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How to Detect Runout -- Practical Tips

There's no easy way to detect runout. Years ago there were some misinformed posts stating that you could tell runout from the sides -- you can't.

Here's what I do:

1) Hold the wood up to a light and splash mineral spirits across the center. Outside light works really well if you don't have good interior lighting. Look at the set from several different angles while sighting down the joint to detect a difference in color between the 2 plates.

2) The smoother the surface, the easier it is to see runout. 120 grit is usually perfect for detecting a color difference.

3) Sometimes a top will look better joined from the outside edge rather than the center edge. The outside edge actually comes from the center of the tree and there is less chance for twist at the center of a spruce billet than at the outside. If the grain lines are tight all the way across and the set is flawless, you can usually get some runout free sets this way. I've done this a lot with mastergrade Engelmann that has had runout. I've ended up with AAA Engelmann (because the grain lines aren't as tight in the center) but no runout.

4) Lastly, I hold the top underneath a very bright light in a dark room and check for voids and flaws. With careful planning, you can sometimes hide flaws underneath the fretboard, rosette, or bridge. Also, you won't be surprised by flaws that appear during sanding. So don't just receive the top the way you get it and think it's good to go -- take some time to optimize the aesthetics through careful joining and body placing.

Ultimately, it takes a bit of skill to detect these slight color differences. Also, some folks don't dislike runout and that makes things much easier because there are a lot of beautiful tops with slight runout. If you make an effort to only stock runout free tops, you will find that the material cost of obtaining inventory will likely double since it is extremely difficult to find runout free tops (the exception being Sitka and, of course, Redwood and Cedar).

Are aesthetics your main reason for choosing tops with no run out?




This is after you've joined and sanded and I've heard you say that you only keep about one in a dozen that you order and send the rest back. So, how do you look for it in raw sets? And do you still exclude some even after you've joined them?

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Pat

There is a fellow in Alaska who sells Sitka spruce. Sometimes he gets boards wide enough and even grain so you can have a top without a center seam. Then, you will not notice the run out.

This is a good topic. I usually hold a fluorescent light tube crosswise above the top plates, the plates being held together as they'll be in the joined top. If the reflection of the light in the top is about 90 degrees to the grain orientation that should mean low to no runout. If the light reflection is skewed at an angle, there's runout. The higher the angle the higher the runout. If I can't for some reason get a good reading I just cut a corner and split it.

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member of the guild of professional dilettantes

In my experience, the best lighting for detecting runout in a rough sawn top is a long fluorescent tube, oriented perpendicular to the grain direction. Hold both halves of the top in the same plane, and view the reflection off the fluorescent light. You should see a narrow band across the wood. If the band is continuous across both halves, there is no runout at the joint. If the bands are offset, you will have visible runout.
Another thing to note is that if the bands are not straight across but angled, that indicates a tree with spiral growth. In that case, there will only be one line across the width of each half that has no runout. This line will always be at the point where the reflected band is at the same level in both halves of the top.

This photo illustrates the effect. The white lines are highlighting the reflected bands. The pink line is straight across, midway between the two bands. The blue lines are at the intersections, and show where the top has zero runout. Note that the runout is in opposite directions on either side of this blue line. The top on the left was from a tree with excessive spiral. If possible, it would be better to join the other edge, since it has less runout. The middle top has less spiral, and much less runout at the joint. The right-hand top was cut from a tree with minimal spiral, and that top has very little runout.



The top on the left is an indication that the wood was cut from long logs, rather than from split billets. In that case, runout will be the worst along the bark edge, which is usually the most desirable to join. If that wood had been cut into short blocks and split, there is the opportunity to saw parallel to the split along the bark edge. That means there will be no visible runout at the joint. Not only is that better visually, but it makes the top stronger in the bridge area. IMHO, runout placed on the outer edges of a top has very little or no negative impact.

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John

John, That's an interesting technique i wasn't familiar with. Thanks for sharing it.

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Jim Watts
http://jameswattsguitars.com

John's tip is very good.

