Acoustic Guitar Construction

I finished closing the box this morning. The past couple of weeks I have been play with two aspects. Before gluing on the top I tuned the tops braces. With the braces glued on and scalloped the top was way to stiff. So I trimmed the braces, mostly around scallops until the top had a pretty good tap tune. Still stiff but not trusting my ears with a free plate I glued it to the rims. I continued tuning the braces keeping track of tops deflection under a 5lb load, the tap frequency with an open back and I tried to see if it changed with a taped on back. In both cases the tops resonance was close; open and with the back taped on. I follow guidelines for how much to trim the braces from a top voicing class I have on DVD from Chris Everett. He does a lot by feel and sound. I relied on his suggestions on where to try removing wood and safe limits. It was interesting to watch the top resonance as I worked on the braces. If for example I lowed the brace inside of the scallop and the resonance moved close to my target I took more off. My order was the tone bars scallops, the scallops on the xbrace, the length of the peaks and then the peaks themself. Ultimately with the top a bit over 200 Hz I stopped and cleaned up the back and glued it on. My target is between 180 Hz and 190 Hz. The bridge and stinging the guitar will lower the top's resonances. Also I need to sand the top and I will need to lower the back resonance. I think I am good shape. The tap tone is great right now.





My biggest effort this guitar went to nailing the neck angle by design and construction, not struggling late in the build to get it right. I do most of my work with the neck angle before I touch the neck as the correct neck angle needs to be in the top such that when the fretboard extension is glued flat to the top a straight edge on the extension should project over the saddle location of the top at a height that combined with the desired string action the strings will be between 12 and 14 mm over the top. My target is 14 mm.

As shown earlier a combination of 30' radiused braces and a mostly flat transverse brace (radiused on the ends) gave me a top with just the correct geometry. I look for a projection of 2.5 mm. One caution this is calculated using my fretboard thickness and my desired action; it is not a magic number. In my case in 14 mm = 2.5 mm + 6.5 mm fretboard + 2 * 2.5 action + 1 mm fret - 1 mm (string tension).



I had already profiled the top of the rims using a 30' radius dish for the lower part of the guitar and a flat dish for most of the upper bout. I checked the fit of the top and adjusted the profile of the rims so the top just fit on with no forcing. I was very close a couple of swiped with a plane on the waist allowed the top to fit perfectly. I doubled check my neck angle with the top clamped to the rims.



I glued on the top and trimmed the overhang with a spiral flush cut router bit , I not sure where the pictures went; imagine a bunch of cam clamps. When I checked the neck angle it was flat; it tool me a couple of days before I realized everything was just fine. More than that I got a new idea on how to adjust a neck angle before gluing on the back.

Note in the following picture that I clamp the neck heel tight to the mold I also clamp the waist to the mold to keep the rims squarely in the mold. I do all of the profile work on the rims with the two clamps inplace. John Hall uses wood screws to attach the heel block to the mold and leaves them there until the box is properly closed.



I got the wrong neck angle with the guitar out of the mold. Until both plates are glued on the angle of the heel bock is not set.

Here is a demonstration of how a slight change in the heel block angle can affect the neck angle In the first picture you can see a ruler clamped to the heel bock is flat against the top; virtually no angle.



With a minimal amount of torque on the neck heel the ruler lifts right off of the top showing close to the correct angle.



So I put the guitar back in the mold with the two inside clamps.



And a recheck of the neck angle; it went back to where I wanted it.



When working on a classical guitar with a spanish heel the neck angle is set when the back is glued on. In that case the angle can be adjusted with shims under the top at the body join and having the neck clamped down while gluing on the back. It occured to me that I could fine to my angle at this point by playing with how the heel is clamped to the rims. Moving the spruce clamping rod I am using off the rims center made a slight change. Also I was able to add a thin shim on one side between the heel block and the mold and that changed the angle a bit.



So with the body properly clamped to the rims I pulled out the cam clamps again and glued on the back.



So two major learnings:

If working with a mold LEAVE the body clamped in the mold until the top and the back are glued on. Boths plates are required to be glued on to fix the heel block angle and the fretboard extension angle. (I am embarrassed to relearn this as I make classical guitar and knowing this is part of that build process. )

One can make minor adjustments to the neck angle tilting the block before gluing on the back.

All is good

I have been making a bit of progress, even with all the isolation time I am not killing myself in the shop. I put in the sound port. This step always makes me nervous. But it went well without issue. In the pictures you will notice a series of ovals of slightly larger sizes. If I muck up the first I just move on to the second ending up with a slightly larger sound port. I managed to make it the size I wanted.

To start I hogged out some bulk with a forstner bit.



I got as close as I dared with the mill grinder. With 4 mm of wood I am really taking off too much wood with the small bit I have. If I am not careful the grinder likes to run a bit.



