Planed Finish VS Sandpaper - Microscopic View

[Stewie Simpson]

If the wood surface is prepped to a burnished surface, it can adversely effect the seal coats ability to adhere correctly to the wood surface. The effectiveness of the seal coat has a direct impact on any other subsequent coats applied. No higher than 220 grit sanding is generally recommended prior to the seal coat. The burnishing effect that can be worked by a finely set smoothing plane has already been covered within previous posts. If your applying a penetrating oil finish, or wax finish, the above mentioned recommendations may not apply.

[Normand Leblanc]

If I understand you correctly Stewie, you are suggesting (post 51 and 61) to sand before gluing and to sand again before finishing if it's not oil or wax. This is assuming that a "burnished surface" is what we get with our planes.

The link you've posted in 51 does say that a burnished surface won't glue very well. In my experience (all my glue-up are prepared with a plane) I've never had a problem. Do you sand before gluing? Who's sanding before gluing?

Normand

[Stewie Simpson]

Normand; that's correct. 220 grit light sanding before adhesive is applied. Most of you have viewed the quality of the shellac finish I am able to achieve on my backsaw handles.

[Derek Cohen]

I do not deliberately sand to-be-glued joints or to-be-finished surfaces. Never experienced a problem with plane-polished hardwoods using oils or shellac. I do not use varnish/films, so cannot comment there.

Regards from Perth

Derek

[Patrick Chase]

I do not deliberately sand to-be-glued joints or to-be-finished surfaces. Never experienced a problem with plane-polished hardwoods using oils or shellac. I do not use varnish/films, so cannot comment there.

Regards from Perth

Derek

I think that the disconnect here is in the leap from "planed" to "burnished".

You're saying that you've finished plenty of planed surfaces without trouble. You're right. I've had the same experience using a variety of adhesives and finishes, including film finishes like poly and a variety of water-based finishes (like many people I use films when wear matters more than appearance).

Stewie pointed out that burnished surfaces present a bonding issue for both finishes and adhesives. He's also right, as everybody who's ever forced an overly tight M&T or dovetail and "bruised" the wood so that it won't absorb glue knows.

The thing is that typical smoothing doesn't leave a burnished surface. Planing usually leaves a surface in which the structure is relatively undisturbed and "open" to both adhesives and finishes. Stewie himself pointed out in post 19 in this thread that burnishing only happens under fairly specific circumstances.

I have seen some degree of burnishing (though not enough to be an adhesion issue) where a rounded/cambered blade transitions from cutting to not cutting. The blade appears to apply a fair amount of pressure to the wood in that narrow transition area, and the resulting burnishing can be detected as a "shiny" band when the wood is examined under grazing light. That's why I try to keep the amount of corner relief of my smoothers less than the shaving thickness, though the tradeoff is that I have to align my strokes more precisely to avoid conventional tracking.

[Derek Cohen]

I think that the disconnect here is in the leap from "planed" to "burnished".

You're saying that you've finished plenty of planed surfaces without trouble. You're right. I've had the same experience using a variety of adhesives and finishes, including film finishes like poly and a variety of water-based finishes (like many people I use films when wear matters more than appearance).

Stewie pointed out that burnished surfaces present a bonding issue for both finishes and adhesives. He's also right, as everybody who's ever forced an overly tight M&T or dovetail and "bruised" the wood so that it won't absorb glue knows.
The thing is that typical smoothing doesn't leave a burnished surface. Planing usually leaves a surface in which the structure is relatively undisturbed and "open" to both adhesives and finishes. Stewie himself pointed out in post 19 in this thread that burnishing only happens under fairly specific circumstances.

I have seen some degree of burnishing (though not enough to be an adhesion issue) where a rounded/cambered blade transitions from cutting to not cutting. The blade appears to apply a fair amount of pressure to the wood in that narrow transition area, and the resulting burnishing can be detected as a "shiny" band when the wood is examined under grazing light. That's why I try to keep the amount of corner relief of my smoothers less than the shaving thickness, though the tradeoff is that I have to align my strokes more precisely to avoid conventional tracking.

Patrick, in your link Stewie wrote ...

If your after a burnished finish similar to what's seen within that video, the hand plane your using for your final pass needs to have a wooden sole. A metal sole wont do it, regardless of how fine you set your shaving. Old school knowledge that wasn't restricted to Japan.

He is implying two things: firstly, that wooden planes burnish wood when they plane; secondly, that he has knowledge of this - personal experience?

In regard to item #1 - I use wooden planes equally with metal planes, and I do no see a difference in regards the finish. Neither burnish automatically in my experience.

In regard to item #2 - I have not seen any indications in the past from Stewie that he has had any interest in, or has built, furniture - his contributions to date have been solely about planes, saws and sharpening stones (which he has shown us very readily). Stewie, perhaps you might show us examples of joinery and finishes in your furniture.

If this sounds a little confrontative, it is. The fact is that Stewie has been making comments for some time that indicate that he knows more than we do, and so contradicts other posters, which I find unpleasant. I'd like to see some personal evidence, rather than quotes from the Internet. I am happy to retract my comment and apologise if he can.

Regards from Perth

Derek

[Warren Mickley]

There are so many weird statements in this thread it is hard to know where to start.

I prepared stick of wood for water testing using a Bailey smoothing plane taking shavings at 0.0002 to 0.0003 inches (maybe 5-8 microns). The iron was sharpened full bevel in less than 90 seconds. The frog and the mating part of the iron have not been "tuned" in the 35 years I have had them, and probably not touched in the last 100 years.

