How do you rip a straight board and not have it spring into contorted shapes
LanceSCV
| Posted in General Discussion on
Like probably all of us, I will go to great lenghts to select straight lumber. I will pick out a great board, say 3/4 x 10″ x 8′ for example, put it on the table saw, rip a two inch wide board off the edge and whamo, the narrower piece now is crooked, bowed, twisted, or in some other manner warped. Is there any way to avoid this as it ends up in a lot of wasted wood.
Replies
I don't claim to know exactly why that happens, release of moisture, internal tension, whatever. It does seem to me that it has seemed to become more prevalent now than in the past. Maybe the wood is less stable or kiln dried too quickly or maybe I've just become more finnicky. What I've done is to "sneak up" on the final size. I first joint one edge and one face and let the wood sit for a few days. Then I re-joint the edge and face and then plane the other face. A few more days of rest and I re-joint if necessary then rip a bit larger than than the finished dimension. After some more rest, I joint and cut to final dimensions. Except for the first time, during each of these jointing operations, I'm only taking 1/32" or so. If it were bowed more than that, the board would need to start out considerably thicker and wider than the final dimensions to get the correct final size.
Once bowed it pretty much stays unless you cut it flat/straight.
PS: I posted the entry bellow first. Then read this one. Not sure why this came above that other one.
ooooops I posted to Quikstep and ment to post to LanceSCV
The first pic you can see the bubbinga bowing as it comes off the saw. Well sort of ( I set the slice back up for a pic after cutting it off).
In the second pic I took two slices that were bowed, put them opposite each other supported only on the ends, gap in the middle, and stacked some other wood on top to "stabilize". After like a year there was no change. Still every bit as bowed as it came off the saw even with constant weight, encouragement , to flatten out.
Enlarge the photo a bunch and you can see the gap. If it was going to change it would have closed up in the middle.
Cross cut it into short slabs though and it is great for small projects.
Yea..
I would invest in a Meter .. 50% humidity is alot.. cold deters drying... Think of moving your bed into a basement with 50 Degree Temp and the Humidity.. would be alot of blankets.. and a loving wife to keep ya warm..
The bottom line is that aside from buying well-dried stock you cannot prevent it from happening. To the extent that it's oversized you can correct the phenomenon after it happens by letting it dry some more, going back to the jointer and then replaning. But one doesn't always have the luxury of the extra thickness or the extra time.
In a word METAL
>Is there any way to avoid this<
You are going to just love metal working.
: )
Your problem is why I stayed away from wood for so long.
Nope . . . cut it to near the size you want from thicker stock, let it rest then finish it to size. Don't move it from one environment into another.
I almost never buy stock that is near the thickness I want but cut it from thicker stock and then pray.
Besides it feels so good buying those big old planks. I feel like Krenov or somethin'.
PS: if it really goes boing when you cut it that is a sign it is going to move back and forth a lot from one season to another; year in and year out.
I believe they call this fire wood. Or fill as in fill dirt.
I call it "action wood".
I
I call it "action wood".
I usually make my rips 1/8 -1/4" over width and dress it down to the findished size with the jointer and planer. If there is more "action" in the wood than I allowed for then I just have to try again. I'll find a use for the first board.
Bret
Drying Faults
The simple answer is that the wood is stressed, and the stress most likely would have been put into the wood during the drying procedure. Some claim that air drying wood prevents stress developing during the drying process, and that it's only a problem if you buy kiln dried wood: this is not true as I have come across enough stressed air dried wood to know this isn't the case.
What you can do about it is a different story. Sometimes you can use mildly stressed wood as smaller parts, but sometimes you have to buy more new wood. If the stressing very bad, eg, casehardened or honeycombed you may very well have a good case for returning the wood to the dealer and getting your money back-- casehardened wood is not "fit for purpose".
You might find this link to an article of mine describing some common wood drying faults useful. Slainte.
