I watched a video about making a Maloof inspired rocking chair out of cherry. They ripped a bunch of 1/8" strips and laminated the rockers. The strips were burned as cherry often does, in some places 50% of the surface or more was burned. They glued it with Titebond III.
I always try to remove the burned area or use a blade that does not burn the wood. Have I been wasting my time? Is it good practice to laminate pieces with burn on them?
(Pretty sure there is a rocking chair stalking me.)
Assuming the "burning" was produced by a saw blade during the ripping process, something I encounter as well, although not over 50% of the ripped surface.
Although I've not closely examined such a burned surface, my suspicion is that the resulting surface is akin to a burnished or polished surface, and that typical wood glue MIGHT not be able to adhere as well to a burned surface as an unburned one. I have no experience gluing surfaces with some saw burning.
It might serve well to keep in mind there is no quality control evaluation process for videos posted to some Internet sites that would eliminate those showing unsafe practices or those contrary to generally accepted recommendations.
I don't see why glue would not stick to burned wood. That is not the concern. The result: good wood/ burned wood/ glue/burned wood/good wood. If burned wood is weaker than good wood the answer is apparent.
If I watched a video of someone making a chair and they didn't know how to rip cherry without burning it I would assume they didn't know much about making a chair either.
...another reason to not feel bad at not having an Internet connection that is practical for watching Internet "educational" material.
I would be reluctant to glue any burn marks on wood. As others have noted the information on the internet is sometimes not very accurate.
I know cherry tends to get burn marks relatively easier than most other hardwoods. I've found that a well tuned saw, good sharp blades and good feed technique go a long way toward eliminating almost all burn marks when cutting. I've made several pieces from cherry and once I tuned up my saw alignment and learned to keep the feed through the cut constantly moving that I only very rarely get even a slight burn mark on cherry. I have a 1 Hp Craftsman table saw and use Freud blades exclusively. For ripping I particularly like the glue line rip blade.
Interesting question. I've done a ton of laminations, but always scraped off any burn. It would be interesting to hear from someone who has glued up burned material and learn whether it worked or not. At the very least, if the burn extends to the edge, wouldn't it be visible in the glued-up piece, and highlight the lams? I always try to make the lams blend together, keeping them in sequence to somewhat replicate the original grains.
It could also be that since Maloof usually made his chairs from walnut, he may have been burning all the time...
BTW, Maloof, the master maker that he was, was trained in industrial design - not woodworking and he took many shortcuts and had many arguably unsafe techniques. Watch an old video of him shaping a leg on the bandsaw if you don't believe me.
Trying to remember the test to see if the wood surface has been burnished too much. Can't recall if it's for glue or finish. The test goes like putting a drop of water on the surface of the wood. If it's too smooth or burnished, the water will sit on the surface. That's not good for gluing. If it quickly soaks in, it's good to go. Might be something to check on the burn marks. Anyone know the details of this test? Edit; I think I found it and added link
Sometimes I think my questions are too long and pointedly detailed. Sometimes they are open ended and too loosely drawn. Hard to get the correct balance.
The article Dick posted is right on point.
The pieces that were ripped in the video were about five feet long and 1 1/2"+ wide. They were probably 90% free of burn but had and area maybe 8" long that showed significant burn, probably greater than 50% of that area. This was apparently related to the grain orientation in that area. So I wondered if that much burn would weaken the laminated rocker if only in that area.
The young man in the video either bought new blades for the process or at least installed blades he had on hand and took out of the sleeve for the purpose. At the very least he switched from rip blades to crosscut blades.
As far as watching videos from idiots or uninformed providers...if I can learn from my mistakes, I can learn from other's mistakes faster, cheaper, and safer. No cherry was burned asking this question here.
I wondered about the burned surface showing in the lamination and assumed they might.
I also use excellent quality blades and good technique and have minimal burning. If I pick up a piece of wood with aged surfaces, I joint or sand them to provide fresh surface. I also have some experience gluing exotics that are notoriously difficult to glue. I was wondering if I was overdoing it.
Off to the shop to burn some cherry and try a drop of water on it. With any luck at all I can burn enough to do the water test and glue some to see if the joints fail or show.
What is correct about this article is that for water based adhesives to bond they must wet the wood. The water bead test is a reliable test to see that the wood will be wetted. The explanation of what causes wetting and why wood might not wet is baloney.
If one was to spread oil on the wood before gluing it would not be wet by the glue. In the practical case of wood not wetting some other chemical has been deposited or formed on the wood surface that repels water. It could be a decomposition product of heating wood, or resin that blooms to the surface or contamination from an outside source.
I used two scraps of cherry, ripping one at a glacial pace on a glue line rip blade, purposefully causing it to burn the wood. the other one I ripped a t "normal" speed resulting in a piece that had only a small patch of burn.
I put a drop of water on one burned surface and one fresh clean surface and waited. It became apparent after only a couple of minutes the water was spreading and setting the surface pretty much equally.
I glued them back together with Titebond Original, burn to burn and clean to clean, and left them over night. Split them with a chisel. Set the chisel right on the glue line on the end and struck it sharply. The burned piece failed right down the glue line with only about 1% of one piece left sticking to the other. 99% failure. The clean piece split about a 1/4" down the glue line and then followed the grain. 99% success. Then I turned it around and struck it from the other end. This time the little patch of burned area failed and the rest of the glue line held up. About 85% success.
I realize this is not a thorough or scientific test, but it's enough for me to conclude it's a good idea to clean the surface, removing the burned area on any joint. And although I am not a hand tool guy, the people that take a pass with a jointer plane have a good idea. Never seen a hand plane burn the wood.
When gluing closed pore woods (Cherry and Maple) I learned early on to give the glue surfaces 2 or 3 passes with 80 grit on a block to "break the mill glaze" whether they were toasty or not.
