I’ve gotten different opinions from a few different woodworkers, so I thought I would ask a larger audience.
After face gluing boards to make a thicker piece (say for a table leg), often one wants to edge joint one side for subsequent sizing on table saw or other next step. If one scrapes off squeeze out on that edge (the one to be jointed) with scraper or perhaps sands it smooth, is that edge likely to cause nick damage to the jointer blades (nicks) due to the difference in hardness of the thin glue line versus the adjacent wood? I was told years ago that this was a bad practice, unless one wanted to sacrifice one end of the knife set, for example.
I saw a video recently on FW (Rogowski, I believe, but I’ve seen other material on FW site and others that were similar) where he said that he scraped off the squeeze out so that he would not mess up his jointer knives too badly (paraphrased, but accurate recall of his comment). He never discussed it other than that comment. But his comment makes me wonder if this is a bad practice in general or just refers to non-scraped situations. I know that edge jointing plywood is a bad practice for this reason.
I’ve used polyurethane glue previously for this type of application and had avoided the usual yellow glues (Titebond II or III, for example) for the above reason. The polyurethane glue has worked well for me for this application, but I still wonder (no, I haven’t done my own comparison test). What is opinon of expert woodworkers on the subject? Are yellow glue lines likely to damage jointer knives (or planer knives)? Is white glue (e.g., Elmers) a better choice because it is a bit softer (“stretchier”)? Is polyurethane the best choice in this case?
Fact-based opinions would be most appreciated. Thanks.
Replies
No, your knives will not be affected unless you are doing hundreds of operations where the glueline is always in exactly the same spot on the knife. Scrape off the squeeze out with a cabinet scrape to minimize adhesive build up on the knives.
I agree that you won't dull your knives with carpenter glue or just about any commonly used glue. Wood fillers on the other hand have a lot of silica in them and are abrasive.
I run a lot of glued up boards through my planner and have never had problems with glue building up on knives, but it stands to reason that the glue residue can build up and reduce the cutting action of the blades, much like stuff builds up on the teeth of saw blades - the blades would still be sharp if the buildup does occur they just don't cut quite right - use lacquer thinner on a brass bristle brush to remove any buildup you find and you're good to go.
I can't see edge jointing plywood as dulling the blades - but adhesives may build up on the blade.
What does cause a lot of blade damage is dust, dirt and crap within the wood. Oak is horrible for collecting airborn dust/dirt as well as picking up dirt particles in the pores every time it's set on dirty surfaces. Rough oak that is stored outside is the worst, but on most wood run through the planner I'll keep an air nozzle handy and I blow everything off before the first passes and check the wood that it doesn't have any small rocks imbedded in the surface.
MDF has all sorts of crap in it, so if a project requires mdf to be run through the planner I plan on replacing knives shortly afterward - it makes me shake my head everytime I see a spark come off of cutting mdf - it's crazy they can't keep the wood fibers cleaner.
Glue
Aliphatic resin and PVA glues such as Titebond and Elmers generally are not hard on planer and jointer knives. I do recommend cleaning up the squeeze out prior to machining by wiping off the excess with a wet rag right after clamping, this is quicker and does a better job than scraping after it is dry.
Some glues such as plastic resin and resorcinol are very abrasive and the squeeze out if left on the panel will quickly damage high speed steel knives.
Plywood, particleboard and MDF use an abrasive glue, in addition MDF and particle board not only contain more glue than plywood but are very dense as well. I would never recommend running any through a jointer or planer.
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