Building a Harp Guitar Part III

There are several ways to make rosette channels from a simple hand held trammel and chisel to a purpose built cutter.  I do several a year, both for my own instruments and the classes I teach, so I use the latter from LMI. There are others available such as one from Luthier Tool. The LMI setup is kind of a pain to set up initially but once set up works very well. I’ve used several products from Luthier Tool and while expensive, they are beautifully made and easier to initially set up.

The problem is the small rosette and sound hole for the harp.  It’s two inches plus and will not work with the conventional cutters.  For this one I took a simple General circle cutter, re-ground the cutter to my rosette dimensions and replaced the center drill with 1/4″ drill stock with a bearing fixed to the top.  When the depth of the cutter is fixed the bearing stops it at the proper depth, much the same as the commercial cutter.

circle cutter

Now the back and top have to be fitted.  I use binding that is a full 1/4″ so that I can cut out the sides and let the main braces of both the top and back run through.  I feel this makes it easier to keep everything aligned.  271Of course, if you are doing a style of guitar without the binding like a Dyer Style 4 you have to inset the braces to the sides because there is no binding.

I always put the back on first so that I can facilitate clean up of any glue left in the joint between the back and the sides.  I use a slow set Titebond and spool clamps to joint the surfaces.  To quote Wyatt Earp “Take your time… in a hurry.”

Before I glue the top to the sides, I make sure the sides have not deformed.  If they have I sand them again to the proper radius.  I then repeat the inletting for the top braces to the sides and glue the top on.

Next time:  Binding and finishing.

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Building a Harp Guitar Part II

Now that we’ve got a bit of history, let’s move on to the actual build.

Even though it looks radically different from a conventional steel string flat top it wouldn’t be foreign to a builder of the latter.  It has an X brace and size that closely resembles a Martin 000. The difference lies in the extra X morticed into the lower half of the bass side to reinforce the top for the 6 harp strings. The bridge plate is also larger to accommodate the extras strings as well.

This is not to say that it is an easy build.  The hollow arm is essentially a hybrid of neck and body, having a head stock and a sound hole.               SH top

The back is pretty similar to a normal steel string as well.IMG-20121220-00204

The head block for the harp head is also a complicated affair that requires some well thought out jigs to reproduce with consistency.

SH harp head

Everything in the build is bigger, including the forms for the body mold.IMG-20121220-00203

A radius form is used for the bracing and grinding the sides to the correct curve.   Instead of a 2 ft. round form a 4 ft. is needed.IMG-20121220-00206All this can add greatly to the expense of gearing up.  I have to say I get a kick out of people asking why hand built guitars cost so much!

The sides are bent using heating blankets (bigger as well) on specially made molds to accommodate the multiple bends.

Next week, sound hole quirks and getting the back and top on.