Double Bass Shimming a bridge slot

[Chris Fitzgerald]

For various reasons, sometimes a setup is basically perfectly workable except for a slight imbalance of the string heights that can't be rectified by simply adjusting the bridge wheels because that affects all four strings. A case in point is a bass that one of my students has where one of the bridge wheels became inoperable because the threads on one side stripped. In cases like this, or in cases where the setup is basically OK but one string (usually the G) is too low, I will sometimes fold up a business card and insert it on top of the bridge notch for that string to keep the student playing comfortably until they can afford the time or $$ to take the bass to a luthier.

This works, but is an inelegant solution that sometimes comes undone after repeated tunings. Clearly the real long term solution is to have the bridge crown cut properly, but for broke college students or someone on a gig who is annoyed with what the weather of the moment has done to their comparative string heights, there must be some sort of temporary solution to raise a string slightly that's better than a business card. Or is there?

Luthiers/setup folks, what say you?

 

[Steven Ayres]

I'm reminded of the aluminum shims that used to come with steel strings (Spiros?), I imagine to help players adapt gut-string setups. They were about an inch long and shaped to cradle the string in the slot, curving away from the string to prevent buzzes.

Thinking about materials that are easily available and don't require more than basic tool use to employ, paper card stock or food-box paperboard is certainly a handy temporary solution. One could use stripped wire insulation as well, which can cling to the string and stay in place a little better.

But if it's not too cold, I think having the shim fall out occasionally is a good motivator to get the bridge fixed properly. Non-metal shims will be reducing the string's response as well, after all.

 

[AGCurry]

I've used the business-card technique. It works, for a while, but it's not ideal.
I recall - years ago - getting a new set of strings that came with little metal pieces that could be placed in bridge slots, under the string. I assume that their main purpose was to reduce friction, but they could certainly be viewed also as shims. They would be better than something made of paper, simply because their hardness would result in better transfer of vibration. For a makeshift/temporary version of these, perhaps aluminum foil folded to the desired thickness? The pressure of the string would compress the pad and perhaps provide better contact.

 

[KUNGfuSHERIFF]

Make a slurry of sawdust and Superglue, fill the slot and shape with files when cured.

 

[neilG]

I can't think of a reason why you couldn't add some wood back to the bridge slot. Have you ever seen the ebony insert used on violin bridges for the E string? Something like that. It requires some precision cutting but seems feasible.

 

[JBarz]

You can buy thin sheets of maple veneer, even as super thin ply, that are a lot tougher than business cards. Glue ‘em in optionally and trim/sand/file to taste

 

[Don Hergert]

Temporary, really in a pinch? MacGyver it.

If this issue is actually the result of a stripped adjuster, I'd find a small block of wood, a dowel or even a part of tree a branch, cut it to the right shape and length with your multi-tool or Swiss Army knife, and prop it between the halves of the bridge leg, alongside the stripped adjuster shaft, to hold the top of that side of the bridge high enough to work properly. That way the top of the bridge remains unmodified for after the stripped adjuster is replaced.

If this is for a chipped or otherwise damaged bridge string slot, I've seen bubble gum work pretty nicely as glue to hold a cardboard shim in place. Not exactly pretty, but bubble gum sticks to everything. Should steam or even chip off to allow a permanent repair.

 

[DoubleMIDI]

A wooden spacer with a hole for the adjuster would work. Could be made of glued veneer sheets to get to the right height.
A helicoil insert would be safer than a wooden thread. I would recommend to her such inserts to avoid ripped wooden threads. Maybe a task for a luthier but done very quickly.

 

[Anne Millington]

A tag of real parchment from animal hide is what luthiers use to line the string slot on a bridge, especially for high-tension thin strings like a cello A string. However, if you see a tambourine in a pawn shop with an animal hide drumhead, snap it up. You will have a lifetime supply of those little tags.