"http://www.richardjonesfurniture.com/Articles/timber-dry-fault/timber-dry-fault.html"
Richard,
Will just add to your post, that in addition to aggressive drying schedules in the kiln, drying stresses can be a result of "wild" or irregular grain in the board. If there is a knot in the board, there will be drying stresses around the knot,( due to the changes in grain direction,) that drying shrinkage has introduced. Even if the knot is not in the board, but the board was taken from the log next to a knot, the grain will sometimes be distorted enough in that board to cause warp, or drying stress that may not be evident til the board is ripped.
Learning to "read the grain" is a helpful skill in choosing a board that will be less likely to take off in 2 new directions at the tail end of the saw.
Ray
I use alot of Jatoba with wild and direction changing grain. I do not always, but for 'sticks' that I think will go their own way. I will rip along the length about 1/3 deep on each face then let it sit on end for a day or two. I 'think' it helps? Some will show stress by twisting or whatever. Some will even split open along the rip on their own. Awhile back I had a rip 'explode' and the half (left, away from the fence) shot across the shop. The feather board did not stop it.
Because of the cost of Jatoba, I will always find some way to salvage long 'sticks'. Most of what I purchase is approximately 2 inches thick. I will match the grain the best I can and then do a lamination of the 'bad wood' for thickness or width. Many times I will laminate a contrasting wood in between.I have lots of clamps so this usually works. I have never had a lamination failure on any I have made.
Depending on the grain, maybe you can get some riff or quarter sawn wood for another project.
A note: If it is twisted wood I usually just scrape it!
Straight boards
I had a woodworking instructor who helped me avoid the wood movement peril you described. Buying good wood at a moisture content of 15% or less certainly helped, and using the right table saw blade for the job was also part of the solution, but he taught me to use time and patience. One of the first things he taught me was to expect some movement. Wood is a living, breathing material.
I learned to take rough lumber and let it settle for a few weeks in the shop so it could acclimatize. Then rough mill the lumber by running the wood through the jointer, planer and table saw but leave it oversized and let it settle for another week. This would allow me to be able to see and read the grain better. I would find that, depending on the grain, I could see if there were some pieces that were more apt to bend and render themselves unacceptable for the use I had first intended. Often, if a piece looked like it had a lot of tension in it, or the grain was inconsistent, I might be able to relegate that piece to another part of the project rather than waisting the entire piece of wood.
After all the wood was rough milled and selected pieces were designated as specific project parts, I would do a final milling at the time I needed the specific piece(s). If, for example, I was cutting a 4 inch wide piece from a plank, I would make the initial cut as wide as an extra 1/2 inch so that I could see the amount of movement I would get and, secondly, have enough wood to be able to plane it down to size. If the piece from that plank had less movement than I thought, the other pieces I took off of that plank would be cut with much less extra margin.
As it turns out, by making cuts with more waist, my total waist on the project was actually being reduced because I was not having to burn whole boards that gave me surprise movement, rendering them useless.
Hope this helps.
Thanks....and roc is right
Thanks all for the help. I think roc has it right…metal is the only answer…and I’ll be happy to trade him a nice straight steel bar for that warped piece of Bubinga…
Reading the grain and working with it
LanceSCV ,
Assuming the matierial is dry and ready when you purchase it the real trick is using the right boards in the right places . A difficult problem for shops that don't want to buy much more wood then they need . I most always buy more then I need . Why take a nice 10" board and cut it down to 2 or 1 3/4" rips . Use those 3 1/2" - 4 1/2" narrow fairly straight boards to rip the narrows , cut panels or drawer faces from the wider boards . The worst hook or Bananna boards I cut into shorter lengths before ripping them into wider shorter pieces when I can .
Learning what to expect from a particular board by reading the grain will help you avoid some problems .
I look for a more straight grained with little character for narrow rips depending on if any detail will be shaped into the edge . The beauty of having a few hundred feet or a unit of hardwood allows you to find the right board .
