Do you remove the burn marks from machines before glue up a joint?
joeleonetti
| Posted in Joinery on
I am taking a local woodworking class to learn how to use machines so I can expand my woodworking know how. Prior to that, I have been toiling away in my garage with hands tools. As such, I’m learning a lot. As I’m discovering depending on the wood and feed rate, machines can leave “burn marks” on the wood. I’m planning to remove the burn marks. Was just curious, do you need to on areas where the burn mark is in the glue joint itself? Not sure if gluing up an area that has a large proportion of the joint with a burn mark is weakened or not. All new to me. Given the kind of joinery involved, I don’t need to worry about removing the burn making the joint too loose. Many thanks.
Replies
Burn marks are indicative of tools being dull or misaligned and well, it’s carbonized so glue will probably not hold on to it. Lesson no.1, sharp tools and well tuned machines.
I don't disagree. Given it's a class at a "public" school. I get what I get there. It's nice equipment. However, I have no easy way to control how sharp things are. At home, with the hand tools, I'm very much into working with sharp tools. For the few machines I want to get, I will have a back up set of blades so that I always have something sharp available in case what I'm using gets unacceptably dull.
How about cherry?
Your question probably spills over into the larger question of when to begin finishing? Stains, marks, imperfections and even foreseeing hard to reach areas of the final piece in my view, should be something you address as you go. My motto is finish early and finish often.
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As you learn, always good to try things for yourself. Edge-glue two scraps boards that have burn marks and then try to break the joint with a mallet.
I just like smacking things with mallets.
Just wanted to follow up. Per my original post, I did plan to remove the burn mark and mostly curious if Ineeded to. It took all of 5 or 6 swipes with a plane finely set to get to fresh wood. Not sure if burn marks are normally that shallow. I'm guessing I removed somewhere between 5 and 10 thou to get to clean wood.
For me, cherry burns easily, and is the only wood that's done it to me. But it doesn't go very deep, as you found
If you planed the edges of a single board freehand you might have introduced a bevel that will affect the glue joint. Search for “jointing edges by hand” on how to get good matching edge joints with a handplane.
I would imagine that the chemistry of burned wood is different than that of fresh wood--more carbon, less water, less cellulose. Some say you should only glue fresh wood--that you should hand plane off (unburned) tenons and edges just prior to glue-up, so the glue will adhere better. If that's true with unburned wood, than the bond with burned wood would surely be suspect.
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