Black locust - how much does it shrink/warp?

[pbarnes171]

Hi, new member here. I'm working as an arborist on the side and have a chance to mill a 30" black locust with my alaska mill (assuming the trunk is solid, the tree is 90% dead). I'm hoping to use the wood late this summer/early fall for rafters for a yurt. 13' rafters.

Not sure how many usable boards I'll get, but I haven't milled/dryed wood before so hoping ya'll can give me some pointers.

How much does locust typically warp/shrink, and would it be OK to use them after letting them dry for 6-8 weeks this summer? Upstate NY, fairly high humidity, no indoor space for drying so stacked outside and covered. The yurt will have a woodstove and so will have very low humidity and moderate/high heat during the winter so I expect they'll continue to dry a fair bit more throughout the winter if I follow through with this idea.

Thanks in advance!

[K-Guy]

This is from the USDA forestry
Drying and Shrinkage


Drying and Shrinkage

Type of shrinkage	Percentage of shrinkage (green to final moisture content)
0% MC	6% MC	20% MC
Tangential	7.2	5.8	2.4
Radial	4.6	3.7	1.5
Volumetric	10.2	8.2	3.4
References: 0% MC (98), 6% and 20% MC (90).

[K-Guy]

Sorry
I can't get it to post correctly but I think you can figure it out.

[pbarnes171]

So it looks like if it gets down to 6% moisture from green it will shrink 8.2% in total volume if I read that correctly? I don't think i'll ever get it that low as it won't be kiln dried (?)

Thanks. That's more than I thought

What about warping/twisting?

[K-Guy]

They don't mention it being a problem. This is the bit they had:

The sapwood of Black Locust is a creamy white, while the heartwood varies from a greenish yellow to dark brown. It turns a reddish brown when exposed to the air. The wood is often confused with Osage Orange (Maclura pomifera). It has a high density and decay resistance. It shows slight shrinkage and stays in place well. It is very strong in bending and is one of the hardest woods in America. It's shock resistance is almost that of Hickory (Carya spp.).

[pbarnes171]

OK, great, many thanks for the info

[Don P]

You may learn about growth stress during milling. Locust is one that the board can tuck itself in your back pocket while only half cut. It tends to have pockets of rot. I prefer to use it for 6x6's and larger but when a board comes off straight it will usually dry well. Keep an eye on your respiratory and wear a mask, it can shut some people down, nasty fine and somewhat toxic dust.

[moodnacreek]

Rip sawing a 30" half dead locust..... well don't let me stop you. [with a chainsaw]  If you pull it off please tell us how it went.

[pbarnes171]

Gotta learn somehow I guess 

[Prizl tha Chizl]

We salvage logged our new to us woods ten years after a TSI had killed all the big locust. What had been left to fall over and rot turned into board and batten for our entire house!

 I found that most big logs had significant heart rot and other pockets like Don p said. Hard on the blade, we hired a woodmizer.

 I've ripped a few with my Alaska mill, (most recently beams for our deck) just to flatten a log for framing. Certainly would not want to make locust 1x with it. Do the math, if there's any way to get them to a mill I'd do it.

After 6-8 weeks of drying you'll still see lots of shrinkage. Also make sure to sticker them well and maybe strap them. The ones that come off the mill straight may stay that way, but those will be few, and the twisty ones will just keep moving. Plan on straight lining/edging them before you install them regardless, possibly in batches as you go/as needed if you're using them that green.

Also, only install the best locust if you're using it for its rot resistance. Clean hard wood can last a half a lifetime, but sapwood and pinkish punky heartwood will rot quicker than pine.

Good luck!

[ZbigniewP]

Hi,


older threat so You've ripped it already. I would be interested to hear how this one went.

have some experience with processing black Locust, logging myslef from my small forest. This year I cut down some 20 smaller size for making/refreshing my 30yrs old  fence posts for my forest area. Yea they make perfect posts, long lasting. Still I used post saver to help them stay well.

Regarding logging the way You cut the hinge is the starting point. Black Locust is a hard wood and it happens thet it will crack some 1' up from the hinge if stressed to much. Pity to loose some material on the bottom. The same for cutting to lenght - try to avoid unnecessary stress on cut. This may result in cracking boards during drying.

So far I always used band mill to mill my locust. Milling fresh may give very good result, teeth must be sharp. This summer I had remaining bottom piece like only 12-13" in dia and some 7' long only. I decided to do small experiment and make small timber of that myslef by chainsaw. Resharpened chain for ripping (some 25deg on teeth) and Gee... this was terrible experience. I'm not a complete novice to using chain saw but ripping fresh black locust was not easy. Final effect not satisfactory to say diplomatically... I got some 6" timber roughly.
Then I put it for air drying (as I always do) and it cracked in the middle some 1' in lenght on one side. Too much twist was inside and maybe stress after logging (see my comment above).
Usually I mill robinia for 2" boards. Thinner is waste of material for me. I air dry them like 2yrs.
Black Locust will probably do very good, definitely strong  and rot resistant rafters. If only You can get them straingt after drying and not cracked (despite waxing ends of course). But when You say the tree is 90% dead - this may be hard to process already. Not every mill will take it, You'll see.
But take it to the mill. You will have fight with alsaskan on this one and result will not be good enough. You'll see.

rgds  

[Don P]

Well that's cool, I didn't know it grows in Europe. And it sounds like it has all the same pests and troubles. Welcome to the forum  .
On shrinkage and stability... remember the old glass insulators on power poles? The pins on the crossarms that slid up inside the glass were made of locust because it was decay resistant and has low dimensional change.