Rebuild Project - Question about Forms and Fit

[Eric Knapp]

Hello,

I'm starting a rebuild of this old guitar that I posted about a few weeks ago.

https://www.flickr.com/photos/ejknapp/a ... 579281126/

I finished a form for it based on the back which was intact with its binding.

The back fits pretty close to perfectly. It's not too tight with almost no gaps.

Then I put the sides in. They came to me as you see them, still glued to the neck and tail blocks. They were once attached to the back which fits the form.

The sides don't want to fit. They are too big and won't conform to the form sides even with extreme hand pressure.

I haven't made the clamping brace things yet and I have some questions before I do.

Why do you think the sides won't fit well? Is this normal that you have to use a lot of force to get them evenly against the form?

What do you think I should do? Should I go ahead and make the internal brace/clamps and see if I can get them to fit? (Yeah, I have to do that anyway.) Should I make some adjustment? This is all new territory for me. What is the wisdom of the experienced?

Thanks,

-Eric

[Brian Evans]

I would make up some internal push-clamps and slowly move the sides out, humidifying as it went. It might take a week to push them out and get them to stay with no pressure, but they really are very close now. I'm really jealous that you get to do this, not me, btw!

Edit: Did you account for the binding and purfling dimension when you fitted the form to the back? The form should be 1/16" clear of the back everywhere, so 1/8" longer and 1/8" wider across all the side to side dimensions. My 1946 Epiphone has 1/16" thick binding on the back, which would be typical.

[Barry Daniels]

It is not unusual for an old guitar back to shrink in width whereas the side will not shrink much from drying. That is because when wood drys it shrinks more in width than length. I would not force the sides to fit the form because that would probably crack them. You have a decision to make. Either take some length off the sides so they fit the back or somehow make the back wider (which would be very difficult). What about the top? Is it the same size as the back?

[Eric Knapp]

I would make up some internal push-clamps and slowly move the sides out, humidifying as it went. It might take a week to push them out and get them to stay with no pressure, but they really are very close now. I'm really jealous that you get to do this, not me, btw!

Heh, I'm trying to make up for lost time, I've had this project guitar for too long.

Edit: Did you account for the binding and purfling dimension when you fitted the form to the back? The form should be 1/16" clear of the back everywhere, so 1/8" longer and 1/8" wider across all the side to side dimensions. My 1946 Epiphone has 1/16" thick binding on the back, which would be typical.

I believe I did but correct me if I'm wrong. The back still has the binding and there wasn't any purfling. Here's a closer pic.

I am assuming that is the original outside dimension. Right?

Thanks,

-Eric

[Eric Knapp]

It is not unusual for an old guitar back to shrink in width whereas the side will not shrink much from drying. That is because when wood drys it shrinks more in width than length. I would not force the sides to fit the form because that would probably crack them. You have a decision to make. Either take some length off the sides so they fit the back or somehow make the back wider (which would be very difficult). What about the top? Is it the same size as the back?

I was wondering if this was the issue. The top fits perfectly inside the back's binding so I'm assuming it's the same size. I don't have the top binding or purfling. One option would be to remove the tail block from the sides. Then trim the sides to fit the form. I could add one of those decorative wedge shaped pieces that I don't know the name of.

BTW, I've decided not to attempt a full restore. I found an Epiphone collector and instrument historian and asked about the possibilities of a restore or rebuild. He said this is not a rare guitar and so much has to be done to it that collectors would consider it a rebuild regardless of what I did. He loved my idea of making it into a modern 7-string guitar with an X-brace. I might even make it a multi-scale instrument. Since the likelihood of ever selling it is extremely low I want to end up with a guitar I would actually want to play. I have enough 6-string archtops already and would love a 7-string.

Thanks for the reply,

-Eric

[Brian Evans]

What are the exact dimensions of the back, length and width? I can compare them to my guitar, it might tell you something. If you need to small up the sides to fit them to the top and back it's a question of taking the tail-block off, the neck block maybe, and trimming the sides so they fit in the mold, then putting the blocks back on.

[Eric Knapp]

What are the exact dimensions of the back, length and width? I can compare them to my guitar, it might tell you something. If you need to small up the sides to fit them to the top and back it's a question of taking the tail-block off, the neck block maybe, and trimming the sides so they fit in the mold, then putting the blocks back on.

The dimensions from the wood edge to edge are 20 1/2" by 16 15/16". And just how does one take the tail block off? It's hide glue, can it be done with just heat or will it need steam?

