Scraping Glue Before Planing
Dried glue squeeze-out can damage planer knives, so it's a good idea to clean glued-up material before further machining. April 13, 2010
Question
My guys in the shop take the time to scrape off the dried glue when we make stave cores for doors. They say they are trying to prevent damage to planer knives. Do you think it is necessary to do this or is it wasted time and effort?
Forum Responses
(Architectural Woodworking Forum)
From contributor W:
I personally like to get my excess glue off earlier before it’s dried hard. It is very good to remove it before final planing or wide belt sanding. The dried glue is very sticky when feeding through machinery, and I'm sure more dulling than pure wood to the knives. If left to the final planing and sanding it causes further variance in the sanding operations and lower quality results, right on through the end, even in the finish. I have seen a coarse belt multi system that was designed to remove all residue at the first belt. Then I do a final sanding.
From contributor D:
Cured glue damage to planer knives is unlikely, with its density much less than most woods. If the glue is still somewhat gummy, then yes it may stick inside the gullets and dust hood, inhibiting chip flow and heat dissipation, and heat can anneal your knives. It is not good practice to plane them until they are cured anyway, as the slight swell from the moisture in the glue hasn't gone away, and you may be laminating to a surface that will eventually cure with slight ridges at each joint, which can possibly telegraph out or even crack your veneer. Glue that is even cured hard is much worse on widebelt sanders, a much bigger worry in my opinion.
From Gene Wengert, forum technical advisor:
Dried glue can indeed damage planer knives, so removal before planing is important. Similar comments about sandpaper. Scraping, often before it hardens, is the usual approach. Note that squeeze-out is good in that it indicates that sufficient adhesive was used. Lack of squeeze-out means a starved joint or part of the joint.
