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darsunt 01-06-2012 08:52 PM

Question about Wood screws breaking
 
When driving in wood screws by hand I've occasionally had screws break off at the head or middle when things got tight. But I've never broken a wood screw when driving it in with a electric drill. Why is this? It doesn't seem logical, since the drill applies more velocity and force you would think it would be more likely to break wood screws.

Ironlight 01-06-2012 09:08 PM

The drill driver applies continuous torque and keeps the screw turning against the friction of the wood. On the other hand, whenever you drive a screw by hand you need with each twist to start it turning again and overcome the initial contact friction of the screw against the wood. You probably torque it pretty hard to get it turning and that in turn fatigues the metal until it fails.

Edit:
I always try and drill pilot holes slightly smaller than the screw's minor diameter (the diameter of the shaft minus the depth of the screw threads). Not only do screws drive easier but you maintain the integrity of the wood grain by not crushing it, resulting in greater holding power. You can also more precisely place the screw.

Also, consider if you're using the right screw for the job. Drywall screws, which have become defacto "all purpose" screws to a lot of people, have fairly weak torsional strength compared to wood screws.

ratherbefishing 01-06-2012 09:52 PM

I've noticed that, too. Try some beeswax on the screw threads.

titanoman 01-06-2012 10:01 PM

Quote:

Originally Posted by Ironlight
The drill driver applies continuous torque and keeps the screw turning against the friction of the wood. On the other hand, whenever you drive a screw by hand you need with each twist to start it turning again and overcome the initial contact friction of the screw against the wood. You probably torque it pretty hard to get it turning and that in turn fatigues the metal until it fails.

Very logical explanation. Well said.

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