See the kerfing so proud? Try to ignore the dye puddling, too.

This is a post full of conjecture.  I’m pretty certain that the kerfing that was installed on the bass guitar kit was installed in ‘creative’ ways.  There is no consistency in how proud it is from the rims of the guitar body.  Since I don’t want to chisel out the kerfing and re-install it [OK, I do, but that costs more money], I’m going to have to plane, sand or carve out the bits that are a bit excessively proud.  We don’t need a bass with an ego [rimshot!].  What I understand from all of my reading, video watching, and general preparation is that when you install the kerfing you’re supposed to pre-bend it and then keep it carefully lined up as you’re putting the clamps/clothespins on the kerfing.  Since the kerfing is put in as a whole strip, but clamped on 3/8″ by 3/8″ it should be easy to visually gauge if you’re missing the height you’re after.  Kerfing wood is flexible, but it’s also still wood and now I have to try to adjust end grain – and that’s just not pretty because it’s more prone to chip and break.

The moral of the story: Do a job of installing your kerfing that you’d be proud of, but don’t make your kerfing proud.

bracing on the old, cracked spruce top

Since my kit’s guitar top died the death of a thousand dry climates I have to re-create the top piece (I’ve already mentioned that, I know).  But as I was studying up on the bracing I kept running into the arc that is on the bottom of the X-brace.  I kept wondering, “But do I need a radiased dish to place the top into?”  And the answer?  No.  The reason is this: the bracing material is flexible and as the luthier shapes the pieces to the brace template the slight curve will be small enough [12' to 30' radius] that the go bar deck [which is another topic for discussion] will press the flexible braces down to the flat top and when the go-bars are removed the slight curvature of the braces will be picked up by the whole top.  This creates tension for resonance as well as creating a shape that (as I understand it) will direct the sound internal to the acoustic guitar through the sound hole.

Bracing is amazing to me from an engineering perspective.  My dad was a civil engineer (now a pastor, the past tense is not to indicate his passing) and so I grew up with some moderate exposure to things like structural engineering and since we lived in Nevada and California earthquakes were part of that discussion.  The whole point of bracing is to keep the wood in tact as it handles the abuses thrown at the guitar body parts.  This isn’t a surprise, but it’s important to recognize it’s job is to handle vibration and keep it down.  Except that the top and back make more awesome sounds when the (right) vibration is up!  So, bracing is rather interesting because the patterns that are out there help structurally, but do impact tone and resonance.  I’m not an expert on bracing yet, but I do hope to become one.

Gnarled Wood

I’m certain that more knowledge exists all over the Internet and that I’ll be editing this post over time, but I wanted to jot down some ideas about wood.  The first thing I want to talk about is the Janka Hardness Test.  This test, which you can read some rather nerdy bits about on Wikipedia if you’d like, tests how many foot-pounds of pressure a species of wood requires to insert a 0.444″ steel ball into the block half way the ball’s diameter (0.222″ inches).  While this test was developed for non-luthier related purposes, it clearly has a use in many wood-related projects.  For example, balsa wood has a Janka hardness value of 90 while redheart has a hardness of about 1,130.  You’d be wise to avoid creating anything instrument related  out of balsa.  I’m going to experiment with redheart  as a bridge material, but when it comes to the actual wood for the saddle to fit into almost all examples are made out of much harder woods such as ebony or even maple.  This leads me to think I may need to laminate the redheart I have with some ebony to create a solid platform for the saddle to handle the string tension appropriately.  Here’s one example from lumberjocks by Randy Bretz [click on the image with 3 bridges].

I’m much more enamored with the grain and colors of wood than some of the other qualities of the woods right now.  This is a bit of a confession in contrast to being purely scientific about things.  If Spruce has the best tonal qualities, but everybody has a spruce guitar, then I’m less interested in it.  The art part of wood working and luthery is definitely more exciting to me.  Speaking of which the tailpiece and bridge on this Rick Toone guitar is phenominal!  It isn’t wood, sure, but the design is so cool I have to link to it anyway  It does however, because of the sound hole being at the bottom of the guitar, show off the wood used.

I need to learn so much more about wood, but at least for now I’m learning about wood’s properties, and I figure that experimenting (even if it ends up showing off some failures) will be good for me to learn and grow.  I’ll post my findings as I do the research.

Creative Commons: Andrew J. Sutherland

This last Sunday I got to hear the excellent Phoenix Youth Symphony play at Denver University thanks to the invitation of our friends. As we watched and listened I was very well amazed by the design of the stringed instruments comparing them to what I’ve been studying for the bass build.  Below are some observations comparing the designs of the two instrument types.  I recognize that they’re different and designed to be used in different contexts (maybe) but there are some qualities that I want to point out.

