what causes the cathedral/flame pattern on flat sawn lumber?

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Forum topic by stevewr posted 01-22-2018 03:33 PM 686 views 0 times favorited 6 replies Add to Favorites Watch
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1 post in 268 days

01-22-2018 03:33 PM

I am wondering if anyone has any insight into why the cathedral/flame pattern results in flat sawn boards.

For some reason I am having a hard time visualizing why this occurs.

6 replies so far

View msinc's profile


519 posts in 646 days

#1 posted 01-22-2018 03:52 PM

Is this what you mean, otherwise could you clarify whether you mean the wood grain such as so called “feather crotch” or “flame”, as above or you are talking about some kind of milling marks, like from a saw?????
If it’s in the grain and you mean feather crotch wood this is due to a fork in the tree. The larger the pattern then the bigger the fork. Big double main trunk trees will have the biggest and most of the time the prettiest. Not sure the exact terminology for it, but basically it’s where the grain is trying to grow both ways or switch directions. You get a different effect sawing it flat to the fork or perpendicular. One thing is for certain, that is if we are talking about the same thing…whatever you call it and whatever the reason it happens….it is rare and it is expensive.

View Loren's profile


10477 posts in 3790 days

#2 posted 01-22-2018 03:58 PM

If trees were totally uniform and straight
flat sawn wood would be more regular in
appearance. As it is, a kink in the tree will
cause grain variation in a flatsawn board
over its length.

View bondogaposis's profile (online now)


4982 posts in 2493 days

#3 posted 01-22-2018 04:30 PM

The reason is boards are sawn from logs and logs are truncated cones in shape. The annual rings are parallel to the sides of the cone. Boards are sawn straight and not parallel to the sides and intersect the annual rings at a slight angle creating a pattern that is parabolic in shape as the face of the board intersects the annual rings.

-- Bondo Gaposis

View Mike_D_S's profile


482 posts in 2356 days

#4 posted 01-22-2018 05:47 PM

This simple diagram will probably help. As noted by Loren above, a tree is not uniform and the grain varies, but as a rule the tops of trees are smaller than the bottoms and the growth rings are continuous. So if consider a perfectly circular tree with perfect growth rings, then you can think of the growth rings are sort of cones. When you section a cone vertically, you get the parabolic shape at the top. Thus the cathedral pattern where the saw cut crosses the growth ring at that point.

My teachers always said this was going to come in handy one day…..

-- No honey, that's not new, I've had that forever......

View LesB's profile


1813 posts in 3585 days

#5 posted 01-22-2018 05:55 PM

The arching, cathedral, pattern is caused during the cutting procedure as demonstrated above. However the “flame” type patters is most often caused by a juncture of two limbs coming together. When collecting turning blank wood from trees being cut down I always try to preserve these junctions of the limbs or trunks.

-- Les B, Oregon

View tomsteve's profile


820 posts in 1361 days

#6 posted 01-24-2018 01:51 PM

I am wondering if anyone has any insight into why the cathedral/flame pattern results in flat sawn boards.

- stevewr


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