some success with resawing

[merrill77]

After several rounds of trial and [STRIKE]error[/STRIKE] learning, I'm starting to have some success resawing on my bandsaw. It certainly seems like setup is everything. I took advantage of the Hartville Tool sale and scored a Kreg Bandsaw Fence. It was not pre-drilled for my 16" Jet, but adding one slot took care of it. In hindsight, buying a good fence (instead of building my own or using clamped-on boards) is the first thing I should have done after buying the saw. Why do bandsaws come without fences? Anyway, after getting the drift adjustment dialed in, blade perpendicular to the table and the fence perpendicular to the blade, I am now getting pretty decent results. The drift adjustment mechanism on the Kreg is not as elegant as I would like, but after a few tries, I've got it dialed in much better than I ever had before. I think that on my last attempt, the resawn boards were the same thickness on ALL FOUR corners!!!

:banana:

I still have one issue, which may not be related to setup or technique. Every one of my resawing attempts has resulted in boards that cupped significantly (1/8" over 6" board width). The cupping is in both directions (with and against grain). In each case the boards cupped facing inwards - by which I mean that if I put the board back together, only the corners touch. The boards in question are white oak, kiln-dried, which have been acclimating in my dehumidified shop for 2-6 months (depending on which lot the board came from). Based on the movement, it appears the boards have higher moisture content on the outside than the inside. Or could this me something else? Case-hardening? Any guesses?

TIA!
Chris

 

[flatheadfisher]

A bandsaw is next on my purchase list. I want to be able to resaw boards too. I will keep in mind the importance of a good fence!

 

[Gotcha6]

Just a theory here, wood typically air dries at the rate of one inch thickness per year, so you've exposed another surface to the air to dry which probably had a larger moisture content than the periphery of the original piece.

 

[Tarhead]

Chris,
I've had the same thing happen to me when I re-saw thick stock and I thought it was either moisture imbalance or the release of internal tension in the board. After resawing I put the unsawn faces together (fresh sawn faces out) and put a bunch of C-Clamps around the sandwich for a few weeks to let the boards settle down. There is always some cupping even after that.

 

[Kyle]

A lot of wood movement is directly related to stress in the wood or the imbalance of moisture within the wood.

If the resawn piece is immature wood, flat sawn or contains different gradients of moisture you will see movement.

I would like to note that the wives tale of wood drying 1" a year is not valid and really needs to go the way of the dodo bird. It is highly dependent upon species and locale as well as drying conditions.

Ex. Black Walnut that is 4/4 will dry from green in 60-80 days maximum as long as the wood is covered and air temps average over 70 degrees during the day.

 

[merrill77]

A bandsaw is next on my purchase list. I want to be able to resaw boards too. I will keep in mind the importance of a good fence!

FWIW, I'm really happy with the blade I'm using. It is a Laguna Resaw King - 1" carbide. I picked it up for $90/123" when they had a close-out last year. I keep it on the saw most of the time (it obviously doesn't do curve cuts). On the piece I was working on today, it ate through 7-8" of oak pretty effortlessly (1.5 hp motor). It leaves a pretty smooth surface on resawing. On thinner wood (such as crosscutting 3/4"), it leaves a very nice surface. Nice enough that I go to it frequently for crosscuts when my table saw is already setup for something else. With the new fence properly adjusted for drift, I may start using it for short rips as well. These factors have significantly reduced my desire to buy a miter saw.

I should probably elaborate on this a bit in a post in the "reviews" forum...

 

[merrill77]

Just a theory here, wood typically air dries at the rate of one inch thickness per year, so you've exposed another surface to the air to dry which probably had a larger moisture content than the periphery of the original piece.

I considered that - but should note that the cupping was immediate. So I believe the stresses were in the board before I started.

If the resawn piece is immature wood, flat sawn or contains different gradients of moisture you will see movement.

