Building a Harp Guitar Part IV

Now we come to the point where it is looking like an instrument!

IMG-20130108-00229The top and back have been trimmed and the binding channels have been cut.  This is pretty much the same as on any guitar… just more of it!  Any of the systems by Stew-Mac, LMI, Luthier Tool and custom setups etc. will work.  For this set up Scott used the Luthier Tool binding cutter with a bearing bit setup from LMI.  Most of these cutter jigs use some sort of trim router and this is no exception.  luthier tool binding cutterThis picture is from their website

As with any system, it takes some practice to become proficient.  The jig has two bearings one on the top and the other on the bottom of the leg.  These have to be in contact with the sides in order to maintain proper depth and width.

The neck on this guitar is a conventional bolt on slot head so I won’t go into much detail on that as I’ve covered this on other posts.

IMG-20130115-00234The finish, while pretty straight forward is complicated by the size of the instrument.  Some creative ways of positioning it for spraying are necessary.

I use a length of 3/4″ pipe and attach it to a saw horse and to the body where the neck attaches.

The other issue is supporting the body for fretting when the finish is done and the neck attached.  A Taylor fret buck is worthless because the harp arm won’t support the edge of the buck so it will give too much when it’s in use.  I use an arbor press when fretting and in this case the body has to be supported when fretting over it.  To solve this, I made a jack to support the top.  I used two pieces of wood about 1/4″ thick, one for the top and one for the back to distribute the pressure and put a small scissor jack
to support the pressure.

In the future, I would probable use a neck joint that would allow fretting before the installation of the neck to the body.

Other than the things mentioned, building a harp guitar in theory is not much different than a standard 6 string.  In practice the larger scale and added strings do add to the complexity above and beyond a 6 or 12 string.  IMG-20130124-01093Photo of Don Alder by Scott Burwell Holloway.


Gibson Style O part 3

During work on the body I was also working on the neck.  As you might expect it was in the same kind of shape. A bad binding repair on the peghead, coupled with a piece of missing head stock overlay. The back was also very banged up.  When the fretboard was removed, big chunks of very brittle mahogany were torn out.  There was a v shaped maple insert in the center of the neck.  Only a third of the fretboard was left after I got the guitar.  It didn’t appear or smell to be rosewood, looking a lot like Macassar ebony.  The Fret House had already ordered a new “24 ¾” slotted ebony fretboard from Luthier’s Mercantile to replace the old one.  It was interesting to compare what I had left of the existing one and the new one to see that they were completely different.  Something I wouldn’t even have checked if I hadn’t read Dan Erlewine, Frank Ford and Tim Shaw’s article in American Lutherie Magazine on the different scales Gibson has used in the past.

The first thing I did on the neck was level it with sand paper stuck to the bottom of my joiner plane.  Then using a simple jig I cut the truss rod slot using a ¼” round bottom up-cut spiral bit.  I used a plunge router to make the cut because I could lift it up after the cut in the peghead, leaving wood in place for the screw in the cover.  The next step was to drill a ¼” hole to join the two slots.  The rod was a double action from Stewart MacDonald and the square ends of the rod were fit into the channel.

The fretboard was next.  I cut the board to shape to the 1 ¾” wide minus the thickness of the ivoroid binding, using the original as a guide.  After heating the binding in hot water I fitted it to the tight curves of the end of the board.  ¼” Holes were then cut for the mother of pearl position markers and the side dots.  With the glue dry a 16” radius was put on the fretboard and it was compression fretted with medium fret wire.

Since the neck had to be cut down and a piece of the peghead binding had been poorly repaired, I decided to replace it all.  By doing this and veneering the back with mahogany, the peghead almost looked new. I filled the missing piece of ebony on the front with dust and glue, taking care to fill the missing filler in the inlay, which thank God, was still intact.  The channels for the peghead binding were done with a router, with the exception of the two nearest the nut as the router bearing would have cut too much out.  Those channels were done with a Sloane purfling cutter. The peghead holes were then drilled to accommodate the new turners.

Before I put the fretboard on the neck, the angle had to be checked.  As you might have guessed 85 years had taken its toll and was at a much too shallow angle to be playable.  One of the things I did when I put the body together was to try and keep the original registration of the scrolls on the top and back aligned with the sides, but I realized that I’d have to slip the block a little.  I heated the back and head block with a silicone heating blanket and moved it as much as I dared, and took up the chisel to finish the job.  I took a full  3/16” off the heal of the neck to get the proper angle.  Luckily there was a lot of wood on the neck and I thought it actually made a better match to what would be a new svelte neck shaft.

