Jointer use for flattening boards

[Myk Rian]

That sure is news to me, I've had no problem removing cup with a sled.

I've done it many times with a sled.

[Jim Becker]

Just to clarify....the purpose of the sled when using a planer to face joint (flatten) a board, regardless of whether it's a bow or twist, is to securely hold the workpiece such that the planer will not "bend" the board as it passes through the rollers. Shims are used to stabilize the board to that effect so that material is removed from the "high spots" on each pass until you get a flat surface. You can then remove the board from the sled and work the other side with the planer.

One thing...if you have to remove a lot of material from one side to flatten it, be sure to consider balancing what's removed from the opposite side to help alleviate moister related warp afterward. This is a judgement call, but it's a "best practice" when milling lumber to remove similar amounts from each side while flattening and thicknessing.

[Cody Colston]

I don't have a jointer. If the board is cupped it can be run face dn prior to the planer. If the board is warped can that be face dn to flatten?
A 4 foot board will achieve a thicker net board than say an 8 ft one in theory?

Yes, yes and it depends.

I rough-cut all my stock to 1" over length before jointing and planing. On a warped board, the shorter the length, the less stock that will need to be removed to flatten a face and then thickness. On a cupped board, it doesn't make much difference if the length is straight.

For the record, using a planer to flatten a cupped face will work with thick boards. On a 4/4 or thinner cupped board, the planer will flatten the cup and then it springs back when the pressure is relieved. On 8/4 or thicker stock, especially hard, hardwoods like Oak, there will be little to no flattening of the cup from the planer if light cuts are taken.

I mill and dry 99% of the lumber I use so if I have a board that is cupped or warped much, I usually discard it and select straighter, flatter rough stock. Life is too short to deal with crooked boards unless it is unavoidable.

[Al Launier]

As several have already noted a cupped or twisted board can be "flattened" on a thickness planer. BUT, one really should use a planer sled. For cupped boards on a sled, shims would be needed to keep the board from being pressed down by the rollers. This is a planer sled I made a while back which allows 3/8"-1/2" of adjustment for the individual supports. The sand paper on each support prevents slippage of the board, as does the stopper board at the end of the sled. Shims used on the sand paper to secure a cupped board will not slide while providing adequate support. http://www.sawmillcreek.org/showthre...52-Planer-Sled