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Well, it's runout, just wavy.

That's what happens when a spruce tree alternates direction of twist.. First it turns one way, then the opposite, then back again... I have a couple tops like that...

To detect runout in an unfinished top, all you need is a good light source. I use a long fluorescent tube, oriented straight across the grain. Lay the two halves of the top together in the same plane and observe the reflected stripe. If the stripe is straight across, that means the tree has no spiral. If the stripes on the two halves are not offset at the joint, there will be no visible runout in the finished top. Angled stripes mean the top was cut from a spiral tree. Even so, if this angled stripe is not offset at the joint, you will not see runout in the finished tops.

I have photos somewhere here that show all of this, and I have posted them on the forums on numerous occasions. Maybe someone has copied and saved them, since the idiots at Photobucket have chosen to be greedy, instead of doing the right thing.

This is not a result of being off-quarter. In fact, the only way to cut a spiral tree with perfectly vertical grain throughout is to cut parallel to the pith along the length of the log. This introduces runout on the bark edge...the edge that is usually joined when processing small diameter trees.

To cut a bark edge joined top with zero visible runout, the billet is split and sawn parallel to the split at the bark edge. This creates a top that is only perfectly quartered at one location along the length of the top. But because the growth ring radius is greatest on the bark edge, the top will have good quarter at the joint, and will only be off-quarter on the outer corners of the joined top, where IMHO it doesn't matter. While cutting a spiral billet, the point along the length where the cut intersects the pith (perfect quarter) is entirely under the control of a skilled sawyer. If you place this in the lower bout, the top will have perfect quarter at the bridge, all the way to the outer edge of the top.

The amount of runout on the outer edge of the subject top is IMHO a nonissue if there is no runout at the joined edge. That is because the top needs to be strongest in the center where the bridge is glued on.

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John

I agree, but I wish there was a way to know.

Here’s the center with naphtha, which to my eye looks pretty even...



whereas the outer edge shows some




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I sometimes use green sticky tape and pull it off in opposite directions to see if any fibers are pulled off by the tape. I like John's light idea best though. I remember his photos. Too bad I didn't save any. Sometimes a flash photo will show the runout too. Another possibility is that there can be localized runout that is outside the pattern. I agree that the worst problem is often buyer perception.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

Tried pulling up with tape, many tapes many ways no lifts.

I'm beginning to think the joint area is ok...

Fluorescent light tube, that is all you need.

Just found the photo online.



The white lines mark the reflected band from using the fluorescent light. The white lines should intersect at the joint for no visible runout. The pink line is the bisection of the two white lines. The blue line (intersection) is the location of zero runout on the top.
The top on the left was cut from a tree with excess spiral....more than 2" in two feet. It would be best to reverse join that top, since the offset of the white lines would be less if the other edges were joined. Less offset would mean less runout difference in the two halves, and less obvious visible runout. The ONLY reason runout is detected in a bookmatched top is because of the difference in runout of the two halves. Flipping one half of the top to achieve a bookmatch reverses the direction of the runout. So a top with two degrees of runout will show a four degree visible difference in the two halves. That is why cutting tops wth no visible runout is so difficult. Any error in sawing along the grain is doubled after bookmatching.

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John

John I remember seeing those photo's years ago and have learned from them but I guess with every rule there is an exception. You can even see in the picture of the top I posted in this thread that the light goes straight across. I also did a split test. The test tile on the far right is the one in question. This is an odd nut to crack. I have never seen one like it before.



This one here is another so called 'master' top from the same supplier that shows obvious runout with the light test, beautiful silk though:

Frank Ford has forgotten more about lutherie than I will ever know but I'm confused by this portion of the article. If a top is off quarter and you open the bookmatch, the grain lines will still go the same direction off quarter on both sides (//////|///////) not (/////|\\\\\). I know it doesn't seem like it but that is in fact how it works. draw some slanted lines on a piece of paper and rotate that paper 180 degrees and the lines will still be going the same direction. Just look at any guitar with an off quarter top, if you look at the endgrain in the soundhole all the grain lines slant in the same direction.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Bryan I think what he means is when you cut the top off the log that is not perfectly on quarter on the outside. Near the pith the grain lines are up and down but as you get closer to the bark they go off. So one half would look like this |||||/////

The jointed top would look like this: ///////||||| ||||||//////

The first few cuts off a perfectly quartered log will be perfectly straight grained but as the bark edge rounds off you start to get slanted lines.

