Electronics > Mechanical & Automation Engineering

Wood Screws Breaking - Not Sure Why

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bostonman:
I'll also add that in most cases I wasn't depending on the drill to begin grinding when it reached the torque setting.

In most cases I set the drill to a low setting, maybe 2, and I'd stop before the screw was all the way in to avoid the possibility of snapping the screw. Then I'd ease it to the final resting spot.

Most times I noticed what while tightened the screw at a setting of 2 may cause the drill to stop with the screw halfway on another, so I'd have to change the setting to 3 or 4.

So I wasn't hammering away letting the drill go full blast until the screw was fully seated. It was more or less a combination of the drill torque setting and me "feeling" the amount of torque on the screw.

Monkeh:
When you've got a piddly little 4x30 screw in wet softwood, you can easily strip the hole out with a screwdriver. You'll not be snapping these screws with a drill on any clutch setting unless they're grossly defective.

I send screws from 3.5x30 to 6x150 with an impact. You may be a tad overcautious.

As for the screws snapping by themselves, that's just brittle screws and wood moving. More screws, larger screws, or nails is the solution. I recommend nails for the panels, and the 'runners' (rails) should be fixed with either really big nails, or in US terms #10x4" screws (or bigger).

Neepa:
I think the problem is you used two screws per rail per board. Effectively trapping a part of it between two unmoving objects; this being the screws.
Now when the board gets wet it tries to swell inbetween the screws which may lead to them fatigue cracking after long enough.

To test this simply remove one screw per rail and wait and see.

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