Class 5: Muti-tasking

Half of our class was missing this evening, which made it a little easier to spread out and get a number of tasks done.  Tonight I finished out the soundhole rosette, did the layout for the bracing on my top and back, cut the X-brace for the top, and glued up the back strip and braces on the back.

Finishing the Rosette

Completing the rosette at this point was down to just bringing the strips of paper and veneer added the week before down to the level of the sound board.  The strips were riding about 1/16th to 1/8th of an inch higher than the sound board, so using a sharp chisel, I worked them down to be closer to flush.  From there, sanding with a small block at 80 and then 120 grit brought the trim level.  A final sanding, prior to later final sanding for tap tuning and finishing, was down with some 220 and a block.  The complete rosette, I'm happy to report, no longer looks like an accident.  I'll try not to go down this course next time.

Gluing up the Sides
Here's a couple of shots,  from the bottom and the top, of the sides being glued up with the end blocks.  Spring clamps were added to the heel block to bring the sides up tight.  Cam clamps were used, three for each block, to bring the whole a assembly together.
The entire assembly is now sitting in the mold in the shop until next week.

Laying out the Top
The heart of the guitar, so to speak, is really the sound board.  This is the component that provides the core vibration and response that give the instrument the bulk of its character.  The top must be flexible, but strong enough to stand up to the longitudinal forces created by the pull and compression of the steel strings.  The layout of the bracing underneath the sound board, therefore, is perhaps the single defining design.

The design used by Edward on his steel string guitars is built around a classic 'X-brace' pattern developed by Martin (and possibly others) in the 1930s or 40s.  The 'X' is the two long braces running from the lower to the upper boughts, crossing and joined underneath the sound hole.  This pattern has been transferred from a template onto my guitar.  The transverse brace runs across the opposite side of the sound hole, and numerous finger braces spread out from the primary X.

After laying out this pattern, I did several test cuts of the X-brace joint before finally cutting this joint in two pre-cut
braces.  Top braces do not have a radius along their length, even though the top will be glued up on a support that will help to provide a curve with a 30' radius.  This curve is gentle enough it does not require the curvature to be set into the  braces before gluing.



Setting Back Braces
The back curvature, however, is more defined than the top.  We are using curvature with a radius of 15 feet.  In order to give some additional support to the back, a center strip of think spruce is glued down the middle of the back.  All of the supports for the back are glued on using a support that already has this curvature.  This is one of the many unique pieces available working in a shop that new luthiers must develop.  There is a caul with the same 15' curve that will be clamped over the back strip in order to provide support during the gluing.

First the back strip is put in place with some help
from masking tape. Masking tape is a great help to lutherie, but one of only a few tools that are cheap and readily available.   In addition to the back from and caul, we are using prebuilt templates and molds for the sides along with additional jigs (such as the router circle cutting jig that got me in to so much trouble) to help move the process ahead.

Another essential element of lutherie is the use of clamps.  Shown here and below are the standard wooden cam clamps that are used throughout the process of gluing braces and many other parts of the guitar.  They can easily run $15 to $20 each, and as you can see in the pictures below, we can easily use 12 or more at a time. 

After the back strip has dried, it needs spaces
set into it for the braces.  These braces, as mentioned, already have a curve set
to their bottom and have been given a preliminary shape on top as well.  Four are glued in to the back to give strength.  Setting clamps for gluing is its own art forms could all be set at the same time.






 Below I found space for 17 clamps on the back so that the braces could all be set at the same time.

 

Another subtle skill, as in all woodwork, is getting just the right amount of glue to ensure a firm joint, but not so much that things get messy and look sloppy.  An example of the latter is shown in the close up below.

Next week I will be fitting and gluing on the top braces as well as putting in kerfing strips along the sides to create a glue surface for the back and later the top.  There is a bunch of work ahead in carving are braces and tuning up the tops to complete the assembly of the guitar body.

Class 4: Finishing soundhole and fitting sides

Rosette Recovery

Last night (12/2) I worked on trying to bring some resolution to the problem with the sound hole.  Here's the rosette after gluing and having the entire top put through the thickness sander (top thickness is a little over 3 mm now).  The inlaid wood looks nice, but inside the rosette the enlarged sound hole is still a bit awkward.  I sanded off the uneven strip of remaining spruce using a rotating sanding block on the drill press.  At this point Edward suggested that I could just leave the sound hole as is.  The larger hole may give an appropriate expansion to the volume of sound from the guitar.

