Acoustic Guitar Bridge Replacement
I recently had the opportunity to perform a bridge replacement on a really cool 70s era Ibanez Concord 699. These were really good guitars, and were unique in that they were all solid wood, with no laminates, and had spruce tops with maple back, sides, neck, and fingerboard. Yes, fingerboard. Don’t see a lot of acoustics with maple fingerboards, so I was definitely intrigued!
The original bridge had cracked through the string pin holes, and had completely come apart. Another unique feature of this guitar, the original bridge was also adjustable. It had a brass bracket holding the saddle, and screws at either end of this bracket to facilitate raising and lowering the saddle, and therefore, adjusting the string action. Pretty cool.
This is what the original bridge looked like at one time before it broke :(
Obviously, by the time the guitar got to me, the bridge had completely come off, leaving a bald spot on the gorgeous solid spruce top. A little sanding to prep the bald spot, and she was ready to have a nice new bridge glued on.
Sourcing the bridge was not an easy task, but I finally found one that was very close. The Retro Parts RP287. It’s a nice rosewood bridge with an adjustable saddle. It was slightly wider in the string spacing, but not enough to make a huge difference. The only thing missing was the hole for the bolt behind the bridge pins, but that would be easily remedied with a well placed countersunk drill hole, and a pearl dot inlay.
Retro Parts RP287. This will make a great replacement for our original Ibanez bridge!
New and (what’s left of) original bridge.
The placement of the bridge is critical to the intonation of the guitar, so I spent a good amount of time measuring the scale length, and marking the location for the new bridge. This is a fairly straight-forward process, but you only get one chance to place the bridge and glue it up, so I wanted to make sure it was right!
Essentially, in order to get the bridge position, you measure the distance between the nut and the top of the 12th fret. This distance is equal to half of the scale length of the guitar. Since the 12th fret marks the halfway point, you then measure the same amount from the top of the 12th fret to a point on the guitar top. This point is the exact scale length.
Now, the saddle needs to be placed at the point of exact scale length plus a small amount of compensation to account for when a string is fretted. When you fret a string, the pitch will raise slightly due to the increased string tension, so the saddle needs to be moved back a bit to compensate for this, and bring the note back to pitch.
This compensation amount varies a bit with string type, desired action, saddle type, etc. but a good rule of thumb that has served me well on 6 string steel acoustics, is to add about 1/8″ (0.125″) to the scale length.
If you are interested on more exact calculations, there is a fantastic calculator available at Liutaio Mottola’s luthier wbsite. You can check it out HERE.
Note that with a compensated, or slanted saddle, I take this measurement on the centerline of the neck and top. That way, the bass and treble strings will be slightly compensated with the slanted saddle, but the D and G strings will land right on the scale length + compensation measurement. This will allow the maximum flexibility when making small intonation adjustments to the saddle later. Also note that this point on the top is where the top of the saddle needs to be placed, not the front of the bridge!
After the top prep, the marking of the bridge location, and a little masking with painter’s tape to protect the soundhole, I’m ready to drop the clamps inside the guitar, and get to gluing!
Always use a clamping caul when clamping…..well…..anything! There are expensive cauls out there, and you can spend some time making your own if you’d like.
Here, I’ve used some scraps from a balsa wood project my daughter had. They are soft enough not to mar, but solid enough to provide good pressure, and they don’t split. They work great!
Clamps in soundhole, cauls present, getting ready for glue!
Next, I prep for gluing. I’m going to use standard wood glue for this bridge. I know, I know…..You can talk about hide glue and vibration transfer and tone until you are blue in your face, but you will never convince me that hide glue is any better than carpenter’s glue for a bridge. Hide glue is a pain to work with. Hide glue also results in lifted and completely separated bridges if the stars aren’t aligned absolutely perfectly, or the temp is .06 degrees off, or there’s a fly near your bench, or a molecule of dust gets in it, or……you get the idea. The stuff is finicky as can be, and I’ve had too many bridges pop off after using hide glue. Don’t get me wrong, it has its place…..just not under the bridges I do unless the customer demands it! But enough of my rant…
Make sure to have any tools and items needed for cleanup at the ready before gluing. I always have some rags, a small bowl of water, some paper towels, and a small screwdriver near by.
I do a “dry run” of placing the bridge, putting the clamps and cauls in place, and lightly clamping them to make sure everything will go as planned when the glue is in there. I take some measurements again to make sure the bridge is centered and in the right position. Then, I release everything, and apply a light coat of glue to the bottom of the bridge.
