Keep Driving the Bus

This week started out finishing up the rosette work. Using the drum sander I took it down so its flush with the top. It sure is pretty and is surprising how you can't feel where the spruce top ends and the rosette begins. This came out a lot better than I expected.

Next we started gluing on top braces. The particular braces glued on this week are done with the top flat. You can see I used the same Go-Bar system as the braces for the back. Next time we will glue the braces that have been arched with a 28' radius for the front. The braces will be hand cut to an exact length later.

Next came more shaping and sanding for the side where back glues on. I used the large 15' radius sanding dish. This was to sand down the kerfing installed last week and make sure its shaped correctly. This took a lot of time and I was a sweaty mess afterward. Had to take several breaks. All told about 45 minutes of working the disc back and forth like you were "driving the bus". 

After the sanding was complete I notched the back where the braces will fit. First, determine the notch locations by laying the back on the body and lining up the back center point with the top and bottom center points of the sides. The lightly clamp the back to the sides at the neck and tail blocks. The sides are still in the mold so now I can stand it up so I can see where the braces meet the back. Pencil mark the sides where the braces meet it and you have the locations. Using a very small fret saw I cut the depth on each side of the brace. Then I used an Exacto Knife like a chisel to carve out the notches. The goal here is to get deep enough so the back contacts the sides without any rocking. Carve the notches out very little at a time to avoid getting them too deep. This took the better part of 11/2 hours to do all 8 notches. Here is a pic of a completed notch. 

 

We had about 15 minutes left, so we decided to route out the body where the neck will join it. This is very easy job and hard to screw up. Just take your time. I used a small hand held router similar to this one. Here is what the rough cut looks like. It will get a final sanding finish. You can see the holes through the block. I decided on a bolt on neck. This makes it simple to remove the neck for a reset down the road sometime. Bolt on neck technology has advanced considerably thanks to people like Bob Taylor.

Next I cut out the tail trim piece. This will be used where the sides meet at the bottom. The sides were already cut close enough that I could have done without it, but Ken says the trim piece provides more stability because you cut it so the grain runs 90 degrees from the side grain.

Time was up, but we stayed a little longer discussing what types of finish we would put on the guitars. I am opting for a satin finish both because I like the look and it allows for more body vibration than a gloss lacquer. We also discussed electronics. Ken recommends the K&K Pure Mini Acoustic Guitar Pickup. because it takes up less space in the guitar and has no battery to leak and damage things. Steve, another guy taking the class has a friend who makes McIntyre pickups. I will check them out. I had been thinking about the LR Baggs Lyric Acoustic pickup. Its microphone based and gets lots of good reviews. I will check them all out before I decide.

See you next time.

One Month In.

I haven't kept up with this because I am basically lazy when it comes to writing. So this post will catch up with everything that has gone on since week one.

Week 2:

First thing we did was book match and glue the top. Its the same process as doing the back which I covered earlier, so no new details on that. I chose Sitka spruce for the top wood.

While the glue was drying on the top, I cut out the sides. I didn't know this before but sides are book matched as well so we had to line those up. Then we used a plastic template to trace out the cut marks. The templates make things much easier and they are available for all different types of guitars. of course the rough cut is larger than the final finish. We will trim and sand to get to the correct depth. For this guitar I chose a dreadnought depth because I want more volume out of it than a typical small body.

This pic shows the sides wetted down in preparation for bending. I was pretty apprehensive about this part. Ken told me that 90% of the time it goes with no problem. That was not a high enough percentage for me to get comfortable with it.

The actual bending process was done using a mold and a bending "sandwich". I try to picture it below to give an idea. Basically it involves the mold itself, then a piece of sheet metal. On top of that is a heating blanket followed by the sides and then another piece of sheet metal. Clamp this sandwich at the base of the mold. Let the heating blanked get to somewhere around 250 degrees. This happens in a matter of minutes. Use a heat proof glove on your hand and start applying pressure to bend it to the mold. Can't go too slow or the wood will burn. Too fast and it will crack. Because the top of the sandwich is basically open, its heating the wood as you apply bending pressure. Once you get it near the waist the mold has a clamp to help guide in. Ken applied the clamp while kept pressure to get it around the upper bout. Once this is done then a clamp will hold the upper part in place. The goal is to get the entire bend in place in about 5 minutes. I will need to cool for about 30 minutes before you take it out. Still warm to the touch. It will spring back a little bit but not to worry because it will go in the guitar body mold where it will get its final shape. If its still damp use a heat gun on low to remove the moisture. If left it can lead to mold. Here is the side after the bend is completed and cooling. See the waist clamp and the end clamps that hold it in place. A pretty busy week.

Week 3:

Recap - Braces are rough cut. Back and front are book matched and glued. Sides are cut and bent. Seems like real progress but only vaguely resembles a guitar.

