Now that the lacquer is buffed to a high shine I can get ready to string up the instrument.

First, the tape is removed from the fretboard and the spot on the soundboard where the bridge will be glued.   Any little bits of lacquer than managed to seep under the fretboard tape are scraped away.  I double check the location of the bridge to assure that the strings are properly aligned with the edges of the neck, and that the bridge location allows the proper amount of compensation for the string length.  As one plays higher up the neck, fretted instruments tend to start sounding sharp.  By moving the location of the bridge a little farther back from its calculated spot–which would be exactly twice the distance from the nut to the 12th fret–one can “compensate” for this tendency for the intonation to go sharp.  In the case of the cavaquinho, I have found that locating the bridge about 3 mm back from its theoretical spot provides the best intonation.  I did not take any pictures of the bridge gluing process, but it was glued to the soundboard with yellow aliphatic resin and held in place with a couple of clamps until dry.

After gluing the bridge, I make the nut and saddle from pieces of ox bone.  I prefer bone nuts and saddles on most of my instruments.  Each type of material, whether it is bone, various types of synthetics, or even ivory, has a characteristic influence on the tone of the instrument.  I prefer the tone of bone, and it is also more durable than plastic.   These pieces are critical to how the instrument will play.  The slots in the nut have to be cut to just the right depth to allow minimal finger pressure to play the notes at the first few frets, yet not so deep that there is any buzzing on the first fret when an open string is played.  Also, all of the slots must be carefully filed to leave the strings at the same height.   Here is a picture of the roughly cut nut being sanded to the same radius as the fingerboard:

After the nut is shaped, I mark the locations where the slots will be and carefully file them.

The saddle is cut from another piece of bone.  It is sanded to the proper thickness to fit in the bridge slot,  then its top surface is reduced to the proper height to allow the strings to be roughly 1/8″ to 3/32″ from the top of the 12th fret.  The strings are a bit higher on the bass side than the treble because the heavier bass strings vibrate more freely, so they need to be higher to keep from buzzing on the frets.   This picture shows how the finished saddle is sloped in such a way as to allow the treble strings to be closer to the fretboard. 

Now the tuning machines are installed.  I prefer to use geared tuners on cavaquinhos because they are more durable and easier to adjust than friction pegs, but I have seen some cavaquinhos with friction pegs.

Finally the strings are installed.  After letting the instrument sit with the strings tuned to pitch for a few days, I make the final adjustments to string height at the nut and saddle and the cavaquinho is finished! 

Here are a few pictures of the finished project.  I hope you have enjoyed reading about it.

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After the lacquer has cured for several weeks it is dry enough and hard enough to be leveled and buffed to a high shine.  The entire instrument is sanded, first with 320-grit paper, then 400-, 600- and finally 1,000-grit.  Mineral spirits are used as a lubricant in the sanding process to help float particles off the surface of the lacquer.  Soapy water is also a good lubrucant, but I have gotten used to working with mineral spirits so that is what I prefer.

Some areas, such as along the heel and next to the fretboard on the body, require extra attention.

 

 The goal is to sand the lacquer perfectly flat but, of course, not break through the finish back to the bare wood.  This is always a difficult process because I apply only enough lacquer to allow me to achieve a level surface.  I don’t use any more than necessary because it would have a dampening effect on the sound.   With this minimalist approach, only a few misplaced strokes of the sandpaper can result in a breakthrough, which requires application of more lacquer and a delay in completion.

After the instrument is sanded, it is buffed for many hours on muslin wheels with two different grits of compound.  The buffing process reduces large, deep scratches in the lacquer surface to small shallow scratches.   The more buffing that is done, the smaller the scratches become.  Eventually the scratches become so small that they are no longer visible and that is when the instrument appears to be smooth and uniformly glossy.

 

( I copied this from my blog about the construction of a 12 string guitar because I think it describes the process pretty well.)

I use nitrocellulose lacquer as the finish for most of the instruments I build.  Each of the many acceptable types of instrument finishes has its strengths and weaknesses.  I have worked with  lacquer for many years and have a pretty good understanding of it.  I have developed an approach to working with it that gives me consistent results.  It takes 4 to 6 weeks for me to get the finish on an instrument.

