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Flattening and resawing warped boards
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=37919		 Page 1 of 1
Author:  Sondre [ Fri Oct 05, 2012 7:26 am ]
Post subject:  Flattening and resawing warped boards
Hello,

I found some old Madagascar Ebony locally. The best board is 38 1/2" x 8" x 3/4" and I was hoping to get a back/side set out of it. The thing is, it is a little cupped - about 1/16" at one end, and a little less at the other end. It is also a little warped lengthwise/diagonally, but it's not too bad. I am able to clamp it flat at the ends with some elbow grease. Would you bother attempting to flatten it permanently? And do you think I can manage 3 slices to get 4 panels? My bandsaw blade is a Woodmaster CT 1" x 0.035 x 2TPI

Thanks,
Sondre
Author:  klooker [ Fri Oct 05, 2012 8:01 am ]
Post subject:  Re: Flattening and resawing warped boards
If the board was flat, you could easily make 4 cuts & get 5 panels - I do it all the time with 3/4" stock & the Woodmaster blade.

I don't know about the cup/warp/twist situation, I've never had any luck flattening a board that thick.

Kevin Looker
Author:  Goodin [ Fri Oct 05, 2012 8:01 am ]
Post subject:  Re: Flattening and resawing warped boards
If you are planning to resaw it you will need one flat side squared up to one flat edge. You could probably get by resawing this board like it is but you won't get as good of a yield as if you had it properly squared up. Of course, if you square it up you will lose material as well, but your band saw cuts will be cleaner and truer. Do you not have a jointer? With a 3/4" thick board you should be able to slice four pieces to about .168" (subtracting bandsaw blade thickness of .025" for 3 cuts). Not accounting for error.
Author:  David Malicky [ Fri Oct 05, 2012 12:27 pm ]
Post subject:  Re: Flattening and resawing warped boards
I would probably start by finding the straightest portion of 31" in the piece and cut it to that 31". Next, a lot depends on how bad the remaining warp is and what tools you have: jointer, bandsaw/fence/compression device. As you probably know, it's best to slice off opposite sides of a board to minimize internal stress induced warping, so both faces need to be flat.
Author:  B. Howard [ Fri Oct 05, 2012 3:27 pm ]
Post subject:  Re: Flattening and resawing warped boards
verhoevenc wrote:
Joint it flat on one face to lose the cup (dot worry about the warp). Just make sure across its width at all pouts its flat. Then, to deal with the warp, resaw with only about 2" of fence in front of the blade. The smaller amount of pre-blade fence you have, the less impact a warp/twist will give resawing. And once thin, it won't matter.
Chris


+1
Author:  dzsmith [ Fri Oct 05, 2012 5:48 pm ]
Post subject:  Re: Flattening and resawing warped boards
I don't own a jointer (yet) but I've had good luck using my thickness planer. I made a sled of melamine with a stop at one end and put wedges under the high spots to stabilize a cupped or twisted board on the sled. I run it through the planer takng very light cuts until I have a flat surface. I think cutting the lumber to be closer to finished size first minimizes waste rather than trying to take a twist out of the entire length of lumber.
Author:  Sondre [ Sat Oct 06, 2012 11:44 am ]
Post subject:  Re: Flattening and resawing warped boards
Thanks for the replies. I do have a jointer, but I'm a little worried that the diagonal warping of the board will mess things up if I use it...

I was hoping to hear success stories about flattening such boards, but I kinda suspected it would be difficult. Anyway, I'm happy if I end up with 4 panels, which seems feasible.

Thanks,
Sondre
Author:  Don Williams [ Sat Oct 06, 2012 1:14 pm ]
Post subject:  Re: Flattening and resawing warped boards
To add to what Chris said, a point fence is the ticket to resawing a twisted board. You will still need to flatten one face, but then resawing should go fine with a really sharp carbide blade.
To easily make a point fence, take a 1" dowel around 9" long, and make a flat along the length of it. Drill a couple of holes for some bolts and bolt that to your fence, making sure to recess the heads into the dowel. You have to attach it to the fence right where the teeth of the blade are though. It may be easier to attach the dowel to a board which you can bolt to the fence. You could also not use the fence, but make one from wood with the dowel screwed to it and have better adjustment capability. You will have to guide the wood through the blade very carefully, but it will do the trick.
Author:  David Malicky [ Sat Oct 06, 2012 2:33 pm ]
Post subject:  Re: Flattening and resawing warped boards
Sondre wrote:
I was hoping to hear success stories about flattening such boards, but I kinda suspected it would be difficult.

It's possible to ~flatten plywood sheets by selective adding moisture or heating/drying a surface, but I've never tried it for resawing solid wood. It would improve the cup, but bow and twist could become worse. And during the first slice it would probably cup back. Overall risky, given the alternatives.

+1 on Chris's advice to drum sand with the concave bow facing the drum (leaving the bow) -- that works well.

If using a point fence, I would first practice a lot with other wood that has twist and bow. It's a nice technique but I've found it's easy to make a mistake that ruins the slice.
Author:  Don Williams [ Sat Oct 06, 2012 5:07 pm ]
Post subject:  Re: Flattening and resawing warped boards
David Malicky wrote:
If using a point fence, I would first practice a lot with other wood that has twist and bow. It's a nice technique but I've found it's easy to make a mistake that ruins the slice.


+1.

Definitely.
Author:  Dkeddy27 [ Sun Oct 07, 2012 10:26 am ]
Post subject:  Re: Flattening and resawing warped boards
I've had great success laminating a piece of 3/4 plywood to the crowned side of the wood being sliced and flattening the plywood on the joiner. You can manipulate your wood being sliced because it is now 1 1/2"! Just cut the slices off the plywood, works great!!
Author:  Sondre [ Mon Oct 08, 2012 6:42 pm ]
Post subject:  Re: Flattening and resawing warped boards
Thanks again for the input! And sorry about the slow reaction...

verhoevenc wrote:
That's kind of what you DON'T want to do. I'm saying LEAVE the warp, all you need to rid yourself of is the cup! Another good choice for this is a drum/thickness sander. If you send the board through so that the concave surface faces the drum then by definition the only part of the board that will touch the table (and register "level") is the part UNDER the drum. That way, you flat it width wise perfectly, but keep the warp. As I said above, with the shortened fence, the warp will be no issue! If you try and plane out the warp you'll lose a LOT more. And then, once resawn thin, a warp won't even matter!
Chris


Yep, I am not worried about the warp when it comes to resawing, and I want to leave it to minimize waste. However, I think the warp might be a problem if I use the jointer to get rid of the cup, because the warp prevents the board from lying flat on the jointer table. I don't have a thickness sander or a drum sander btw...

Like I said, I am able to clamp the cup flat. What if I glue several pieces of e.g. 2" x 2"s across the width of the board to force the cup flat? Then I resaw with a short fence and the 2" x 2"s facing outwards. Will the internal stress in the ebony mess things up during resawing?

I may be overthinking this - I just want to waste as little as possible of this beautiful wood... I will make sure to practice on some twisted/cupped scrap first.

Thanks,
Sondre
Author:  Bobc [ Wed Oct 10, 2012 8:43 am ]
Post subject:  Re: Flattening and resawing warped boards
Sondre you can glue and clamp it to another board that is flat using newspaper between the glue joint. Or use the 3/4" plywood method as suggested above. Either method will work.
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