Thread: Thicknesser tear out in glued up joins

Are those tear out faces the face you will be gluing in the first lamination? If so then the tear out will have a negative effect on both the joint strength and appearance, but not to an unusable standard, only to a perfectionist. It will leave fat glue joints in the areas of tear out where the glue has acted as a gap filler but will remain strong enough. You could just send the boards through the thicknesser again in the opposite direction taking off 0.3-0.4mm.

If those faces are for the second glue up, then you don't need to worry about it because you will need to resurface the first lamination before cutting and flipping the end grain upwards. Be sure for your first glue up that you have all of the grain direction running the same way, even if you are dealing with some reversing grain. spotty is good like that, hard and reversing grain, looks good to the end user, pita for the poor maker.

Thanks kuffy.

It's on a mix of first and second glue faces.

Should the tearout disappear if I put them through with the grain direction reversed... even if the cutters are a little dull?


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Possibly. If the grain direction is wandering up and down along the length, reversing the feed direction simply changes the area in which the cutters are cutting against the grain and will tear out that area instead.

When you plane with the grain with dull cutters, the timber gets compressed, it always gets compressed to some extent even with razor edges on your knives, but with dull knives the compression is much more, but it should never tear out chunks. When you plane against the grain, the knives are able to get under the timber fibers before cutting them and then lift them up and out as it trys to cut unsupported timber. dull cutters makes this much worse, but sharp knives do the same thing. Think of catching your fingernails on the edge of a bench. Because there is nothing on top of your fingernail to prevent it from bending backwards, you end up with a sore finger without a fingernail!

When I plane boards, I look at the grain direction. A good majority of the time by looking at it I can't tell which way the grain is flowing, so I pat the cat with my cotton backed gloves. Patting with grain is smooth. Patting against the grain, the cotton gloves catch. So now I am "pretty sure" which way the grain is flowing so I can shove it through the thicknesser in that direction. But possibly i've got it wrong and chunks get torn out on the first pass. I rotate the board and take another pass, and possibly chunks get torn out again, this is where I choose the lesser of two evils.

Solid advice. Thanks heaps.


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