  People often ask me how many coats of lacquer I apply and I am never really sure what they are hoping to hear in response.  An easy answer to the question would be that there is only one coat, since subsequent layers melt into and fuse with previous  layers when they are sprayed.  I do have an approximate count of the number of times I point my spray gun at an instrument, so I could tell people that there are 15 to 20 coats of lacquer.  However, there is no consistent definition of what a “coat”  represents as far as a quantity of lacquer.  Every person who sprays can apply a different amount.  There are three ways to vary how much lacquer is applied with each pass of the gun: first, one can increase or decrease the volume of lacquer that comes out of the gun by adjusting a needle valve; second, by changing the speed at which the gun is passed across the surface, different amounts of finish material will be deposited on the surface; and third, by changing the thickness (viscosity) of the lacquer, more or less will remain on the surface after the volatile solvents evaporate.  So my concern with telling people a specific number is that they might think it is either too many or too few coats, even though we aren’t necessarily thinking of the same amount of lacquer.  I usually end up telling people that I don’t know how many coats are on the guitar and that I use just enough lacquer to seal all of the wood pores and to allow me to sand the finish perfectly flat and buff it to a high shine, which is true.

Here are a few action shots of the spraying process.  In addition to the particulate respirator, the other very important safety consideration, which is not visible, is my use of an explosion-proof exhaust fan.  Nitrocellulose is volatile and without this type of fan I would be at great risk.

Cavaquinho Neck Shaping

August 1, 2011

The last big step before putting the finish on the instrument is to carve the neck.  I have found that a final thickness of about 0.625″ under the first fret and 0.75″ under the 9th fret works very well on cavaquinhos.  The neck has to be thick enough that it can withstand the tension of the strings without bowing forward, yet thin enough that it is comfortable for the player.  There is no truss rod strengthening the neck of the cavaquinho, but the dimensions I listed achieve the goal.

Initial wood removal is done with a spokeshave.  A spokeshave has an angled cutting blade like a plane, but it has handles on either side of the blade, rather than a long plane body.  Whereas planes are ideal for making long, flat surfaces, spokeshaves are a perfect tool for shaping curved surfaces like an instrument neck (or a wooden wheel spoke!)

After I get the neck shaved down to roughly the shape I want, I use rasps to remove the final bits of wood and to smooth and refine the shape.

Next, the ebony heel cap is glued to the bottom of the heel.  After the glue dries I scrape the ebony flush with the heel.

The last construction detail is to inlay a my logo into the peghead.  On instruments with bigger heads I put my entire last name, but in this small space, an abalone “Z” on an ebony background looks better.

Now the entire instrument will be scraped and then sanded up to 220 grit in preparation for the application of the nitrocellulose lacquer finish.  Before I spray the finish I will mask off the fretboard and the area of the soundboard where the bridge will be glued.  I will also cover the sound hole to keep lacquer from getting inside of the body.

The fretboard is now perfectly flat and ready for installation of the frets.

I will use narrow fretwire (0.053″ wide) on this instrument.   This wire is standard on mandolins and ukuleles.  A typical guitar fret is 0.080 to 0.100″ wide, but that would feel strange on such a small instrument.  I buy fretwire in 2-foot lengths.  Before I use it, it has to be cleaned to remove any oil or other residues that might keep it from staying seated in the fret slot.  The fretwire is bent to a smaller radius than that of the fretboard, as illustrated in this picture:

Bending the fretwire in advance helps it conform to the radius of the fretboard a bit more easily.

After bending, the fretwire is cut into pieces that are a bit longer than the slots on the fretboard.  Then the pieces are installed using a hammer with a brass head.  Brass is soft, so this hammer reduces the chance of damage to the wire and the fretboard itself if there are any misdirected strikes (not that such a thing would ever happen to me!).  The back of the neck is supported by a block of wood to increase the efficiency of the hammer strikes.

After all of the frets are in place their edges are trimmed with a fine file.

