I had kinda a hard day yesterday. I spent about 3 hours building a bridge heating caul out of half inch aluminium and swivel mounting it on a vera nice C clamp.
I then customized a baby pry bar big time, then heated up the aluminum and went at it. I of course had high hopes the plate would pop out after two mins heating, but no joy. Tried it again with same results.
The bridge plate is exactly the right size too, and was plenty hot enough. It was just installed two years ago with Lapages white glue
It like some possible ideas about what I might be doing wrong, and some pics of your tools for getting under this difficult plate.
This is 4th time in twenty years I have done this also, so I'm not totally new to this... I also have no problem customizing some tool to get this job done.
Kerry, I use a stewmac bridge plate heater which has worked OK on the couple of plates that I've removed. It's looses heat fairly quiclky and I had to reheat it a few times to get the plate hot enough, ( both were with the bridge in place so there was more mass to heat) Your plate looks good but you are attaching it to a metal clamp which is, basically a big heat sink so I'm wondering if your problem is that you are loosing too much heat into the clamp and not into the wooden plate.
The scraper I use was made from a large screw drivers. It's not as wide as your scraper but it does the job if used with care.
The plate still sizzled my spit when it came out after the second attempt Ned. I need something a bit more like your tool here.Mine is so wide, it is impossible to feel if it is getting against were it needs to be.
yuck...... you spit on your bridge plate heater? ;) Must be working on an Ov*tion......
I'll try to remember when I am in the city shop tomorrow to get you a pic or two of our cartridge type heated plate popper and the shop-made tools that we use to separate the plate from the bottom of the top.
By the way I had, with the operative being "had" a client who owns a music store in a little town and has quite the collection of vintage guitars. He called me in about removing and replacing a plate on a vintage Gibson what "was...." worth about $8K at the time. I quoted, he objected, I held firm, he b*tched and moaned, I left. During our conversation I let him know that this, removing the plate, is not all that difficult but it is risky and one can separate the center seam... without judicious use of heat and attention to duration as well.
I get a call a couple of weeks later about how to repair the center seam.... Will these people ever learn that this is a "skilled" trade and your average Crapsman 125 piece mechanics socket set and some good will is not enough at times....
What a shame for the instrument though, that's the really sad part to me.
I was expecting quite a few more posts on this ... Thanks Hesh. Always a pleasure reading your stuff, and I await those photos!
Not really sure why it isn't working for you.
- (maybe this is a bit silly) But are you sure the clamp is deep enough (it looks rather shallow in the picture), could it be the aluminum plate isn't touching the bridge plate?
- Could it be the top is radiused/ bowed so you're aluminum plate isn't making full contact with the bridge plate (maybe just on the sides). Or is there enough clamping pressure to flatten the area/ and thus making full contact? Maybe cut some grooves in the aluminum plate to make it a little more flexible
- Can you tell us whether the heat is transferring well enough (by feeling the temperature change at the top, since the bridge is off)
- And (by judging the picture) I think the edge on the pry bar is too thick/ blunt looking to get in the joint/ under the bridge plate.
Let us know how it goes!
Here's a shot of two trusty tools I use for coaxing-out bridge plates.... old chisels, heated and bent-back. The edge angles are opposite on each one, but they both have their uses.
Like Jelle mentioned, your clamp looks a bit shallow, like there's a chance it could be "bottoming-out" on a brace before it actually contacts the bridge plate? That's what happened with a very similar clamp I built, and the answer was to build-up a 1" square riser-block to sit atop the end-pad of the clamp.
So, for sure it is in full contact, and braces are not blocking. Top was hot too. I think that Jelle is likely correct about the leading edge of the pry bar.
One of our members here,Erin Randolph who is a Facebook friend ( and who does an amazing amount of high quality instrument repairs and does Photo Essays and puts them on Facebook) said that he has to do this job quite often, and his big trick is to wrap the caul in a wet cloth and snug it up tight the night before the work is done.
Ned, I made a new tool just like yours yesterday with a blowtorch and a benchvice. I sharpened flattened top edge too. I will have another go at this today...
Be careful with it, Kerry, until you get a feel of how it works. I should have warned you that the narrow blade and wide gap between the blade and handle make it fairly easy to work around braces but the trade off is that the narrow blade doesn't spread the force applied around as well as a wider blade does. It's easy to split the plate and, while I haven't done this, it's probably easier to split the top too.
This blade isn't like using an artist knife on a fingerboard extension. This is more like a crow bar used for prying but you have to remember that prying requires a supporting surface which, in this case is the top. (Equal and opposite reaction and all of that.) Be careful not to force thing too much. One thing I like about the narrow blade is that I can rock it just a bit side to side to apply pressure along the length of the plate but it doesn't take very much pressure to do this It's very definitely a "finesse" tool.
Btw, the blade was hammered thinner and flatter for a bit more width.
I have had excellent results using cellulose sponge cut just a bit smaller than the bridge plate shape and about 3/8" thick. I wet the sponge, not dripping but wet, place it on the bridge plate and leave it on till the next day. This type of sponge will hold water evenly throughout and won't loose it's water out the bottom from gravity. When I hit it with my 1/2" thick, heated Aluminum caul, the water in the wood generates steam and the bridge plate comes off easy with tools similar to those already posted. If you don't use the right kind of sponge, you may end up with water where you don't want it, this is important. The sponge trick works great, the last big Martin bridge plate I pulled just needed gentle coaxing with a bent tool to start it but came out perfectly the rest of the way with just my fingernails doing the pulling.
Paul has my method.
sponge on the plate w/ the guitar flipped overnight.
I put some clear tape on the backside of the sponge and elevate the guitar so it does not get too damp in there.
then I use a heating blanket w/ a thermostat so I can keep heating while I slide some thickish feeler gauges under.
remember runout is reverse on the inside!
Here is another pic of my heater and caul.
getting the glue to let go should be the focus. If you need a scary looking hook I think something is wrong.