Planed Finish VS Sandpaper - Microscopic View

[Stewie Simpson]

If we extend Stewie maximum benefit of the doubt in interpreting his post (which I believe to be a basic courtesy), he only says that a wooden sole is necessary to cause burnishing. He doesn't say that wooden soles are always sufficient to cause it.

To be honest, the only sort of well-tuned plane that I would expect to apply enough pressure to cause honest-to-goodness burnishing is a Japanese jointer with a 3-contact-point setup. In that case all of the downward planing pressure is concentrated in those small contact points, and that could easily be enough IMO. Note that the 2-contact-point setup used for Japanese smoothers wouldn't leave a final burnished surface, because both contact points are before the blade - any burnishing is immediately removed.

Poorly tuned planes are a different matter. I've seen burnishing from blades with severe tip-rounding and consequently negative clearance, such that the blade has to be mashed into the surface to cut. In that case you end up with a small spot with very high pressure just behind the cutting edge, which crushes the wood structure. Normite planers can present similar issues.

Patrick; you need to use them to fully understand the difference in surface quality. It doesn't show clearly within the link attached photo, but I can guarantee you all 3 of those English style wooden soled planes would show signs of being burnished from the timber they were being worked on. Do you honestly believe that the burnishing is being restricted to the soles of the planes. Your comments about burnishing being restricted to the 3 point contact of a Japanese plane lacks depth of understanding.

regards Stewie;

They’re certainly as quick as any metal alternatives, and my wooden smoothing plane can take on anything a metal plane can, leaving a far superior finish.

http://www.theenglishwoodworker.com/...wooden-planes/

[John Stankus]

I need to go back and read the whole thread thoroughly, but this appears to be an opportunity to take a few scientific measurements to address some of the comments.
I have been planning on getting the Contact Angle Goniometer set up that a colleague bought but has since left the University. The Contact Angle Goniometer is an instrument that measures the surface energy and wetability. Should be able to measure both the different surfaces and using some standard surfaces measure the properties of some of the common finishes. I will also have to check with my buddies up in the engineering department and see when the new scanning electron microscope should be up and running. I don't think they have an Instron tester (measures the strength of the glued joints) but they may have a simpler tester that can get us the same info.

John
(teaching chemistry is my day job )

[Patrick Chase]

I realized after my post-storm earlier that there are multiple senses of "burnish", ranging from simply "polishing up" the wood to applying significant pressure (for example with a rod) to actually compress the grain/pore structure.

Since the topic of this sub-thread was finish and glue adhesion, let's be clear that we're referring to the latter sort of burnishing, that compresses the structure of the wood by crushing and thereby closes off the pore structure on the surface. The other form of "burnishing" does not significantly impact adhesion. Typical crush strengths of hardwoods perpendicular to the grain are on the order of 1000 psi, and about 10X that parallel to the grain. Even if we (very, very conservatively) assume that only 1% of the total sole area is initially in contact, even the smallest plane you show would require hundreds of pounds of downforce to compress and thereby close off the surface in a manner that impacts adhesion.

Stewie, this is consistent with what everybody else on this thread has told you: Planing with a flat-soled hand plane (even a wooden one, of which I have and use a couple) does not prevent glue/finish adhesion. While I don't doubt that you get terrific surface quality from your planes, it is physically impossible that doing so is actually closing off the structure of the wood, and so I don't believe that it is causing whatever finish/glue adhesion problems you may have experienced. I think that's also where Derek, Warren, and others are coming from.

[Stewie Simpson]

Patrick; your misunderstanding the logic. While a burnished surface may accept a pva glue, its bond strength long term is far less reliable than that generated by a wood surface that has been abraded. You like to drop names to support your case, well you can add Pat Barry and Wayne Lomman to my list. I could talk more about the long term reliability of applying a surface coating to a burnished wood surface, the likely causes of Peeling and Flaking of the top coat surface, and the likely ramification as a result of seasonal changes in the moisture level within the wood, but since your wanting to restrict the conversation to the OPs subject of a glued surface, I wont go there.

regards Stewie;

[Normand Leblanc]

I think that the sole area of a plane is much too large to burnish the wood surface as described by Patrick in post 93.

On the other end, it is the blade tip (which have a small area- the sharper the blade the smaller the area) that could be responsible for some more serious burnishing. I'm not saying that it's causing a problem for me with glue or finish.

Normand

[Steve Voigt]

Patrick; you need to use them to fully understand the difference in surface quality. It doesn't show clearly within the link attached photo, but I can guarantee you all 3 of those English style wooden soled planes would show signs of being burnished from the timber they were being worked on. Do you honestly believe that the burnishing is being restricted to the soles of the planes. Your comments about burnishing being restricted to the 3 point contact of a Japanese plane lacks depth of understanding.

