This is the Bay State guitar that I work on sporadically. The back has been off as long as I've had it, more than 20 years. When I got to the point where I was going to put the back on again, there was not a single spot where things lined up. I had the "L" brackets from a previous project, following Frank's example. No matter how I tweaked it, getting rid of a bulge in one place would only produce another bulge somewhere else. The turnbuckles were helpful at keeping the waist lined up, but, again, needing constant readjustment. Half an hour or 45 minutes were about all the frustration I could take. The lesson that I've learned over the years is that bad thing happen when I continue in that situation. Better to go do something else, and come back later. After multiple sessions, I think it is finally ready to glue.
Thanks Frank for all your great examples
Backs shrinks, especially if they are off for a long time. The rim will shrink too, but not as much. You can force the rim to fit to the back with the tools you have, but when glued, you will have built in a lot of tension in the back. Most likely, the bottom will crack in the weakest spot soon or after a while. I know that for a fact, I don't do this anymore.
So, what to do? If the shrinkage is not too major, a common practice (for me at least) is to compress the rim deliberately at the narrow middle (what is that called anyway?). This way, the rest of the rim can be perfectly matched to the bottom. When glued, the excess edge of the back have to be removed to match the rim. The fresh wound may have to be colored. This will be pretty invisible when done, but you may not have a 90-degree angle on the sides to the top/bottom where the wood is removed. Only really noticeable when checking with a square. Doing this, the screws at the narrow middle is not needed, instead a screw between the neck and bottom blocks.
Otherwise, wood has to be added. Putting a nice backstrip between the bottom halves can be a great way to do this. The bottom braces and the middle reinforcement on the inside (what is the name for THAT?) has to be reglued. The big problem is to get the backstrip tight and level with the bottom without shaving off any original lacquer. Another way is to add a wooden binding around the bottom, maybe only on the edge of the back without cutting into the sides. One drawback to this is that the edge of the bottom often is rounded off, leaving a recess when gluing a binding as thick as the bottom everywhere else.
On another note, the maple bridge plate across the top is a real tone-killer. I talk about that (and much more) in my article in the latest issue of American Lutherie. Interestingly, the main response I've got from the article so far was a free (except the shipping to Sweden) Bay State guitar from around 1888. If you haven't seen this, have a look.
Roger , I think the names you need are "the waist" (the narrow part between your ribs and hips .)
The centre strip is sometimes called the "Marriage strip " I hope this is some help but these are not technical names .
Thanks for the input and suggestions. All those aluminum braces look pretty heavy duty, but they are not really applying a lot of pressure. It was mainly a matter of getting the pressure evenly distributed. Interestingly, the back was in a concave form, like a section out of a wide cylinder. The concavity was on the outside surface of the guitar. I had to remove all of the back braces, but when I did, the back flattened right out. The spruce back braces did not shrink as much, over time, as the BRW. Makes me wonder if the BRW had not been aged as much as the spruce, although all wood shrinks more with the grain than along the length of the grain.
I'm going to try gluing the back as it is, and just hope for the best.
The maple bridge plate is a duplicate of the one that came out, but without all the wear and tear.
Thanks again, George
Roger are you saying that the bridge plate should be spruce and not maple ? You seem to be an expert on parlour guitars so I am interested .
"Waist" and "Marriage strip" are added to my vocabulary :)
Well. It's a long story, the article in the latest issue of American Lutherie is all about that. In short, yes, I like the bridge plate to be spruce with reinforcing hardwood buttons around the stringpin holes to cope with the wear from the ball ends. The hardwood maple bridge plate will compress the sound and make it less dynamic. Especially if it's across the whole top, with that you are left pretty much with the sound of the strings themselves, not the full sound from the spruce top.
Roger , thanks for that , there is a big difference spruce / maple .
Hi Folks, Can anyone point me to where I can learn details on Frank Ford's use of the L brackets to create a body clamp? I've searched the forum using different phrases (L Clamp, Turnbuckle, etc.) but haven't come up with anything that properly describes how to build and use this as well as where to source them. Thanks very much!
Is this the discussion you were remembering?
Thanks Mark, That's the very article that got me started. As I recall, I ordered a 2 foot section of aluminum L beam 3" by 4" and cut it up in 1/2 " sections. It made a terrible mess out of my bandsaw. Aluminum dust was everywhere, but the worst part was getting it out of the bandsaw's tires. I ended up with far more brackets than I thought I would ever need, but 40 of them are involved in the current project.
Tapping the brackets for 1/4-20 was also very tedious.
Before I even knew about Franks brackets, I did my own jig to be able to reglue bottoms on old guitars. I used the cheapest small clamps available, cut off the bar and reused only the part with the helix and the handle. With that and a rectangle piece of wood and a cheap angle iron, I made the same sort of brackets, only more adjustable and flexible. The clamp can be adjusted up and down about an inch, with a wooden backplate I can mount the brackets anywhere I like. The clamping part of the bracket can also be twisted to the sides if needed. I made some 20 of them in a day or so, and I have used them for more than 10 years.
Cheaper, easier and in my opinion better (well, not as strong or nice looking!). You can see them in action here: https://gammelgura.se/wordpress/?page_id=2196