Wood internal stress

[stvrowe]

I thought I would show this example of wood that clearly had some pent up stresses.  The material is African Mahogany, has been acclimating in my shop for about 4 months, and was straight as an arrow until I did a bit of resawing.  The thickness started at 31 mm and I was splitting it down the middle into 15 mm thick pieces.

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[Michael Kellough]

I've had plywood with enough internal stress to require re-ripping even though every cut was made with the guide rail. I'd rip an 8 foot panel and push the halves together and find a nearly 3 mm gap in the center. With careful placement of the guide rail both halves could be "cleaned up" with just one more cut but it sure is annoying to have to do double the work. Although that beats ripping it on the table saw and never knowing internal tension was the reason all your subsequent "square" end cuts are not parallel with one another.

sorry about your bent stock Steve...

 

[jbasen]

I've worked with quartersawn white oak that had internal stresses.  As you rip cut the wood on a table saw, the wood came back together closing the saw kerf.  It would pinch the back side of the blade (this was before I had a table saw with a riving knife) which could kick-back the work piece [scared]. 

Ripping became a two person job where one person would stand behind the saw and as the work piece started to clear the blade they would insert a wedge in the cut; keeping the wood from pinching.  Very scary.

 

[Tinker]

I always kept a few small shingle wedges at my RAS to use whenever using it for ripping.  I had been told of the kickback problem with RAS's by a carpenter friend and he told me about the shingle pieces to prevent.  I was in my teens, but just once in a while, I listened to advice even tho I knew everything at the time. : :
Tinker

 

[jacko9]

Great picture Steve, I've seen that happen many times in many kinds of wood.  I keep small wedges on hand to keep the kerf open while ripping.

Jack

 

[nickao]

In my experience Internal stresses are not eliminated from acclimation time or kiln drying. I have about 2500bd feet of misc exotics that have been kiln dried and sitting in the same space for 3 years, the same town for near 7 years.  I was resawing some  5/4" x 11" Santos Mahogany last night and it pinched so hard it stopped my 220V 25amp band saw in its tracks. I got a wedge in there fast, but had to use a hammer to get in in there.

The band saw has become my go to tool instead of my table saw. Internal stress in wood causing kickback, etc played a big part in that. The table saw is of course invaluable to me, but now my shop is based on the band saw. It's safer and can do 85 % of things I formally used the table saw for.

If anyone new is starting a shop I suggest making the band saw the center of operations instead of the table saw. If I could have only one tool it would be the band saw. It may only be my perception , but I notice woods now tend to have far more stress than when I was coming up. Maybe they grow the trees faster, dry it differently or it might be in my older age I am more paranoid(and have access to far more wood and species), but it seems once a week I get wood doing crazy stuff when I cut it.

 

[stvrowe]

I should have noted that I did this operation on the bandsaw as the width of the piece being resawn was 80mm.  I noted the condition about 1 meter in to the resaw.  Needless to say, this would have been very problematic on the tablesaw.

 

[jacko9]

I should have noted that I did this operation on the bandsaw as the width of the piece being resawn was 80mm.   I noted the condition about 1 meter in to the resaw.  Needless to say, this would have been very problematic on the tablesaw.

I have experienced the same internal stress in ripping no matter how long the boards have been stacked in my lumber rack.  With both the table saw and bandsaw I have had to insert wedges every 12" of cut.

Jack

 

[Stephen B]

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When my father was at school in the 1930s, they used to insert a horse hair or wood splinter at the end of the teacher's cane. Over a week, and with use, it would split.  [smile]

Edit.

Nice workbench Steve, more pictures please.

 

[leakyroof]

Reminds me of some Purpleheart that I ripped into 1" wide strips a few years ago. I had to screw the strips to my project instead of just gluing them on or adding a few domino tenons... [embarassed]