Acoustic Guitar Construction

While locked up in social distancing I have been working on a commision. This will be a Martin (xbrace) style 00, 12 fret short scale guitar. It has been awhile since I have built an X-braced guitar but for the playing style and what this client is looking giving him a Martin sounding guitar is the right choice. Going back and forth a bit I assembled a kit from which to build.



With some really figured and flamed Hawaiian Koa. I felt really guilty about the Koa as it was an auction item in the Seattle Lutherie Group auction that went way below cost.


Unfortunately the sides were a bit too wild and their was a flaw in a dark figure line on a side that seperated when bending. Amazingly not on the venetian cutaway side but in the wide curve on the non cutaway side.

I did have a lot of Koa so I grabbed another set of sides that were a good color match. Still figured but not as much flame. Same back as the previous picture just different lighting.



So the second set of sides I thinned to just under .080" and I scraped the inside of the cut away to .070" from just past the waist through the cutaway bends to the end.



I sprayed them both with supersoft II, wrapped them and let them set under some weight (a big piece of ebony) overnight.





No problem with these bends in my fox style bender. While bending the cutaway I heat the bottom side of the cutaway area with a heat gun. I really took my time screwing in that last tight bend. I also used my stainless spring steel slats as my soft steel ones seem to ebonise koa. I learned that on my set of broken sides. It can be sanded out but I could also avoid it using stainless. I really need to take care removing the cutaway side as the spring steel can blow it up. (happened to a friend of mine once).









To get the heel block just right I put poster board under the guitar sides in the mold (not shown) and I traced out the pattern for the heel block. I glued that to chunk of mahogany and cut it out on the bandsaw.



I used to try and glue in the heel block in one go. Now I glue first to the non cutaway side and then glue the cutaway side to the block. To assure alignment I set a couple of clamps while the sides are in the mold to hold it in position. I then remove the clamped block and side from the mold to make sure I can really clamp it.







I also glued on the tail block, a cut and slight shaped piece of mahogany.



I radiused the back to 15' and the lower bout of the top to 30'. First the back. My side templates are really close to the correct shape for both sides. They are close enough that I cut the sides pretty close, leaving just enough extra to safely put the radius on the heel block without making the guitar too thin.

You can see in the first picture before doing any sanding the rims fit tightly on the radius dish



I do a combination of sanding and planing. I mark the top of the rims and the blocks with pencil. I sand for a bit, turn the sides over and plane where the pencil mark was sanded off. I repeat this unto the heel block is completely sanded\ planed to the correct radius.





When the back was radiused I turned it over and put tape on the blocks. The tape is to stop me from sanding the back on the top's radius dish. This was a procedure I had to learn multiple times.



I leave the dish back side down in the 15' radius dish and radius the top firstI radius the lower bout to just past the middle of the waist with a 30' and then use a flat disk to clean up the upper bout.



I went ahead and installed some kerfed linings on the back side. Pretty straight forward. I do remove a bit from each of the kerfed blocks around the cutaway so that they do not run into each other on the tight bends.





I took it back to the 15' dish and cleaned the kerfed linings up. I will do the top linings after I have a top and I can make sure the rims are profiled for the correct neck angle.





On to the top and back tomorrow.

Thanks for the build thread. This will be a very nice little guitar. I love 00 12 frets! especially one built the woods you have chosen. looking forward to watching the progress.

Just a little more progress I joined the back and the sides and am ready to start the rosette. My plan is to reflect a bit what martin does with 3 separated rings. The inside and out side ring will be BWWB where the W will be maple. The inside rung will be a wood ring With a thin black purfling line on the inside an out of the ring.

Not show but I did measure the young's modulus of the back and top plates using the Tap method in the Gore/Gilet books. THis gave me my target thickness for the top and back. The top will be just under 3 mm and the back will be 2.6 mm.

I cleaned up and joined the edges with a lie nelson low angle jack plane (I love it) and used my LMI jointing jig to glue the sides together. I am finally getting good results with a plane. For both of the plates when put together before clamping I already had a full line of squeeze out and the two plates sort of sucked together.







