Removing the scratchplate and bridge - how long to heat?
 

My current project is renovating a 12-string that I rescued in quite a dilapidated state from a middle school music department (it's a Japanese-built "Delta"). It is sanding down nicely, but I'm having some trouble removing the bridge and scratchplate.

There is plenty of guidance on the web to heat them with a hair dryer (including a recent post on this forum here), or to "use" naptha (how precisely to use it is usually left to the reader's imagination), neither of which seem to be helping. Could someone who's done it comment on how long these components ought to be heated before the heat gives the required play? That's something that doesn't seem to be addressed in other forum discussions and on other web pages. Are we talking about heating them for a few minutes, after which the scratchplate should start to peel and the bridge to loosen, or am I just being impatient in expecting results in the first ten minutes of heating? If it makes any difference, I'm not particularly worried about damaging the finish - it's already damaged and will be meeting the sharp side of some 150 grit sandpaper minutes after the bridge and scratchplate are removed!

The scratchplate (pickguard, I assume) can be removed with a hair dryer slowly heating the plastic until it can be very slowly peeled up.

The Bridge is another matter. It is probably not removable just through the use of a hair dryer. If the glue does not release uniformly, and you try to lift it, you will pull out more than the finish: Some wood fibers will pull up and strip away into the finish. Then you have another problem to solve.

Most luthiers, when removing a glued bridge, use a small silicone heating blanket designed specifically for that purpose. Depending on the glue that was used, it can require heating the entire bridge uniformly up to 250ºF to 350ºF before the glue will release, and even then there is a danger of pulling wood away.

Go to Frank Ford's website (www.frets.com) where you will find a tutorial on the entire procedure. No other source of info is more detailed or accurate.

Thanks, but that doesn't really answer the question; I understand that the general principal is to heat it and at some point it ought to be sufficiently pliable to peel the pickguard off, but I've tried taht and haven't had any luck. My question was about time: how long to heat, not whether to. Frank's website doesn't answer that question at all (and doesn't even mention removing the bridge, so far as I can see).

This, for example, suggests using an iron to heat the bridge. Well and good - but for how long?

You're not baking a cake. You heat it till you can start to lift it without the top coming along too.

A heat gun or hair dryer should get your pickguard ready to begin lifting in about a minute, more or less.

Much harder to give a time for heating a bridge--there are too many variables. I usually take bridges off cold on older guitars, using an appropriate knife to separate the bridge from the top. It's not a technique that I think I can describe adequately here.

When I removed my scratchplate, I used a hairdryer. Put it on medium or high heat ,low fan. Point the hairdryer at the edge of your pickguard , maybe six to ten inchs from it , and with the hand that isn't holding the hairdryer , stick a finger on the spot that the hairdryer is pointing at. When the heat gets uncomfortable for your finger... it's getting too hot for your guitar. Take the sharp edge of a guitar pick and gently ease it under the edge of the scratchplate. Once you've lifted an edge just continue with the heat source , very slowly lifting against the resistance of the glue. Do not get in a hurry, peel it off slowly. Think of it like a scab on your knee , slow steady work at the right speed and angle , or you will start the wound bleeding . Make sense ?

Simon,
I did a little bridge removal tutorial here on the AGF awhile ago. Maybe you can find it but if not, here's the brief summery.
1) cut out a mask the shape of the bridge from CORRUGATED cardboard. This will protect the top from the heat of the iron.
2) You'll need to pick up a pallet knife from an art store. Putty knife is too thick. You'll need a pallet knife.
3) With the mask secured to the top, set an iron on the bridge. No steam, just heat. There's really now magic formula as to how long it will take to let go. I just put it towards one end and let it sit for ten minutes or so (around 200 degrees) then check to see if the pallet knife will work under a corner. If it will then I move the iron to the other end as I work the knife under the bridge. If it won't just heat it some more. Be patient.
4) Once you can get the knife under the bridge, work from the outside-in. In other words, work from the edges towards the middle, all the way around. It's not wise to poke all the way through and work towards one end. Because that end will show a lot of tear out.
5) This is the absolute most important step. If you listen to nothing else I've said, listen to this. Do not, for any reason, pry upward on the bridge. Even if you only have a small area to go and you're sure it will let go. I guarantee the bridge will take a chunk of top with it. Just work the knife in a side-to-side action under the bridge until it's off. If you find it too hard to move the knife, heat it some more.
Hope that helps.

Is it really necessary to remove the bridge?

Simon,
I took Paul Woolson's advice a while back about taking the bridge off of my Takamine F345. He is spot on about taking your time. It took me about 1 1/2 hours going very slowly. I used a pallet knife I purchaced from a local art store. The project turned out great, thanks to Paul. Looks like my new bridge has alway's been there. I used a little travel iron.
Good luck
John(valky guy)

I'm no expert, but another thing to consider is the type of glue that's holding the bridge down. From you description of the guitar, and not knowing its "maintenance" history, it could be anything. If somebody stuck it back on with two-part epoxy......best of luck.

I did it per snkysnake's comment - the pickguard came loose slowly, although it left the glue behind, which took a while to clean up.

Paul, that's great advice, and if I still remove the bridge, I will tackle it that way. Placida raises a great point, however: I had been all set to reply that, well, yeah, it kind of is necessary to remove it. But that stripping the top would require stripping the bridge was something of an unexamined assumption on my part; now I come to think of it, it may be possible to sand around the bridge. Given the difficulties of getting the thing off, going around it should really be the first option so long as it doesn't impede the broader goal of refinishing it.

Removing the bridge will make it a lot easier to do a clean refinish. It is very difficult to sand the bare top properly, since that requires sanding with the grain. And buffing out the new lacquer close to the bridge is more complicated with the bridge attached.
I am not saying it couldn't or shouldn't be done, since many Spanish classical guitars are finished with the bridge attached. But they are rarely as clean-looking as those guitars that are finished before the bridge is glued on.
I have never seen the need to use a heat blanket for removing a bridge or fingerboard. A 250 watt heat lamp works just fine, using a corrugated white cardboard mask. The heating time will vary, depending on how dark-colored the bridge is, how thick it is, and how close the heat lamp is placed to the surface. Roughly, it takes 5 to 10 minutes to soften the glue (250 to 275 degrees F.), but you can get a good idea how hot it is by brushing some water on the surface. If it sizzles, it is hot enough.

I'm not actually relaquering it - the new finish is going to be done with tru oil only. Still, my supposition had been that, as you say, it'll be difficult to sand it cleanly with the bridge still attached; I'm going to give it a try, and if that doesn't work out, I'll take a run at removing it. Thanks for the time frame. :)