Bowed stock after re-sawing on table saw

[Rick Hubbard]

I’ve run across a perplexing problem that I’m SURE someone on this list has an answer for….

Recently I acquired a large quantity of 2 X 12 oak planks that were salvaged from a remodeling job. The planks were used as chair rails around large student dining halls at the university where I work. This means that they were inside and not subjected to the weather so they are in near perfect condition. They are also coated with some kind of finish (varnish?).

Here is my issue: I don’t own a band saw, so in order to get some ¾” stock from these boards I ripped some pieces 3 ½ wide then ran them through my planer to cut through the varnish. Next turned these pieces on edge and ripped them again (cutting only half way through on each of two passes). What baffles me is that after making the second (re-saw) cut the stock immediately bows so much that it is basically unusable.

Does any one have any explanation for this phenomenon?

Any suggestions for resolving the problem? Does it have something to do with trying to re-saw on a table saw (I’ve used this technique before on hemlock 8/4 and it seemed to work OK).

Would this problem be solved if I used a band saw (I’m hoping for a “yes” answer to help me justify a major tool purchase to my “Department of Health Education and Warfare” [aka LOML]).

Thanks for the help.

Rick

[tod evans]

rick, unfortunately a bandsaw won`t cure your warping problems. the wood is warping because you`ve changed the internal stresses by cutting it, not just in thickness but in width also. if you have plans for this lumber i`d suggest cutting to length slightly oversized, and leaving it in your shop without finish, to acclimate for a couple of weeks before trying to resaw. and even this won`t assure you of the boards behaving, wood moves by its very nature and oak moves a lot......02 tod

[Ian Abraham]

Yup.. you can have a nice stable wide board, but that doesn't mean there is no internal stresses present.

Sometimes you see that stuff happening right off the sawmill, but if you cut a balanced board thats centered on the log it will stay nice and straight... untill later when some poor woodworker tries to rip it in 1/2 :(

Suggestions... run the 2 boards over the jointer so they are straight again.. or put them on the spare pile for use as shorts where the warp wont be an issue.

And try again with another board :rolleyes:

Cheers

Ian

[John Huber]

Here's what I do with thin resawn stock. Resaw and drum sand to about half the thickness of the desired finished board. These thin boards almost always are crooked, but they are flexible. Match a pair with opposite crookedness. Push them into alignment; tack them together with short brads from what will be the inside face of the finished board. Glue them together in a vacuum press, which gives uniform pressure, straightening from the bearers, and a thin glue line. The result is a very straight board that is unlikely to change shape in the future.

A side benefit is that you can use the best wood on the side that will be visible and the poorer wood on the side that will be hidden.

[Rick Hubbard]

Thanks for the input, everyone.

I had a hunch that the "internal stresses" thing would come up in the course of conversation, and I suspect that is the case here.

One thing I always wonder about, however, is a good explanation of why this stress always seems to manifest itself in a situation like re-sawing and not so much in plain old ripping.

Here is a somewhat related (true) anecdote:

I used to have a neighbor who was a sawmill consultant for Potlatch Corporation. He told me he went to American Samoa many years ago to help setup a new mill there. He mentioned that one particular species of log was so "stressed" that after the logs were cut and sent to the green chain that the boards immediately began to bow and curl so badly that the conveyor chains could not find a place to hook them and that once they were pulled off the chain into a cart, they would actually fall off the stack!

I don't recall what kind of wood he was talking about, but in any case I'll bet none of it has ever come to this continent (unless that is where Home Depot gets its 2x4's).

Rick

[Chris Padilla]

Trees growing at strange angles (pith off-center) will often have many more internal stresses than tress growing normal. Tree limbs an also have some strange streses. You often never know until cutting and freeing those stresses.

This is the nature of the beast in wood: a forever-living breathing creature! :)

[Pete Bradley]

One thing I always wonder about, however, is a good explanation of why this stress always seems to manifest itself in a situation like re-sawing and not so much in plain old ripping.
Rick
I suspect one factor is that a rip typically leaves you with pieces that are still fairly rigid while the area over which stresses were released is relatively small. A resaw opens up a big area working against a relatively flexible cross-section.

Pete

[Ian Abraham]

He mentioned that one particular species of log was so "stressed" that after the logs were cut and sent to the green chain that the boards immediately began to bow and curl so badly

Some of the Eucalyptus species are like that. I've sawn some logs where the boards where lifting 6" off the log as you cut them. Sure is a lucky dip when you try and resaw boards like that :D Maybe if I was to start making rocking chairs? :rolleyes:

Cheers

Ian

[Michael Adelong]

Would this problem be solved if I used a band saw (I’m hoping for a “yes” answer to help me justify a major tool purchase to my “Department of Health Education and Warfare” [aka LOML]).

