Mortises in laminated workbench legs
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In one of the youtube videos, Paul Sellers says the leg mortise hole should go right through (i.e. perpendicular to) the glue surface. How important is this? If I make my mortise hole parallel to the glue surface (so that it “splits” the lamination), do I risk delamination or any other kind of problem?
Ideally I think the mortice would go perpendicular to the glue lines make cutting the mortice more predictable. If it’s possible, then do this.
Sometimes that simply isn’t possible e.g. morticing two perpendicular sides as you might in a table leg etc.
I have done this both ways and haven’t have a problem morticing “across” laminations when I have to. I guess that it’s possible that they could split, but if the glue joint is good, I would say it’s unlikely. If doing this, maybe make sure that the wood around the mortice will be as supported as possible e.g. in a vice or clamp some blocks to the side to achieve the same effect. With a workbench leg, it’s probably thick and strong enough that there would be no problem anyway.
If your mortise is right through the glue line, the grain structure will be intact above and below the hole. Along the glue line, the grain structure is cut open and therefore weaker. I hope this explanation makes sense to you, I can’t put it better.
Anyway, why bother, if you have the choice? Even if there is no explanation, I am sure, that Paul Sellers wouldn’t have mentioned it, if it weren’t important.
Dieter
Thanks both of you, very helpful. The reason I asked is that I can do it both ways, but it would look slightly better if I do it the “wrong” way. Not very important, so I’ll probably do the mortise perpendicular.
Hugo; You ask why bother. This was not explained in the video, and being an academic I have a need for understanding the reason for any advice. If the advice was based on aestetics or tradition, I would not feel a need to follow it.
djupal, I asked “why bother”, because I wanted to know.
By the way, one doesn’t need to be an academic to question things, just an active mind. Sometimes I am shocked to see, how people take for granted what they are told. An inactive mind makes us cattle!
Dieter
For what it’s worth, having thought about this more and looked…
I also have some middle quality store bought furniture that has laminated legs and there are sometimes mortices across the laminations. Whilst not conclusive in itself, it does suggest that the original advice might be ideal/best practise vs some kind of categorically correct thing to do.
You could still test both ways, possibly on a smaller scale, so you can actually break the joints. It might need three tests for each method, to check rotations in all directions.
Perhaps I’ll do that eventually, sounds like a fun project.
Dieter
Interesting. Wood strength and construction techniques is a fascinating topic. Testing it myself is a good idea 🙂
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