Replies

1. 
   citrouille | Sep 05, 2006 07:22pm | #1

   NUTS

2. 
   jackplane | Sep 05, 2006 07:37pm | #2

   Yep.

   Nuts.

    

3. 
   JohnWW | Sep 05, 2006 08:19pm | #3

   Case hardening is a real problem, but a good kiln operator can avoid creating it.  Your furniture maker just needs a more savvy wood supplier.

   John White, Shop Manager, Fine Woodworking Magazine

1. 
   Alan Az | Sep 05, 2006 08:42pm | #4

   Can you explain what you mean by "case hardening"?  It is a new term for me.  thanks in advance.Alan

   Started Learning, Still Learning, and still don't know enough!

1. 
   mapleman | Sep 05, 2006 08:55pm | #5

   Alan,

   I believe case hardening is caused by improper drying conditions in the kiln. If you take a board and rip it on your tablesaw, you can spot case-hardening if the board pinches tightly together after the cut, or spreads wildly apart. Of course, you could just have gotten a bad board with lots of compression-type grain in it. I would say of you bought a handful of boards from a supplier and they all bowed or pinched together then you would have a problem with case-hardening. Stick with reputable dealers who dry their own lumber if possible, and ask them about case-hardening. If they are taking measures to prevent it, then they would be someone I would stick with. If I'm not mistaken, air-dried lumber doesn't have these problems. Hope this helps.

   Lee

1. 
   Alan Az | Sep 05, 2006 09:11pm | #6

   Thanks, that helps a lot.Alan

   Started Learning, Still Learning, and still don't know enough!

1. 
   John_D | Sep 05, 2006 11:16pm | #7

   If you really want to get an understanding of this topic, check out Bruce Hoadley's "Understanding Wood: A Craftsman's Guide to Wood Technology".  It was recommended to me as the definitive reference to understanding wood as a building material, and for me it's lived up to its billing.  I got it at Amazon but you can find it at any good bookstore.

   If you're on a budget, you can learn a great deal from the Forest Products Laboratory's excellent Wood Handbook, which you can buy as a book from several vendors, or download for free directly from the FPL on the web (big file, 14.3 MB, but WORTH IT).  Chapter 12 (1.3 MB) can be downloaded separately, and is all about how wood is dried, etc.

   I've studied through Hoadley and the FPL handbook, and they've helped me a lot in learning how to design projects taking wood movement into account.  Hope this helps!My goal is for my work to outlast me.  Expect my joinery to get simpler as time goes by.

2. 
   Alan Az | Sep 06, 2006 08:22am | #15

   Thank you for the information.   I downloaded the Wood Handbook and have scanned some of it.  It will definitely help.  Am looking at picking up the other book as well. Alan

   Started Learning, Still Learning, Plan to keep learning!

4. 
   oldusty | Sep 05, 2006 11:34pm | #8

   Dan ,

            When you get a batch of material that is case hardened it often makes you want to knot  work with wood anymore .

      Often times these same boards will also show characteristics of cell collapse , timber bound or stress and mineral streaks . These are the day's you wished you worked steel .

     fortunately not all solid stock has these traits ,

            Your pal is overstating things a bit

                                                             dusty

1. 
   citrouille | Sep 06, 2006 12:19am | #9

   I have been making furniture for a living for what ? almost 40 years ?
   I bet I didn't come across 10 lots of lumber with stress related problems.C.

1. 
   oldusty | Sep 06, 2006 05:55am | #14

   Hi citrouille ,

                         You got me beat by about 10 years , that's a lot of sawdust !

               Now over the years while only a few whole lots of Wood have been afflicted many , many boards have passed over my TS only to wind out  bit , how bout you ?

        I don't joint those boards , I straight edge them on the TS first .

                          regards                     dusty

1. 
   citrouille | Sep 07, 2006 02:04am | #17

   I buy lumber by the bundle, if a board starts to act weird on me, I use it for shorts, chop it up and make the best of it.
   After all if we wanted everything perfect we would buy plastic !C.

2. 
   bldrbill | Sep 06, 2006 03:12am | #11

   Dusty--Does improper kiln drying cause mineral streaks?  I am now working a batch of red oak with occasional mineral streaks and some is really beautiful.  I'm carefully selecting it to use in RP doors.  I have never really known what caused the streaks--thought they came out of the soil. 

1. 
   oldusty | Sep 06, 2006 04:41am | #13

   hi bldrbill ,

                    To my knowledge mineral streaks are not caused from the KD process , rather having to do more with the soil and growing conditions .