You don’t need a ton of clamping pressure to get a good joint. Just enough to get good compression, and squeeze out any excess glue. Start cleaning up the excess right away by dampening a cloth rag and folding it over the end of a flat screwdriver or similar flat object that can be used to get to the very bottom of the joint where the bridge meets the top. Run the screwdriver/rag combo down the seam of the joint to wipe out the excess glue. This needs to be done several times. Tighten clamps, wipe away excess, repeat. Also, pay attention to any other areas of the bridge where glue will squeeze out. This particular bridge does not have holes cut through for the pins yet, but many do. You will want to remove excess glue from these areas also.
Once the clamps are fairly tight, and all of the excess glue has been removed, leave the bridge clamped up overnight to cure.
Bridge all glued and clamped and resting for the night.
The next day, I remove the clamps, do any final glue cleanup, and prepare to cut the holes for the string pins, the bridge screw, and the saddle adjustment screws. At this point I tape up a vacuum cleaner hose to suck up some of the dust. This, of course, isn’t necessary, but I hate cleaning, so I try to do it as I go. ;)
I also add some protective tape around the bridge to protect the top.
I start with string pins. The RP287 has holes started, but not all the way through, so I center punch the existing holes and drill them through with an 1/8″ bit. A 3 degree tapered reamer is then used to finish the holes out to get a good fit to the pin. I’ve used a bit of painter’s tape here on the reamer to indicate when to stop for the hole to be the perfect size. This was done on the first hole by trial and error, reaming and then pressing in the pin until a proper fit was achieved.
Then it’s on to the bridge bolt/screw. Some bridges have these, others don’t. There was no provision for one on the replacement bridge, but the original had one, and the customer wanted to have one on the replacement. I had some 1/4″ pearl dot inlays left over from a fretboard project that would work perfectly to cover the new screw.
I simply drilled a 1/8″ hole for the screw, and then counter sunk the hole with a 1/4″ brad point center bit. This will accommodate the screw nicely, and is the perfect size for the inlay.
After installing the screw, I slip the washer and nut on through the soundhole, and tighten it down. Make sure it’s tight, because once the dot is glued in, it will be next to impossible to remove without some damage to the bridge!
The dot inlay is them dropped in place with a drop of super glue to hold it in.
Finally, I drilled a 3/16″ hole at either end of the saddle slot to accommodate the screws for the adjustable saddle.
Reaming the bridge for the string pins.
Drilled, reamed, screwed, and in-layed!
Now comes the sanding. Lots and lots of sanding! I start fairly aggressive at 220 grit to get the inlay smoothed out, and then gradually work my way down to 2000 grit. Rosewood has a beautiful finish, and really doesn’t need any treatment other than a good sanding and perhaps some oil, but I usually just sand it down and let the beautiful grain shine through!
Sanded, and ready for strings!
After the bridge is sanded and polished, we’re ready to string it up! I do another test fit of the pins, and seeing they are good, go ahead and start stringing her up.
Since this bridge is adjustable, we can set the action with the adjustment screws. This is really handy. Normally, I would need to file and sand the bottom of the saddle at this point to set the action, but here I just need to adjust the screws like on an electric guitar bridge! I like to aim for about 3/32″ on the bass side, and 5/64″ on the treble side at the 12th fret. Of course, if this bridge weren’t adjustable, I would want to do a final adjustment with the customer playing it to get it to their liking.
After setting the action, and stretching and settling the strings a bit, it’s time to check intonation.
This is done with a good quality tuner, and fretting the open note, the note at the 12th fret, and sounding the 12th fret harmonic of all the strings. All of the notes on a given string should be the same (the 12th fret note and harmonic will of course be an octave higher). If the 12th fret notes are sharp, the string length needs to be lengthened. If they are flat, the string needs to be shortened.
The intonation came out very well in this case thanks to a good bridge placement, and no additional adjustment was required.
If adjustment were required, however, the saddle can be filed on the front or back of where the string breaks over the saddle to adjust it. File the front of the saddle to move the break point farther back to increase the string length, and file the back of the saddle to move the break point forward, and shorten the string length.
With the action and intonation set, it’s time to take a spin on this old girl who’s been given a new lease on life! She plays and sounds awesome, and I can’t wait to see the smile her owner’s face after being able to play her again!
This was a really fun project, and I think it came out really well.
Let me know what you think in the comments below!
Ready to make some sweet sounds again!