Planer thicknesser curls timber

[Aaronf]

My thicknesser when run down to 18mm curls the timber like a banana. I start by planing one face flat. I then run the timber under the thicknesser and plane the opposite face down to 18mm. By the time it comes out it's like a banana! What am I doing wrong? I'm using in feed and out feed rollers. The lengths are around 2mtrs.

Aaron

 

[custard]

Aaron, a better working practise is to flatten one side, thickness the other side, then after that thickness down to dimension but alternate the board on each pass. This is so an equal amount of material is removed from each face. If the outer layers of the board are dry but the centre is still wet, then removing too much from just one side is absolutely guaranteed to produce the result you describe.

 

[EddyCurrent]

It sounds like stress in the timber is causing the bending. The best way is to cut the timber to rough size at least a day before planing to let any stress out.

 

[Tetsuaiga]

2 meters is quite long, its pretty hard to plane long heavy planks unless you have a big planer.

When I built a workbench recently I only needed to use the thicknesser as the timber was straight enough in its long direction already. I imagine most good timber is like this, so maybe try only thicknessing and flipping then see if its good enough.

 

[RogerS]

Custard is bang on the money. Alternate sides is crucial.

It's also worth making an extension table for the outfeed. It doesn't have to be fancy. Mine is simply two pieces of wood, hinged, and the end of one has an aluminium flange with a couple of slots in it that fix over a couple of small bolts tapped into the end of the outfeed table.

 

[Aaronf]

I was using in feed and out feed rollers, since I was convinced this was the cause. I was naive in buying some rough oak, thinking my spanking new planer thicknesser would sort it out. The oak only started off at about 25mm, by the time I had one good face I flipped the timber and planed until I had two good faces, by which time I was near 18mm as it was, so didn't really get a chance to alternate. Lesson learnt, pick planks more carefully and make sure there's enough thickness to alternate.