The information in the original post can be applied before and after a top is joined. Sometimes you will find that even if a top doesn't seem to have any runout at all, once you join it and sand with fine grit, there will be slight runout.

Runout is purely a cosmetic topic -- the runout would have to be extreme for it to cause a structural issue.

And yes, I return over 90% of the high grade tops from LMI because of runout. Most of it is slight but it still personally bothers me. LMI charges a restocking fee for this and so I usually place an order for around 75 tops with a $500 restocking fee -- its worth it to me. I might find 5 to 10 tops that I think are suitable -- that's why I say it costs me about double to source runout free tops. Some vendors are very good about selecting tops for you if you have special requirements. Again, runout is not a flaw, it is just an aesthetic I don't like. The reason I posted this information is because a forum member asked how I detected runout. If you are building sub-$5k instruments then I wouldn't be too picky about it unless it just really bothers you -- many players absolutely don't care and some will hate runout.

Clearly and simply demonstrated, John. Very nice tip, too. Thank you.

serendipity - I was just pondering about this recently.
Great info - thanks guys!

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

John

Great tip

Ed

Simon - thanks very much for starting this thread and sharing your methods. Thanks to the others who have chimed in as well. John - super helpful info and pictures. Thanks!

Charlie, who is this Simon person you are referring to ???

If I may add, John's method is excellent and will get you 95% of the way there but IMO, you will still miss subtle runout with that method. It's hard to tell from a photo (it may just be the light), but the 3rd photo in John's post seems to have some barely there runout about 2/3 from the top. In my experience, the only way to completely eliminate runout is to use mineral spirits under good lighting -- many times I've found that the runout is only visible with mineral spirits but looks fine otherwise. When I say no runout, I mean absolutely no color difference at all when moving across the center joint -- relatively few guitars seem to meet that criteria.

Here's a quick link to a soundboard gallery from this complete asshat of a builder named Fay -- shoddy work but no runout on his tops

http://fayguitars.com/Guitars/Gallery/soundboards.html

This may be stating the obvious, but I'll do it anyway:
If you seek out suppliers who cut from split billets, you stand a much better chance of getting a top with no visible runout. While it is a common method on huge Sitka trees, it is much less common on the smaller spruces like Euro or red.
In the case of red spruce, there are only a few who do cut from split billets....and that does not include the most famous one located in Missouri.
In addition to the visual, you can also detect runout by feel. Rub the top with your fingers along the grain in both directions. If there is runout and you rub against the grain, it will feel grabby. It should feel smooth when you rub in the opposite direction.
It's like rubbing the fur on a short-haired dog or cat.

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John

I was taught the the same lighting method by Alex (Alexandru Marian) .
It's very useful when purchasing wood (especially when I have to pay a hefty amount for shipping)
and I have a good idea how much runout top has before receiving it.
That is provided the supplier knows how take the top wood with the flash lightning.

Here's a previous thread that Alex elaborated.

http://luthiersforum.com/forum/viewtopic.php?f=10101&t=38227&p=501510&hilit=runout#p501510

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Sen CL Goh
http://senguitar.blogspot.com

Good stuff!!! thanks

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MK5acoustics.com

Most useful thread on this topic I've ever come across. Thanks all, for sharing your knowledge and tips.

I'm working a top right now that I thought was run out-free, but after getting the rosette in and taking it down to final thickness, I can see a little of that telltale offset sheen appearing. It will be interesting to go do some experimenting with the other tops that I have in my stash.

Thanks again!

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George :-)

Sen, seems we got the answer from the same source.

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member of the guild of professional dilettantes

Yeah you are very right, Miguel.
Not only this though, I have learnt lots of other valuable knowledge from Alex too!
I'm pretty sure that you too!

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Sen CL Goh
http://senguitar.blogspot.com

Not to derail the thread, but you're right. Alex has been an invaluable help and a good friend.

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member of the guild of professional dilettantes

Thanks Toonces for starting this thread and to John for the great explanation and pictures of how to detect runout.
This is something I have been struggling to figure out the best way to detect it on the sets I have been buying lately so this info is quite helpful.

Thanks again,
Bob