Mystery solved

A month or so ago I did something awful to my planer knives, but unfortunately didn’t realize it until much later. I showed you the result at the time: a series of ridges on a freshly planed workpiece.  

Obviously, I ran something through the planer that chipped the knife edges repeatedly, and didn’t notice until that later planing session. Although only a short time had passed, I was clueless as to what it could have been. 

Well, I found out. A couple days ago I needed a small piece of oak and reached into the offcut bucket next to my table saw. In looking it over, I happened to hold the scrap at just right the right angle and saw tiny reflections as the light caught it.   

A closer inspection revealed bits of metal slightly embedded in the surface. (They’re not easy to see in the photo above, so I’ve circled a few in red.) Brushing a hand over the surface dislodged a few, but the rest were pretty well set into the wood. I knew immediately what I was looking at: the culprit that destroyed my planer knives. 

That offcut came from trimming a piece of oak to size before planing, then ended up in the bucket. Didn’t notice the metal bits then. (Perhaps I trimmed it with that face down?) After the quick planing task, I must have proceeded with what I was doing, removing the first hints of ridges while sanding. 

So, where did those metal bits come from? They seemed like something you’d get if you were grinding metal, but I hadn’t done that. How’d they get into the wood? That’s easy, just walking on a board with metal bits on it is enough to set them into place. Then, stacking the lumber would have set them even more solidly into the surface. 

Clearly, I bought the oak in that condition, most likely at a Big Box. I’m sure I made a cursory inspection of the board’s condition, but those bits were tiny and I never saw them. Of course, I never looked specifically for them, either. That’s the lesson here, of course, that not every hidden defect is made of wood.