Planing Boards-Am I Doing Something Wrong?

[steve swantee]

Just wondering how you go about planing your rough lumber? My standard practice is to face plane my boards on one side on my 16" jointer. Once I have that side flat-it lays perfectly flat on my jointer or benchtop-I move to my 15" general planer and remove roughly the same amount from the other side of the board, and then continue to run it through on opposite sides until I reach my desired thickness. More often than not, when I reach final thickness my board has a bow in the length of the board. Sometimes a pretty significant bow. I am removing similar amounts from each side of the board and when the board leaves the jointer the jointed face is dead flat.
Have I been making a mistake in planing entire boards and then cutting parts from them? These are 7-9 foot long boards. Should I instead be cutting parts to rough size and then face joint and plane to thickness individually to minimize bow? Could the wood also be contributing to the problem?-internal stresses, etc.? It is kiln dried yellow birch if it matters. Frustrating.

Steve

[James Phillips]

I use a handsaw to cut my boards to manageable sizes before planing. I think the average woodworker can truly flatten a small board much easier than a large one. Many folks mill it slightly oversize and let it acclimate a couple of days before final milling.

[glenn bradley]

James beat me to it as I am long-winded ;-)

My reply is, of course, based the way I do it. There are many correct ways and we all fall into some process that yields reliable results for us. So, here's a couple thoughts:

1. I make my boards close to the size I require prior to most milling operations. That is, I would not joint a 5' board if I knew I was going to crosscut it into a 2' and 3' board anyway. I do leave boards at a minimum size so that jointing and planing are not hazardous. Any deviations in your material are exaggerated by the size of that piece. That is; a bow from end to end on a 8 foot board may require removal of 1/8" or more of material to acquire a flat surface. If I cross cut that board into 3 pieces, the deviation is reduced as is tha amount of material I have to remove to get to "flat".

2. You do not mention a step in your process where you let the material set following the initial milling. I bring my parts (or larger pieces that will contain parts too small for individual milling) to an over-sized dimension. I then let them set for a couple days to get over any reaction they may have to suddenly being thinner, narrower and shorter. I will then mill to near final dimension allowing some small amount of fat in some areas for final scraping, planing, sanding, etc.

The process you describe is giving you the result I would expect. Don't get me wrong; I am no guru. I just learned the hard way eased by discussions with the fine folks here.

[steve swantee]

Hello Glenn. The bow is present after the initial planing. Sitting for a period of time does not seem to affect them much.

Steve

[Sam Layton]

Steve,

You join and plane the same way I do. Except, when I do a project, I cut all of my parts to rough length. Now it is easer to join and plane a 2' board than an 8' or 9' board. Stress in a board makes it do funny things. When you cut your parts out to rough size you remove some stress prior to joining and planing. When I make stiles and rails, I often cut them larger than I need, and may join and plane a second time if needed. There is no need to join and plane a 9' board unless you need a board that is 9' long.

Sam

[steve swantee]

Think I'll start doing the same, Sam. It always just seemed like a good idea to plane the whole board in one piece and then cut all my parts from it, but I can see where this method could cause issues.

Steve

[Chip Lindley]

...The bow is present after the initial planing. Sitting for a period of time does not seem to affect them much.

Good advice on basic milling operations from all above. One thought (well, two) I have is:

(1) Perhaps your planer setup is helping to bow the lumber. This could be due to the bed rolls set very high off the planer bed, allowing the board to flex as it moves through. This could cause the board to "dish out", or bow over it's length. Unless planing rough lumber, bed rolls should be set only about .002" above the planer bed.

(2) The chip breaker/pressure bar is exerting too much, OR not any pressure on the board as it passes the cutterhead. Too much pressure, combined with high bed rolls could cause the board to really flex.

Adjust your planer to specs, and see if things improve. I rule out the lumber as being at fault, because reaction wood problems should show up as cup or bow after flattening it on your jointer; before any thickness planing. You are only seeing the bow after it goes through your planer.

[glenn bradley]

Hello Glenn. The bow is present after the initial planing. Sitting for a period of time does not seem to affect them much.

Steve

Exactly. The problem appears after milling. Letting the board set allows any additional activity to settle out. Now remill your oversized and (hopefully) stablilized lumber to final dimension.

I am on board with Chip as the planer seeming to be the focus of the problem. However, I have had boards with one side jointed flat, lose that position when the other side is planed. Due to that experience I can certainly suspect the planer as a primary candidate but, not for sure.

Definitly a good call to assure that your machine is on spec. If you find something peculiar while going through the check-up, that'll pretty much seal the deal, eh?

P.s. I have recently done the dance with some mahogany that would spring every which way after any and every cut. Only one board out of the batch however ;-)

[Peter Quinn]

There are a lot of variable in play here, like the woods actual moisture content, shop relative humidity, stress in the wood, machine set ups. But rest assured, wood moves. I've seen it with my own eyes! Before the economy went south, I used to make a lot of passage doors, which meant a lot of stiles at 8' long or more and 6" wide or better. You flatten one face perfectly, then plane the other side, and start flipping the boards, and they start moving around on you! A pile of 80 pieces this size was pretty common for me, so you see a lot of different levels of stability. It helps to yell out "Hey, which joker switched my wood? My boards were flat!" Unless you work alone, then thats just crazy.

One thing that does help is rather than randomly flipping and planing, actually look at the stock before each pass, and always plane crown up. You take material off the high side and it will tend to bow back or straighten out. Sometimes, if the winds are favorable and the wood faries are pleased, you may get a flat board this way, or at least flattish. And keep your stock removal to .040" maximum per pass, even .030" is better. Your planer may be capable of taking off more, but the wood wont like you for it.

That said, I cut any parts longer than 15" to no more than 5" longer than I need for final length before milling. For short parts, like say rails on narrow doors, I will leave a board long enough to yield up to three or even four parts and mill this as a unit. You just can't process shorts effectively or safely. But everything else gets cut as short as possible, ripped maybe 1/2" over on width maximum, then milled. And if I'm trying to loose a lot of thickness I may use the bandsaw to skinny things up, I will likely mill all parts twice with a good rest in between, and I may do both. Flattening and planing full boards simply will not work if you intend to split them into smaller parts later.