Planed Finish VS Sandpaper - Microscopic View

[Stewie Simpson]

The crushed and burnished surface inhibits adhesive wetting
and penetration. If the adhesive does not completely penetrate
crushed cells to restore their original strength, a weak joint
results.

Thanks Kees; appreciate the research.

Stewie;

[Kees Heiden]

Of course, we should add that such a crushed and burnished surface stems from tools (jointers and tablesaws) with dull blades and from very coarse abrassives like used on these big stationary belt sanders.

Handplanes with a sharp blade do not crush or burnish.

[Stewie Simpson]

Kees; with respect, if you go back to the OPs video, the water test proved the surface had reached a burnishing point without the use of a mechanical machine, such as a power jointer, tablesaw, or stationary belt sander.

I do appreciate the time taken by you to track down that resource material.

regards Stewie;

[Kees Heiden]

I explained in my post on the previous page that a good look shows how the droplet decreases in height over the length of the video. At 1:20 the angle between the surface and the droplet is certainly less steep. I think this makes the droplet test not so usefull in practical use. You need to take a very close look.

In the mean time, experience shows that a handplaned surface is no problem to get a good glue joint. The oldest in my own experience, my kitchen, has a lot of edge glued panels that saw a hand plane as the last tool on the surface of the joint. After 6 years it's still going strong. That's just one datapoint of course, but it shows that a handplaned surface is not a recipe for disaster.

[Pat Barry]

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.

This is exactly the point I was making earlier. It would be great if there was physical test data to back up the resultant physical strength though as so much discussion energy is concentrated on perceptions. I don't think Brian or Warren or other competent hand woodworkers NEED to abrade their cleanly planed surfaces prior to, for example, edge gluing two panels. I'm sure they will get perfectly acceptable and long lasting glue joints. For that matter, if a person is doing a similar task with a powered jointer I am also confident that the surface prep will also be plenty good for glue joint strength and longevity. Per the manufacturer, all that's necessary is a pair of clean and dry surfaces that fit tightly to each other and adequate glue, clamping pressure, and time in the clamps.

[Patrick Chase]

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?

Pure water has very, very high surface tension (polarity and all that). Just about everything you can conceivably add to it reduces that surface tension considerably. The fact that water beads on or is slow to penetrate a given surface doesn't say much about "water-based" finish or glue. The people who formulate those know all about beading and penetration issues in general, and have a very large toolset at their disposal to deal with them.

I agree with your points about power tools (other than supersurfacers). The rotary motion basically pulverizes the wood at the start of each pass, and annihilates the surface structure of the wood. You do not want to glue or finish machine-cut surfaces (again with the exception of supersurfacers).

EDIT: Toned down.

[Pat Barry]

I'd like to see an equivalent SEM photo of the surface that comes of my Rigid planer, er pulverizer. LoL. Its not bad excepting the snipe.

[Joachim Schmidt]

I'd like to see an equivalent SEM photo of the surface that comes of my Rigid planer, er pulverizer. LoL. Its not bad excepting the snipe.

Here they are:

Oberflächengüte.JPG
These SEM Photos I have got from an Investigation of superplaners from a German University.
Translation:
from left to right, wood spruce
milled with sharp tool, (if planer or shaper was not mentioned)
milled with dull tool,
planed with superplaner.

Perhaps this will explain, why it is not a bad idea to plane the surface of joints with a handplane afterneath the jointer. Too they can explain the perception of depht of grain of a hand planed surface.

Hope this was helpful.

Joachim

[Frederick Skelly]

Thank you Joachim!

[Allan Speers]

I can plane some things with ease, others with supreme frustration. I'm in awe of those who can plane everything with ease. I approach each project with the intention of using no sandpaper, and then inevitably hit some vicious tear out and have to resort to it.

Card scrapers, grasshopper, card scrapers!

[Patrick Chase]

I'd like to see an equivalent SEM photo of the surface that comes of my Rigid planer, er pulverizer. LoL. Its not bad excepting the snipe.

I think that Joachim's post addressed your request. I've seen similar SEMs in the past (and maybe those exact ones, they look familiar) and have seen real adhesion problems when gluing machine-planed surfaces.

IMO the issue has more to do with the rotational nature of the motion than with any deficiencies of the blades. When you initiate a cut by penetrating the surface of a fibrous material like wood you will always cause some distortion/damage to its structure. The problem with planers and jointers is that they penetrate the surface about 100 times per inch, leaving a microscopic trail of destruction in their wake. Supersurfacers and hand planes avoid that by making one long, continuous cut.

[Curt Putnam]

Pure water has very, very high surface tension (polarity and all that). Just about everything you can conceivably add to it reduces that surface tension considerably. The fact that water beads on or is slow to penetrate a given surface doesn't say much about "water-based" finish or glue. The people who formulate those know all about beading and penetration issues in general, and have a very large toolset at their disposal to deal with them.

I agree with your points about power tools (other than supersurfacers). The rotary motion basically pulverizes the wood at the start of each pass, and annihilates the surface structure of the wood. You do not want to glue or finish machine-cut surfaces (again with the exception of supersurfacers).

EDIT: Toned down.

So are you saying that I should not face glue the boards out of my DW735? I'll be gluing up 4/4 soft maple to make 24" of bench top? That's a lot of surface for an old man to hand plane.

[Patrick Chase]

So are you saying that I should not face glue the boards out of my DW735? I'll be gluing up 4/4 soft maple to make 24" of bench top? That's a lot of surface for an old man to hand plane.

For vertical lamination of a solid benchtop it may not matter. Benchtop thickness is typically driven more by stiffness/bending than by strength. If a solid benchtop is thick enough to be an adequately stiff platform for woodworking, then it will be capable of withstanding far higher loads than it will ever see in use. That in turn means that you probably have a lot of bond strength margin.

To put this in perspective, Franklin specifies >3000 psi sheer strength (ASTM D905) for all 3 varieties of Titebond when gluing maple to maple. Assuming that you're making a 2" thick benchtop you would have ~50 square inch bonds, that can resist shear loads of tens of thousands of pounds. If you lose, say, 50% of that strength due to nonideal surface prep then it's going to be a nonissue.

Bond stength is more of a concern for joinery, for example the strength of a miter or lap joint is often determined by the glue. That's the sort of application where you would worry about using a machine-planed surface. You might also worry about bond strength if you're creating a weight-optimized benchtop structure, like a torsion box (the whole point of a hollow structure is to use less material for a given stiffness, which in turn reduces the amount of strength margin you have).

[Patrick Chase]

Card scrapers, grasshopper, card scrapers!

Indeed. Even with a good "hook" the surface isn't quite as nice as from a well-tuned plane, but it beats sandpaper by a mile.

[Pat Barry]

Here they are:

Oberflächengüte.JPG
These SEM Photos I have got from an Investigation of superplaners from a German University.
Translation:
from left to right, wood spruce
milled with sharp tool, (if planer or shaper was not mentioned)
milled with dull tool,
planed with superplaner.

Perhaps this will explain, why it is not a bad idea to plane the surface of joints with a handplane afterneath the jointer. Too they can explain the perception of depht of grain of a hand planed surface.

Hope this was helpful.

Joachim

Thanks Joachim. That center photo is definitely from a 'pulverizer'!