Milling lumber is one of the most fundamental of woodworking activities and FWW has published many articles on milling techniques, all of which I’ve read. Recently, I decided to replace my carpeted stairs with hardwood. And of course, being a woodworker, I decided to mill my own treads and risers rather than buy prefab ones from a big box store. My floors are red oak and the stair stringers are already sheathed in 3/4″ ply so I decided to mill 4/4 Red Oak for my treads and risers. I purchased 10-ft x 12″ boards and ripped them down the middle to fit my 8″ jointer. Then I cut them to rough lengths (40″). I jointed one face dead flat on each board and then ran them through my thickness planer. Then I let the boards rest on their long edge for about a week. All but a few of the boards bowed during this rest period. Back to the jointer and planer. Flatten one side, check. Plane to thickness, check. However, I started to notice that when the boards came out the planer, they were bowed again. Back to the jointer, then planer, and walla- nice smooth bowed boards and a ton of saw dust. About 15% of the stock I purchased was actually too bowed to use at all. For the rest, I might be able to acheive 5/8″ thickness. That’s a lot of work, waste, etc. for achieving what should have been an easy and quick job. Does this story sound familiar? What’s going on???
I checked the moisture content of all my boards which were all between 5.5 and 7.
Is it common for red oak to contain abundant internal stresses?
Did I just get a bad batch of stock?
How can avoid this problem in the future? Buy thicker stock?
Replies
Are the boards flat sawn or quarter sawn?
Lytus:
Without seeing these boards I'm guessing this is flat sawn rather than quarter sawn wood. I have a couple hundred board feet of quarter sawn red oak in my basement that is 14 years old. None of the boards are cupped or bowed like you are describing. Look at the grain patterns on these boards. Is it straight, or basically rises towards one end, or does it rise to both ends? If the jointed side bows as much as the planed side I tend to think the problem is with the boards. If the jointed side is staying flat the problem is with your planer. Hopefully someone else will have a productive thought. It's a tough call without seeing these first hand.
gdblake
Most of the boards were flatsawn. Quartersawn boards were a lot more expensive so I tried to pick out boards where the grain appeared riftsawn when possible. However, most of the in stock boards were 10-12" wide cut from trees not much wider than that- so most were flatsawn. The problem is definitely with the boards because the whole board bows out of the planer- both the jointed and planed sides. I guess I've learned a lesson. Pay more to get quartersawn or 5/4 stock and spend more time examining the wood before purchase- although I thought I had done the latter- spending 90 minutes picking out 80 bd ft.
- Lyptus
Red oak
Sorry I do not have any advice but have a story to share. 30 years ago in high school shop I made a dining room table out of oak. I glued up the top and set it aside to work on the base. Weeks later when I got back to the top it was so bowed it was not useable. That was the last thing I have ever made out of oak.
Phil
Welcome to milling rough lumber
Lumber can be subject to all kinds of stresses. When milling, two in particular can be problematic. One is internal stresses from either drying or tension in the wood, and the second is different moisture content in the wood.
The first, internal stresses, tends to exhibit itself soon after cutting; that is when the stock seems to twist or bind on the blade as it goes through the cut. Sometimes it takes a little time, but it usually happens fairly quickly. Trying to use wood with straighter grain patterns will help. Also using stock that is close to the final size will help as well. Ripping down the center of a board, unfortunately can reveal a lot of stress. If you want a 6 inch wide board, it helps to start with a board 6 1/2 - 7 wide. The other thing that can help when you rip is to try to separate the board into similar grain patterns, i.e. cut the flat grained part away from the vertical/rift grained part. This is also helpful when you need some quartered stock for frames, but then can use the flat stock for the panels.
The second problem in milling is different moisture content in the wood. This is caused by the fact that in most of North America, the humidity changes a lot and frequently. As a result wood tends to constantly be gaining or losing moisture. Resawing to thickness, planning more off one side than the other, having one side more or less dense than the other, can reveal different moisture content in the wood relative to the environment. As the moisture equalizes, the board bends, bows, twists, and/or cups in the process.
In general, stock should be used as soon as possible after being milled to final thickness, width, and length. Otherwise the wood should be left in the rough if possible. Unfortunately in real life, that isn’t always possible.
If it was possible, skipping the week at rest would helped. Past that though, as long as the boards can be nailed/screwed flat on the stairs, they should be usable. They will probably continue to warp even if planned thinner. Gluing up 3 narrower boards together right after thicknessing will also be more likely to yield a more stable board.