I get that concept but in the linked article he says:

"PH: one small thing to add here—this effect can also be caused by "bookmatching" reasonably well-quartered spruce pieces with grain that is not 100% vertical, and whose grain opposes like this:

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\|////////////////////////////////

Each side will reflect light differently, giving the same effect as wood that's not riftsawn, or which has runout."


But this is not how the grain goes when you open the bookmatch. Even if the top runs off quarter across the board, the bookmatch would still be going the same direction.
You would have either (//////////||||||||||||||///////) or (||||||||//////|///////||||||) depending on which side you jointed. This is not to say that I don't believe him when he says that off quarter can lead to the two toned top effect when runnout is not present. I'm just trying to figure out what is going on. I'll confess that I don't always use perfectly 100% VG top wood

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Oh ok I didn't read the article

You are right, that's wrong.

A bookmatch where one side is flipped could give you the grain match Frank mentions. Why would someone do that? Ask the guy gluing up hundreds of tops a day.

It seems like some people's clients are getting hung up about the look more than what the guitar sounds like. At one time runout was not a consideration when buying an instrument. Even a good quality top can show some runout under finish. As builders we all have to choose where we draw the line. It looks like the wood cutters are going to have one more semi-cosmetic criterion for grading their tops.

I've generally found the spruce tops with stripe figure to be good ones. The stripe is, of course, caused by changes in run out over time. Sometimes you can trim a top down a bit to get to the place where there is no relative run out at the center join, and go from there. For the most part people will not object to run out so long as it doesn't show at the center join.

Often trees will start out with the fiber direction parallel to the axis of the tree, and develop more and more twist as they grow. The usual 'bark' match will show a lot of run out, but 'heart' match will look better. This also gets rid of a lot of the run out wood, and can work OK. I used a top like that in my plate tuning video, as an example of one that would be hard to get right: it was. It ended up with asymmetric brace profiles to compensate for the twist, but it sounded good.

In theory run out reduces the long-grain stiffness of the wood from what it 'could' be. In practice it has to get pretty extreme to reduce it by much. It is certainly presents a problem in keeping the bridge down, though. On a top that has some figure, such a 'bear claw', that is caused by changes in run out, I'll find a spot between wiggles where there is no run out, and try to get that to where the bridge sits. No sense in making life harder for yourself...

Well I guess I’m going to call ok on this...


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Thanks folks...

As always, these discussions give many of us a better idea, beyond the cosmetic, of what to look for when buying our tonewood. Thanks Ed!

Alex

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"Indecision is the key to flexibility" .... Bumper sticker

Not to mention when shopping for $13,000 guitars!

Andy

I'll know more once I cut out the soundhole and can split it.

Generally I don't care about runout, within reason, but this was aaa and looked pretty extreme.

Good thread, thanks John Arnold! Tailwinds.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I picked up a top from a new (to me) supplier at the last GAL conference. First look showed just as much runout on the edge as in the original picture. I talked with the guy and he said that this tree had a lot of twist, but that it was cut so that the join would have no runout at all. The runout only started from that edge and increased as it moved out. I took a gamble and bought a couple of tops since the silking was perfect, it met all my stiffness checks, and the price was cheap.

What do you know, he wasn't lying. I planed the two bookmatch faces smooth, and put on a little shellac. Then moved them in relation to each other to see how much they have to be off-plane to avoid the color difference due to runout. There was only about a 1 degree difference in the plates to make the coloration identical in all light directions. That's a great match to me. I haven't built a guitar with it yet, but I would not hesitate to use it.

Before this experiment, I would agree with most here that it was a junk piece of wood by looking at that split. But a good woodcutter can make good on even a twisted tree if they know what they are doing.

Paul M.

I guess that is something to consider when buying tops. Make sure they are rectangular so that you can choose which book matched edge to join. Some of the best tops I've ever had, and have, though are one's where the guitar shape barely fits in.

I'm really not a fan of nosed tops. Hard to keep deflection data consistent.

Yeah that too. To stay consistent what I do is just use an average for the width. It probably causes the calculations to be way off but what else can ya do? I have very few perfect boards and the ones I do have are very old. So in the real world it seems it's great to use scientific analyses for determining good tops but you still need old school experience unless you want to just trow away a perfectly good top simply because of it's shape... I don't

The only species I get with nosed tops is adi which I hardly use.