It started as a 8" wide, premium quarter-sawn board with no sapwood. Judging by the nearly-vertical growth rings, this probably came from a good-sized tree. So I'm guessing the latter. But just guessing, unfortunately...

 

[Gofor]

I have had the same effect when resawing and ripping kiln-dried wood. Because the humidity here is high, the wood frequently will have more moisture Outside than Inside after a few weeks in the garage that results in the cupping inward. The up side is that if you let it set a couple days or more, some if not all the cupping will disappear as the fresh cut side begins to equalize.

However, be aware that you will also run into this symptom on a smaller scale when you plane the wood and when you rip it. I have found it best to "rough plane" (getting close but not on the dimensions) on both sides of the board, enough to get a flat surface, and then wait a couple more days before final milling to dimensions. I leave at least 1/16th on each side (1/8" overall), and sometimes more, as some boards also like to develop a slight twist during this stage. If the boards are less than 1", I will usually run through the thickness planer right after resawing, as the roller pressure is enough to hold them flat while giving a flat surface. When hand planing, I just wait a few days.

As for ripping, I usually rip to 1/4" over, and then let it set for 3 or 4 days. I have had 2' long boards, 1 1/2" thick warp over 1/8" when first ripped, but settle down to 1/16 or so after a few days.

Just one of those things you deal with using 6% mc lumber in a 65% humidity shop I guess. I like the dead bugs of kiln-dried, but have less problems working with air dried. The trivet table I just made for my MIL is an example. I bought the wood a couple weeks before getting started. Drafted my design and developed my rough cut list/layout. I then cut the boards to length, planed to smooth on both sides, and ripped to rough dimensions. All warped and twisted some. After 3 days, I was able to close in on the final dimensions, and glue up the leg posts. after a couple more days, I was able to get them all trued up, square and milled for joints. All went together very well after that as the wood had stopped moving. What would have taken some here a day took me well over a week, but it wasn't the fault of the sawyer, the lumber, nor the kiln drying. It was just a fact of life working in a garage shop environment.

JMTCW from a still-learning novice. The set time may be time you don't have, but it will make your job a lot easier when you can.

Go

One caveat: All kiln-dried lumber is not the same. I have had great luck with that bought from Scott Smith. Some I bought from one of the commercial shops in Raleigh actually cracked and split on one side of the cut when crosscutting to length several 8" wide 8/4 boards. That was a stress problem that may have been from the tree, but also could have been from too aggressive a drying schedule. If you run into frequent problems like that, you may want to consider another source.

 

[DonDeJ]

A few years ago I got a book for Christmas called "Understanding Wood" by R. Bruce Hoadly. It has a real good explanation of how air temperature and humidity in the air relate to the moisture content of wood. There's a whole lot of other information about wood, too. Highly recommended reading for any woodworker.

 

[Mike Davis]

You said all four corners are the same thickness but what about the center?

If it is the same then all of your problem is wood stress and moisture differential. But if the center is either thicker or thinner you could also have some blade tension issues.

 

[merrill77]

You said all four corners are the same thickness but what about the center?

If it is the same then all of your problem is wood stress and moisture differential. But if the center is either thicker or thinner you could also have some blade tension issues.

I don't have a reliable way to measure the thickness of the panel in the center (short of cutting it in half), but when I put the other sides (the outsides) together, nothing but the centers touch. I should mention that the panels have already been through the planer. Only one light pass was required to take off the marks left by the bandsaw.

 

[CarvedTones]

I don't have a reliable way to measure the thickness of the panel in the center (short of cutting it in half), but when I put the other sides (the outsides) together, nothing but the centers touch. I should mention that the panels have already been through the planer. Only one light pass was required to take off the marks left by the bandsaw.

If you have nothing else, use your drill press. Put a bolt through the center hole in your table with fender washers and put a large brad point bit in the chuck and adjust so you can crank down and have it touch the bolt (with the drill off). Note the depth on your gauge. Slide the board in and crank the bit down to it (still with the drill off). Note the depth on the gauge and do the math.