Water beaded up on the surface and remained for 10 minutes or more. Water beaded similarly on a section prepared with a beech trying plane taking 0.002 shavings (50 microns). A small portion was then abraded at 220 grit and 320 grit and a drop of water was absorbed in about 5 seconds.

A planed section was burnished using a small piece of smooth hardwood; this section absorbed water much faster than the clean planed area, but not as fast as the abraded area. This is the first I tried putting water on a burnished area; I have no explanation for the results.

There is no problem using water stains or glue on a finely planed surface.

I read the 2006 Fine Woodworking article on planed and sanded surfaces. At the time I noted on another forum that all of the samples tested, both the sanded and the planed, were given a light initial coat of finish and then sanded. The wood itself was almost certainly abraded also in this step, so it was no wonder that the samples yielded very similar results. They were all sanded. A friend of the author came on the forum and chastised me for being too rough on the author who he said was a young amateur. It is hard to believe anyone still makes reference to this study.

[Wayne Lomman]

In the real world of commercial cabinet and furniture making, you always finish the surfaces to be glued either by fine sawing or sanding, never planing either by hand or machine. This is absolutely critical if you expect the furniture to last beyond the minimum 10 year structural warranty to which I work. This has been a principle for way longer than the 40 years I have been in the industry because I was taught by guys who were old when I started. You can argue all you like over hand planing vs machine planing, but the bottom line is don't glue a planed surface. I'm sure everyone has examples of their work that are fine, but do you have at last count about 12,000 examples that have not failed (that's chairs, I can't count the other stuff)? If so, I want to hear about it because I love to learn new techniques, especially ones that save work. Cheers

[Brian Holcombe]

Wayne, have you glued a planed surface? Furthermore have you glued one that has failed? Can the failure be attributed to the surface finish?


I'm suspect of your conjecture, while I appreciate your experience I think you're speaking entirely from hearsay on gluing planed surfaces but feel free to correct me with your real world experience in doing so.

[Wayne Lomman]

Brian, yes I have. I have had the misfortune to work in shops where this was the norm. I also have had the good fortune to work in excellent workshops where gluing planed surfaces was almost a DCM offense. Cheers

[Brian Holcombe]

So you glued a planed surface, it failed, then you tracked it down to the planed finish and not the fitment or some other reason?

[Warren Mickley]

Wayne, I have been gluing hand planed surfaces professionally for four decades. I think the joints are a little less noticeable.

I certainly have had to repair chair seat joints that were not hand planed. Chair seats are particularly vulnerable to breaking because of the their use. Here in Pennsylvania the better makers use single plank seats to avoid these problems. A glued up seat is considered cheap. You do not speak for all professionals.

[Stanley Covington]

There are so many weird statements in this thread it is hard to know where to start.

I prepared stick of wood for water testing using a Bailey smoothing plane taking shavings at 0.0002 to 0.0003 inches (maybe 5-8 microns). The iron was sharpened full bevel in less than 90 seconds. The frog and the mating part of the iron have not been "tuned" in the 35 years I have had them, and probably not touched in the last 100 years.

Water beaded up on the surface and remained for 10 minutes or more. Water beaded similarly on a section prepared with a beech trying plane taking 0.002 shavings (50 microns). A small portion was then abraded at 220 grit and 320 grit and a drop of water was absorbed in about 5 seconds.

A planed section was burnished using a small piece of smooth hardwood; this section absorbed water much faster than the clean planed area, but not as fast as the abraded area. This is the first I tried putting water on a burnished area; I have no explanation for the results.

There is no problem using water stains or glue on a finely planed surface.

I read the 2006 Fine Woodworking article on planed and sanded surfaces. At the time I noted on another forum that all of the samples tested, both the sanded and the planed, were given a light initial coat of finish and then sanded. The wood itself was almost certainly abraded also in this step, so it was no wonder that the samples yielded very similar results. They were all sanded. A friend of the author came on the forum and chastised me for being too rough on the author who he said was a young amateur. It is hard to believe anyone still makes reference to this study.

Warren:

Thanks for going to the trouble to test water penetration and share the results with us. Exactly as one would expect.

I don't have access to my old issues of FW magazine, but I recall the article I referred to was published around 1978 to 1979. By 2006, FW was not worth reading, and I know nothing of the silly study you referred to. I applaud you for trying to correct the author.

Stan

[Prashun Patel]

Isn't a lot of what we see in that video due to the surface tension of water?

I know that water has a higher surface tension than oil and I think even ethanol. I thought in fact, this is why some people add a drop of liquid soap to water when using it as a lubricant for (ironically here ) wet standing. I would suspect that pva glue has additives to counteract the surface tension of water and cause it to penetrate. I experience oil finishes (even dreaded polyurethane) and shellac to adhere just fine to planed surfaces.

I wonder how one could reliably design an experiment that compares this effect. Just seems so hard to control for this over time...

"Stewie pointed out that burnished surfaces present a bonding issue for both finishes and adhesives. He's also right, as everybody who's ever forced an overly tight M&T or dovetail and "bruised" the wood so that it won't absorb glue knows."

Patrick, this is a curious statement that I hadn't considered before. in fact recently, I've been attempting to make my M&T and dovetails compression-fitting. I was under the impression that the better the fit in fact the less job the glue has to do.

[Pat Barry]

Warren's results for water droplet absorbtion, coupled with the original video, and Wayne's experience all indicate that better glue adhesion should be with a lightly abraded surface. There is then a disparity wherein the best glue-line appearance would be with a cleanly planed pair of surfaces but a stronger joint might not be the best appearance. Tradeoffs like this are always being made. I don't see why this doesn't compute for some.