Next I use a leveling stone to assure that the tops of the frets are all on exactly the same plane.  This is essential to getting good action and playability when the instrument is strung up.  Any high or low frets would create buzzing problems.

After leveling the tops of the frets I use a fine file to “recrown” the ones that might have had their tops flattened a bit too much by the stone.  Here is a picture of a fret being recrowned with a file.  A small metal plate protects the fretboard from being gouged by the file.

Next, the edges of each fret are rounded.  This gives the fretboard a nice finished look and makes it more comfortable for the player because it eliminates any stray burrs that might otherwise remain on the fret ends.  This step is done with a specially made quarter-round concave file.

Finally, I sand the entire fretboard with 320- 400- and 600-grit paper to polish the frets and smooth the ebony. 

The fretboard is now done and the next step will be to carve the neck to its final shape.

 

Now that the neck is attached it is time to complete the fretboard. 

I used to make my own fretboards, starting by slicing the wood and scraping it to the right thickness and curvature, then carefully laying out the fret positions and sawing the fret slots with a hand saw.  I would spend the better part of a day making a single fretboard and invariably there would be small errors in the position of at least one or two fret slots.   The location of the fret slots is critical to the intonation of the instrument.  A mislocation of 0.010″ can have a very discernable effect on intonation, particularly at higher frequencies, and I am sure I was frequently off by at least that amount.  Whenever possible I now purchase fretboards already slotted.  The suppliers of these boards use CNC equipment for precise slotting and that gives me the best chance of producing an instrument with accurate intonation at all positions.  The cavaquinho has a 13.875″ scale length–the same as a mandolin.  For this instrument I am using an ebony fretboard.  My first operation is to taper the board to its final width, which will be slightly more than 1 1/8″ at the nut and 1 1/2″ at the 12th fret.  This instrument will not have any inlays on the surface of the fretboard, but there will be dots along the side for position markers.  The dots are installed by drilling 1/16″ diameter holes and gluing in a short piece of white plastic rod.  When the rod is sanded smooth it leaves the appearance of a side dot.

Next, I make sure that the gluing surfaces of the neck and fretboard are perfectly flat, then I glue the fretboard to the neck.  In this photo you can see a small nail in the first fret slot.  There are actually two nails–the other one is at about the 14th fret.  They are used to keep the fretboard aligned until the glue sets up.  

After the glue dries, I trim the end of the fretboard flush with the soundhole and sand out any minor imperfections in the surface of the board.

Fret installation is next.

It’s now time to make the neck.  I have used mahogany for the necks of all of the cavaquinhos I have made so far.  Mahogany is a great material for instrument necks.  It is strong and light weight, easy to carve, and stable in the face of changing climates.  This last point is of greatest importance because we want the instrument to remain playable on dry days as well as wet ones.  If the neck were to expand and contract markedly every time the weather changed, there would be endless problems with fret buzzes and string action, and that would make for an unreliable instrument.

The first operation is laminating the heel block onto the neck.

Next, I mark the outline of the neck and cut it on the bandsaw.

I now turn my attention to the end of the neck that will join the body. 

There are many acceptable methods of joining the neck to the body.  A dovetail joint, which is common in guitar construction, could be used.  Alternatively, the neck could be pinned or bolted to the body.   I prefer to use a mortise and tennon joint that will later be reinforced with dowels.  Each method of  joining these parts has its strengths and drawbacks.  I have used the mortise and tennon approach on most of the instruments I have made over the past 25 years and have gotten very consistent results.  The big drawback to this approach is that it is very difficult to align everything properly so that the neck is at the right angle to the body and that the centerline of the neck goes straight down the middle of the top.  The advantage of this approach is that once the joint is assembled it never moves and it has no gaps, so no string energy is lost in the neck-to-body joint.

I use a table saw and bandsaw to make the tennon at the end of the neck.  I didn’t think to take any pictures while making those cuts, but here is the roughed out tennon.

I will use rasps and files to make adjustments to this side of the joint, but before I do that, I need to cut the mortise out of the headblock on the body, which I do with a handsaw and chisel.

 

Next I check the alignment and make any necessary adjustments on the tennon or the gluing surface of the neck’s heel.