The first design difference is the playing position.  Clearly the cello body size requires a lot of posture considerations to make sure that the instrument is playable with both bow and fingertip.  The bass guitar, however, is almost always played with the neck extended away from the midsection of the musician.  This creates a totally different level of intimacy with the instrument and a different angle by which the musician hears their instrument.  The playing position definitely impacts what sorts of other things can be done with the size of the body and some of the ornate curvature.

The cello is also fretless without markers.  Students learn with various markings in place (often tape if I understand correctly) and develop muscle memory practicing scales and gaining familiarity with every millimeter of their fingerboard.  The bass often has fret markers (but not always) and many fretless basses have some sorts of indicators to help their players.  This is a generalization, so it shouldn’t be considered too heavily in design difference.

The major piece that stood out about the cello to me was that it is engineered for acoustic amplification (read about the design on wikipedia).  Since the top (often spruce) part of the body needs to resonate and vibrate with the vibration of the strings and compete with other instruments in the orchestra the cello allows all of the string’s energy to focus through the bridge and into the wooden structure.  I spoke to one of the cellists after the concert and he pointed out that the f-hole cutouts in the cello are positioned where they are to allow for maximum vibration of the top piece at the bridge.  The bridge makes solid, but low-footprint, contact with the top piece and the neck and tailpiece hang out over the body reducing any chance of the rest of the instrument to reduce vibrations or change tone.  The bass guitar design almost always (though there are exceptions) includes the fretboard (a very dense, low vibration piece of wood) reaching out across the top of the guitar reducing vibration and therefore reducing resonance and impacting tone and volume.  Additionally most bass guitars have a bridge with holes in the middle of it for strings to be attached to.  This further reduces (acting as a top and bottom brace) vibrations.  The acoustic guitar’s design is less than optimal in comparison.  Of course guitars like the archtop guitar may improve upon these vibration issues.

I really enjoyed analyzing the bass guitar and the cello as I watched the symphony.  I’m no less passionate about creating the bass despite its differences, but the fun of the analysis is to think about what one might do to help improve the design or offset deficiencies.  Maybe in a future post I can point to some other guitars I’ve found in the last two months that have some fun design differences that compensate.

The Fretted and fretless fingerboards

To the left in the photo on this post you’ll see a fretted bass.  It is on my fretted acoustic bass guitar (a Dean for those of you who care, it was inexpensive and fulfilled an itch, just in case you’re wondering why I didn’t buy a hand-crafter bass).  To the right of that is the unfinished (and out of focus) fretboard for the bass build.  Since I have a fretted bass, I’m going to make this new build a fretless bass.  This comes with some commitment on my part to actually figure out how to make that sounds good when I’m playing, but it also removes some of the pressures I have to get the frets and the fretboard perfect on a guitar kit that is old enough that it is bound to bring some difficulty with it.  Also: I like the sound of a fretless bass guitar.  A lot.

I am toying with the idea of buying some blonde/light veneer and filling the slots so as to help make the lines stand out more prominently.  I had considered trying to get some black wood, but that seemed counter-intuitive to me, so we may go with something more contrasty to see what we like.  Since I have so much red on the guitar I had considered a red fretline as well, but I eventually decided something else would work better.  We’ll see if I like that idea still once it is complete – before I install the fretboard I can put the veneer in, look at it, and if I don’t like it, I can order another blank and start over.  I may also just go into Woodcraft (the nearest supply store for fine wood working) and hold the fretboard up next to some of the veneers and pick the one that  makes the most sense.

The redheart blank, the original ebony bridge, the hofner bridge, and the golden tailpiece

So the default bridge that came with my bass guitar kit was very normal looking ebony (which is beautiful, don’t get me wrong).  But I wanted something that stood out.  I got it in my head to copy some of the design queues of a 1932 acoustic bass guitar I’d found pictures of online searching for bass guitar designs: I’d go with an almost archtop bridge design, but with the flat top.  That means a bridge piece and a tailpiece.  I ordered some Hofner replacement parts that got here and they showed off their niceness, but their string spacing is quite narrow compared to the neck I have (and like).  If I used them I’d get a lot of fretboard room on the outsides, but the look would be awkward at best.  There’s only one thing left to do: make my own.