 

[Chris Fitzgerald]

I would love to have a couple of those metal things several of you described earlier on hand. On my own bass, most of the time I love the setup, but every once in a while I’d like to bump the G up a pinch while leaving everything else alone. Just to be able to get under it a tad more with the RH, and for pizz balance with the other strings.

I don’t play a lot of BG any more, but I sure appreciate the ability to do individual string height adjustments easily. I wish that were easier to do with our antiquated beasts.

 

[Ryan in PDX]

every once in a while I’d like to bump the G up a pinch while leaving everything else alone.

Thanks for bringing this up. I'm in that situation. You've recommended the business card shim before, and I'm curious what else others bring up. Anything involving a file still looks like wizardry to me.

 

[Ron Lacey]

I also have this issue. I’ve got everything tweaked just right but I need to raise the G string a tad. Several good ideas already. For the sawdust and superglue mix does it matter what type of wood?

 

[Ed S]

A tag of real parchment from animal hide ...

Just asked a luthier who suggested lambskin.

 

[Reiska]

I also have this issue. I’ve got everything tweaked just right but I need to raise the G string a tad. Several good ideas already. For the sawdust and superglue mix does it matter what type of wood?

I have used maple dust, but I recall people using baking soda, as it`s white powder. It`s the super glue that does the hard work, I`ve used epoxy ( I quess? ) and it comes out darker than plain maple when cured.

 

[Don Hergert]

i like cyanoacrylate (superglue, crazy glue, etc.), but I only trust it unquestionably for non-tension filling and some very light adhesion, on mostly cosmetic things.

I've repeatedly seen the mixture of baking soda and cyanoacrylate crumble under string pressure with bridges and nuts; as such I no longer trust that mixture.

If for quick and dirty emergency fixes where tension is involved, I'll only use cyanoacrylate with powdered hardwood or powdered bone shavings, and then, be prepared to fix it properly ASAP.

On an item like a nut or a bridge, it's necessary to "dam off" the area that needs to be built up. Usually masking tape can do this, but the cyanoacrylate, which is very thin, will probably still leak and be a mess to clean up, so be prepared for that; if possible separate the part being worked on away from the rest of the instrument, and use gravity to try to avoid getting cyanoacrylate all over any nice finished areas...

Of course if it's a viol-family bridge being worked on and if it is removed for this work, be aware of your sound post situation.

Shape the powdered hardwood or bone shavings inside the "dam", then drip a very few drops of cyanoacrylate over the shavings until they are minimally saturated. Keep in mind that the more cyanoacrylate you apply, the more will leak.

Cyanoacrylate mixes like this tend to shrink as they dry. As such, multiple layers may be desired to achieve an optimal effect.

Give it a few minutes to dry, and then remove the masking tape. Then get your needle files and fine sanding films out to do the final shaping.

Of course also be prepared to have your fingers stuck together, or to whatever you're working on.

 

[jmpiwonka]

I’d say the business card works fine for the duration of the lesson. Maybe a while longer.
For the real fix I would try to make maple veneer work. Glued on the leg then trimmed up.
Second would be the helicoil if it can be found in the proper thread for the bridge adjuster. A little more involved than the shim but it would be stronger and also make the adjuster operable again.

 

[james condino]

$3 tube of CA glue, an old popsicle stick, and a $4 chainsaw file; don't overthink it.

 

[Ron Lacey]

$3 tube of CA glue, an old popsicle stick, and a $4 chainsaw file; don't overthink it.

Thanks, my granddaughters go through enough popsicles that I could probably build an entire bass. I’ll go dig one out of the trash.

BTW overthinking is my signature move

 

[GretschWretch]

$3 tube of CA glue, an old popsicle stick, and a $4 chainsaw file; don't overthink it.

I am so happy to read this. My flotsam box of craft and popsicle sticks has just become legitimized for luthierie.

 

[walterw]

i think i'd rather cut out that too-deep notch into a clean, flat V shape, inlay a fresh piece of solid maple with the grain in the correct direction, smooth and shape it to match the surrounding wood and then recut the notch

that way the string is riding over solid maple rather than any kind of shim or glue composite