Book Matching?

[G7MOF]

I've noticed that when an instrument back is classified as book matched it very rarely is!
I know the wood is vertically split and at that point should be perfectly matched. After carving to get the right thickness on the outside and the centre the book matched grain goes up an down even though the centre doesn't really move during the carving process (Much).
Why should/does this happen?

[Ivan Kelsall]

There was this thread a while back which might answer your question :- http://www.mandolincafe.com/forum/sh...-Mandolin-Back
Ivan

[billhay4]

Well, two thoughts occure to me here. First, when you carve into the wood, the grain can change so the bookmatch is altered or destroyed. Second, and more common, bookmatches pieces reflect light differently, so they can appear to be different when they really aren't. This is particularly true of flamed wood, but is also the case with quilted.
Folding the two sides of the wood out like book pages means the grains reflect oppositely, not the same. Thus the light reflecting from the two sides is different. Slip matching can reduce this effect.
Bill

[Pete Jenner]

Smoke and mirrors really. If you look really carefully at the grain, you will see that most of the time the halves are indeed book matched. The flame or figure doesn't match in these cases and rarely if ever will in highly figured wood.As Bill says, the only way to get an approximation of flame matching is to slip the halves one way or the other - in which case your back is no longer technically book matched.

[sunburst]

Book matched means a piece of wood is cut through the center, then the two pieces are opened like the pages of a book. It does not mean the two halves have identical but opposing grain. That can only happen if in case of veneers, where the wood is sliced with a blade and there is no wood lost to saw kerf. Even then, if the wood is sanded for finishing some of the surface will be lost and the grain pattern can change slightly.
In the case of a carved arch top (and back) mandolin, the wood is sawed into two pieces, so some wood is lost to saw kerf, then the helves are glued together and carved into the arched shape. More wood is lost from the surfaces during the carving process, and when it's all done, the grain pattern can look very different on the two halves. If the grain lines are diagonal through the piece, or if the piece is flat sawn, the change can be more dramatic than if the grain is perfectly vertical in the piece, but the wood is book matched none the less.

[Spruce]

That can only happen if in case of veneers, where the wood is sliced with a blade and there is no wood lost to saw kerf.

Check this out:



My Hawaiian banjo-playing friend is checking out the "Wall 'O Koa" at Wintergrass...
It's remarkable how thin those veneers must be to preserve that matching...
And this is about 1/3 of the wall...

[Austin Clark]

That wall at the Bellevue Hyatt is incredible in person!
Thanks for the pic, Bruce.

[Ivan Kelsall]

Thanks to Billhay4 & John Hamlett for the explanation.The un-matched grain of 'book-matched' backs has puzzled me & the fact that they will reflect light differently,hadn't occurred to me,but then again,i'm not a builder who's seen it 'hands on',
Ivan

[Jim Hilburn]

Bill hay touched on this but to me the main thing that makes bookmatching look as though it wasn't is the yin - yang, the positive - negative, the in phase - out of phase, the dark and the light. In figured wood this means the light streaks on one side are the dark streaks on the other.
If you look carefully at strong quilt you will perceive that one side looks like tops of bubbles and the other looks like craters because you've actually cut through the center of what is essentially solid bubbles. This is what I call the Indy - outy effect.

[G7MOF]

Check this out:



My Hawaiian banjo-playing friend is checking out the "Wall 'O Koa" at Wintergrass...
It's remarkable how thin those veneers must be to preserve that matching...
And this is about 1/3 of the wall...

It looks like he's Tap Tuning that wall...

[Steve Sorensen]

It took a while to wrap my mind around the idea that, for carved-back instruments, as the arch curves down from the high point you are getting further away from the cut that created the book.

To use the book analogy, than means that if you opened a 100 page book at page 50, 50 and 51 are adjacent, but you are now going to be going in opposite directions as you delve deeper on one side or the other . . . So, in the "book" of a mandolin back, by the time you get to the recurve at the tail, the wood on one side the glue joint is "page 10" and on the other "page 90". Still the same book but different parts of the story!

Steve

[Pete Jenner]

It's just as well this is bedtime reading.

[David Houchens]

I used to adjust my back halves to try and align the figure to the closest possible position. I have grown to like the look of positive/negative as much as dead on. I've had end matched ( cut end to end from a long billet thats width only gave three pieces) that I liked as much or better than book matched.
I cut a Kay bass heel out of a piece of tall, quartered maple. It was the onlt piece that would be quartered that I had. The grain looked nothing like the bass neck but I used it anyhow. By the time it was carved down to match the neck, the grain that had been in the middle of the piece could not have been any closer to the grain in the neck if I had planned it. Sometimes we just need to let wood be wood.

[sunburst]

It took a while to wrap my mind around the idea that, for carved-back instruments, as the arch curves down from the high point you are getting further away from the cut that created the book.

When I "wrapped my mind around" that notion, I started flipping them over. In other words, if you look at the two sloping halves of the un-carved back blank, you're seeing the two surfaces of the cut that created the book match. It requires milling the joined edge to a 90 degree angle to the rim side of the blanks before jointing the halves. and that means milling off a little more wood, but it keeps the match between the back halves looking more similar as you carve. Also, since I use almost exclusively quartered (vertical grain) backs, the match holds up pretty well anyway.

[G7MOF]

Yes, But at the point of the cut don't they have to be identical?

[Jim Hilburn]

This is one project I'm working on. This is a pretty consistent quarter sawn piece. Did I get it perfectly matched when I glued it? I'm pretty sure it's very close but even if it's not it will never look identical.
The curl is like a wave running through the board and we're directing that wave. That means what is the peak of the wave or convex side on one half is the concave of that wave on the other and reflects as a negative.

[Tom Coletti]

Here's a bookmatched cherrywood back for a Dobro kit that I'm working on. Even though the flame and grain match well, the way that light hits the wood makes it seem slightly off in places, or it makes the flame more prominent on one side than the other.

--Tom

[John Arnold]

The curl is like a wave running through the board and we're directing that wave. That means what is the peak of the wave or convex side on one half is the concave of that wave on the other and reflects as a negative.

That is the reason for the practice of shifting the match lengthwise by the spacing of one half curl. Instead of lining up a concave with a convex, you can line up two convex curls. That only works well when the curl has uniform spacing, however.

[sunburst]

Yes, But at the point of the cut don't they have to be identical?

If you'll review post #5 you'll find that only sliced veneer can be identical. I've wished for a magic, kerfless saw all my live, but alas, we must remove wood between the halves whenever and however we cut them with a saw.

[testore]

I'm surprised that this is such a big topic. I've never given it a second thought. I saw it in two and glue it, I think it always looks awesome.

[Michael Lewis]

Or you can use a one piece back. No seam and it matches.

We usually use two piece tops and backs because that is generally the most economical use of the wood. One piece backs requires a larger tree than a two piece back, and consequently there seem to be more two piece back wedges available. This is especially true for guitar size instruments.

[Jim Hilburn]

Hey, Gary, I had the same reaction to the " neck torque" thread but a question was asked and there is an answer. Inquiring minds you know.
By the way, on my last post my devious auto correct on the ipad changed dicect to direct.

[Pete Jenner]

By the way, on my last post my devious auto correct on the ipad changed dicect to direct.

No offence Jim but that's probably because dicect isn't a word. Not in English anyway.

[Killian King]

dissecting

[Jim Hilburn]

Well I have my own imaginary language.