Even when the materials have been dried to prefection there are always a few boards with minds of thier own so to speak. I can be machining like 50 piece and each one is fine then all the sudden one piece chips out or splits or otherwise can not be used .Each board can be different .
regards , dusty , trying to tame Alder today with some stress in it
Long & Short
The short answer is that cutting wood (all wood, dry wood less so, the wetter the wood, the more so) releases stresses in the wood that result in the wood changing shape.
One phenomenon that causes this is called "case hardening".
The long answer will change the way you look at (and work) wood. It is well worth the small investment in time and money. To give credit where it is absolutely due, I learned about it from Chris Schartz, on his blog.
The long answer is this: R. Bruce Hoadley. 1980. Understanding Wood. Newtown: The Taunton Press.
Good luck!
Hi Jammer and Dusty
I think a lot of the problems stem from the fact that there just aint all that many good trees out there anymore.I have noticed that there is a lot more 'reactive' wood in a lot of the boards you get. By reactive I mean the stuff that comes from trees that grow against wind, gravity etc and from branches. The cells in the trunks and branches are different types on each side. to counteract the forces they are growing against and contending with, and when they are converted to boards they go ape. The old time sawyers knew all about these types of things and those trees wern't selected. Now they take anything.
wot
Can't second strongly enough the referral to Hoadley's book. Jam packed with useful and helpful info.
When rough milling lumber, also cut to width plus an allowance before re-sticking. Yu want to find out as early as possible if the wood is going to be a snake.
In addition to the earlier thoughts, the board may have included reaction wood - the tree may have been leaning as it grew. Once in a while one will find a board with excessive movement when ripped. I'll discard such. If two or more boards in your purchase show this problem, a refund of purchase price might be requested. Lumber cut by a reputable mill, and properly kiln dried, should not have lots of such occurrence, in my opinion.
Don , Reaction / stress wood and otherwise boards that have a mind of thier own are not really reason enough to refund in reality . there is no implied guarantee that a given board will do what we think it should . In fact if the board makes the grade as in FAS and meets the criteria for that species in clarity heart / sap and width pretty does not count .
Just so folks don't think they should run and return a batch of lumber because 2 pieces were reaction wood , the reaction wood may have little or nothing to do with the drying of the lumber no, as said not all boards are perfect in fact damn few are imo . Our medium is not a very forgiving one .
regards , dusty
The unanswered question, of course, is how to tell in advance that a particular board is under stress. Does bird's-eye maple go squinty and angry looking? What about other woods? Does it help to lay them on the couch and talk to them for a while? Or, how about just giving them a nice hug before cutting? ;-)
I don't give those boards a hug - I threaten them with the woodstove. Works most of the time.
FWIW, I have both airdried (8+ years) and kiln dried (then air dried 4 more years) and both will do this whacko stuff sometimes.
Quartersawn boards without knots much less so. Plane sawn with knots much more so.
Brent
The unanswered question...
Ralph, sometimes you can tell there might be stresses.
For example, core collapse sometimes gives itself away because the wide faces of the board are lumpy rather than either flat or slightly cupped towards the bark side of the plank-- this applies particularly with plain sawn (tangential) planks. Cupping itself may also indicate stress, depending on the severity of the cup.
Honeycombing is a strong possibility if the wide faces of tangentially cut wood are thinner at the mid-point than at either edge, eg, the wood is cupped on both faces.
In both these examples the material is more than stressed, it's useless.
Severe edge bend is another fault to look for as this may indicate one edge came from near the pith of the tree, ie, unstable juvenile wood. Anything that's excessively bent, bowed, cupped or in winding needs treating warily. You could try talking to it on a psychiatrist's couch which is where your suggestion may have humorously leading to, but I suspect that won't work, ha, ha. Slainte.
Singing works great
I have found that if I am singing "Take it Easy" the boards all behave themselves nicely on promise that I will soon take off my ear protection. Once removed i realize how 'talented' my singing voice is and quit immediately.
Now that is stress relief....
AZMO
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