On 30 Oct 2004 11:35:26 GMT, wrote:



Well it's really to find out how much torque is needed to screw them
in successfully and how much will break them. I'm looking for a new
cordless driver and want to know what sort of torque figure is useful
and how much is simply too much. The cordless driver specifications
give their maximum torquer but nowhere can I find any figures for how
much torque is actually needed to screw screws in.

I think that it's going to be a tough one to work out.

If it was threaded components going into metal, then it's rather
easier because you are trying to avoid distorting something, stripping
threads or shearing the stud/bolt and the materials are reasonably
predictable.

For screwing into wood, there are a whole bunch of variables:

- The species and to some extent moisture content of the wood.

- The type of screw - e.g. standard, double threaded, serrated edge
etc.

- Size and depth of pilot hole if any.

- The type of screwdriver

- Whether lubrication is used


For example, at one end of the spectrum, I have a Senco collated
screwdriver which takes screws on a plastic band. Typically they are
3 or 4mm types with a square slot head. It's really fast for
panelling and drywalling work and will comfortably drive the screws
through ply or plasterboard into constructional softwood.

At the other end, I was rehanging an oak door into an oak frame today
because I needed to reverse the opening side of the door.
Since oak contains tannins which eventually corrode steel as well as
for aesthetic reasons I wanted to use brass screws.
However, brass will not stand up to high torque driving (it will shear
or the screwdriver cams out) and oak is tough material, so to achieve
this, I drilled carefully sized pilot holes and put in normal Spax
screws to cut a thread. Then I removed the steel screws and put in
the brass ones easily.

I used stainless steel screws in aspects of my cabin construction and
found that these had a tendency to shear unless there was a reasonable
pilot hole.

Some of the Spax and Turbogold etc. screws are claimed to be able to
be driven into wood without a pilot hole. I've found this to be
moderately true into softwood as long as it's away from an edge or end
and one isn't looking for a particularly good finish. Trying this
with hardwood, doesn't seem to work. Either the screw shears or cams
out, and there is a mess.

For applications using the larger sizes of Spax screw, I tend to pick
the pilot hole drill carefully and then using a combined drill
countersink, drill to the correct depth. Occasionally with larger
ones, a touch of some lubricant (e.g. candlewax) on the threads
helps.

So in terms of the torque needed to drive the screw, I think it would
be pretty hard to determine that because there are too many variables
with wood. If the concern is over having too much torque and
shearing the screw, then I would say that if it happens, the pilot
hole arrangement was not right or if shearing happens when the screw
is fully home, the clutch setting needs to be reduced.



--

..andy

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