Sunday, February 19, 2012

Harmony H700 Repair

My brother brought over a 1947 Harmony H700 archtop guitar that belongs to a friend of his.  A local music shop had botched a nut installation and the guitar had neck problems that required running the bridge to its lowest position to get the action playable.

In the late 1940's, this guitar sold for about $20 in the Sears mail order catalog (around $200 if adjusted for inflation today).  The guitar has a maple body and spruce top.   It is a really nice old guitar that has good sound and "vibe" to it so it is very worthy of repair.

On inspection, you can see that the company painted the guitar with a sunburst pattern as well as an artificial fiddle back pattern on the back and neck.  You can see in this photo that the areas where the paint has been worn away show non-figured maple.

The stampings seen through the "f-hole" show that this guitar was made in the first half of 1947 (F 47).
The reason why the neck is funky is because the glue joint and tenon of the neck/body joint has become distorted over the years.  A paper shim has been inserted into the gap showing separation of the base of the heel from the body.  You can also see a fine white line to the left of the heel where the body side has cracked when the heel glue joint failed, taking the top half of the body side with it (area between the crack and top binding).
Because there is no binding covering the end grain of the back piece, it looks like the back has shrunk over the years and has pulled back from the side.  The body however sounds solid when you tap it and I can't get even a .0015 feeler gauge into the joint so this does not appear to be a fatal flaw.  A humidifier in the case could help this out.
The guitar's neck has a very pronounced "V" shape to it as shown by these profile templates.  You can see from the wear on the neck that a previous player used mainly the open positions when he played (thumb wear below the headstock) and that he used a stand that supported the lower guitar neck (wear near the base of the neck).  A strong magnet does not detect any iron in the neck so unless there is a bronze or ebony truss rod, this guitar's neck might be shaped this way to strengthen the neck.  BTW the frets are bronze.

Using an inspection mirror through the "f hole" you can see that the manufacturer used reinforcing cloth to help prevent chipping of the fragile f holes.

This is a shot of the head block inside the guitar.  Light can be seen coming in from the outside through the crack in the side of the guitar.  This is the same crack that was shown from the outside earlier.  I assume that the neck tenon fits into this block and I wonder if this block has separated from the side causing the crack?  A neck reset might be in order here but since they cost between $200 and $350 anything we can do to prevent doing this is all good.
 This is the tail stock as seen from the inside and the hole in it is for the strap button.  You can see glue extruded to the sides of this block.  An ad from 1949 says that these guitar bodies were made with a special "plastic glue" and this does not look like hide glue to me.
A new bone nut was made and glued into place.  This dramatically improved the guitar's sustain and tone, so far so good.
Here is a view of the heel joint gap with a flashlight shining a light through it.  The body was protected with masking tape and the joint was cleaned up with 220 grit sand paper.
 A custom cut wooden caul with a protective cork lining was placed at the base of the body.
A piece of .010 brass shim was made with a series of hole in it.  This was loaded with Tightbond glue and the joint was filled with glue.
The heel caul had an angled bevel cut into it that matched the cant of the base of the heel.  Another caul was placed on the fingerboard and lashed to the heel caul with an old E string so that when pressure was exerted on the heel caul, it did not slip off of the base of the heel.  This is a photo of the bar clamp in place and a small amount of glue seeping out of the joint as pressure is exerted on the heel so we know the joint is filled with glue.
 Here is a final photo showing that no light can be see through the heel joint.  The crack in the side of the guitar body also closed off as the heel was brought back into contact with the body.
Unfortunately, this glue joint failed just seconds after the clamps were released even though there was no string tension on the neck.  It was a nice thought, but the force of the tenon joint which has been distorted over the many years of string tension was stronger than the glue bond.  The good news was that the glue failed not the wood of the body or heel so there was no damage to the guitar.  Now I know that a neck reset is the only solution to this guitar's neck problems.  Fortunately, this guitar still plays well down the neck which is where the owner usually plays it so all is good in the end...

After thinking about the neck for a couple of weeks, my brother and I decided to work on the adjustable bridge.  The high E string buzzed up the neck at the 15th position on up.  Upon further inspection it was apparent the the notch in the saddle for the high E string was cut more deeply than the other notches.  We deepened the other notches for the strings (even compensating for the B string) and set them to a 12 inch radius to match the fingerboard radius.  This allowed up to run the saddle up a little bit to get clearance up the neck on the high E string.  Now she plays well up and down the neck and we avoided a costly neck reset for the time being!

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