Class 8 and 8.5

Last week and during a short class last night we worked to finish our tops and on gluing them to the body.  I have to say that I find myself challenged to perform even basic steps cleanly at the moment.  I'm not sure why things have been so difficult for me - unreasonable expectations, false sense of skill, general winter malise - but I've been messing up on some very basic steps.   Anyways, the work over the last two weeks is not presented in chronological order since I've been moving back and forth between tasks over the two classes.

Triming the Back 

One further step before finishing work on the top was to flush trim the back that we had already glued on.  It's been put face down so that the edges could be trimmed flush.  I've marked the direction that I want to move the router, working in from the top of the curves, so that I don't rout against the grain.  The router is equipped with a flush trimming bit - a guide below the bit sized to the bit prevents the router from traveling in any deeper than the sides against which the guide runs.  Hence the back is cut flush to the sides.

Trimming worked fine.  To prepare the body for gluing on the top, we also sanded the sides and kerfing on the top on a sanding dish with a 45' radius.  This slight curve is meant to add more stength to the top and can improve tonal qualities.   However, this was another area where I got myself into trouble.

It's a little hard to see in this picture, but despite using the sanding dish, I managed to overwork my sanding and end up with one side sanded down more than the other.  The picture shows the  remaining difference after Edward helped even things out using a wooden block plane to remove small amounts of wood from the high points.  It will be hard to see in the finished guitar, but the trebble side of my guitar will be slightly deeper than the bass - creating a slight wedge shape.  Edwads suggested that maybe it will be easier to play as a result.....

Finishing the top

Below I've tried to illustrate some of the further steps taken in the process of paring down the bracing with the intent of keeping the top strong while bringing out its 'tap tone'.  Tap tone refers to the sound eminating from the top when held up and tapped.  The goal in our process is to try to get 4-5 seconds of sustain out of the tops, with a good clear sound that has strength in the lower and middle ranges.

Initially, much of the work done was to plane down the X-brace and scallop a  smooth spiral curve into the ends of most of the braces.  Generally, this is a step I can handle at this point, but still with some challenges discussed below.
	The scalloping on the X-brace and tone bars was also done in the middle of these longer pieces of wood.  Wood is also removed with a chisel from the sides of the braces, trying to created a domed  'cathedral' shape along the cross section.  Trying to do this with any elegance with a rounded chisel has been giving me fits.
The small finger braces and the tone bars are actually curved down on the outside edge to become flush with the top.  Inside the braces are down to just a couple of millimeters for a total thickness including the top itself of about 5 millimeters.
	The ends of the transverse brace are also scalloped and the middle is 'cathedralized'.   The end of the X-brace at the bottom of the picture gave me problems.  When I tried to scallop the end, the grain gave me problems and took a bit of a nosedive.  I  was left with sort of a flat angle down leaving very little wood at the end.
The flat brace above the transverse brace needs to have a groove rounded out for access into the truss rod with a wrench.

Gluing the top

Through this process we got a resonable tap tone out of my top.  I haven't been especially  happy with the cleanliness or the elegance of my carving.  And generally, I continue to be hard on my top, adding a couple more dings.  I'm not sure why this has been so difficult for me this time around.  As with the bottom, notches are cut out of the top to fit the braces (X-brace and transverse) into the sides.

These allow for a stronger fit with the sides.  Initially, the notches are sized for fit horizontally, then further wood is filed out so that the main surface of the top makes a flush fit with the kerfing.

A bead of glue is laid all the way around the kerfing and over the end blocks and then the top is put on and clamped.  Next week we'll finish off the bodies by flush triming the top and doing some initial sanding of the sides.  Then we'll rout out grooves around the bottom and top seams to allow for the  bindings.  Despite my travails, I still think the guitar will look alright.

Class 7: Back from Break

Class met again last week for the first time in four weeks following a two week winter break and a snow day.

Over the Break

I went in once over the break to work on catching up; I glued most of the bracing on my top and installed an end wedge from a piece of Koa that should match the bindings I'll be using.  There are two purfling strips surrounding the wedge; the wedge shape is used to try and get a tight fit with the sides.  By cutting in this shape, the wedge can be pushed into the sides until it fits.  I ended
up with a slight difference in the angle of my wedge and the angle of the slot in the sides, so the fit wasn't as tight as it could have been, but  cosmetically it should be fine.  This week I cut the excess wood and purflings flush to the sides with a back saw.

Fitting the Back

Another step tonight was notching out the sides and kerfing so that the braces on the back would fit snuggly within the sides.  This increases the instruments strength (in case it's dropped).  The notches are made by laying the back onto the sides while they are in the mold and marking the sides of the braces.  The notches are then cut out by making a shallow incision in the side for each notch, then using a small chisel to cut out the notch.
The trick, which is hard for me, is to not overcut the notch with the saw.  It's better to start with a shallow notch and to work it out and deeper with a small file.  The fit with the back can  checked by putting a small light inside the mold and then placing the back on top.  The seam between the back and sides can then be checked for light, indicating a brace that may need to be made deeper.

Glue Up

The sides are back were glued up by running a generous seam of yellow glue all the way around the kerfing.  Leaving the sides in the mold, the back is placed onto the sides and secured with a generous serving of clamps (that's about 2 dozen wooden cam clamps at about $18/clamp in this picture).  Clamping pressure is exerted down the sides with the bottom of the clamp pressing on the side, not on the mold.




Here's the results.  Some clean up of the squeezed out glue is still needed.  Also, the back still extends out past the sides - but
it's a good milestone.

Progressing the Top

When I came in over the break I glued on most of the top bracing.  At the start of class I still had two long braces to glue on, extending out from the X-brace.  Once these dried I began the process of planning and curving the braces.  These are the first steps in tuning the top - probably the single most determinate process in giving life to the guitar.  The goal is to remove wood from the braces in order to lighten the top and allow for greater sustain of the sound.  The top is the vibrating membrane that gives the guitar depth and volume of sound.


At the same time, there needs the braces need to remain strong enough that the top can resist the longitudinal forces applied at the bridge by the strings.  This is a compressive force that tries to bring the neck and body together.  Removing wood from the braces, therefore, must be done with an eye towards retaining strenght.  The initial step is to plane down the X-brack and curve the ends of the other braces.  From there we'll go towards scalloping the braces - adding horizontal curves to complement the vertical curves.  We'll also finish the tuning next week by sanding the top.

Unfortunately, I've set my top up to need some extra sanding.  While working on curving and planning the braces, I left wood fragments between the top and my work surface, thereby adding a bunch of small imprints and one good divit.  The little ones will hopefully sand out, but the larger divit is probably there to stay.  All in all, lutherie remains a challenge.  I'm not yet at the point where I've anywhere near full command of the steps
that I'm executing - probably be a number of years (and a few more instruments) to get towards any basic command of the tools and skills.