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Here's an approach some people use. Hold the plates under a single fluorescent tube light oriented perpendicular to the centerline of the top and look at the reflection of the light on both sides of the centerline. With no runout, the reflections line up across the centerline. With runout, they don't line up. They get shifted in opposite directions on each side of the centerline. The greater the runout, the greater the shift.

The photos below were posted some years ago by John Arnold on Mandolincafe.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Thanks jay! Yes now I remember something about the long fluorescent. Suppose LED would work also.

Pat

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Pat

No need for naphtha. Put the two halves side by side in the same plane and view them with a long light source oriented crossways. This can be a fluorescent light or a strip LED. There will be a reflected band across the grain of each half. If there is runout, this band will be at an angle, rather than straight across. Runout at the joint will reveal itself by viewing the reflected band in each half. If they are offset, then the finished top will show runout.
I just looked at the previous post with my old photos. Note that the angle of the reflected band reveals the spiral growth. The greater the angle, the more spiral (and by inference, more runout). With spiral growth, there will only be one location on the width of the top where there is no runout. This is where the horizontal line drawn at the same level on both halves intersects the reflected bands, which is at the blue line. Note that the direction of the runout is reversed on either side of the zero runout line.

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John

I do a slightly destructive test - I cut a sliver of wood off the opposite edge of each plate and split them and calculate the runout on both edges. That gives me a number and allows me to join the edge with the least runout, or if I want to exclude a defect, at least know that the edge I join is acceptable.
Jointing the top often eliminates where the sliver was taken, so no great loss of width is made.

Thanks for posting that Frank Ford link. I had forgotten about that site and how helpful it is. I came across it a couple decades ago and read all of it. It really helped me understand the stuff being discussed on the forums when I was trying to get started.

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Bryan Bear PMoMC

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

Yeah I've done the split test once before only to realize after the first coat of shellac on the fully assembled guitar the runout was visible. That was a Carpathian top too. Another test I like to do is with a soft cotton glove rub your fingers along the grain in one direction then back again. If you feel resistance in one of those directions then that is the runout sticking out.

So, "figured" wood is full of runout?

Is the runout issue one of construction or long-term survival of the top or both?

That’s a great tip and a very practical way to check it. Thanks!


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Here is a link to a really good discussion on runout on the ANZLF:
http://www.anzlf.com/viewtopic.php?t=3438

Aside from demonstrating methods to check for runout there is a picture that shows how runout becomes increasingly evident as runout increases.

Thanks all. Could someone offer some tips for buying soundboards from internet suppliers to avoid runout?

That's a lovely question. Seeing as the only grading of soundboards is cosmetic, my limited imagination wishes me luck at getting a useful answer. I think vendors don't address that characteristic, it's not included in grading. Buying soundboards from sources whose woodcutting starts with split billets would be a start. Bring money.

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Peter Havriluk

in theory, runout used to be part of grading. In 3A, you shouldn’t see runout, in 2A maybe a bit. It’s one of the things that is supposed to be a factor in grading…

Yes, curly wood is defined by localized variations in runout. In general, curly wood is less stiff and weaker in the grain direction.
The main issue with runout tops arises when the bridge pulls up, or when removing a bridge or bridgeplate. In that case, the direction of inserting a spatula should be opposite (N-S, versus S-N) on either side of the center seam. The problem is, bridges lift from the bottom side, and bridgeplate removal on X braced guitars is most easily accessed from the bottom. That means that on half the top, there is a chance of having chunks of the soundboard come up with the bridge or bridgeplate. Not fun.

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John