Jul 22, 2016

F907 Bridge Modification / correction

Please see this gallery showing how I originally replaced the adjustable metal bridge "insert" with a rosewood insert having a slot for a bridge saddle;

Not long ago, I replaced my Micarta with a bone saddle. As you can see, the saddle height is very shallow and the break-angle is almost non-existent. I got to the action I like (went too far I guess) but the saddle height is a real issue. There is no downward pressure on the saddle, and in a couple of the photos, you can see that the saddle is pulled slightly toward the nut. The saddle slot is worn a bit which complicates the situation

The neck relief was off slightly - not bad for a 44 year-old guitar. I corrected that, but it didn't address the real problem, of course.

The correct solution is a neck-reset, and even though this is a guitar that I am emotionally attached to (my very first one) I can't justify paying for a reset and not inclined to do it myself. 

So, my solution is to shave the bridge 1mm. I spent a lot of time (off and on, since I am not in a rush) planning this operation. The bridge is actually fairly thick, and can afford to go on a 1mm diet.

Martin's spec for saddle protrusion is 3/32 min to 3/16 max (2.4mm - 4.8mm)
I currently have 2mm, so shaving the bridge 1mm will give me a min of 3mm bridge protrusion. My action is a bit too low, so I should end up with about 3.5mm when done. I will work on the new saddle to get the final height. All of this should get me the cut-angle I need for proper downward pressure on the saddle. The distance of the pins to the saddle doesn't make it easier btw. 

Shows the thickness of the bridge. About 8mm in the back. 

Patient is preped for surgery

I marked a line on each side that represents a 1mm cut, and taped the sides so they are't damaged while I am shaving the top. I will blendin the sides as a last step.

The new bone bridge blank is very thick, which gives me a lot of flexibility with compensation. It will fit nicely into the slot.

I am also replacing the nut with a hunk of bone, but that is too boring to detail. 

I will post more photos after the surgery is complete. 

She is looking forward to post surgery life. 


Surgery was a big success. It took about 3 hours in my 95 degree garage but we made it. 
I shaved about 1.5 mm from the top of the bridge and then made a new compensated bone bridge. I added a bone nut as a bonus. 

Better cut angle:

New bone nut:

Showing off the Grevin Tor-tis 30's style Pickguard. 

Plays great!

Action is slightly higher than what I had before, but I wanted to make sure there was enough downward pressure on the saddle. 

I set to Martin 000-28 specs of course if possible. Here is what I have now:

Bridge height: 8/32
Saddle protrusion: 5/32 bass, 5/32 treb
Neck relief: 0.010
Action at 12th fret:  3/32 bass, 3/32 treb ( I will lower a hair at next string change. 
Action at nut, 1st fret: 0.020

Dallas Dreadnought-Style Acoustic

I discovered photos of a Dallas branded acoustic guitar. It appears to be a dreadnought size and shape but hard to tell in the photos. 

It was made in Japan.
Uses the same truss rod cover as most Jedson and Terada acoustic guitars.
It seems to have most in common with the Jedson 9000