Inspired by some other luthier’s work I’m going to make a tailpiece that extends upwards off the bottom block of the guitar and allows the strings to be attached to the guitar without running through the top, and I’m going to create a redheart bridge for the strings to run over [I may laminate this to be ebony & redheart].  I’m still trying to figure out if I’m going to setup the soundhole normally, make it an oval, or do something more exotic.  With redwood and redheart I’m hoping I don’t  find the colors clashing too strongly because the dualing reds would be a bad idea.

The tailpiece I’m hoping to make with a lamination of ebony, redheart, and redwood.  The redwood is for looks and will be the outermost layer and the other two woods will provide strength.  I plan on giving the piece a bit of a curve at the end top to create a cove for the string ends.

The redwood guitar top, unfinished

Since the old kit had a cracked top I had to order a new top with new brace wood.  Luthier’s Mercantile International  (LMII.com) is based out of Healdsburg, CA, and they’re about an hour away from where there are Sequouia trees.  I was born about an hour away from Healdsburg, and even closer to the sequoias, so when I needed a new top I jumped at the chance to get the redwood top from “home.” The new top  is red, as you’d expect, but it’s also just cool on a sentimental note.  I also got cedar brace wood instead of spruce because I’m a rebel.

This top needs to be planed at the joint for a very, very tight and perfect fit.  Then it will need to be glued and clamped to dry.  I have seen several techniques on how this is done.  One is Robbie O’Brien’s technique [he may not be the originator, but he teaches it].  Another, similar, technique (found in Build Your Own Acoustic Guitar, page 60) is to use a 3/4″ thick piece of plywood with nails at the left and right side of the two pieces that are to be jointed with a 1/4″ baton (or scrap of wood) raising the joint while placing the nails.  Once the nails are set (but protruding) the edges can be glued and placed between the nails with the baton (or scrap) removed. Clean up the squeeze-out of glue.  It is important to place parchment paper below and above the glued joint and place even weight across the joint while it dries.  When I get to this process I’ll blog about it and take as many photos as possible – maybe even some video.  Since I hope to make more than one guitar over time I may try both techniques and then compare the two.

The top wood will also need to be “thicknessed.”  This means to sand or plane the surface down to its optimal thickness for sound wave resonance.  This is a great opportunity to identify the grain pattern and any special bits you may want to draw attention to.  Robbie O’Brien suggests a drum sander (if you can afford one), and of course I don’t have one.  Jonathan Kinkead (again in Build Your Own Acoustic Guitar) suggests using a plane very carefully, and at a diagnol.  Since wood can chip out, and the top board is already very thin, this needs to be done with patience and a firm, but gentle hand.

Finally a card scraper (cabinet scraper) and sanding blocks may be used to clean up the entire wood surface and confirm its readiness for the rosette (if you’re going to install one) and bracing.

The sides, the neck, and the old, cracked top from the acoustic bass guitar kit

As of this post I have never made a wooden instrument.  I do play the piano, drums, guitar and bass guitar and have for several decades, though.  In the interest of transparency I have to date cut a coconut in half, and that is it.  I can now make percussive sounds akin to Monty Python’s Holy Grail’s skits wherein the knight rides with his manservant clopping coconut halves together.  Now that you know that I’m under-qualified, let me tell you the following:

About three years ago [maybe four, I haven't kept track very closely] I received, as a gift, an acoustic bass guitar kit that someone had started but was unable to finish [they died].  I stuck the kit in the closet and it has sat there until this last month.  I got inspired to dig it out because my brother’s neighbor makes guitars and I realized that I wanted to learn how to make guitars and pursue something with physical results since I make software for a living.  Since my brother’s neighbor lives 1,000 or so miles away, and since there are books, blogs, forums and various online resources like the O’Brien Guitar video series on YouTube, I decided to get reading and watching and learning so that I could finish the kit.

One more thing: the guitar assembly was started in Florida where the humidity is somewhere near 110% and was then shipped to Colorado.  I believe our average humidity is somewhere near 35%.  The guitar kit (shown at the top this post) has some rough bits and I even started to remove the kerfing because the accuracy wasn’t what I thought it should be.  I’m glad I stopped because a plane will take care of the waves in the kerfing.  Additionally the spruce top that was started cracked badly due to the humidity difference.  I had to order a new one top and bracing for a new top.  This will require a bit of reverse engineering, but we’ll make it work.

This blog is going to journey through my making of the acoustic bass guitar [ABG],  as well as notes and discoveries I make along the way.  I hope to assemble other guitars in the future, including a classical, a steel string, an arch top, and a mandolin.