Once I was satisfied with the neck I put the truss rod in, filled the gaps in the mahogany with dust and epoxy and glued the fretboard to the neck.  The neck was thicknessed with a Wagner safety plane and contoured with rasps and files.  The ebonized stripe in the center of the neck was lost and I thought it would very difficult to redo without a lot of head scratching so rather than spraying the stripe on with color, Jim and I decided to leave it out altogether.

After finishing the contouring, I sanded down to 320 grit and joined the neck to the body.  The neck angle had positioned the fretboard so that it didn’t contact the body by the sound hole, so a piece of spruce was fashioned to make up for the gap. After rounding the part of spruce that was under the exposed edge of the fretboard, it was barely visible.  When the glue was dry I re-contoured the body to blend in to the narrower board.  Jim had supplied mammoth ivory bridge pins, end pin, and Waverly’s with real ivory buttons, so that was a given.  I have one, yes just one, ivory nut that I’ve saved for about 30 years. And while I don’t put elephant ivory on my new guitars, nor would I put it on any modern guitar I repaired, I thought this is the instrument for it.

Next week:  Finish, set up and trouble shooting.

Set ups and such

Now that we understand truss rods a little better, let’s move on to nuts, saddles and compensation… is that a band?

Nuts and saddles have been made of many things… plastic, ivory, bone and even mother of pearl.  Of all these bone is the top choice.  It’s easy to get, cheap and transmits sound very well.

Cutting the slots for strings in nuts is more complicated than it sounds.  The spacing between the strings is not equal.  Simply taking the space and dividing by the number of strings will give you a spacing that feels awkward to play.  The thickness of the strings has to be taken into account.  The thicker the string the more space.  Lutherie tool shops such as Stewart MacDonald have rulers that will give you correct spacing if you don’t want to agonize over the math.  While you can get away without this tool, the files to cut the slots are a must and they’re not cheap.  In the smaller gauges they can be quite fragile as well, especially when you get to .010″.

I usually start by taking a .060 depth as my target and dial in individual preferences from there.  If you do go too deep you can use some of the bone dust and cyanoacrylate glue to build it back up again but it will not last as long as pure bone.  On customer’s guitars I just start with a new nut blank.

Making the saddle is a little easier.  Martin uses a 3/32″ thick saddle but most makers (including myself) use one that’s an 1/8″ thick.  This has the benefit of being stronger and gives more area for compensation (more on that later).  The bottom of the saddle and the slot should be perfectly flat.  This is critical for the nut as well.  If both are not in direct contact your sound will suffer.

The top of the saddle should be the same as the radius of your fret board.  Radius gauges are available but you can simply take a piece of card and trace the end of your fret board to get the radius.

Using files and sandpaper radius the top of the saddle.  Don’t worry about the height yet, it should be high.  String your guitar up and measure the height of the string at the 12th fret.  It should measure 3/32″ from the top of the fret to the bottom of the string on the base side and about 4.5/64″ on the treble. If it’s higher (most likely) remove double the distance from the saddle.  Example if you are a 1/64th high take 1/32″ off the bottom of the saddle.

Once the height is dialed in you can intonate the saddle.  Every guitar has a scale length. Martin uses two, 25.4″ for Dreadnaughts etc and a shorter one for 00’s and 000’s.  Scale length affects the sound to some extent.  Shorter scales tend to be a little sweeter, longer scales more open and rich.  Some fingerstyle guitarists prefer scales that are 26″ or more. The scale is measured from the beginning of the fret board to the saddle, theoretically anyway.  The strings actually have to have a greater length to play in tune.  This is because the string is not laying flat on the fret board but suspended above.  The higher the string the more it needs to extend beyond the scale length.  This is also true of string diameter.  The bigger the string, the more it needs to be compensated.  This is why steel string saddles are slanted at the bridge.

One of the tricks I like to use is to take a piece of the high E string (.009 to .012″) and place it under the string you wish to intonate so that it is in line with the saddle.  Now pluck the string in open position and tuned to pitch, then fret the string on the12th fret.  If the pitch of the fretted note is different you can move the piece of string forward or backward until it is. If the fretted note is sharp move the piece of string back, if flat move it forward.  When you are satisfied, mark the position of the piece of string.   Take the saddle out and use the files again to shape it.  Don’t take it to a point but round it over so the string breaks over the saddle gently.  Now your guitar should be in tune all the way up the fret board.

I do find that all this goes down a little better with a nice Chardonnay!