Thursday, January 23, 2014

Another Acoustic Tool -- Part Five

I mentioned in the last post that I had completed gluing the body together and the next step would be cutting a channel in the top and back edges for adding binding (purfling).

I've learned that this process too can be done in a couple ways.  If I were a 'real' luthier, I might do this by hand with a homemade tool created from a broken saw blade, but that seems like it's not a simple procedure.  Remember, I said I like simple.  So, I chose to build a special router table, which would work a little easier for me.  This whole construction effort took about two hours and a few buck worth of scrap wood I had laying around collecting dust.  Geez, I love it when a plan comes together.

I surface mounted a small craft router under the top working surface near the edge so that the remaining open surface is where the guitar body will rest during the channel routing process.

The router blade can be moved up or down for precise adjustment in depth of the channel.

A special adjustable fence had to be fabricated to adjust the thickness of the channel into the side of the guitar.  We're not talking about a channel the size of the Grand Canyon, so the movement of the fence is minimal. The binding is slightly more than one-sixteenth-inch thick and about one-quarter-inch deep.

The body of the guitar will ride on the fence base up against the adjustable nose.  By carefully moving the body surface against the nose and perpendicular to the the router blade, the channel can be cut into the body with very little difficulty, so long as I pay attention to what I'm doing and don't get lost in some Muddy Water's blues trip evolving from the recesses of my mind.

More Acoustic Talk -- Part Four

This acoustic guitar building project has been a great learning experience.  I've created special tools, and I'm learning how to use them.  I've assembled odd shaped pieces and shaped some odd pieces.  I've learned that sound is greatly affected by the parts and pieces used in the delivery process.  And, I'm learning there is a helluva lot of thought, planning, effort, and meticulous work that goes into this hobby.  Perhaps someday, if I live long enough, I may be able to say I'm a novice luthier.

The top, back and side(s) assembly was the last thing I posted about, which was pretty straight forward, but also tedious, time consuming and a bit mind numbing.  If I screwed this up, the game would be over . . . but, I didn't.

When the sides, heel, and tail blocks are matched up and glued, the next step in the process is to add lining (kerf) to each of the side edges.  The lining is there for stability and for a surface on which to glue the top and back.  Kerf is a finely serrated piece of mahogany, which can be easily bent to conform to the shape of the guitar sides.  Yes, it takes thirty eight small spring clamps to properly hold tension on each surface during the gluing.

It's almost time for gluing top and back onto the sides, but small vertical spruce ribs need to be glued to the sides at the upper bout, waist, and lower bout to add just a little more stability to the guitar.

I've discovered several different ways with which to apply pressure to the top and back surfaces during the gluing process, and I created different tools for the purpose, but I chose the most simple process for me . . . I like simple.  I cut a sheet of one-quarter-inch ply (it's very flexible, but sturdy) in the shape of the body mold; drilled a series of corresponding holes in the sheet and the mold.  After dropping in the completed guitar sides, I applied glue to the kerf, smoothed it around evenly, and centered the top in position on the kerf.  It took a couple minutes for the glue to become tacky enough to carefully lay the sheet on the top surface without moving the top.  Once the sheet was down, I started adding screws to the holes in the sheet, and commenced to tighten then just enough in a criss-cross manner (I learned this years ago from my grandfather, when we were rebuilding the engine in my first hotrod), until all surfaces were tightly assembled together.  This was a little tricky in that the top has a very slight arch to it.  After the top was securely glued and allowed a 24-hour cure time, I did the same process for the back.   But, the back was more delicate, because it has a compound arch to its surface, which required a whole lot more attention to alignment and movement, and because of the shape, I allowed the glue to cure for 48 hours.  You can see from the photo above how the back required a great deal of surface pressure.  

These photos show the assembled body with the top and back glued in place on the sides. After allowing the glue to continue to cure for a couple days, the overlapping top (spruce) and back (rosewood) material was removed and the edges sanded in preparation for routing a channel in each surface for binding (purfling) to be glued in place.  

If I learn nothing else, I got the lingo down pat.  ;-) 

Saturday, January 18, 2014

Acoustic Progress -- Part Three

After leaping into the acoustic guitar building arena, there was ample activity in creating jigs and tools especially associated with the project.  I could have avoided this if I was lazy, incapable, or willing to spend money like a drunken sailor (oops, now I've just pissed off my military friends in the middle east, whom I've gifted with guitars and amps).  Commercially crafted tools are expensive, but no more useful than what I have had the enjoyment of creating, and lots of beer money left for me.

You've already seen some of the tools in a prior post, but here are a couple other shots of special stuff.

I've learned there are a couple ways to attach the top and back of the guitar to the finished sides, and one of those ways is to use clamps such as the one shown here.  It's a simple screw-type arrangement with cork-faced 1-1/2" x 3/4" wood blocks drilled to accommodate a 8-inch threaded 1/4" shaft with rubber pieces to protect the surface of the guitar. Washers and a wing nut completes the job.  The clamp is placed against the guitar side, when the glued top or back is in place, and the nut is tightened to apply pressure to the surface during the gluing process.  Pretty simple to build and use, and a lot less expensive than commercially available items that look and work the same.

A cabinet scraper is another essential tool, but when you live in a place that has limited supply of specialty tools, it's sometimes easier (and more fun) to create your own. I used a paint scraper blade attached to a custom handle, and voila, a useful tool.

I've been diligent about taking progress photos along the way, so that if I undertake this process again, I'll have a leg up on the project.  And, it's nice to be able to sit back and admire what these old hands have been able to accomplish along the journey.

Shaping the top and finishing the rosette around the sound hole on the outside surface was the first step.

Then came bracing on the inside of the top.  I chose to replicate the Martin guitar pre-WWII scalloped bracing that was used on the D18s and D28s, because of the deep warm sound created from this arrangement.  This process required a whole lot of research, and thanks to the web and a few vintage book stores I was able to find plans and helpful information.

Bracing for the inside of the back is a little less involved from the standpoint of style, but there is one thing that makes this a bit complex.  The back must have a slight crown to it, so the bracing has to be cut to form that crown, which is dimensional from the center to the ends.  Thanks to great layout diagrams, this was a relatively easy process.  The center wood strip is there to stabilize the bookmatched surface of the the back, which like the top it is constructed from two pieces of material glued together on the edge.

Properly shaping and fitting the sides to the required dimensions is crucial to the overall design.  If I screw this up the top and back will not fit properly, and the neck will not join the body correctly.  Here's where the body jig comes into play.  The shaped sides are placed into the body mold and carefully positioned on 'center' with the mold, and any excess material is then marked and cut to fit.  Measure twice or three times, and cut once!  There is no gluing it back together to get it right.

When the sides fit perfectly, thanks to the help of the spreaders I built, the heel and tail blocks are glued in place.  Then the lining (kerf) is glued to the top and back inside edges of the sides, which is the surface on which the top and back are glued.

I'll post more photos with explanations as progress is made.  So far, so good!  I keep my fingers crossed so that anything unexpected is 'good'.