That end of the neck is complete for now, so it’s time to make the peghead.  The wood being used isn’t wide enough to make the peghead shape that I want, so I glue some mahogany wings to extend the width of the head.

After the glue dries, I scrape the extensions flush to the rest of the head then glue on the peghead veneer.  For this instrument I will use a koa veneer because of the koa body.  After the veneer is on, the profile of the head is cut on the bandsaw.

Now the holes are drilled for the tuners.

The last operation I perform before gluing the neck to the body is shaping the heel.  It is much easier to do this before the pieces are attached.  I use rasps, scrapers and eventually sandpaper to shape the heel.

 

After the heel is shaped the neck can be glued to the body.  The shaft of the neck is kept square for now because it will be easier to attach the fretboard if there is a flat surface for the clamps.

After the neck is glued, I drill two holes through the edges of the mortise and tennon.  The holes are half in the mortise and half in the tennon.  They run almost the full depth of the joint and are exactly the right diameter to hold two pieces of oak dowel.  These dowels will be glued into the holes and they act as an additional means of anchoring the neck joint.

 

Binding the Cavaquinho

May 23, 2011

After the glue dries on the back, the body is scraped and sanded smooth in preparation for installing the binding around the edges. 

Binding an instrument serves two purposes.  First, it has an aesthetic purpose.  The choice of binding material can greatly enhance the attractiveness of the instrument.  (Incidentally, in guitar building terminology “binding” is the outermost strip around the body and “purfling” refers to the strictly decorative lines inside of the binding.) Second, binding protects the highly delicate end grain areas of the top and back of the instrument.  When the instrument is new, there will be a film of lacquer sealing all of the wood, but as time goes by this film may become damaged through normal wear, particularly around the edges of the body.  If that damage is sufficient to expose the bare wood of the soundboard or back, those exposed areas become susceptible to cracking.   Bare wood will absorb and release moisture several times faster than the protected wood, which creates uneven moisture content and localized areas of stress.  When extreme, this will result in a crack in the wood.  By installing a strip of binding, the end grain of the top and back plates are more likely to remain protected and sealed, even if the lacquer chips away, so there is a smaller chance of a crack developing.

This instrument will be bound with spalted sycamore to match the soundhole ring.  Here I am slicing what will become the binding strips from a larger piece of sycamore.

The first piece of binding to be installed is the “tail graft” which is at the bottom end of the body where the two sides meet.  I usually like to use a wedge-shaped piece of wood for this graft because I like the way it looks.

This photo shows the body clamped to a fixture that I made to allow the tail graft slot to be routed into the body.

Here is the untrimmed tailgraft glued into the slot.

After the glue dries I trim the tailgraft and scrape it flush with the sides of the body.

The sycamore bindings were sanded to a thickness of 0.060″ and bent on a hot pipe, just as I bent the sides of the instrument.  I am going to put three very thin purfling lines around the body for decoration and to match the design around the sound hole.  These black-white-black lines are each about 0.015″ and are flexible enough that they do not need to be bent on the pipe.

I use a router with a specially designed bit to create a two-step ledge.  The inner step is very shallow–about 0.030″–and is just wide enough for the purfling lines.  The outer step is about0.20″ deep and is the proper width for the binding strip.  The resolution of my camera isn’t fine enough, but here are a couple pictures of the process.  Routing the channels on small instruments like this can be a lot more difficult than a guitar because they move more easily and are more difficult to hang onto.

Now the binding strip and purfling lines are glued into their respective channels.  I use wood glue and hold everything in place with strapping tape until the glue dries.  Only one half of the top or back is glued at a time.  Ths first half has to be completely dry so I can get a clean saw cut at the seam where the other half will start.

After all four sections are glued, everything is scraped and sanded flush to the top, back and sides.

I am finished with the body now.  Next I will start to make the neck.

