Mystery of Screws
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How
often have you started to do a small job in the
house only to find you don't have a suitable screw!
They are either too fat, too long, not fat enough
or not long enough. If by some miracle the
screw fits, you don't have a rawl plug!
A trip to the DIY shop beckons, but by the time
you have found the screws, sorted out which size
and which head shape you want, queued at the checkout
and got home, there is no time left to do the
job. Sounds familiar - well here is a little
bit of basic information which may help in future.
Size
A wood screw is described by two
measurements.
The length and diameter (of the shank).
The length is obvious.
The shank is given a gauge number with 6, 8 and
10 being the most commonly used. The thing
to remember is the higher the number the thicker
the screw. e.g. No.10 is thicker than
No. 6.
Head
shapes
There are three head shapes to choose from,
all intended for different uses.
Countersunk - this is intended
to screw right down until the head is flush with
the wood surface, leaving nothing protruding.
In order to accomplish this, the hole has to be
made big enough on the surface of the wood
only, to allow the screw head (which of course,
is larger than the shank) to drop down past the
surface. Used in most woodwork, door hinges and
is essential when making children's toys in order
to prevent accidents.
Raised - these have a flat tops
and are usually used on such
things as door furniture that have partly countersunk
holes.
Round - these are used where
the holes are not countersunk at all.
Slots
The most common type of slots in screw heads are
the traditional
single slot on which you use the standard flat
screwdriver, and the
cross slot. This cross slot was originally
designed for the Phillips
screwdriver and some of the foreign screws are
still of this design,
where only a Phillips type screwdriver should
be used. However,
the majority of cross head screws are now Supadriv
or Pozidriv
which require a screwdriver with a special tip.
If you try to use a
Phillips screwdriver on Supadriv screws you will
find they won't
grip. N.B. If you use a power screwdriver
choose screws with the
Supadriv slot. The screwdriver locks into
this making the job much
easier,.
Thread
Twin-start screws have a sharp thread and hardened
body, this
enables them to be driven in much faster and makes
them ideal
for use with power screwdrivers. Standard threads
are O.K. for general jobs using a traditional
screwdriver.
We
must thank Mr. George Gouraud for the following
information regarding a screw which I have omitted.
"It
is a Canadian invention called the Robertson Head.
This screw has a square, flat bottomed "slot"
and is available in all the sizes found in other
head styles, as well as having 4" slot sizes.
The advantages of this type of head are:-
1:
It will not "cam out" as you tighten
or loosen it, as happens with the Phillips head.
2:
The screw can be placed on the driver bit and
will stay there even if you are driving it into
either an
overhead or downward facing work piece."
Thank
you Mr. Gouraud.
TIPS
-
Be
sure to get the right screw for the job, particularly
with regard to length. Just a fraction
too long can result in damage to a decorative
surface or the screw coming right through
to the other side. Too short and they may
not be up to the job in hand.
-
To
make screws easier to remove at a later date,
rub soap on the thread before screwing in.
Thanks
to Geoff Smith of this one
We
have, however, been advised that soap can
attract moisture which results in the screw
rusting, (see next tip).
-
If
you apply a little grease or Vaseline to the
thread when inserting new screws they will
be easier to remove should the need arise.
Do not use soap as this attracts moisture
which can result in the screw rusting.
-
To
avoid splitting the wood make start holes
before attempting to insert the screw.
This can be done with a bradawl for small
screws in soft wood or, alternatively, with
a very small drill bit.
-
Avoid
several screws following a wood grain as this
can lead to the wood splitting down the grain.
courtesy of
http://www.hintsandthings.co.uk/
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