     Seems like Eastern Red Oak has more color  the farther south it's grown . The region the tree is grown in certainly plays a part in the actual look and hardness of the wood .

    The Appalachian Oak and the Southern Oak can be especially hard and brittle compared to the Northern Oak .

           I guess I was thinking about everything that can be wrong with a board at the same time .

                                       dusty

1. 
   bldrbill | Sep 06, 2006 06:48pm | #16

   Thanks Dusty--whatever causes mineral streaks, they can provide the opportunity for some really nice one-of-a-kind pieces.  I wouldn't consider them a defect unless I were trying to match something existing.

1. 
   gb93433 | Sep 07, 2006 07:57pm | #18

   whatever causes mineral streaksMinerals being sucked up out of the soil. Trees growing in wet areas will typically have more.

2. 
   KeithNewton | Sep 08, 2006 01:21pm | #20

   From my own observations, I think that most mineral streaks are caused by injury to the bark, at least enough to thin it enough to start loosing moisture in small locations. Woodpeckers can surely cause them. I think what happens is that the sap passing the injury is exposed to air, causing oxidation to whatever minerals are in the wood, and in some cases even an increase in viscosity or jelling, so that what would otherwise be a hollow cell, there may be cells loaded with a higher concentration of this solidified extractives.

3. 
   gb93433 | Sep 08, 2006 04:27pm | #21

   You are right. I had forgotten about that. The end user usually does not like discolorations. The only time they are graded out is if there is shake. When I was grading lumber and would see those discolorations I would bang on them with the board rule to determine if there was any shake. A lot of times if they were dark there would be. Each species of wood often had different colors. For example poplar would often have a purple color whereas maple would have an array of colors such as green and brown. I have seen those streaks caused by nails or from when the sap was drawn to make maple syrup. Some colors just amaze me where they come from.I have actually seen lumber coming from the southern US that had mineral in it because of where it was grown.The NHLA defnes it on page 118 as "Mineral Streak: An olive to greenish-black or brown discoloration of undetermined cause in hardwoods.
   http://www.natlhardwood.org/pdf/Rulebook.pdf

4. 
   citrouille | Sep 08, 2006 10:52pm | #22

   "I have actually seen lumber coming from the southern US that had mineral in it because of where it was grown."I didn't have a chanche to verify this but I was told that yellow poplar growing in areas where there is no coal in the ground tend to have much less or no mineral streaks.C.

5. 
   mike_b | Sep 06, 2006 02:44am | #10

   Lots of good replies from those more knowledgeable on kiln drying than I am. I doubt your friend is nuts, but his thinking seems as limited as the "hardwood only" guys who say there is no use for sheet goods and veneer in fine woodworking. But hey, if he's making nice stuff from what he's using, more power to him.

6. 
   forestgirl | Sep 06, 2006 04:37am | #12

   I'll quote the Hoadley glossary statement for you on case hardening, but by all means, get the book.  You won't regret it!  "A condition in dry lumber wherein residual drying stresses leavae the outer layers under compression but the inner core in tension."  When boards such as this go through your table saw, being ripped, they can perform some dangerous antics as they go through the blade, twisting or closing and pinching the blade.

   Your friend may not be nuts, but he doesn't have a very good lumber supplier it would seem.

   forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 
   

7. 
   gb93433 | Sep 07, 2006 07:59pm | #19

   Casehardening—A condition of stress and set in
   wood in which the outer fibers are under compressive
   stress and the inner fibers under tensile stress, the
   stresses persisting when the wood is uniformly dry.

   at http://www.fpl.fs.fed.us/documnts/usda/ah188/intro_gloss_index.pdf

   from the website http://www.fpl.fs.fed.us/documnts/usda/ah188/ah188.htm

8. 
   philip | Sep 09, 2006 12:16am | #23

   Case hardening has already been well explained. You might like to know that some timbers are susceptible to this condition-an example is Imbuya.A competent kiln operator will use the right drying schedule to minimikse the risk.And there are some timbers that are susceptible to case hardening even if they are being naturally air dried.
   I think that any furniture "manufacturer" who uses only sheet material because of case hardening problems is nuts-or paranoid about kiln drying.

   Philip Marcou
1. 
   forestgirl | Sep 09, 2006 11:41pm | #24

   "I think that any furniture "manufacturer" who uses only sheet material because of case hardening problems is nuts-or paranoid about kiln drying."  Or disingenuous about why he uses sheet goods?  A bit lazy maybe??  Or not patient about selecting stock??forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)