I get daily calls asking me the cost of repairing this and repairing that on an acoustic guitar. Many times I am able to put a figure to it and many times I tell the caller that I would have to take a look at the instrument before giving a figure.
But almost every week I receive a phone call asking me what the repair cost would be for a lifting bridge. Some of the more inquisitive ones even ask me how I propose to tackle it, what glue will I use, etc, etc. I have to explain that not all bridges lift to the same degree, or at the same place. How much and from where the bridge is lifting eventually become price-determining factors. These also determine the course of action to be taken while re-gluing the bridge. I have repeated this answer so many times that now it goes like pushing ‘play’ on a recording machine.
So, this blogpost is actually about how I determine what to do with a particular lifting bridge. The hope is I stop getting those phone calls, though I realise that this blog goes so far and no further.
The following are some of the common scenarios that I encounter and what I do with them. Having said that I feel it correct to also clarify that these methods that I am going to describe, generally work. However, in many cases, I do have to take a different path though the problem is the same.
If, for example, the bridge is slightly lifting (when you can push in the corner of a notebook paper, say, some 1mm and no more) at either or both wings
I like to push glue under the wings, clamp them down, and hope and pray it holds. One could let wings lifting as little as this be, but then the end of the bridge closest to the end block takes the maximum strain from the string tension. Even a centimetre of lift anywhere on this end means that it will certainly weaken the rest of the perimeter.
Another scenario is when the wings are stuck solid but the centre of the bridge is lifting.
In such a situation, I prefer to take off the bridge completely and re-glue it back properly. I said I preferred that route, but I do give two scenarios to the owner.
- I try to push glue in and if it sticks, so much the better, and
- If it doesn’t stick, we have to take the bridge off completely and you have to pay for both processes.
Then there is another situation where the bridge is lifting right through its extremity closest to the end block
Here, there are no options. The bridge can only be taken off, both surfaces – the top and the underside of the bridge – cleaned of all glue residue, and then the bridge is stuck to the top.
An extreme form of the same situation is the photograph headlining this post. In such a case, the ‘patient’ is rushed into the OR and surgery performed under anaesthesia. Later, the patient comes into ICU, then to the recovery room and then the general ward, before discharge.
These were three common bridge-lift situations, and no matter what I prescribe, follow or preach, the fact is that the correct and the best way is to take the bridge off whenever a part of it starts rising, clean both surfaces, re-glue, clamp, and then give it ample time to cure.
But here is why bridges lift.
9.5 times out of 10 that I have taken the bridge off a guitar, I have seen this. If you can understand it through my drawing, there is a millimetre or two’s worth of margin all round the underside of the bridge and the same margin on the footprint of the bridge on the top too. While on the underside of the bridge this margin defines the extent to which the glue was spread, on its footprint it marks the area that the lacquer intruded on the footprint.
The funny thing is that ‘intrusion’ never seems to look a if it happened by mistake. In fact, it looks as if it was planned to be that way. Why that should be so, is the intriguing part.
The part of the bridge closest to the end block is where there is most stress of the strings. Go back on top and look at that main photograph again. That is exactly what the strings want to do to your bridge. With that margin left on the underside of the bridge, it doesn’t take much for the bridge to start lifting. That phenomenon is compounded by the lacquer intrusion on the bridge footprint.
Are there bridge designs prone to lifting?
Yes! And the following is my understanding of bridges and how they function under string tension.
Of the two bridge designs, which one do you think has a greater propensity of failing?
The string-through bridge without the bridgepins is my culprit. Why? Back to the main photograph and understanding which way the strings are pulling. The string-through bridge only aids in getting itself ripped off (pun intended) due to its sheer design.
The more common bridge with bridgepins lets the bridgeplate take the first onslaught of string action. If your bridgeplate is made of a good hard wood, all is good, otherwise…, read about belly bulges in this blog!