But I digress. Here’s a detail of a piece of furniture I designed and made . This is urea formaldehyde glue ( extremely rigid)
The furniture is probably beautiful and functional, photos are notoriously poor evidence for accurate analysis. Nontheless my first impression of your lay-up was "Yeesh, those are bad, thick & variable gluelines, possibly improper viscosity, certainly low pressure/poorly distributed pressure, and possibly too long open before pressing"
Literature suggests "good" gluelines are in the range: "The glue line thicknesses for wood joints are generally from 0.13-0.18 mm (0.005-0.007 in.) thick for glued assemblies"
More importantly: "There is a strong relationship between glue line thickness and loss of joint strength. The strength of all the glued joints decreases when thick glue lines present. The thickness of a glue line introduces one of the more fractious factors in bond formation because it directly affects how the glue line functions"
"Thick glue lines frequently occur in the manufacturing processes due to thickness variation in adherents, poor preparation of gluing surfaces, inaccurate machining, warping or moisture induced dimensional changes (Marra 1992), lack of adequate pressure methods, non-uniform adhesive spreading and the use of adhesive mixes approaching the end of their pot life."
The paper addresses gap-filling glue specifically for engineered products where a thick glueline may occur for multiple reasons. Even this glue, tailored for gap filling, develops ever decreasing bond strength as the glueline thickness increases past 0.18mm:
"The effect of gap-filling phenol resorcinol formaldehyde (GPRF) adhesive on the shear strength of wood joints when thick glue lines present was studied. A number of wood-to-wood joints were manufactured using the press-gluing fastening method with various thicknesses of GPRF adhesive. Th e results showed that the shear strength was signifi cantly aff ected by the glue line thickness, so the strength decreased as the glue line thickness increased. Th e strength decreases by 10.52 % at a glue line thickness of 0.25 mm and by 39.48 % at a glue line thickness of 0.48 mm. Th e adhesive may be used for bonding up to 0.25 mm glue line thickness that is 43 % more than the normal glue line thickness (0.18 mm)."
Although published in Turkey, I found this paper through links starting at the NFPL & have read many others over the years.
http://www.woodresearch.sk/wr/200601/07.pdf Also, do keep in mind that the subject is gap-filling urea. Standard urea performs even worse as the glue line increases only minimally. A real problem with many straight urea glues is that they have a half-life and gradually self destruct.
smt