Then I just used a series of rasps and a bit of sandpaper to carve the wood right to the template line.











While waiting on some purfling I put some work into the neck.

I used my router table to make the truss rod channel.



My neck angle is going to be 1 an a bit. I used some trig opposite side from adjacent and angle to determine the height of a shim to give the correct angle on my table saw sled.



You can see the shim tilts the neck just enough for the angle I want. I also cut a 3° angle on the cheeks as well to fit the body. For a 00 steelstring 5° would be better. Bit 3° was close enough and I use 3° for my classical guitars.





I have this big tenoning jig for my table saw. But it sure was a lot easier to set it up on my band saw and cut the it out.



I made the tenon a tad big allowing me to size and fix centering issues with a rabbet plane.



I cut the mortise into the guitar for the neck using a luthiers tool body clamp. It is nice because ti has a bit of yaw adjustment so that I can place the template right on the center line. On a cutaway with the neck flush to the side check and recheck the center line for the neck. The center line to the cutaway defines the width of the neck at the body join. It is a pain to goof this up.



Now just swap out the centring template for the mortise and route away



YIKES! not that way. I looked at it for a moment or two thinking somethings wrong. It would not be unlike me to spend all this time setting a cut and running the guitar.

I turned the jig around and recentered and finally routed out the mortise. Sorry no pictures. I use a DEWALT DW621 with a template guide to make this route. It is the only thing I do with this router.



I cut most of the excess tenon out on my bandsaw and cleaned it up with a chisel.





Amazingly the joint and angle are just like I want them at this stage.







I put a 15° angle on the peghead veneer and glued it to the head stock. Sorry I did not take a picture gluing it on.
I clamped a small brass stop where I wanted the headstock veneer and made sure it was square.





I took a beginners free covid CAD class from a spanish luthier Paco Chorobo and designed a headstock shape to replace the slot head that my 00 usually has. He has a registration link on his home page https://chorobo.com/en/home/. With the template on I roughed out the headstock shape. I will probably finish the neck tomorrow or the next day.

The body still needs to be bound but I decided to finish the neck before the bindings. Curious about how well I got the neck angle, I doubled taped the bridge on and checked.
Just like downtown!


A pretty clean fit as well.


For the bolt on neck I only use a STI-225 Brass self tapping insert. I have had to find these a few times. the last time was on amazon. https://www.amazon.com/4-20-Tapping-Thr ... B002GPHRSA. These bolts are great for end grain applications. The slot on the bottom are the knives for cutting the threads not a screw drive slot. It is confusing as there are other threaded inserts that have a screw driver slot. Here is how I set them up to be installed.



I marked out my insert holes.

I uses a 5/16 inch drill bit to drill. I used this fancy hole drilling jig I picked up at a hardware store to drill straight holes on the tenon. I think this is the first time I remembered to use it and it worked out great. In the past I used my drill press by rotating the table on edge. The tool also worked as a clamp proving some support to the tenon as well.



I have a set of hole centers that work great for transfering the hole pattern to the heel block in the mortise.







I installed the insert and sealed the threads with thin CA. Careful as it is a pain if CA gets in the threads.





I use the same insert 5/16th bit to drill the holes in the mortise. The 5/16 gives a bit of slop to make it easy to find the insert.

I any case the neck bolted on with out issue. When I really bolt the neck down I will use belleville washers to help lock the bolts in.


I also drilled for the truss rod and notched the body to allow installation of the neck with the truss rod. I also made sure that I had access to the truss rod.











Lastly right before this lunch break I cut a close profile on the neck and used my safe-t plane to thickness the headstock.





Not shown I also use the Safe-T plane to taper the neck. I put a shim at the nut location that matched the amount a taper I want. For example if my taper was 16 mm to 19. I will use a 3 mm shim. With this work the neck is pretty well roughed out. On to tapering the fretboard

I finished today tapering the fretboard. Not much new. I did move away from calipers for laying out the neck as I always ended up a .25-.5 mm off using 2 separate measurements. Today I use a handy ruler I got from stewmac that has a centering layout on one edge. I do not end up with accumulative errors that I need to fixup.



I ripped close to the layout lines on the bandsaw. cleaned to the line with a bench plane.





I used a couple of 1/16 drill bits to index the fretboard on the neck



The final step was to trim the fret board. I used a 3" radius

Before gluing on the fretboard to the neck I did another pass at all of the neck angles as it is a pain to change with the fretboard glued on. The neck angle was great but the neck was tilted just a bit toward the bass side. With a squared off heel it is really easy to change with a plane on the heel cheeks. This went OK but one caution and a tip. When planing the heel cheeks it is easy to blow out the back of the cut. So always plane away from the fretboard face. I still had extra wood on the heel cap side but it still helps to relieve the edge of the cut about the amount you will remove. I took a few strokes off the heel cheek but the angle did not change. If this happens do not take more off; rather find what is holding the neck to keep it from moving. Tip. I fit a thin sheet of 400 grit sand paper under the cheeks all the way to the tenon and with the neck pushed down pull it out from the side. Do it a couple of times. Pull the neck and check where the sandpaper is hitting. WIth a chisel I remove any wood not on the heel cheeks that is being touched by sand paper. I repeat this until only the heal cheeks are being marked and being marked all the way across. On the cheeks I only remove the lightest of shaving from the area marked by the sand paper. Off of the heel cheeks I am more aggressive.

