Mechanics Of A Screw Joint

No matter what screw is used, you should drill at least two holes — a shank hole and a pilot hole — to drive it into the wood. However, before drilling any holes, something needs to be said about the mechanics of a screw joint.

clamping action. The goal of a screw joint is to pull the front piece of wood tightly down to the back (anchor) piece. The key to this is that you're not really screwing into both pieces of wood. The threads of the screw grip uidy the anchor piece. The front piece is simply held tight by the screw head — in effect, a clamping action takes place.

glue joint. This mechanical action is even more critical when glue is applied to the joint (as is the case most of the time in woodworking). The screw actually serves as a spot clamp to pull the two pieces of wood tightly together until the glue dries.

mechanical action. This is where it's easy to get into trouble. In order for the mechanical action of this joint to work properly, the screw threads should not grab the front piece; they should only grab the anchor (second) piece.

If the shank hole isn't deep enough (or there's no shank hole at all), the threads will "catch" in the front board. Then as the screw enters the second (anchor) board, the threads will maintain any gap that exists between the boards — and you lose the clamping action of the screw.

Even if the two boards are held or clamped together, the screw can only hold them in that position. It can't pull the front piece down any tighter without stripping the threads.

I'm sure this has happened to all of us. You try to screw two boards together, but they won't pull tight. So you push down hard and give it an extra twist. All this does is make your arm tired, and frequently strips out the threads or breaks the screw.

The problem is that the threads have gripped the front board and are maintaining the gap between the boards.

Woodworking Tools and Installation Tips

Woodworking Tools and Installation Tips

There are a lot of things that either needs to be repaired, or put together when youre a homeowner. If youre a new homeowner, and have just gotten out of apartment style living, you might want to take this list with you to the hardware store. From remolding jobs to putting together furniture you can use these 5 power tools to get your stuff together. Dont forget too that youll need a few extra tools for other jobs around the house.

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