Casehardening in Wood

[Ed in Tampa]

Keep in mind a saw mill cuts green wood all day long , the kerf on their blades are quite a bit wider than the blade in some cases by as much as 3/8 inch , it allows the dust to be carried away and not bind with the blade , wet wood contains sugars , sugars get hot and melt and will attach to the blade and burn , the gullet of the blade is designed to help carry the dust away when the cut is real deep. a wide kerf blade and slowing down the saw and feed rate along with making multiple passes on such thick wood in the scenario above could help but is not the cure for using wet unstable wood . JMO

I do not think the situation is too wet of wood but wood that has different levels of dryness. The outside of the board are artificially dried but done in a manner where the drying is not completely done in all parts of the wood. The outside is dry but the inner core is very wet.
When cut this tension created by the incomplete drying then forces the wood to move in strange ways. That becomes a problem when the kerf clamps shut on the blade.

[garys]

I guess I've been lucky. I've been working with my Shopsmith steadily for over 30 years and have never run into a piece of wood that failed to cut cleanly with either my circular blade or with my bandsaw as long as I feed it straight and at the proper speed.
Some years ago we redid our kitchen with hickory cabinets. To finish the job the way we wanted, we did all the other wood in the kitchen in solid hickory too. That included the window and door frames and trim, the baseboards, the pantry door, and all the hickory filler pieces to fit the premade cabinets into the available space. It was all only 3/4" stock, but the saw handled it very nicely.
I've also used my Shopsmith table saw to rip down oak 4x4s into 2x2s with no problems. Of course I had to feed slower, but the Shopsmith handles it just fine.
I've never encountered any of that hardened wood that gives problems, even when using scrap oak pieces used in shipping by semi truck.

[Hobbyman2]

Keep in mind a saw mill cuts green wood all day long , the kerf on their blades are quite a bit wider than the blade in some cases by as much as 3/8 inch , it allows the dust to be carried away and not bind with the blade , wet wood contains sugars , sugars get hot and melt and will attach to the blade and burn , the gullet of the blade is designed to help carry the dust away when the cut is real deep. a wide kerf blade and slowing down the saw and feed rate along with making multiple passes on such thick wood in the scenario above could help but is not the cure for using wet unstable wood . JMO

I do not think the situation is too wet of wood but wood that has different levels of dryness. The outside of the board are artificially dried but done in a manner where the drying is not completely done in all parts of the wood. The outside is dry but the inner core is very wet.
When cut this tension created by the incomplete drying then forces the wood to move in strange ways. That becomes a problem when the kerf clamps shut on the blade.

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Thanks Ed .
I understand what they were saying however IMO
improper drying is just improper drying , JMO at the kiln all wood dries from the outside in unless it is over heated and than the sap cooks out the end grain ,if you put a small piece of wet wood in the microwave for a minute or so you can see it boil out , when the heat is to high the sugars thicken and even crystalize just like over heated maple syrup , the syrup is sap , so by the description { to some degree } all wood even air dried wood is case hardened if used before it dries internally seasoned or cured or what we all ways called "stabilizes" ??? if you watch the video the guy was trying to cut a verry thick piece of wood and it was burning against his blade ,IMO his cut may have been way too deep for his blade and his saw, wet wood " may have " multiplied the trouble but unless stumpy checked the moisture content of that piece before his video he is grasping at straws ?? . internal stress is not the same thing as wet wood , internal stress is normally caused by the growth of the tree , a tree growing on a hill side can have more internal stress than one growing in a meadow . and one growing along a river bank that has seasonal floods will be even different than one growing in a dry area . a limb hanging from the tree may have different internal stress than the tree trunk we had some Brazilian mahogany yeas ago before it was banned in the USA , its moisture content was near 8% , when you cut it you could see the board bow . when you sanded it it looked as if you were sanding end grain in places . {that was called shake} and was full of internal stress when cut , needless to say it was miserable to work with, Last year I cut a few pieces of walnut on the SS that was still green, moisture content was above 15% and I had no issues , but the wood was only about 2in thick and I made shallow cuts , same with hickory and Oak ,I cut several pieces any where from 2 inches thick to 6in thick with a moisture content above 10% it was for the entry way we just completed , My point was when cutting wet wood or improperly dried wood it is best to make shallow cuts nor more than 1inch deep and never deeper than the gullet of the blade , and use a wide kerf blade . this keeps the sugars cool and the saw dust away from the blade to some degree, if ya watch a bandsaw mill some use water to cool the blade and wash away the sugars and dust when cutting wet / green/ wood . this fella has a video of the pitch build up on his blade from green wood and why they use a lubricant such as water . https://www.youtube.com/watch?v=uZYLOTfVrVk

[edflorence]

Well, I'm glad I'm not totally bonkers! Here's the old Nick and Drew video I was thinking about:

https://shopsmith.com/ssacademy/SS_Arch ... lude_2.htm

Chris

He seems to be talking about a different phenomenon although he also calls it casehardening. Rather than about kiln drying, Drew is talking about machining and how a previously machined surface, if allowed to stand, will case harden compared to freshly surfaced. Maybe it is related?

I think both phenomena are similar in that they both involve the workpiece drying in a non-uniform manner. In one case, the core stays wetter than the shell of the piece and in the other its just the immediate surface that dries out, which does not seem to create the same internal stresses as the first case. Surface drying does create absorption issues, as Drew demonstrates. I found both videos to be informative and worth watching, but would add from my own experience that they left out an important implication of case hardening. Stumpy talks about the piece binding against the back of the saw blade if the kerf closes up due to case hardening, but does not mention that what that means is that one absolutely must have a splitter installed on the saw. Pinching the back of the blade equals kickback which equals potential tragedy. While it is interesting to understand what is going inside improperly cured wood, it is much less interesting to experience a table saw kickback.