After I glued the top, one of the plates had a dark area right on the seem edge. I thought it would sand out, but ultimately decided ti wouldn't. I ripped through the joint, cut out the color and rejoined





Much better

Sorry it has been awhile. I have made a lot of progress and taking pictures. I have been slow to update the build blog as I have been distracted with covid 19. When I am on a computer I am obsessed with looking at news stories or facebook and I never get posting. I may break up my progress into multiple post to keep them from getting too long. Thanks goodness for the ability to organize my pictures in the order taken.

For a rosette I decided to give a nod to martin with a three ring rosette. To keep it mine I have the inside ring include a Koa wood ring. My first rosette did not pass my quality control so I tossed my first top. I did not feel too bad as I was already thinking through how I was going to provide a bit of cross grain stiffness as the top I had did not have it. The inner and out rings were two bwb purflings (maple for the white). I did not have the correct size bit for my good router (you will see it in a bit) so I pulled out my dremel. It made such a horrible channel that after some futile ideas I tossed the top. Hey always need back strips, soundhole donuts and popsicle braces so not a big loss.



I think in this picture you can see how bad it looks. I think the issue was both bearing runout and a shitty bit.



I ordered some good router bits on amazon and while waiting thicknessed and added the back strip on to the back. Amazon is fast in Seattle.







WIth the new router bit a Freud 1/16" double flute straight bit the new rosette came out clean. I did not bother taking pictures of joining my second bearclaw sitka top.





Much nicer.


I joined some koa cutoff



I used a tape method to glue the two half. The tape is applied with the one piece at an angle to the other. The tape tension pulls the parts close when they are flattened.





I did not take a picture of how I made the second koa ring but I did the first the same way. I keep the router at the same depth used to make the channel in the top. I make an inside and outside cut so the ring is the correct size. Then I run it upside down through my thickness sander until the ring drops out.

Here are pictures showing from the first rosette showing how I did it.





Here you can see the difference between the two router setups. The second picture was a second attempt to get a clean ring using the dremel.



Here it is right after gluing everything in but before I leveled the rosette.



I used a scraper to level the rosette. It was timely as Robbie O'Brien offered a free live online sharpening class. I tried his method. I did end up with a very sharp scraper. It involved multiple sharpening stones and a burnisher. I will probably stick with my file and a burnisher method. Not quite as sharp but fast! I did get through the entire leveling process with one sharpening and it took shaving till the end you can see the few Koa shaving what cut at the very end. So maybe with Robbie's method one ends up with much better edges.



At this point one can see how the body is going together.





Note the headstock template, I made it after a free online CAD class given by Paco Chorobo a spanish luthier and Flamenco player. He had us download LibreCAD a very full function 2D open source CAD program. The class was really good.



To close this post I profiled the top and covered it with 5 mil mylar.

Moving on ... I leveled the back kerfed linings in the 15' radius dish and spent a bit of time getting the tops profile correct with a combination of a 32' radius dish and a flat dish. I use the radius dish mostly on the lower bout and the flat dish mostly on the upper bout. I want the body to have close to the correct neck angle before gluing on the linings. Not shown ... I clamp on the unbraced top and use a straight edge laid on the fret board extension area and projecting over the saddle position. I want to see 2-3 mm of height over the top at the saddle location at this point. That way I know I am close. I will fine tune the top rim profile before closing the box.





I started to glue on the kerfed linings



While waiting on the linings I cut a scarf joint, cleaned the faces with a plane and glued the headstock to the neck.







While the neck glue was curing I install a bunch of side supports into the rims







I cleaned up the neck joint and neck face with a plane, laid out the nut and the 12 fret and made a stacked heel out of the remaining neck wood. It was really close, I almost had to use another block of Mahogany for the heel, but I did not have any that was as light as this piece.



Before I forgot I end stalled my slight more fancy end graph treatment. The center strip is ebony with a black and peach wood purfling. I used a scraper as a straight edge and a scalpel and chisel to cut and clear the channels





Now I am ready to start the braces

To brace the top I made a bunch of 5/16" brace stock. I wanted it all to start at 5/8" tall so I pulled out my new band saw guide and ripped a 1 mm strip off the brace wood. I cleaned up the brace wood in my belt sander until it was just 5/8" tall.







I stacked some guides to get my 5/16" width and ripped the board.