I used a centering tool when I checked for center and when I was happy I rechecked the neck angle. It should not have and it did not change.





I remember to install the truss rod and using the index pins I drilled and a long caul. Glued on the fretboard.





When I started to prepare the neck for carving, I realized I had an issue with the scarf joint location. This neck layup was originally made for a classical. I could not thin the headstock and keep the scarf joint right under the nut like I wanted. If the scarf joint was properly located I could have worked in a volute that blended properly with the neck shaft's ebony strip. This was not entirely a surprise so I installed a Koa back strip. I used the Safe-T plane to remove 2 more mm from the back of the head stock and hand blended a transition to the neck.



I made the tight bend on a hot bending iron. The koa bend without issue.



With some carefully placed clamped the curve closed really well.



After I let the wood dry still clamped I used some structural epoxy and glued the backstrip on.



I trimed all of the excess koa off and moved on with the hope that the koa backtrip would shape correctly as I naturally carve the neck.

I alway layout the first set of facets on paper and the neck. WIth this simple cathedral shape once the primary facets are carved I can see the addition facets without penciling them in.



I hog most of the wood off with a spokeshave and finish the facets with a rasp. on the nut and heel side.







I literally just go back and knock off the corners of the facets with both the spokeshave and the rasp. I then go back and knock off the new corners with the rasp or a scraper.

Here it is getting close. After this point I cleaned up headstock transition and blended it all into the neck. I use a combination of chisels and scrapers for this work.



I drew a rough outline of the heel and planed and rasped a rough shape. It is pretty close. I will finalize the heel once a I decide on a heel cap.



First I planed in the angle I wanted



Then I started shaping the corners. While shaping the corners I am cutting all the way until I am blending the curve into the neck. I use very long strokes with the rasp thus assuring that I end up with smooth lines.



With the headstock shaped I marked holes for the tuning machines and the logo



Finally I will move on to binding the box. I have been hating the idea of bending for the cutaway.

I got the bindings and the pruflings installed. Nothing fancy, Ebano Rocklight bindings. Two BWB purfings together the W is maple. I bend the normal side in my fox style side bender, and I bent the cutaway side by hand on a bending iron while the waiting on the binding in the fox style side bender. I found out that Rocklite bends like butter completely dry with the bending iron at 11 (Nigel stopped by and added the extra temperature setting. ) I also found out while touching up the bindings from the fox bender that Rocklite can take a set. This is I could not bend it on the bending iron, or at least when I did it sprung back to the set shape. This was not an issue I just pulled the binding in with tape on the guitar. I was just surprised. I had just finished bending the cutaway curves, but I could not tighten the lower bout curve on the normal side after they cooked in the fox bender.







I have learned before binding to level the sides. They really need to be sanded to very close to final. One does not want to level the sides when the bindings are installed. I use this fancy drum sander that I bought from Grizzly. I first pencil all over the sides to make sure I hit low spots also to make sure I do not go too far. The drum sander can remove wood fast, So if I do not see pencil I am not sanding.





I use a Fleischmann binding jig with a 1" router bit and the LMI set of bearings. I happily went back to having the cutting index right on the router shaft after a couple of years trying a variety of binding jigs that used a 1/4" end mill and an adjustable index. The separate bearings are a pain, but once setup I can be sure that no mater where on the bearing I cut I get the same depth. On any of the other binding solution if the index and the bit are not properly aligned the depth of the cut varies. I am sure other who are really good at setting up their tools do just fine. I had a completely hassle free time routing all of the binding channels and the purfling channel in the top.







I fit the binding and use a chisel as a scraper if there are any places I need to clean up in the channels. I used a fancy purfling cutter to score the top of the cut away and chiseled out the waste.



Also before installing the binding I knock off the inside and the outside corners of the bindings. Knocking off the inside helps them seat easier in the channel, knocking off the outside helps to keep from braking the tape as it is pulled tight.



I hate it when one of the bindings at the joint is not completely seated causing a misalignment of the the purfling lines. So I generally clamp both ends at the same time



After a lot of glue and tape and leveling the purflings, it all looks good.

John...with a tapered headstock and 3x3 tuners, how can I deal with the taper and keep the posts at right angles to the headplate surface? I like the idea of a tapered headstock but I have no idea of what considerations I need to make in order for the tuners to be happy.

Thanks!