08-29-2015, 09:26 AM
Ok, all the discussion(again/still/whatever ) about clamping pressures/success/technique aside, how do you actually test the glue joint?
I used to make a lot of picture frames. I have picture framing vises as well as band clamps. I experienced a lot(one out of 6 or 7) failures early on with dense or oily woods. Purpleheart, bubinga, bloodwood, hard maple, and cocobolo are examples.
The problem occurs on miter joint frames, half lap/overlap/etc frames are not affected.
Found a solution. Mini biscuits create a much stronger joint by giving the glue more area and a different density wood to join. In this case, the mini biscuit does make a stronger joint.
Now, the problem is my testing method. I simply drop the completed frame(after a 24 hour+ time in the frame vise/band clamp) so a corner hits the floor first from waist high.
However, that only works for small frames(12x12 or smaller and 1" wide or wider stock).
Larger size(or more narrow stock) get a torsion test by stretching/compressing the frame on opposing corners just enough to stress the joints.
I've glued white oak stock 1&1/4" thick(for stair landings), red oak stock for bench/cabinet tops, and 1by pine stock(for a door) and never even thought about testing the glue joints.
I glued spalted sycamore to walnut(TV tray legs and stretchers) and had 50% failure because the sycamore was too soft. (Was trying to make metal free joints) The joints held, but the sycamore stretchers simply came off, leaving a layer of wood/glue. Had to clean, reglue and add some brads.
Not the best choice of woods, but was what I had on hand when the need arose.
I used to make a lot of picture frames. I have picture framing vises as well as band clamps. I experienced a lot(one out of 6 or 7) failures early on with dense or oily woods. Purpleheart, bubinga, bloodwood, hard maple, and cocobolo are examples.
The problem occurs on miter joint frames, half lap/overlap/etc frames are not affected.
Found a solution. Mini biscuits create a much stronger joint by giving the glue more area and a different density wood to join. In this case, the mini biscuit does make a stronger joint.
Now, the problem is my testing method. I simply drop the completed frame(after a 24 hour+ time in the frame vise/band clamp) so a corner hits the floor first from waist high.
However, that only works for small frames(12x12 or smaller and 1" wide or wider stock).
Larger size(or more narrow stock) get a torsion test by stretching/compressing the frame on opposing corners just enough to stress the joints.
I've glued white oak stock 1&1/4" thick(for stair landings), red oak stock for bench/cabinet tops, and 1by pine stock(for a door) and never even thought about testing the glue joints.
I glued spalted sycamore to walnut(TV tray legs and stretchers) and had 50% failure because the sycamore was too soft. (Was trying to make metal free joints) The joints held, but the sycamore stretchers simply came off, leaving a layer of wood/glue. Had to clean, reglue and add some brads.
Not the best choice of woods, but was what I had on hand when the need arose.