I cut the x brace legs to size and marked out a 30' radius on the bottom



Planed them close and (not shown) finish sanded the bottom on my radius stick.



I transferred the angle of the X from my plans to the braces and made the first cut with a razor saw. I use the saw like a mirror to make sure I am straight up and down. I set the brace in the vise so that cutting down to the vise is the correct depth. I cut both braces at the same time. one is cut bottom side up the other topside up.



Using the first cut and a bit of brace stock as a guide I mark out the second cut with a scalpel, cut to depth with the razor saw and clear with a chisel.



I must have cut the angle close!



I cleaned up the radius of the X brace on my radius dish.



Marked out the brace pattern on the top using my template.



I glued it down in the radius dish in my go bar deck.



I did a rough scalloping of the x braces. I place peaks 3" from the edges I start the scallop right at the bridge patch.



I double and triple check that the bridge patch is correctly located.

Using a template I cut out a bridge patch out of some sort of rosewood. I think Panama Rosewood. I make double and triple check that the bridge patch is correctly located.



The cats were even there to check



Sure that it was correctly located I glued it to the top. I could have used a caul, but I have a lot of go bar sticks.



Using a bandsaw I preshaped the rest of the braces. Probably the last time. I find them just as easy to carve once glued to the top, like I did with the X brace.



I radiused the braces and glued them top the top on a radius dish.



I only radius the ends of the transverse brace leaving 4 inch in the center flat. This helps keep the top flat under the fretboard and avoids over arching the top. I have a special caul with the opposite shape when I glue it to the top.



The arch of the top is perfect. The drill bit at the saddle location is 2.5 mm the exact height I was looking for with the straight edge flat on the neck extension area.



A bit more rough carving and gluing on the popsicle brace gives me a top ready to mate with the rims.

With the top braced I moved on to the back. Before bracing the back I need to prepare some back bracing stock. I rip some brace wood in my bandsaw slightly oversized and the sand to size on my thickness sander. I then use my router table and a 17.5° degree bevel bit with a guide bearing to put a gabled shape on the top of the braces. I made a special jig just for this operation.
I have some screws to hold the brace in the jig and run one side then the other through the router.













I got the brace stock to length and measured where I wanted the braces and made a single cut with a scalpel through the back strip for each brace using a machinist square. I then come back using the brace and the square to cut the the second cut ensuring a tight fit.



Not shown but I just clear and clean the channel with a chisel.

With the channels cut I put a round shape on the back strip. I used to do this before cutting the channels but I found I could get straighter cuts when the strip was still flat. Not really a big deal, but it helped. To make the radius block to sand the strip I very carefully opened my drum sander and carefully sanded the radius on its 4" drum.





I used a radius template to draw a 15' radius on the bottom of the braces and used a plane followed by an LMI brace sander jig to profile all of the braces.







To glue the pointy braces in the gobar deck and I take scraps of the brace stock and glue it together forming a prefect caul for these braces.





As my plan is to make this an active back I used the fancy looking back design from Trevor Gore. It combines a three transverse brace pattern with the lower transverse surrounded by a set of radial braces. These braces were also radiused and glued up in the go bar deck. It was a little tough to keep these braces from wanting to scoot when clamped so I did not get pictures except one while setting to to glue in the gobar deck.



I tapered the ends of all of the braces down to about 2 mm. I use a simple tool to make sure I get the final height of the brace correct. It is so simple but it saves a lot of time. It takes me under 30 seconds to carve an end.







With the top and back braced, I prepared the rims for the top and back.

I clamp the top and or back onto the rims while the rims and the mold are clamped making easy access. I make the brace location with a scalpel to get an accurate mark. I also pencil the cut to make it easier to find the scalpel mark when I transfer the cut lines to the top of the linings.





I route the inlets into the linings with a pencil mil grinder. It is in a real simple base I bought from John Hall (Blues Creek guitar) To set the height I use the actual brace. Even though all of the braces should be the same I still set for each brace.



I trim all of the brace ends with a razor saw and a chisel.



Now the top and back both fit on the rims. I am ready to clean up all of the braces and inside of the guitar sanding to 220. But I leave that for another day.





I am excited about this bearclaw top once under finish. Even with the thin layer of shellac it is taking on that 3D look.