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On McKenna's thread, he described a recent situation regarding runout and how it escaped him until the finishing process. So how do you avoid runout completely? It is difficult and it takes a trained eye but here are the things I do to ensure no runout.

FYI, subtle runout is not a bad thing. Some clients won't like it but the vast majority won't care unless it's super noticeable. And unless you are truly aiming for the ultra high-end market, eliminating good tops just because they have the slightest runout is cost prohibitive. I've always built with no runout tops but I do that for ME. It bothers ME and I sure as hell wouldn't go to all this trouble unless my guitars were at the base price they are at now. IF you are sub $5k, I'd encourage you to just aim for nothing worse than subtle runout. If a client wants a perfect, no runout top then charge them accordingly [$500 to $1k upcharge because it will cost you that much in the long run].


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Steps to Avoid Runout
1) Determine which side of the top to join. The vast majority of soundboards are sent to us in an orientation (tight grain in the center and wider grain on the outside) that maximizes runout. If one orientation has runout then try the other side. Sometimes you can get lucky and have the side that comes from the center of the tree be the centerseam. You often have squirrely grain and defects in this region but I probably get 50% of my this way. This orientation always tends to minimize runout.

2) Prepare the joint and sand both sides of the joint to 220 grit. Any space will interfere with your ability to detect runout and any rougher than 220 grit makes it much harder to detect as well. It also helps to sand 0.010" or so off of the surface to get rid of any oxidation that may mess up the true color of the top.

3) Wipe the top with mineral spirits and observe in different lighting setups. Outside and indoors under a florescent light is what I do. It helps to tape the joint together from the back so the joint stays together. I view the top upclose and from about 10ft away. I also view it at various angles.

Tops with NO runout will create invisible seams. IF you can see the seam at all, then you have some degree of runout. Also, you are only concerned with the top when viewed straight on. If it looks good straight on but shows some subtle color difference across the joint as you view from a sharp angle, then it is still a no runout top. You just want it to look perfect when viewed straight on and from slight angles as well.

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One last thing, Sitka is an amazing spruce and it tends to have very little runout. IF you have a customer that specifies no runout, steer them in that direction.


I hope this helps !!!!

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Simon

This is hugely informative and a very nice and generous follow-up on the original thread. Thanks for taking the time to share your expertise.

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Pierre Castonguay

The downside of this is that once you sand to 220, it's 'worked wood' and you can't return it...

I don't worry about that too much as most suppliers won't care that you took off a few thousandths of wood. Generally, I comb through things in stages. I can easily detect anything but subtle runout at 80 grit. So I comb through and find sets that I think are promising.

You can also knock the surface down with a razor blade - this will shine up the surface but is not aggressive enough to get rid of deeper grit marks. This is a quick way to further comb through sets and pick out runout.

Good tips

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Josh House

Canadian Luthier Supply
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House Guitars - Custom Built Acoustic Instruments.
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One sneaky way to "eliminate" runout if you have a uniformly spaced, straight and fine grain, paper white top is to do a "slip match" rather than a "book match".
It doesn't really eliminate the runout, just makes it less perceivable.
Personally, I just let the runout show.