Replies

1. 
   roc | Feb 21, 2012 12:34am | #1

   I am not trying to be mean . . . you are not going to like this

    >what do i do straighten the boards?  Any suggestions would be appreciated.<

   1.  Back up and practice on scrap until you know what you are about.

   2.  To learn what you are about begin at square one which is learn woodworking.

   To do this take classes, read books, have a friend show you etc.

   It is too involved to teach all that to you in a chat room.

   THE BOTOM LINE :

   Often bowed stock happens when you resaw.

   The board can not be "straightened".

   It must be milled flat by removing everything that doesn't look like a flat board.  The wood removed is called waste.  There can be considerable waste in working wood.  It is a fact that must be accepted when working wood.

   In the books look for how to " Four square " stock.

2. 
   noviceneil | Feb 21, 2012 03:02pm | #2

   resawing

   I agree with Roc, however, here are a couple "pointers"...part of the bowing issue may be from not enough tension on your blade, too small of a blade (you should have at least a 1/2 inch resaw blade). and not having your guide blocks properly    set. Also pay attention to the feed rate through the blade, you may be going to fast.

   Another thing that may help is to initially run the wood through the tablesaw (using a high auxillary fence) with the blade as high as it will go, then flip it end over end so the same face is against the fence and run it though again. Now you have two kerfs that the band saw blade can track and this will cut down on some of the bowing.

   There are a couple of good bandsaw videos out there that would be helpful, the one by David Marks being my favorite.

   Hope this helps,

   Neil

3. 
   RalphBarker | Feb 22, 2012 10:26am | #3

   Remember, too, that resawing will expose new surfaces that have a different relative moisture content than the outside surfaces of the original plank, and may also release tensions that are internal to the original plank. Both factors can introduce a new shape to the resawn boards.

   Try stickering the resawn boards, perhaps with some weight on top, and let them acclimate to your shop with the new (more moist) surfaces exposed to the air. Once they re-dry, the bow may have relaxed.

   The same is true with thickness planing. If one planes only one side of a board, it is likely to distort for the same moisture-based reason. That's why it is recommended that both faces be alternately planed, so both sides have new surfaces exposed.

   The real question, I think, is whether it makes sense for the average woodworker to buy thick stock with the intention of resawing to conventional thicknesses. Thicker boards usually command a premium on top of the actual board feet contained in the stock. Thus, it may be more economical to buy stock of "standard" dimensions, particularly when one considers what is lost in resawing and resurfacing.

1. 
   mwill87428 | Feb 23, 2012 01:04pm | #4

   Resawing

   Thanks to all for your help.

   Ralph, this is what i had in mind when i posted my original question. Unfortunately i stated it rather poorlly.

   The evening i cut the boards i stickered  them and applied weight ( about 100 lbs).  The next day i took the 3 best boards and planed (by hand) the convex side until flat, thicknessed them close in the table saw and finished with the hand plane.  I had originally wanted .750" thickness but had to settle for around .680".

   The board that was bowed the worst at about 1/4 in the middle seems to be responding to the weight.  I checked it this moring and it is about 1/8" now.

   When you buy a large board such as i did, is it good practice to season the board in your shop for some period of time before you break it down?

   I just finished a project building 4 dining room chairs out of maple.  All of the pieces for that project were resawn from a 12/4 board that has been in my shop for about 3 years.  I didn't have any problem with bowing on anything that was cut from that board (although they were much shorter than the Walnut boards).  I guess that is why i started to panic when the Walnut bowed so badly.

   Thanks again for the help

1. 
   RalphBarker | Mar 02, 2012 11:51am | #8

   Embracing a board's inner "sproing"

   When discussing wood movement, I'm often reminded of an explanation about the pricing of a less-expensive set of Japanese chisels. Part of the explanation for the lesser price for the set I chose was that the oak used for the handles had been "aged" for only ten years.  ;-)

   There are two factors that will influence cupping or warping when resawing: unequal moisture content, face-to-face, and internal stresses being exposed, as Don mentions below. Your experience with the 3-year old plank suggests that the time in the shop gave that plank time for the internal moisture to equalize throughout the plank. Remember the rule of thumb for air-drying milled lumber - one year per inch of thickness? So, the three years in the shop was about right for a 12/4 plank.

   Striving for equal moisture content on the exposed faces is the primary reason behind the recommendation for alternating faces when thicknessing a board in a thickness planer. The same would hold true with resawing. If you have one bone-dry face paired with a (now exposed) soggy internal face, the new board is bound to warp in some manner. How it warps is controlled by grain direction, previously hidden internal stresses, etc.

   For example, one strategy, if you have a use for 1/4" thick stock, would be to remove that amount from each face of the original plank, and then resaw the interior to something slightly thicker than your desired size. Then, let the resulting stock relax (and equalize, moisture-wise) for a while. That way, you are less likely to have extreme differences in relative moisture content between face pairs.

