Guitar 101: September 2012

Yes, I am really getting close to finishing but there are still a few more parts to make before I can put strings on it. The nut and the saddle need to be sized and shaped, the bridge needs to be glued on and the tuning machines need to be installed on the peg head. All of these are critical but the bridge is the most daunting. It must be secure because of the tremendous amount of stress created from the string tension. It also must be perfectly positioned to insure the guitar will play in tune. Before I started spraying finish on the guitar I carefully measured and marked the position for the bridge on the top. I had previously cut, shaped and finished the bridge from rosewood. Many luthiers finish the bridge by polishing it with a buffing wheel. Since I do not have a buffing wheel, I hand sanded to 320 grit and then hand rubbed it with 0000 steel wool. This is the same method I used on the finger board giving both a nice luster finish. I put a final finish on both the finger board and the bridge with Behlen's Fingerboard Oil. This oil finish darkened the wood and enhanced the grain and tone. There are a couple of different methods of gluing the bridge in place. The traditional and most widely used method uses glue and special clamps that have a deep throat and are fitted through the sound hole to clamp the bridge in position. These clamps are expensive and it takes at least two and preferably three to firmly attach the bridge. As you might expect three clamps of any size going through the sound hole at the same time would be a tight fit and great care would need to be taken to not damage the hole or the finish of the guitar. The second method uses a special vacuum frame rather than the cumbersome clamps to put pressure on the bridge while the glue dries. I decided that I would try to make a vacuum clamp while the lacquer finish was drying. I already had a vacuum pump, the most expensive part of the clamp system, so I started building wood prototypes. My first attempts were based on a vacuum clamp that I had seen in an LMI catalog. I think this fixture is made from aluminum. My design was made from wood, much more brittle than aluminum. It cracked and broke as soon as pressure was applied by the vacuum. I re-made it strengthening the design with thicker wood and paying more attention to the direction of the grain. This version seemed more stable but I still had problems with finding a suitable rubber gasket material and rubber membrane material. Ultimately I had to order these from LMI. They were not expensive and they worked great. Basically the frame was a simple rectangle made from 3/4" oak (maple would probably work better because of the tighter grain) with a rubber membrane attached to one side. I had a little trouble attaching this rubber. I ended up gluing it with J-B Weld epoxy. On the other side of the frame I attached the solid rubber gasket material. A hole was drilled in the frame to allow the vacuum hose to be attached. The frame fits over the glued bridge on the guitar top with gasket down. The vacuum pump is turned on, sucking all the air out of the frame. This causes the rubber membrane to suck down and put pressure on the bridge, clamping it in place. It worked great and it shortened the drying time because of the vacuum.

Gasket side of vacuum frame.

Rubber membrane side of frame.

Frame in position over bridge.

Bridge glued and taped in position.

After taping holes were drilled and two bridge pins were inserted.

Vacuum frame under pressure.

Frame, pump and hose - entire vacuum system.

Detail of frame under pressure.

Detail of vacuum gauge showing 24 pounds of pressure.

After successfully attaching the bridge I decided to work on the nut. I had purchased a bone nut blank and a bone saddle blank from Stewart MacDonald earlier in the process. When I attached the fingerboard to the neck I left a space or slot for the nut. It seemed logical to leave the space rather than removing it later with a chisel. The nut blank was over sized so it need to be trimmed to length and shaped before attaching it to the neck. This was a simple task. I inserted the nut and marked the appropriate length with a pencil, then used my fret saw and miter box to cut off the excess. The nut blank also was to tall and needed to be shaped. I inserted it in the slot again and used a half pencil (a pencil that I sanded off one side to make a flat side) laying flat on the frets to mark the height and radius of the neck. I then sanded down the nut using the pencil mark as a guide for radius and height. I left the nut proud by about 1/16" so the strings would be above the frets. The top of the nut was rounded over on both sides and ends then polished with extra fine steel wool. After sizing and shaping I applied wood glue and clamped the nut in place on the neck.

Marking the nut with the flat pencil.

Flat pencil transfers the fret height and radius.

Marked nut blank.

Trimmed and shaped nut.

Glued and clamped.

