Toothing planes and adhesion

[Christopher Charles]

Hello all,

I have a toothing blade for my scraping plane and have done a bit of hammer veneering. The experience has gotten me thinking about the practice of roughing surfaces to improve glue adhesion. Especially when empirical glue tests generally demonstrate wood failure before glue failure (at least with modern glues) on joints that were smooth when glued.

After I toothed my bench top, it occurred to me that perhaps toothing is employed in traditional veneering primarily to provide "sticktion" between the veneer and base during hammer veneering (more specifically to increase the lateral force required to move the veneer once lubricated by the hide glue).

And that the general idea that roughing surfaces is a hold over from veneering? I recall it being taught as a general principle in my middle school shop class-i.e., that everything should be roughed up with sand paper prior to gluing. Or perhaps my shop teacher had been into too much glue....

Thoughts?

Chris C.

[allen long]

Wow, I have only heard the term stiction in engineering in primarily at NASA - usually in regards to a cross between sticking and friction. Technically, roughing or toothing increases the surface area for the glue to adhere. The smoother the surface, the less surface area is available at a molecular level. Whether that makes a practical difference is another matter. Your teacher was not sniffing glue.

[allen long]

Wow, I have only heard the term stiction in engineering in primarily at NASA - usually in regards to a cross between sticking and friction. Technically, roughing or toothing increases the surface area for the glue to adhere. The smoother the surface, the less surface area is available at a molecular level. Whether that makes a practical difference is another matter. Your teacher was not sniffing glue.

[allen long]

Wow, I have only heard the term stiction in engineering in primarily at NASA - usually in regards to a cross between sticking and friction. Technically, roughing or toothing increases the surface area for the glue to adhere. The smoother the surface, the less surface area is available at a molecular level. Whether that makes a practical difference is another matter. Your teacher was not sniffing glue.

[Matthew Hills]

I used a toothed blade on my bench to flatten without gross tearout. I don't mind the texture, but don't really see much practical value in it.

For glue joints, I've seen both views espoused.
Here's one example where Popular Woodworking queried Franklin International:
http://www.popularwoodworking.com/techniques/best-wood-glue-surface-smooth-or-rough

I haven't really worried too much about this and just glue up straight off my table saw or hand plane.

Matt

[Doug Hobkirk]

For glue joints, I've seen both views espoused.
Here's one example where Popular Woodworking queried Franklin International:
http://www.popularwoodworking.com/techniques/best-wood-glue-surface-smooth-or-rough

I haven't really worried too much about this and just glue up straight off my table saw or hand plane.

Matt

The message in the link seems pretty convincing that smooth (as long as it's not burnished - if a drop of water will soak in) is better.

I realize I am gullible - but why would I doubt Franklin (Tite-Bond makers, my glue)?

What's the opposing point of view? I want to learn...

[Mike Siemsen]

The best glue joints are made when both surfaces are in full contact. There is a study on this by the Forest Products Labratory. When I edge joint boards for glue ups I don't tooth them, I use a jointer plane. Toothing does keep veneer from slipping around and the joint is strong enough.