Thanks,

-Eric

[Brian Evans]

Mine is a smaller size than yours so comparing wont work, sorry. I guess I would try a hot spatula, similar to taking a fretboard off.

Brian

[Chris Richards]

I did a very similar project posted here http://www.mimf.com/phpbb/viewtopic.php?f=5&t=3347 and had the same problem as you. In the first instance I forced the sides to fit with forms and although it worked initially, long enough to finish the guitar, the sides split away from the top and back after a few weeks and I had to do the whole thing again this time cutting the sides and getting them the correct length to fit the top and back, so I wouldn't go down the route of forcing them to fit.

[Eric Knapp]

I did a very similar project posted here http://www.mimf.com/phpbb/viewtopic.php?f=5&t=3347 and had the same problem as you. In the first instance I forced the sides to fit with forms and although it worked initially, long enough to finish the guitar, the sides split away from the top and back after a few weeks and I had to do the whole thing again this time cutting the sides and getting them the correct length to fit the top and back, so I wouldn't go down the route of forcing them to fit.

Thank you, that's great advice and it is what I'll do. I own this guitar so I can do whatever I want with it. I'm using this as my learning experience and the motivation to get my shop back up to being usable. My guitar is in much worse shape than the one you did so there's no collector value. When I made furniture I would never force something together with clamps. All the joints had to go together with no force and the glue just held them that way. I am assuming that's a similar principle in guitar making.

Your repair job was quite beautiful, by the way. I hope I can do good work some day too.

-Eric

[Eric Knapp]

Well, now! It looks like my sides and back might be the same size after all. I made the push clamps with a simple naive implementation. They seem to work well enough for now.

As I was trying things out I noticed that the mold itself was too small. It was the right width but was not long enough. I tweaked the mold and the back fits perfectly to the sides with minimal clamping pressure with the push clamps.

This project seems fully backwards from making a new guitar. Fitting the mold to an existing guitar seems like a different skill and I'm making this up as I go.

Thanks for all the help. Next I am starting on the neck. I have to make a new one so the adventure begins.

-Eric

[Michael Lewis]

Eric, try to get the sides to meet the back evenly EVERYWHERE at the same time. It may take a bit of slight shimming here and there to push the sides in to meet the binding on the back. You have enough shop experience to know what needs to be done, and to figure out how to get it done. You really don't want the binding to over hang the sides at all, but it's sort of OK if the binding has a very slight step in from the sides. Often you see factory made guitars with this condition, which I think is from scraping the finish off the binding and that leaves the little ledge. Obviously it is best to have everything totally even all round, so strive for perfection and settle for excellence. You're doing very well.

[Eric Knapp]

Eric, try to get the sides to meet the back evenly EVERYWHERE at the same time. It may take a bit of slight shimming here and there to push the sides in to meet the binding on the back. You have enough shop experience to know what needs to be done, and to figure out how to get it done. You really don't want the binding to over hang the sides at all, but it's sort of OK if the binding has a very slight step in from the sides. Often you see factory made guitars with this condition, which I think is from scraping the finish off the binding and that leaves the little ledge. Obviously it is best to have everything totally even all round, so strive for perfection and settle for excellence. You're doing very well.

Thank you, Michael. This is great advice that I will certainly do. Most likely I will be replacing the binding as it's in bad shape. There is no binding or purfling on the top so I will have to bind that and I might as well match the back. Even if I re-bind the back it still seems important to get it to match as closely as possible. That was my instinct and I'm grateful to hear a serious expert say it.

And a special thank you for the encouragement. That means a lot and will keep me going for a long time.

-Eric

[Barry Daniels]

If you are going to route and install binding then you have some leeway in the fit of the top to the sides. Just be careful because a binding job will mess up adjacent finishes.

[Michael Lewis]

By replacing the binding the whole 'equation' is changed. Fit the parts together in a workman like manner, rout for the new bindings and move ahead. As Barry mentions, finish is easily effected by the solvents in most glues, so extra care is needed unless you use a water based glue like Titebond. For any plastic binding use a solvent based glue, for wood or fiber bindings you can use Titebond.

You are going to have to refinish the sides, and that will present another issue to consider. I usually mask the bindings when spraying the color coats. It may be easier to refinish the whole body, but there are ways you can avoid that if you can make things go well. It's a lot easier to install and scrape bindings if you don't have to protect the finish.