ruler on top of the assembly and aligned it with each two corresponding marks and scribed marks across on top of the linings with a scalpel. A mark was also done about 1/4" down the sides of the linings, to indicate the depth of the notches.
With a little razor saw I did two cuts for each notch on the inside of the mark, holding the saw approximately at 45º angle, ending the cut where the linings meet the sides and at the bottom of the notch. After that the waste was cleared away with a 1/8" chisel until the notch was all squared up.
Finally brace ends were trimmed to about 2.5mm inside the template, first with a razor saw and the cleaned up with a chisel and it was time to do the final fitting of the notches.
It proved to be quite a fiddly ordeal. Suffice to say that the notches didn't line up perfectly and I had a hard time determining which notches were cut slightly out of alignment, which were not, which were simply just too narrow and what not. Suffice to say, I was quite surprised to find out how tricky this part of the building process turned out to be.
Eventually I got it to a point where the braces were seated fairly nice and firmly, with only the odd gap showing here and there. Hopefully not too big a deal and if my Alhambra Luthier Model is anything to go by it's not an uncommon feature.
The depth of the notches were a little easier to deal with, and more importantly, trim to a tight fit. Here I set my calipers to the height of each brace end and used that as a reference to pare the bottom of the corresponding notch to the proper depth.
Last I cut little bevels on the ends of the braces to make room for bits of waste that hadn't been cleaned out of corners of the notches and to give excess glue somewhere to go to, other than being squeezed out in the open.
CUTTING THE BACK GRAFT TO LENGTH
The back graft also needed to be trimmed in order to fit snuggly up against the heel and end block respectively. I started with the end block. A straight edge was laid on top of the assembly, aligned with the brace notches for the lower back brace. This way it was simply a matter of butting a ruler up against the end block and measuring the distance to the straightedge to establish the length needed for the back graft to fit up against the end block.
This was done while the assembly was lightly clamped to the solera, just enough to keep it flat and in contact with the cork shim all around. If I hadn't clamped it, the body would have been tilted upwards slightly because of the neck angle.
The back graft was trimmed using chisels only. I thought of sawing it first but decided to try just to make the cut with a chisel using the polished surface of the back as a mirror to monitor the squareness of the cut. If the chisel wasn't held perfectly square the mirrored image would not be in line.
This method worked rather well, but as the cut got deeper the chisel started to crunch the work a little creating a slight peek where the cut was done. Luckily I had to trim the back graft a little further which took care of the problem, not that is was really too a big deal.
The graft was trimmed at the heel end in the same manner.
GLUING THE BACK ONTO THE ASSEMBLY
With the back held in place I was able to turn the guitar around and see the fit through the soundhole and it looked like everything was in the right place. I did a dry run with clamps as I knew that was going to be a cumbersome ordeal, more on that later.
A long bead of glued was laid on the rim and spread out with a finger tip. I tried to be a little more generous than I've been in the past as I knew the kerfed linings would provide a lot of nooks for the glue to escape into. I spread the glue to a semi transparent film that covered the rim, heel and end block completely. Cumpiano suggests doing this with two fingertips forming the glue to a little peak in the center of the rim. I tried that too, but I don't know if it made much difference in my case. It was as if the glue tended to collect towards the center of the rim anyway.
While I was spreading the glue I suddenly realized I forgot to write a little inscription to my two sons that I'm making the guitar for. And so I stopped the glue spreading and grabbed a soft pencil and wrote: "Til Frederik og Albert, fra Far, 31. marts '08" in mirrored writing while my hands were shaking and the adrenalin was rushing. Being a one-man-band, I also had to take photographs all while the glue was slowly drying. Probably not the best way to go about things, but what is done is done.
Nevertheless, I eventually got the back placed on the rim and attached the first spool clamp on the end block, next up a big Bessey bar clamp was put on the heel with the 15' radius template doubling as a caul. Then spool clamps was added at the widest place of the lower bout, then the upper bout, the waist and slowly all the spool clamps was put in place covering the entire rim.
TRIMMING THE OVERHANG
After 2 hours all the clamps were removed and it was time to trim away the overhang. I tried to do this with a chisel as I did when I trimmed the overhang of the soundboard, but it was quite difficult to work the hard bubinga. Instead I resorted to my two spokeshaves, a flat bottomed one for the bouts and a curved bottomed one for the waist area.