We moved the sides to the mold and then glued in the neck and tail blocks. The neck block has some important holes and routed slots that must be in an exact position. Fortunately this is easy if you just make sure the neck block is flush with the top of the sides. Tail block is not as fussy but line it up with the top anyway since it will save you a lot of sanding to get it flush. Notice the wax paper under the blocks. That is because its just sitting on a flat board, not the top or back of the guitar and the was paper keeps you from gluing the whole thing to the board. Simple solution.

Notice the blocks don't appear to be flush. The guitar is facing top-down so you this is the back. This is normal at this point and you will need this to get the back radiused properly.

Time to move on to some shaping work for the back braces. Flat top guitars are not flat. The aren't like archtops, but the backs are arched to a 15 foot radius and the tops are arched to a 28 foot radius. This increases their strength and volume. These are typical Martin radii. Other guitars are different depending their maker. I don't have any pics of this but basically you take a rough cut brace and clamp it to a radiused template and run it through a router. For the back I made four 15 foot radiused braces.

Next I cut out the back using another template. Lay the template on the back and line it up with the center line. Trace out the back along the template. Then trace again using a half inch spacer so you have an outline of the back a half inch larger. The template also contains locaters for the braces so mark those while you are here. Cut on the outer line with a band saw.

Then the back was depth sanded to about .086 inch using a Performax 22-44 drum sander. This is an expensive piece of equipment. I need to either find an inexpensive one or figure out something else. Martin is about .095 so this is thinner. This is Kenneths preference and he says is the major reason why his guitars sound better. The back resonates better and adds depth to the sound. Some cheaper guitars have backs that don't resonate at all and just reflect the sound. Martin likely keeps theirs a little thicker to preserve the sound they are know for. It probably also leads to less cracked backs during the production process.

Next glue the braces in their proper locations and clamp them using a Go - Bar clamping system. This thing is a little Frankensteinish looking but holds the braces in the right place with the right amout of pressure. Below the back is a 15 foot radius dish. The clamp pressure molds the back to the radius matching the braces. I think one can be made for much less than the StewMac price. Notice the radius dish has sandpaper on it. This is because it is also used to sand the back of the sides and neck and tail blocks to match the radius.

Week 4:

I moved back the sides in the mold to start adding the kerfing. This will go on the top and bottom of the sides and its what the guitar top and back actually glue to.

The first step is to level the top of the guitar by using a large sanding disc that covers the whole top. Turn it back and forth until the top is level. It helps to put pencil marks on the edges of the sides so you can tell when the disc is touching everywhere at once. This was a little tedious and took about a half hour.

The kerfing will need to be bent but the process is much simpler than bending sides. Simply dampen them and heat them on low with the heat gun. After a few minutes they are flexible enough to bend by hand into shape using the sides in the guitar mold. Clamp them and let them cool. The will spring back but retain enough shape for you to apply glue and put them back in place. Add a huge pile of clamps and let it dry. The clamps are actually office binder clamps you can buy anywhere. Cheaper and more effective than the StewMac clamps. I have read you can use clothespins as well.

Took the back out of the Go-Bar and now its time to start doing the final carving on the braces. This is another item I was nervous about because they are glued in and its real easy to break rule #2 (don't mess it up). I clamped the back to  the work bench and went to work. The carving is done using small hand planes and a chisel. Use the planes and chisel to rough it in. Sandpaper gets you the rest of the way there. Ken gave me some instruction on how to properly use the chisel. He carved on side of a brace to show me what it should look like when it was done. I went slowly and the extremely sharp high quality tools were much easier to use than I expected. The center of the braces is given an steep rounded profile kind of like looking at a bullet. The ends are a curved slope to the sides. It only took me about 10 minutes per brace side. After sanding they came out perfect.

Week 5:

I worked on the kerfing for the back. First I had to remove the extra wood from the tail block using a rasp that removed wood pretty quickly. Since the blocks needed to be radiused I removed most of the wood from the end where it contacts the back of the guitar. Then I used a 15 foot radiused sanding disc to clean up the back the same way I did the front. This time it didn't take as long. Maybe ten minutes. Then I bent and glued in the kerfing in the same manner as I did the front last week.

Next I started working on the guitar top. It was book matched and glued earlier so I depth sanded it down to about .118 inch. Tops are thicker than backs. Then using a template I traced out the top and locating marks for the braces. Cut the top out with the band saw.

Next step was to cut out for the rosette and sound hole. I use a drill press hole cutter to route out the ring for the rosette. Cutting through the top is a violation of rule #2 so I had to be careful to go about 2/3 of the rosette thickness. It will be sanded flush later in the process. The rosette required some light sanding to fit firmly in the hole. Once satisfied with the fit, remove it and add glue to the soundboard side. Reinsert the rosette and clamp it. The gap at the top is typical because it is under the fretboard and won't be seen.

That about catches things up. See you next time.