Rather than take this path, I decided to add on inside the rosette.  Using several strips of fibrous paper and one strip of maple veneer, I built up inside the rosette.  After evening out the sanding so that there was no remaining sign of the old spruce, I set two layers of paper, one layer of veneer, and then one final layer of paper.  The strips were cut to be tight so that no clamping would be required.  Three applications of a quick  setting, very fluid super glue were then made to the strips to set the hole package.  When I come back next week, I should be able to sand the strips back down to the inside of the rosette.  I 'm hoping the effect will look reasonably professional and intended, as if there were a ring of ebony set inside.

Fitting Sides

The other task for the evening was to trim the sides that were bent last week so they would fit flush to each other inside the mold and can be joined by gluing in the tail and heel blocks.  Sides are trimmed by pulling them tight inside of the mold and marking where they match the midpoint (end of a single side).  Using the band saw and belt sander, the sides were trimmed close to this mark so that both would fit inside the mold when bolted together.  It is important to trim bit by bit to get the tightest fight between the two sides so that the resulting joint will be tight and help hold the sides inside the mold.

Here's what the two sides look like put together inside the mold with the heel and neck blocks put in place but not yet glued.

 

The shape of what is to come is getting clearer!  A slight curve was put on the inside of the heel block with some light sanding so that the butt end of the guitar will have a slight curve.  Edward has switched over to using laminate at this end instead of the traditional mahogany in order to add strength, especially for those guitars that get dropped onto a strap end pint.

The mahogany neck block on the other end had two holes pre-drilled to later accept the neck.  The necks will be joined flat up against the end of the guitar using two bolts.  The top of the guitar is currently face down, and the still serves as the primary registration due to the curve (15-16 foot radius) put into the back to end strength to the instrument and to better let it respond to changes in humidity resulting in changes to the size of the back.  The bottom of the neck block (up in this picture) has had a preliminary curve put into it to match the back  Later on it will be sanded down to this curve in a sanding bowl. Next week I'll be gluing this all up, sanding down the rosette, and starting work on putting braces into the back.

Class 2: Rosette and Preparing to Bend Sides

Soundhole Rosette

I continued to work through a couple of iterations of the radii I would need to define the inside and outside curves of the rosette. 

These were laid out on paper and then on the piece of spalted maple.  The maple was taped with double sided tape onto a piece of MDF in order to be cut with a router with a circle cutting jig.  The router is equipped with a downward spiral flute bit - the downward spiral helps to ensure that the edges of the cut are not torn upward.

Afterward, the resulting circle had to be carefully separated from the MDF in order not to break the ring; inevitably,  however, it did break into a few pieces.  Once broken, however, it is easily reassembled.  Additional 'grain' can be added by using a pen to color the would around the fractures, but I'm skipping that step.

Here is the ring (now in 4 parts) ready to be laid into the soundboard next week.  In order to define the channel into which the pieces will be inscribed a channel will be routed in the sound board.  Layout of this channel has to also allow for room for an inside and outside strip of purfling as well as the glue joints between the wooden rosette ring.

Edward estimates that each glue joint adds .005" to the required channel with, and the purfling strips measure .060" across.  The channel width, with two purfling strips and associated glue joints, must be a total of .130" wider than the ring.  Measurement of the ring is taken off of the MDF on which the ring was cut out.  The measurements are then increased the required  amount and then laid out on the top.  A dry run to sizing the channel will also be done on the MDF board on which I am working.  The ring is about .080" thick, so we need to get the router bit depth a little shy of that (about .070") so that the rosette sits a little proud of the soundboard prior to thickness sanding.

Bending

Half of the class bent the sides for their guitars today.  I'll do mine next week, but got them set up with the binding strips in preparation.

Each of the two sides was taped up with a binding strip on the top and bottom so that the bindings can be bent together with the side in order to have the same curve.

The bending process begins with soaking the wood for several hours.  Each side is then heated in a sandwich made of the side, encased by two pieces of sheet metal, encased by heating blankets (see the first picture in the sequence below).  These blankets can get north of 500 degrees, so the sides heat quickly and give off steam.  After heating for a while, the whole package is firmly forced into the mold then clamped together for the sides to cure.

Here's the sequence, demonstrated by Edward

Edward uses the following timing in this sequence:

1. Heating blankets are plugged in and the side is heated for 2.5 minutes.
2. While still heating (use gloves), the side is forced into the mold.
3. At the 4 minute mark, the heating blankets are turned off, so as not to overheat and burn out over time.  LMI recommends using the blankets with a rheostat or other control so as to not overheat and burn out, but Edward uses these timings based on full throttle.
   
4. After a 30 seconds, (4.5 minute mark), the blankets are turned on for another 45 to 60 seconds.
5. At about 5:15 or 5:30, the blankets are unplugged and the sides are left in the frame for an hour before unclamping.

All three sets done last night seemed to unclamp and come out fine.  Next week, I'll be bending my sides and finishing the channel for the rosette so that it can be glued up.