Fixing a broken arm vintage Fender tremolo

My friend Zsolt Benkő is a brilliant blues guitar player and my great guitar tutor. When I spent 3 months in Hungary last year with my family, he showed me a MIJ Fender Strat vintage tremolo bridge. It was a rusty, worn piece of hardware with a broken tremolo arm. The threaded end of the arm has broken in the sustain block and the remaining stud is buried deep inside.

 

 

"Sic transit gloria mundi"

“Sic transit gloria mundi”

Look at those rusty, worn saddles...

Look at those rusty, worn saddles…

The remaining stud of the broken tremolo arm is buried deep in the hole.

You can see the rest of the broken arm buried deep inside the hole

You can see the rest of the broken arm buried deep inside the hole

“Just give it to me” I said with great self confidence “It’s gonna be a piece of cake to fix.”

I was wrong. I was definitely wrong.


 

Typical tremolo design

Typical tremolo design

Here is the design of the vintage tremolo.
The base is steel plated with copper and nickel, the saddles are also bent steel. The intonation screws with the spring attached to the end of the base plate. Six countersink beveled holes makes the knife-edge to swing the bridge on. A large and heavy sustain block is attached to the bottom of the base plate made of zinc alloy (aka Zamak). The base plate and the sustain block has a matching hole for the tremolo arm. The thread for the arm is tapped into the lower part of the hole in the sustain block.

This hole is not perpendicular to the base plate, it has about 15 degrees angle. The thread starts about .1-.15″ below the top.

The Zamak is known as relatively heavy, soft metal, prone to chip or crack under high dynamic stress and can be worn by the constant movement. Fortunately enough, tremolo movements are usually not so frequent to result quick wear out. It seems that the arm was weaker…

I’ve started with dismounting and cleaning the hardware then I tried to remove the broken stud from the thread. My plan was to drill a tiny off-centered hole into it that I can use a pin to rotate the piece and unscrew it.
The plan didn’t work. I was able to rotate the remaining part, but it didn’t elevate. The thread was also damaged and there was no way to unscrew it.

My next attempt was to “drill it apart”, actually, to demolish it with a drill bit until I can remove the remaining chips.
It wasn’t easy. Since the stud is deep inside the hole and the axis is not vertical, it was difficult to maintain the right position and direction. After a couple of minutes of careful and slow attempts the half of the length and diameter of the stud has gone – but the rest began to revolve together with the drill. It took almost half an hour until I could fully remove it and the drill also have eaten some small chips at the top of the hole.

Versachem Titanium Epoxy - Active Guitar

Alright, what I got is a slightly deformed elliptical hole with totally damaged thread. I chewed long on what will be the best solution. I ended up with a plan to drill a slightly larger 5 mm hole in it, and tap a 6mm thread. Then fill with metal epoxy and tighten a 6 mm steel bolt in it. The epoxy will fill the gaps between the wall and the thread and fix the bolt. I will cut it flush to the top then drill a 4 mm hole in it and tap a 5 mm thread to restore the original thread. It sounded good in theory, but in practice it raised some issues.

It went smooth until I drilled and tapped the 6mm thread. I used Versachem epoxy (it’s seasoned with titanium) and an ordinary steel machine bolt from the hardware shop. I let it dry for 24 hours, although the instruction says it need 4 hours only – just to stay on the safe side. The upper part of the bolt sawed off and I filed/sanded flush.

The hole on the sustain block with the steel bolt sealed by the titanium epoxy

The hole on the sustain block with the steel bolt sealed by the titanium epoxy

And there came the though part.
I needed to mark the center and the angle of the drill precisely – otherwise there’s no way to do it properly.

Wolfcraft hobby drill stand

Wolfcraft hobby drill stand

My “workshop” was just a temporary one and I missed a lot of tools, so I had to come up with some “Macgyver” solution – well, the whole luthier craft is full of such inventions.
I had no drill press. The only similar tool I owned there was a hobby-grade Wolfcraft drill stand, slightly flimsy and wobbling. There was no angle adjustment, it can be used only vertically. To set the sustain block properly I’ve created two wooden wedges and used them to support the block at an angle. With the help of them and many trials I was able to set the position in a wise just right under the drill bit.

First attempt to drill the angled hole - the block supported by two wooden wedges

First attempt to drill the angled hole – the block supported by two wooden wedges

I used a cobalt-steel drill bit that has already proven when I drilled the broken stud apart.

The drill started to spin and I slowly pushed the arm down until the tip touched the surface – and it slipped away immediately because of the angled contact and the wobbling drill stand about 3-4 mm off. 🙁 I’ve tried a couple of times again and the hole got deeper – but the same time it became also wider, getting too close to the edge. Well, that wobbling drill stand isn’t a reliable tool at all.

I ended up with a rather huge “crater” in wrong position. I swore a lot and decided to have a break until next day. At least I added some metal epoxy again to level the hole.

After the failed drilling - the "crater" already repaired with the epoxy

After the failed drilling – the “crater” already repaired with the epoxy

The next day I realized that I need a jig. Something that keeps the drill bit in place. I also decided to work in multiple phases, starting with two size smaller bit and do it in 3 consecutive steps.

I took an L-shaped metal and drilled 3 holes with ascending bits. That became my guiding jig.
I used a clamp to hold it on the sustain block and started to drill with the 2 mm bit. It worked!

The drill guide jig I "macgyvered" in work

The drill guide jig I “macgyvered” in work

Then came the 3 mm, still went well. I proceeded to the 4 mm. Unfortunately, the jig started to wobble a bit but the already drilled pilot hole helped to keep the bit in position. WIth slow and careful back and forth movements (to check the right position I was able to drill deep enough to hold the position well. Jig removed and I continued using some dripping water to cool the bit tdrilling the steel.

And finally: Success!

Mission complete!

Mission complete!

Tapping the thread was a breeze although to start it at the angled hole was a bit tricky.
After cleaning the particles it looked perfect. I tried the arm from my Casio MG510 MIDI-guitar and it screwed in smoothly.
Next step was to sand and polish the top of the sustain block to maintain the best contact with the bottom of the base plate. I removed the rust from the saddles with a copper brush.
I used a Dremel with a small burr to round the string-through holes edges and hand polished them to allow the smoothest movements for the strings.
The string wear on the saddles were so deep that I decided to not level them fully because it needed to much removal of material. I rather smoothed and polished them to get a very slight curved top. I also sanded and polished the knife edges to remove any small deformations. An abrasive cord did the job well.

The fully refurbished bridge

The fully refurbished bridge

When I assembled it I realized that there’s a minor problem: the position of the new hole wasn’t 100% accurate. It’s slightly off-centered to the hole on the base plate so when I wanted to screw the arm in it stuck. The cure was to slightly enlarge the hole on the base plate. After that all went smooth.

Before...

Before…

... and after

… and after

My friend has got a nice, clean refurbished bridge that will serve him for many years and I gained a great experience by the repair.

Play the blues, Zsolt!

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