   Getting back to the original story, I can envision a Japanese master chisel maker cutting oak handle blanks, and saying to himself, "One day, my grandson will make a fine chisel handle from this fine stock."  ;-)

   Patience, Grasshopper? Yeah, right.  ;-)

1. 
   roc | Mar 02, 2012 11:22pm | #9

   Thank You

    >1/4" thick stock . . . remove that amount from each face of the original plank, and then resaw the interior . . . let . . . relax (and equalize, moisture-wise) . . . less likely to have extreme differences in relative moisture content between face pairs.<

   Hey once again I leared something !

   Thank you for helping make this chat room worth coming back to.

1. 
   RalphBarker | Mar 03, 2012 11:59am | #10

   Just wait . . .

   Just wait until I start posting photos of nude boards taken with my 8x10 camera!  ;-)

   View Image

2. 
   roc | Mar 03, 2012 07:54pm | #12

   Look Kid . . . Listen To Your Father . . .

   Two very hansom guys !  And so alert and intelligent looking.  It appears the big one is conveying wisdom to the smaller one.

4. 
   sabulba | Feb 24, 2012 08:23am | #5

   hi...

   i am not much sure that it will work or not so i think you should have to take a advice from carpenter which has enough experience to do this kind of work.

5. 
   noviceneil | Feb 24, 2012 10:45am | #6

   I agree with Ralph on the resawing. I tend to resaw when a project calls for thin boards, 1/4-3/8" thick. It galls me to take a 4/4 board and plane it down to those dimensions...I just can't stand the waste...most of the time I can cut in half the amount of wood used by doing this.

6. 
   donkondra1 | Feb 24, 2012 01:10pm | #7

   Bowing is caused by...

   Couple things could be going on here.

   First, it is a good idea to acclimatize the wood to the shop conditions, uneven moisture content can cause the bowing. 

   Whether or not the boards bow I always allow some time to pass after resawing and before jointing and thicknessing.  Sticker the parts, store them on edge or lean them against the wall. 

   Adding weight is only a temporary solution.  The boards will return to whatever shape they want to be :)

   Second, it may simply be internal stresses in the board that are released when cut.  That can be caused by enviromental growing conditions or improper kiln drying.

   About all you can do is pick you boards carefully.  Sudden changes in grain direction are likely to have internal stresses.  Flat saw is more likely to bow than quarter sawn.

   Rough cut all your parts to length before resawing and plan on having to deal with some movement.

   Neil suggests kerfing the board on the table saw first.  This may help with controlling bowing of the blade but it will have no effect on the bowing of the board in its length.

   Cheers, Don

7. 
   donkondra1 | Mar 03, 2012 12:11pm | #11

   Forgot to mention

   Too late now but there is a solution, it's called reverse bent lamination

   Resaw the bowed board down the middle and glue it back together on a flat surface such as your workbench.

   Once it's dry you can treat it normally, ie., joint and thickness.

   Cheers, Don

   
1. 
   townsend | Aug 15, 2012 02:58pm | #13

   Don,

   I just read your post on reverse lamination to eliminate a bend in re-sawn wood. I have not heard of this before, and I have a follow up question about this.

   For some context, I am building an altar for a church. The style is a pedestal table. There is a picture of my 1/4 scale model attached. The top will be 63" x 22" x 3/4. I want the top to be book matched so I have re-sawn a 8/4 mahogany board which is 12" wide. The boards are acclimating in my shop. So far it seems that I will be able to mill and joint them without a problem. I.e. I do not see much warp, twist, bow, etc.

   Since my top is not supported in the corners, I want to do as much as I can to keep the top flat over time.  I considered using a honeycomb top, but settled on using the apron, which is "hung" from the top, to provide stiffness while allowing cross grain expansion of the solid wood table top.

   Perhaps reverse lamination might improve stability with time. However, if I understand your suggestion correctly, the plies of the laminations would be the width of the board, or in my case 11”, or 22” for the glued up top.  Typically I use DAP plastic resin glue for bent laminations which are generally less than an inch or so thick at the glue line.  By that I mean the cross grain in the glued joint is never much more than an inch or so. 

   My concern is the seasonal expansion/contraction for a 22" wide mahogany top. It does not seem compatible with plastic resin glue.  Both laminates will be expanding/contracting at a similar rate, so the stress at the joint will be less than it would be if one side was fixed, but overall the joint will be stretched and compressed over time.  Is it possible that a different, more compliant glue might make this reasonable and desirable.

   It seems to me that my project is too wide to benefit for this reverse lamination process.  However, since I am not familiar with it, I would appreciate your thoughts and comments.

   Thanks you,

   Allen Townsend