[OpenSCAD] Is this the best way to do what I want?

wolf wv99999 at gmail.com
Mon Sep 21 03:33:56 EDT 2015


Tongue and groove is a joint intended to not-be-glued, as it makes for  poor
joint strength in tensile loading across the joint, but good strength
without glueing transverse to the tongue. Wood joints have in the past been
developed with the properties of hide glue in mind, and that means a very
brittle joint that cracks easily along the joint line. Luthiers use this
brittleness on purpose; when they need to open e.g. a violin for repairs, a
slight hit with a hammer on a glue line will separate  the top plate from
the carcass without damaging the wood, try that with a more modern glue such
as PVA (white glue).
Since the PVC glueyou want to use is rather brittle when dry, and because it
shrinks while the solvent evaporates, a tongue-and-groove joint with play
between tongue and groove would be a weak joint as it is susceptible to
impact failure. If you can, use a tapered joint, such as this:
<http://forum.openscad.org/file/n13946/Taper_Joint.jpg> 
and clamp firmly until the glue has set. There is no need to slavishly
follow this design, all that is needed is that the long sides of the taper
are 5-10 times the dimension of the short side to make a joint at least as
strong as the base material. I have built masts that way for wooden sailing
boats. The example picture is from a commercial wood joint, where knot-free
wood has been created by cutting out the knots, and jointing the remainder
with minimum loss of material.



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