Cavaquinho Back

May 9, 2011

The next phase of this project is making the back.  The two bookmatched pieces of koa are glued together then scraped and sanded to a thickness of about 0.060″.  The approximate shape of the instrument is cut out next.  Although this instrument is small and not under nearly the amount of tension a guitar experiences, there is still a concern about the stability of that center seam, so a small spruce strip with grain oriented perpendicularly to the seam is glued to the inside surface of the back.  (This reinforcement is not necessary on the top of the instrument because several braces, along with the bridge plate and the bridge, cross the center seam and keep it stable.)  Here is a picture of the reinforcing strip being glued.  The strip is about 0.080″ thick and is barely visible under the board that I use to distribute the clamping pressure.

The center strip is sanded to a gentle curve, then notched out with a saw and chisel where the two back braces will be located.

The cavaquinho has two braces on its back; one at the waist and one at the widest point of the lower bout.  The braces are made of quarter-sawn spruce and are about 3/16″ wide and 1/2″ tall when glued.  The surface of the braces that is glued to the back is not flat, but instead has a  25 foot radius sanded into it.  This radius gives the back a small but noticeable curve, which most people find more visually pleasing than a completely flat back.  The curve also  increases the strength of the back and may play a role in reflecting sound when the instrument is played.

After the braces are glued, they are shaped with a plane, chisels and sandpaper, much the same way as the soundboard braces were shaped earlier in the project.

The sides of the cavaquinho are now trimmed to the desired height: 3″ at the tail end and 2 3/4″ where the neck joins the body.  This is done with a plane and sandpaper.  After the sides are trimmed, the kerfed lining is glued in, just as it was along the top edge before the soundboard was attached.  The primary function of this lining is to increase the surface area for gluing the back.

I want to keep the back braces as long as possible and  secure them at their ends so they won’t pop free.  This was easier to accomplish when I attached the top because I could glue a block of wood over the end of each brace after the soundboard was installed.  When the back is put on, I will not have access to the inside to glue in similar blocks.  Instead, the kerfed lining is carefully notched out where the braces will be, and only to the depth of those braces.  These notches will serve to lock the back braces in place.

After making sure everything fits perfectly and that the notches are exactly the right depth, the back is glued to the sides.  I like to use as many clamps as I can fit around the instrument in order to ensure that all points are in contact with the side linings and that there will be no gaps.

The body is now assembled.  The next step will be to add binding around the top and back edges.

The braces for the soundboard will be made from hand split Adirondack Red Spruce.  This is the same material I use to brace the soundboards of my guitars.  The main support for the soundboard is the X-brace, which is composed of two intersecting braces that are about 1/4″ wide and 1/2″ tall at theie highest point.  Their gluing surfaces are not completely flat; they have a small arch-about a 30 foot radius–which, when glued,  gives the soundboard a very slight dome shape.  The dome actually improves the strength of the soundboard, part of a phenemenon known as LaPlace’s Law of the Bubble, but I won’t get into that.  After the braces are shaped and notched where they intersect, they are glued to the soundboard with as many clamps as I can fit into the tight space.

After the glue dries, I plane the X-braces close to the final shape I want them to have.  They are about 1/2″ high where they intersect, but their height steadily decreases, to less than 1/4″, as they approach the edges of the soundboard.  Also, they are not left square on the exposed surfaces, but are gently rounded.  Rounding the braces reduces their weight but doesn’t significantly reduce their strength.  Tapering the braces also reduces their weight and allows the soundboard to vibrate more freely peripherally, yet keeps the middle area strong, where the tension and compression forces are greatest.

Next, I glue a small “bridge plate” between the legs of the X braces directly under where the bridge will be.  This is another “improvement” I have made from the original cavaquinhos I copied, designed to help stabilize the soundboard yet not compromise the instrument’s tone.  Bridge plates are very common in classical guitars and almost universally found in steel string guitars.

Once all of the braces are glued, they are planed and sanded to their final shape and cut to the right length.  Here is a picture of the soundboard ready to be glued to the sides:

The kerfed lining is removed from the sides where the braces intersect. 

Now the soundboard is glued to the sides.

After the clamps are removed small “feet” are glued between the sides and the ends of the braces.  This virtually locks the braces in place and greatly reduces the chance that any brace will ever come loose.  This is another guitar construction technique that I have applied to my cavaquinhos.

Now the soundboard is finished.  Back construction is next.