Koa\Bearclaw Sitka Spruce 00 Steel String Guitar blog:


Apr 25 2020

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.

May 6th 2020

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

May 15th 2020

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"

New headstock design : thin headstock.pdf

With the template on I roughed out the headstock shape. I will probably finish the neck tomorrow or the next day.