Red oak tends to be fairly stable; those big pores seem to equalize moisture well. Even so, a 15% reject rate is not too bad, even with S&B stock. Those pieces can always be used for smaller parts.
In short, rough cut the stock; let it sit; thickness, rip, cut to length, and use as soon as possible.
i know its frustrating
Hey, one question I have for you. when you say you flattened one face then ran it through the planer, did you take equal amounts off each side. Keeping things in equalibrium is important for wood as well. I try to flip each piece with each pass through the planer. It does make a difference. Second, consider your application and degree of bow. If you are making treads then if bow is not major it should not matter. You also mentioned it bowing after it came out of the planer. Any wood that moves that fast could just be stress wood. I've had boards I've ripped warp laterally as it exited the blade. That wood goes in the scrap box for small pieces to use. If you bought a lot, I'd go back to the supplier.
I did try to take equal amounts off each side but it was not always possible. For instance, inital jointing of a bowed board yields a board that is thinner on the ends and thicker in the middle. It takes several passes through a 12" planer to achieve even thickness throughout. By that time, it has bowed again- in the same direction as before. As the board gets thinner, the force of the planer rollers forces the bowed mid-section flat so it keeps getting thinner but stays bowed and the bowing gets worse as the board thins. I think if I had started with thicker 5/4 stock all around and avoided any boards with stains or those with grain in relief many of my milling problems would have been alleviated. By grain in relief, I mean some of the boards I picked out seemed to exhibit a shrunken early wood with the late wood in relief. Without exception, those boards that were like this had to be trashed because of internal stresses and internal cracks which only revealed themselves after milling.
- Lyptus
Bad luck
It sounds like you may have ended up with some bad wood in the lot. Properly dried red oak should be pretty stable, even flat sawn. However, bowed wood does tend to stay bowed, even if the board has been jointed and planed correctly. The grain can often force its will on the board despite our best efforts. The grain relief that you mention is not common in properly dried red oak, at least it should not be super pronounced. Sounds like the wood was over dried or got wet and dried to quickly at some point; that would expain the honeycomb in the board. That would also expain the tension problem in the wood.
That said, they are stair stringers. If the bow isn't too bad, nail them down bow-up in the middle and if they don't pop back up, good enough.
Don't feel too bad. This stuff happens to everyone. Cherry is also supposed to be stable, yet I have a bunch of it that wants to be airplane propellers and boat sides.
At 10' long and 12" wide,
At 10' long and 12" wide, those are big oak boards. You don't mention what the end grain looks like, but I am going to guess that this is southern oak with wide growth rings as you just don't see that much northern oak that big these days. The honeycombing and uneven surface you mention in a later post are an indication of case hardening of the wood caused by too aggressive a drying schedule and improper stress relief in the kiln. I've seen a lot more of that come out of kilns in the South. Warm climate oak is harder to dry, and southern white oak is even worse.
Trim carpenters like southern oak since is comes in bigger pieces, so retail lumber yards like to stock it. It's murder to run through a molder since any profiling unleashes hidden stresses.
I build a lot of stain-grade and paint-grade projects for remodels out of 4/4, 6/4 and 8/4 red oak and I'd say it's clear you ended up with a batch of bad boards since most times the way you milled the boards should have worked out just fine. If you have an idividual board or two and the grain is a little off I'd say it's a case of a battle of wood grain pulling the board in differing directions. However if it's happening with a number of boards then you are a victom of poor kiln drying. There are detailed articles on kiln drying that explains the many problems that can arise and the industry terms for it....but that doesn't help you much in the middle of your project. I've been fortunate to not have kiln drying problems since my supplier deals almost entirely in red oak that's been air dried.
I'll bet you could tell this was going to be a problem from the first cut on the table saw - I watch the kerf for boards with dramatic internal stresses while rough cutting and set aside those that start to move as they are either ripped or planed since the amount they move can be a deal killer and rarely gets better the more they're milled to size.
In your case it's hard to know what to do with the boards short of setting them aside and obtaining a better batch. Stairs require flat stock and fighting bowed oak is difficult at best.
I'll also add that normally stairs not originally built for hardwood treads and risers are rarely a good base to build on and you'll fight the uneveness the whole time. When I have a job like that I'll use a lot of hardwood shims and PL Premium polyurethane construction adhesive to even out the ups and downs so you'll have stairs that not only look good but will pass building code.
Best of luck and watch the riser height on your first and last step :)
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