Replies

1. 
   jdbutler999 | Jul 05, 2004 10:13pm | #1

   Try taking an equal amount off of each side....it may help to minimize the cupping.

2. 
   RickL | Jul 06, 2004 12:22am | #2

   Try a coarse blade on the bandsaw. Too many teeth on the table saw blade can generate heat. Try a dedicatd rip blade with fewer teeth.

1. 
   Dave45 | Jul 06, 2004 02:29am | #3

   You're releasing a lot of built in stress when you rip a board and bowing is pretty common.  You might try stacking your pieces flat (or even bowed a little in the opposite direction) and letting them 'relax' for a day or so.

3. 
   DougF | Jul 07, 2004 09:37pm | #4

   Or, you could consider a craftsman style sleigh bed.

   Kidding aside, the comment about creating eqaul tension release by rippping all sides will help the probelm and as will band-sawing the slats. 

   Doug

4. 
   gweisenburge | Jul 08, 2004 12:09am | #5

   As Dave said, due to tension within the material pieces may bow after ripping. To insure their final straightness, you'll have to begin with wider or thicker pieces and then joint each after your first rip, followed by ripping again or planing them to the final thickness or width. Of course, remember to put the jointed surface against the saw's fence or the planer's table.

   It's difficult to predict whether a workpiece will leave the saw straight, even when ripping flat and straight, quarter sawn, straight-grained material, although that's what I'd begin with. That's because tension may be due to wild grain or improper kiln drying.

   When ripping solid stock lumber (not plywood) you should use a rip blade, but the blade itself has little if anything to do with the  straightness of the offcut pieces.

   Namaste,

   Gary

   http://gwwoodworking.com/

5. 
   PhillipB | Jul 08, 2004 12:51am | #6

   cje,

   I have to agree with what Gary just posted - how you slice the stock has nothing to do with why it bowed. It does, however, have everything to do with whatever tension has been contained within that particular piece AND the worst offender is improper kiln drying.

   About 2 years ago I had the honor and privilege of restoring a altar in a church which was 150 years old. In so doing I was using mahogany for most of the work. One day I was in the process of re-sawing a piece of this stock which was about 20" long by 4" by about 1.5 " in thickness. I was band sawing the 1.5" width into two 3/4" sections. When I was about 4" from reaching the end, the stock just exploded and I'm not exaggerating when I say explode because it was loud enough to be heard over the noise of the band saw and pass through my 15dB hearing protection. I've seen my share of stress when re-sawing but never anything like this. This particular board had been in my possession for about 3 years or so and had always been straight with absolutely no twist, cupping, etc. to indicate stress. In addition, the grain was straight as an arrow. BTW, when putting the 2 sections back in their original position, there is a gap of about an inch in the middle of the two boards very close to the center of the length. So you never know what you will get when you re-saw.

   Regards,

   Phillip

1. 
   Dave45 | Jul 09, 2004 04:00pm | #7

   Phillip-

   The same thing happened to me several years ago while ripping a piece of 1x4 pine on a radial arm saw.  The cutoff piece was opening away from the blade as I ripped and about 12"-18" from the end it just exploded off the saw.  Scared the bejesus out of me for sure!!

   Oddly enough, I was able to collect the pieces and finish the cut (after a brief calm-down break) and the piece I wanted was perfectly straight.  Go figure. - lol

6. 
   chairmake1 | Jul 10, 2004 03:10am | #8

   I've had this happen several times - I belive that it is caused by improper drying - rushing the process. Also - there is more moisture in the middle that on the outside of the board - so make your cuts and then sticker the bowed parts (with the bowed side up) and then place some weight on the top of the pile. I a couple of days your parts will have relaxed and you can proceed with the milling process.

   Hope this works out for you-

   Robert

1. 
   jackplane | Jul 12, 2004 05:03pm | #9

   I'm guessing you're ripping oak- notorious for its case-hardening. This is not easily corrected. If possible, I'd switch to a different specie; any other good hardwood,cherry, poplar,etc.

1. 
   Pondfish | Jul 13, 2004 08:26pm | #10

   Case hardening will always result in high stresses in dried lumber, but the drying process in even non-kiln dried lumber can (and will) result in internal tensions that are not apparent until the wood is cut.  Leaving the wood to re-equiabrate for a week or two is not a guarantee that the cup, bow or twist will disappear. 

   What works for me is to cut work to rough dimensions, let equilabrate in the shop for a week or more, then do the final dimensioning.

   Good luck

   Paul in Tinton Falls

7. 
   hammer1 | Jul 14, 2004 03:10am | #11

   Anytime you rip or resaw a board in half the probability of bowing goes way up. It doesn't have anything to do with drying or the saw. It happens with all types of lumber KD or air dried, soft or hard. As others have said it deals with dynamic tension. You could improve your chances by only getting one piece out of your 3/4" stock, planing equal amounts off both sides. When ripping wide stock the only way to deal with it is to cut oversize and to rejoin to straight or cut it up for small pieces. The stories about the lumber suddenly splitting open is a good reminder to never be pushing in line with the blade, especially with bandsaws. The pressure caused by releasing the tension is often the culprit in table saw kick backs also. You may want to increase your slat size, 3/8" can get kicked out fairly easily on a bed.