Thanks for the help.

Rick

Rick.. No, it won't. The first board that I ever resawed on my brand spanking new BS literally exploded on me. I made the newbie mistake of not paying attention to anything other than the 3 or 4" immediately before and after the blade. If I had looked up, I might have noticed that I was in the process of making a 10 foot long pair of white oak tweezers. The far ends were touching, but centers of the 2 halves must have been 4-5" apart. When I got to within the last 2 inches of the cut, the darn thing exploded. The left half knocked the aluminum fence off of the saw, and then settled in the throat of the saw, and the right half lept about 2 foot off of the table.

To add insult to injury, my jointer was misaligned and I destroyed both halves trying to straighten them out.

Michael

[Chris Barton]

Think about it this way, the outsides of the board are the driest and the inside the wettest and suddenly you expose the "guts" to air and that causes the stress and the warp.

[Ray Bersch]

Would this problem be solved if I used a band saw (I’m hoping for a “yes” answer to help me justify a major tool purchase to my “Department of Health Education and Warfare” [aka LOML]).Rick

Well, it looks like no one has told you the truth, Rick, so I will - a good 14" band saw will solve all your problems - guaranteed. So go out and buy one and tell your wife that I said so - then I need you to tell my wife that I need a new 8" jointer - deal?

Ray

[Mike Wenzloff]

Hi Rick,

Sometimes the internal stress issue can be mitigated by alternating the sides one is resawing form. That way the boards have both sides guts exposed more or less equally.

Makes for more work as regards keeping the piles straight if one wants to keep them in sequence as you need to stack each face cut into separate piles, oriented properly and then make a single pile, which in turn will be stickered in sequence...that's where drawing a wide 'V' on one end of the board helps.

And this method doesn't always help enough. Some boards are just down right evil when resawn. I had a Padauk board literally explode once. Threw shards across the shop and the bang it made brought my wife out to check on me.

I also would encourage you to get and learn to use a BS if you are going to do much resawing. Makes life much easier.

Take care, Mike

[Charlie Plesums]

If you are serious about resawing, forget the 14 inch import bandsaws. Theoretically they resaw, but I would get a few good boards, then it would destroy the next few, then go back to good behavior, etc. Finally I got a heavy duty bandsaw with a carbide blade for resawing, and kept the 14 incher for curve work.

Incidentally I was making some doors today from sipo (like mahogany), all cut from two large boards. Doing one rip (and only one of the rips) the stresses were so bad that it pinched the riving knife so that I couldn't push it through the saw... I had to stop the saw, pry the board off, and cut it from the other end. All the other pieces from the same board were fine. The board only warped about 1/16 inch in 2 feet, but it wasn't a gentle warp...it was stuck tight.

[Rick Hubbard]

Well, it looks like no one has told you the truth, Rick, so I will - a good 14" band saw will solve all your problems - guaranteed. So go out and buy one and tell your wife that I said so - then I need you to tell my wife that I need a new 8" jointer - deal?

Ray

Actually, I brought up the proposition to my wife last night. To my complete surprise she said, "Sure, go ahead if you need one." Then she added, "We'll just cut off the heat to the shop this winter and the money we save will pay for it."

Does anyone know how well a bandsaw will work at 25 below zero?

[Chris Padilla]

Does anyone know how well a bandsaw will work at 25 below zero?

I think the BS would be fine...I wonder about the operator! :eek:

[glenn bradley]

I have read and followed the advice to plane or joint boards on both surfaces to minimize bowing. It helps but as pointed out; oak moves . . . a lot.

[Mike Kelly]

If you are serious about resawing, forget the 14 inch import bandsaws. Theoretically they resaw, but I would get a few good boards, then it would destroy the next few, then go back to good behavior, etc. Finally I got a heavy duty bandsaw with a carbide blade for resawing, and kept the 14 incher for curve work.

Incidentally I was making some doors today from sipo (like mahogany), all cut from two large boards. Doing one rip (and only one of the rips) the stresses were so bad that it pinched the riving knife so that I couldn't push it through the saw... I had to stop the saw, pry the board off, and cut it from the other end. All the other pieces from the same board were fine. The board only warped about 1/16 inch in 2 feet, but it wasn't a gentle warp...it was stuck tight.
I have had the same problem that Charlie had while ripping 4/4 oak. It gripped my splitter so tight, I had to shut down the saw and pry it off. It happens so don't feel bad. Pick up the next one and keep making sawdust!

[Jason Hallowell]

You could try de-stressing the wood some before ripping. This would entail stripping all of the finish/varnish off, exposing the wood to very humid conditions for a day or two, and then slowly drying/re-acclimating the wood. I have had good luck doing this with some woods. Even just planing or sanding all of the finish off and letting the wood acclimate to it's new home for a while will often help quite a bit.