Hello,
I need help understanding if my design is bad or if there is something else causing the wood to split along the grain in the same place on multiple units. This was cut from a 3/4 inch panel. I’m having a high defect rate where the wood splits somewhere along the thinnest upper part of the piece. The wood is at least 2 inches wide there. There are no other warping or splitting issues anywhere else. It was finished with urethane before the split occurred and the moisture content of the wood before being cut was 9.9%. It seems like larges changes in temp and humidity cause it to split after being finished. Please tell me if my design is bad and needs to be wider than 2 inches in that location or if the problem is more due to the wood panels. Thank you.
Jason
Replies
Can I ask what the various holes are for? If this is mounted to something using those holes, or something is mounted to it, that could be causing the splits.
2 inches should be wide enough. Either the wood is wetter than you think, or it's crappy wood.
Thank you for your reply. It split before the holes were ever used but they were meant for mounting. Is a MC of 9.9% acceptable or should it be lower?
It looks more like a process issue if the crack is appearing in the same spot. Note the crack is at the curve (weakest point) where the tools apply their greatest torque / pressure as you move around the inside perimeter of the hole. Try leaving the wood longer (than 2 inches) and trim to length after making and routing the hole. Also reinforce the edges so that the tools can't exert pressure at the curve causing the area to fail. The steady pressure of the router and round-over bit exert pressure along the grain. I don't think moisture content is your issue. As the wood moisture changes after finishing the problem becomes more visible. Also you can rescue the part by applying thin CA glue to the crack and clamp it tight. The failed area will be healed forever and you shouldn't see the crack at all. Good luck.
Thank you for the reply RevBob. I will try your suggestions. Hope that I can stop these cracks.
I like RevBob's thought process, but not sure this is the situation (or maybe I don't fully understand the post). The crack does not appear while machining the piece, but after all work has been done and a finish has been applied. I think the upper section is drying to a lower moisture content faster than the wider, lower section and this variation in drying is causing the crack. Would be interesting to see what happens if you made one with a MC of 6-7%.
I would guess it's more to do with moisture content and movement than the actual tool processing.
As noted, the crack is appearing at the narrowest point where the cuts meet. Typical panel glue ups are stable because the wood moves together. In this case, you've got a large hole cut into the middle of it and now those boards at the top part are independent. My best guess is that the board adjacent to it that runs the full length is moving at a different rate than the narrow section, and it's cracking at it's weak point along the grain. Cracks are like electricity... path of least resistance...
If you're really stuck on that design try drying it more, down to 6-7%. If not maybe try making it a bit wider. Depending on where you live it's unlikely it will go dryer much more than that in your home (or wherever you're using it).
On a side note, that looks like it's one of those finger jointed panels? I'm always wary of those. Not because they're not stable, but they're made up of shorts and throw away pieces. I've got a small panel at home that's all cracked to hell on the underside. That could also be playing into things.
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