Umm, what? Yes, the burnishing is restricted to the sole of the plane. The sole is burnished from being rubbed hundreds or thousands of times against wood. Whereas on the piece being planed, the blade is exposing freshly cut surface on every pass. Only rear half of the plane is rubbing against the piece being planed, exactly once; then that surface is removed on the next cut. Or not, if it's the last cut. It's not enough to cause burnishing. You might want to think it through before condemning people for lacking "depth of understanding."

[Stewie Simpson]

Normand; you will have to excuse me from this discussion, I was hoping to get some decent time in the workshop during daylight, and its just turned 1.30pm.

regards Stewie;

[Stewie Simpson]

Steve; I wouldn't expect any different from your response. Must go; workshop time.

regards Stewie;

[Patrick Chase]

Umm, what? Yes, the burnishing is restricted to the sole of the plane. The sole is burnished from being rubbed hundreds or thousands of times against wood. Whereas on the piece being planed, the blade is exposing freshly cut surface on every pass. Only rear half of the plane is rubbing against the piece being planed, exactly once;

Ironically the sole of the plane in the video that started this discussion probably didn't even touch the final surface. It was a Japanese smoother, and if it had the 2-contact-point setup typical of such planes then its blade was the only part that ever touched the freshly planed wood.

[Steve Voigt]

Steve; I wouldn't expect any different from your response.

If by that, you mean that I used logic and facts instead of word salad and innuendo, then I agree. Thanks for the compliment!

[Steve Voigt]

Ironically the sole of the plane in the video that started this discussion probably didn't even touch the final surface. It was a Japanese smoother, and if it had the 2-contact-point setup typical of such planes then its blade was the only part that ever touched the freshly planed wood.

That's true. And the difference between rubbing that surface once (as with a Western woodie) versus not at all might matter in the Japanese woodworking tradition, with its extreme attention to surface quality, but I doubt it would be noticed by most, and certainly would have no effect on glue adhesion or finish absorbtion.

[Stanley Covington]

That's true. And the difference between rubbing that surface once (as with a Western woodie) versus not at all might matter in the Japanese woodworking tradition, with its extreme attention to surface quality, but I doubt it would be noticed by most, and certainly would have no effect on glue adhesion or finish absorbtion.

Hear hear!

[Stewie Simpson]

Left it too late to spend more than 1 1/2 hours in the workshop. Installed some extra Laser Light roof sheeting last week to improve the natural lighting. Being a warm day outside, its as hot as a Turkish Sauna inside the shed. Earlier start needed next time.

Stewie;

[Stewie Simpson]

If by that, you mean that I used logic and facts instead of word salad and innuendo, then I agree. Thanks for the compliment!

Ease it up fella's, there are too many daggers being pointed in my direction.

If you don't like the message, that's fair enough, but there's no need to destroy the messenger. This is meant to be a friendly open forum where logical discussion takes place. Its not meant to be a Gladiator's Arena, where the victor looks to the Emperor of Rome for the thumbs up, or thumbs down.

regards Stewie;

[Kees Heiden]

Relax guys

There seems to be a contradiction going on here. The surface needs to be wetted, otherwise the glue doesn't work so well. The same message comes from this paper:

http://www.fpl.fs.fed.us/documnts/fp...tr113/ch09.pdf

They also show the droplet test (fig 9.1) , if the droplet stays balled up, the surface isn't good enough for a good gluebond. But at the same time the paper sais:
Experience and testing have proven that a smooth, knife-cutsurface is best for bonding (Page 9.4 at the top).

Now, we see the high droplet on the planed surface in the japanese video and how the droplet is a lot more smeared out on the sanded surface. What's up doc? How can they recommend a planed surface, while the droplet test sais otherwise?

When you watch the Japanese video very carefully, you will see how the droplet on the planed surface in fact DOES spread out. At 1:20 into the video the droplet has lost its very steep angle to the surface, indicating that water has penetrated the surface.

But the sanded surface seems to be even better in this droplet test, so why the advice to use planed surfaces? I think this is more about how a plane makes the surface very flat with very sharp corners. Sanding always dubs over the corners a bit. This leads to a more visible glueline. In strenght I doubt there will be much difference bewteen a 220 grit sanded surface and a planed surface.

Of course, the article talks about using electrical jointers, because that is what is being used in most professional shops. The danger here is working with dull knifes, which readilly burnish the surface, imparing the glue joint. Sanding after using a blunt jointer is in fact a very good idea. Even better would be using a handplane.