The blade were set so it was fully detracted at the side that was on top if the guitar body, while on the other side the blade was protruding a little. This way I virtually eliminated the danger of accidentally taking material off the sides. I started using the deep cutting side of the spokeshave and slowly moved the tool over to a finer cutting part as the work progressed.
When I was done I took the guitar off the bench and just for fun tried to hum into the soundhole to find the natural resonance of the soundbox. It ended up being an A - 110Hz or perhaps a tad sharper than that. I have read some makers aim for somewhere between a F2 and F2# - about 90Hz, but since this is 3/4 sized instrument it is not surprising that it ended up a little higher.
OOPS - A FEW MISHAPS AND A NOTE ON THE SOLERA DESIGN
Just before I was going to glue the back on I decided to trim the overhang from a 1/4" down to, well, something less. As I still had the template line showing on the inside of the back plate I quickly took it to the bandsaw and trimmed it down about an 1/8".
But when I dry fitted the back I realized that somewhere along the line (probably when I marked for the notches) things had gone a little out of whack and the back was sitting 'low' on the assembly, sticking out at the end block and being about 1/16" short at the heel.
In retrospect I should either have left the back alone or marked a new saw line while having the back in place on the rim. In itself it is not to big a deal as the mishap will eventually get evened out by the binding and purfling, though that is not really the point. I must remember that one for next time.
As I took the clamps off after the gluing I also noticed that the back had slid a 1/32" to left at the end block, something I didn't pay any attention to as I thought the fit was tight enough to hold the plate in place. Obviously not! This will have some impact on whole look of the guitar as I now have to inlay the end graft a little off center in order to align it with the back center. I just hope it won't so much that it will be noticeable to the naked eye.
I really liked the spool clamps, however, it is now apparent that I would have been much better of cutting slots for them all the way around the solera instead of just doing it for the support blocks and drilling holes for the rest. Unscrewing and screwing wingnuts on 36 spool clamps takes considerable time in context of a gluing procedure and inserting the clamps into holes from underneath the solera is no laughing matter either. Sliding them through slots, preset in size, would have made the whole process so much easier.
I think I'll have to rethink my solera for the next one.
BUILDING UP THE SPANISH HEEL
RADIUS SANDING THE RIM
SHAVING THE RIM
FINISH SANDING THE RIM
MARKING RIM FOR BRACE END NOTCHES
MARKING RIM FOR BRACE END NOTCHES
CUTTING BRACE END NOTCHES
CLEANING OUT BRACE END NOTCH WASTE
MARKING BRACE ENDS
CUTTING BRACES ENDS
PARING BRACE END WASTE
TRIMMING BRACE ENDS LENGTH FOR FINAL FIT
MEASURING BACK BRACE END DEPTH
MEASURING BRACE NOTCH DEPTH
BEVELING BRACE ENDS
MEASURING FOR EXCESS BACK GRAFT
CUTTING BACK GRAFT
PARING EXCESS BACK GRAFT WASTE
ADDING GLUE TO THE RIM
GLUING THE BACK TO THE RIM
SPOOL CLAMP CLOSE UP
TRIMMING BACK PLATE OVERHANG
THE COMPLETE SOUNDBOX
THE COMPLETE SOUNDBOX
RADIUS SANDING THE RIM
SHAVING THE RIM
FINISH SANDING THE RIM
MARKING RIM FOR BRACE END NOTCHES
MARKING RIM FOR BRACE END NOTCHES
CUTTING BRACE END NOTCHES
CLEANING OUT BRACE END NOTCH WASTE
MARKING BRACE ENDS
CUTTING BRACES ENDS
PARING BRACE END WASTE
TRIMMING BRACE ENDS LENGTH FOR FINAL FIT
MEASURING BACK BRACE END DEPTH
MEASURING BRACE NOTCH DEPTH
BEVELING BRACE ENDS
MEASURING FOR EXCESS BACK GRAFT
CUTTING BACK GRAFT
PARING EXCESS BACK GRAFT WASTE
ADDING GLUE TO THE RIM
GLUING THE BACK TO THE RIM
SPOOL CLAMP CLOSE UP
TRIMMING BACK PLATE OVERHANG
THE COMPLETE SOUNDBOX
THE COMPLETE SOUNDBOX
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