BSD #56 Q&A
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Hi guys, time for another Q&A edition of behind the sawdust. We have several really interesting woodworking questions to answer, so let’s get started!
Q- What’s a core box bit?
A- This one is related to the video we just released about using core box bits to make virtually any custom molding profile you can imagine. The simple answer is a core-box bit is a cove cutting bit without the bearing. But it’s interesting to consider how they got their name. The term “core box” is rooted in the metal casting trades. In order to create a hollow area inside a cast part, such as an engine block, a packed sand cylinder had to be inserted into the mold before the final pour. Those cylinders are called “cores”, and they were made ahead of time, at least in the old days, in a wooden mold called a “core-box”. Patternmakers might use what were called “core-box planes” (Stanley designated theirs as #57) to create each half of that mold. Core box router bits cut that same semi-circular shape, and the name has stuck. However, some people call them “round-nose bits”, which does make more sense if you aren’t familiar with the tools of an old-time pattern maker. For modern woodworkers, core box bits are used to cut coves. They don’t benefit from the bearing guides found on standard cove bits, but that makes them more versatile because they can be plunged into a workpiece to cut a more complete, half-circular shape. This is very useful in many situations, especially for creating molding profiles.
Q- How do I test a tool’s sharpness?
A- The simple answer to that question is- Does it cut well? A chisel, or any tool for that matter, is sharp enough when it performs to your expectations. But there are several tried and true tests to check its sharpness.
Light test: Hold a tool up to a source of light and look carefully at the intersection between the bevel face and the back of the tool. Imperfections will reflect the light back at you. If no light is reflected from that fine edge, it's sharp.
Fingernail test: Place the edge on one of your fingernails, and apply light pressure as you attempt to shave the surface of the nail. If the tool skids across the surface, it's dull. If it immediately catches on the nail, it's sharp.
Endgrain test: Perhaps the best way to test an edge is to put it to wood. I keep a scrap of soft pine on hand for this purpose. A sharp tool should shave a the ends of the fibers cleanly. A dull tool will tear at or crush the fibers.
Q- What is case hardening?
A- Case hardening can occur when wood isn’t dried properly. A board may look nice and straight, but when you rip it on the table saw, it immediately starts to warp and twist. If you haven’t experienced it before, you will eventually. A simple way to explain it is, when the outside wood fibers dry (and therefore shrink) at a much faster rate than the inner fibers, tension is created. That tension may be held in check by those outer fibers- until you cut into the board. The tension is then released, and the board warps. This is considered a serious defect, and cause for returning the material to the dealer or mill. A good mill will steam their boards at the end of the drying process to minimize this effect.
How can you determine if a board is "case hardened?" Unfortunately you can't tell just by looking at it. You have to do a test. Starting from about 2" from the end of the board, crosscut three or four 1" pieces. Then, lay those pieces so that one of the fresh cut end-grain faces is facing up, and cut a couple of kerfs into the end, like you are making tines on a fork or comb. If the "tines" quickly bend inward, closing the kerfs, the wood is case hardened.
Q- My planer’s infeed rollers aren’t pulling in the boards like they used to. What can I do?
A- This is a very common problem. In fact, I was watching a video on the Make Something YouTube channel the other day, and David was stumped by this same problem. Fortunately, there’s an easy solution. Clean your rollers. Resin buildup can cause them to lose their grip. A rag and some Naphtha will take care of that. Resist the urge to hold the rag on the roller while the planer is running, it’s a good way to lose your hand. After cleaning the rollers, apply a coat of paste wax to the bed of the planer. Let it dry and buff to a slippery surface that your boards will slide across easily. That should solve the problem, even if your rollers are a little worn. Depending on the type of wood you run through it, you may have to repeat the process fairly frequently, especially if you plane a lot of pine.
That’s it for this Q&A edition of Behind the Sawdust. Be sure to hit that subscribe button. And for more woodworking tutorials, tips and tricks designed to make you a better woodworker, check out the latest issue of stumpy nubs woodworking journal. You can read and subscribe for free at stumpynubs.com
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Video about using core box bits to create custom moldings: https://youtu.be/FLmUHJXWpD8
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