Replies

1. 
   woodman300 | May 01, 2003 08:49pm | #1

   I would guess the reason to mill the wood wet is that it takes too long for the log to dry out. It takes up to two years to air dry lumber that is cut 2 inches thick as it is, so if you leave the tree as a log who knows how long it would take.

1. 
   davamoore | May 01, 2003 11:47pm | #2

   And with all that moisture trapped in there for so long, it would probably be next to impossible to keep all sort of microbes, critters and other small creatures from getting in there and starting the rotting process.  Just picture a log on the forest floor.

   The whole milling and drying process is meant to accelerate drying to such a degree that all the small things (Jon Arno and Stanley Niemic -- sp? -- probably have the scientific names) don't have a chance to get going before it's too late.

   David"The world that was not made is not won by what is done" -- Mundaka Upanishad

2. 
   Clay | May 02, 2003 02:06am | #3

   Good question.  Maybe because a large log is likely to petrify before it dries?

3. 
   DonaldCBrown | May 02, 2003 02:29am | #4

   I once watched the milling of timbers recovered from old warehouses and factories. These were huge beams--maybe fourteen inches wide and 20 inches deep--from slow-growth southern longleaf pine, and they'd had more than a century to air dry.

   By the time the bandmill reached the center of the timbers, liquid water was visible on the surface.

4. 
   JeffKurtz | May 02, 2003 02:37am | #5

   You're right about the cracks, just look at a piece of dried firewood.  Years ago when folks cut logs for a cabin it was desirable to store them for several years in an old barn and pack loose straw around them - all to keep cracking to a minimum.

   A second reason would be to avoid the clouds of fine sawdust one would encounter in the sawmill - a hazard to the lungs and a fire danger as well.  When I used to saw every once in a while a dry log would get past the scaler.  A few inches into the cut and there was so much dust in the air that you couldn't see a thing, and it screamed so loudly you couldn't hear at all.  (Probably didn't do the saw any good either.)  We'd just drop them off the carriage and send them to the chipper

   Jeff

1. 
   fdampier5 | May 02, 2003 04:52am | #6

   the saw mill does it wet because if you did it dry you'd have to stop every few boards to resharpen.  I planed white oak both wet and dry.. wet I could plane all day.. dry I was sure to have to change blades after one timber sometimes less. 

        Noise too!  dry sawing sets up a racket worse than wet sawing..

          

2. 
   DavidxDoud | May 02, 2003 07:49am | #9

   Years ago when folks cut logs for a cabin it was desirable to store them for several years in an old barn and pack loose straw around them - all to keep cracking to a minimum.

   could you reference this for me? - - it would seem to me to be an exceptional case - log buildings (particularly 'years ago') were shelters of convenience,  the most quickly erected with minimum tools using resources close at hand - having some experience,  I can't imagine hewing a cured log -

    thanks,  DOUD

1. 
   JeffKurtz | May 02, 2003 02:35pm | #10

   Can't remember the reference off hand - read it in an old book written in the 1940's (years ago to me) which belonged to my grandfather.  Notice that I said desirable, don't know how often it was done - at least by the early settlers.  Now that I think of it, I have several friends who have built log homes and they've had problems because the logs weren't dried properly.

   As for hewing a cured log, if one is using pine, the most used material up in these parts, it would probably be easier.

   Jeff

1. 
   GHR | May 02, 2003 09:35pm | #11

   I think the only issue is economic. You cannot store logs until dry, mill it and sell it for a profit. So you rough saw it, and either dry it and finish milling or finish milling and dry it.

   Machining dry wood cannot be too hard, because we all do it.

   Certainly, saw mills have equipment specialized for handling green wood, but they could have equipment for handling dry wood.

5. 
   StanleyNiemiec | May 02, 2003 06:51am | #7

   Based on some off the top of my head thinking there are many reasons for milling logs green.  These include:

   Due to differential shrinkage (radial vs. tangential) drying whole logs results in more or less uncontrollable checking.  As such this checking might and probably would affect all grades of lumber and would therein devalue the material.

   Someone mentioned drying time and that is absolutely correct.  To dry whole logs would take an incredible amount of time (and if placed in kilns) vast amounts of costly energy.  If a mill is required to have a large number of logs drying in inventory, the mill overhead costs would be astromonical.  Remember that for many mills, log costs account for somewhere in the neighborhood of 80% of their production costs.

   Additionally, only about 60% of a log is converted into lumber.  It would be foolish to dry slabs and sawdust especially if there were any costs associated with the process.

   The strength of wood is inversely proportional to its moisture content.  Dry wood is therein harder than green wood and therein additional energy would be required to power the saw.  Harder wood would also reduce production throughput at each machine center.

   If a saw does not have sufficient bite, the sawdust that is produced is of a smaller particle size and therein more likely to spill from the gullet.  With spillage the saw gets pushed to one side or the other and as a result sawing accuracy diminishes.

   As wood gets harder, more heat is generated by the frictional forces of both cutting and in rubbing.  Saws would be more likely to overheat and if a saw loses its strain on the front edge, the saw will snake in the cut.  If the snaking becomes really excessive it can cause a wreck. 

   As the wood is harder, sawtooth configuration would have to change and with teeth with larger sharpness angles (the actual angle of the tooth) gullet capacity would diminish meaning that sawlog diameter capacity would have to be reduced.

   As someone mentioned dust would be a real problem.  Dry, airborn sawdust is a very definite respiratory problem but it is also an explosion hazard.  If a sawyer would rock a blade (hit a stone or a nail) a spark might be generated that would literally blow the mill up and likely kill most of the workers.  Not a good idea!  Sawmills are already sufficiently dangerous. 

   Also as someone mentioned decay and stain in the log would be uncontrollable.  This would waste large volumes of wood especially in the outer areas of the log that have both the greatest amount of sapwood (alway non-decay resistant) and the clearer, higher and more valuable grades.

   And finally, were the wood to dry in log form, internal drying stresses developing within the log might make it impossible to saw and get flat lumber.  Sometimes there are growth stresses in a green log that will pinch a saw  --  if drying stresses were present I think production rates would greatly diminish and many logs would have to be kicked off the headrig.

   Did I miss anything?

6. 
   Shepherd1800 | May 02, 2003 07:13am | #8

   The main reason is that the wood is just too hard when it is dry.  Green white oak cuts like butter, when it is dry it no longer is that easy to cut.  The moisture helps lubricate the saw blades.

   Stephen Shepherd

1. 
   StanleyNiemiec | May 02, 2003 10:34pm | #12

   It is a general misconception that water is a lubricant in relation to saws and sawblade performance.