Q: We are selling cutting boards out of edge-glued hard maple. We buy the panels and then cut them to size, shape them and so on. We are getting complaints that some of the boards are developing cracks in pieces. What is going on? What adhesive should we be using? Would RF gluing help?
A: I assume that the splitting is occurring at the glue line and not in the wood. A glue joint should be stronger than the wood itself, so this should not happen normally. The question is "Why is the glue line weaker than normal?" There are several issues that need to be addressed in order to answer this question.
First, the adhesive used must be somewhat water resistant. That is, the adhesive should be one that has a chemical bond taking place and then would be advertised as being water resistant. Without water resistance, it is possible that the washing of the board will begin to cause the glue to dissolve and the joint will be weakened. Likewise, heat will soften the adhesive and cause the joint to weaken.
Second, a dishwasher will be hard on the wood and adhesive joint. I suggest that you specify that the boards never be put into a dishwasher.
Third, if the manufacturer claims that he used a water-resistant adhesive when making the panels, then the joint itself is being poorly manufactured. Oftentimes this low quality results because the individual staves are cut and then allowed to sit around for a day or so before they are glued. In the heating season, the ends of the staves will dry out a bit and then will be slightly too narrow when they are glued. Because of the gap, the ends of the joints will fail when stressed.
Fourth, the U.S. Food & Drug Administration has some requirements about the type of adhesive that can be used for wood that is in food contact; see 21 CFR 175.105. I do know that Titebond II and III, as well as some hot melt PURs, meet the requirements for cutting boards, and I am certain there are others that also meet the government requirements. It would be prudent to make sure that the adhesive being used meets government requirements.
Fifth, an RF gluing process would not necessarily help, compared to cold clamping. However, as some adhesives require heat to cure, the RF process will have more choices for adhesives that could be used, compared to the options available with a clamp carrier. But a properly made cold clamping joint will perform well in this product.
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