The next step was to do the same thing with the saddle blank. It was carefully measured and cut to length. Then it was marked for height and radius by placing it at the end of the finger board and using the flat pencil to mark it. It was sanded and filed down much like the nut. The saddle is not glued in the slot on the bridge, it is held in place by a tight fit and eventually by the strings. It needs to be removeable to adjust the action of the strings.

I then installed the tuning machines in the head of the guitar. I marked and drilled holes in the head when I finished shaping the head. The holes needed to be reamed out for a perfect fit for the tuners. This was done carefully and slowly with a 5 degree reamer until I got a tight snug fit. The tuners are designed with a threaded retaining ring that attaches from the top and holds each tuner in position. There are small finishing screws on the bottom that keep the tuners from twisting.

Tuning machines ready for installation.

Reaming holes for perfect fit.

Blue painters tape applied to reamer for depth guide.

Finished tuner installation.

Back installation.

The bridge pin holes now had to be drilled and reamed for a tight fit for each pin. The pins that I had purchased were a 5 degree taper so the same reamer I used to fit the tuners would work for the pins. I had previously drilled two of the holes for position of the bridge on the top. Now, I needed to drill the other four remaining holes and carefully ream them for a perfect fit.

Reaming the pin holes.

At the same time that I purchased the bridge pins, I also purchased a strap pin. It matched the bridge pins but is slightly larger and is inserted into the bottom of the body. Attaching this was simple but was a little frightening because a hole must be drilled through the body. Yes, the same body that I have been laboring over for a year now has to get a hole drilled through it. What if the hole isn't centered or what if the drill bit slips, or what if the hole chips out, or what if, what if, what if. . . Can't stop now, suck it up and just do it.

Reaming for final fit.

Reaming.

Testing strap pin for fit.

The last thing before putting the strings on is cutting slots for the strings on the nut. Again a pretty difficult and important part. The strings must be perfectly spaced for playability. They must be the right size allowing each string to slide through but not to big to allow movement. Man!!! this precision makes my head hurt. All of my books basically say that I need to purchase a set of sized nut files. I agree but this will cost another $80.00 plus shipping and remember I have already spent enough for two new Martins. I know, I keep telling my self that's not the point but when will it all stop? Well, I decided that it's stopping now, so I'm going to figure a way to cut or file these slots with the tools I have! The first important step is to determine the spacing. Some of the books just say to divide the space evenly for the six strings but others say that you need to allow more space for the base strings and less space for the treble strings. This later statement seems to make sense to me but how much more or less? Through out this project, for over a year, I have been faced with problems and things that I had no reference or knowledge to figure out a solution. Most of the time I was able to go to the Internet for answers. What a great resource, you can always find an answer on the Internet. Usually you find several answers and a how to video as well. The problem is, you don't always know if they are the correct answers. This time I found a web site that had a program formula that you could enter in the specific size of the neck and the size of strings and it would automatically calculate the exact spacing between each string. I took this information and drew a template in Adobe Illustrator with the exact string size and spacing. I attached the template onto the nut with spray adhesive and started cutting and filing. I bought an inexpensive Xacto craft saw that the blade was the approximate width of the thinnest E string. I used this to cut the slots for the thinnest two strings. For the wider strings I used my fret saw and started rolling it side to side to widen the cuts. I finished off the widest slots with fine jewelers files that already had. It seemed to work without having to buy an expensive set of files. I was now ready to string the guitar! HALLELUJAH!!!!!

The string spacing template attached. Mat board attached in front and back to protect the fingerboard and head stock.

After over a year I finally finished! The guitar looks great and more importantly it sounds great. No one was more surprised than me. When I was cutting the slots for the frets in the finger board I made the comment that if this guitar played in tune it would truly be a miracle from God! Well, miracles still exist, this guitar is proof. The only problem. . . it didn't make me any better. I have always heard that it was not the violin that made the master but the master that made the violin. I guess that holds true for guitars as well. Oh well, I'll look better while I am attempting to play. I think that is what's important anyway.

It has been about a month since I finished and the guitar sounds better everyday. Even my untrained ear can tell a difference as it mellows and ages. I did take the strings off and pulled the bridge to sand down the back to reduce the string height. The string action was acceptable but a little high. I think it is better now.