On Sat, 04 Sep 2004 21:32:05 +0100, Steve Jones
wrote:

What is the purpose of a self tapper screw, and when would one use such
a screw?

Machine screws go into ready-threaded holes, cut with a separate tool.

Traditional woodscrews are quite crude things that cut their own way
in, usually with a thread that tapers in diameter considerably.
Because they mangle the wood so much, they usually have a plain
parallel section to the top of the shank. This locates in place like a
nail. If a long parallel woodscrew was threaded all the way long, it
would have drilled itself a clearance hole by the time you got to the
top of it.

Self tappers appeared in the '50s (they're tricky to make - took quite
a bit of steel metallurgy to make something hard enough, yet cheap).
First intended for thin, soft sheetmetal like aluminium, they're quick
and cheap to install. They also cut a reasonably neat thread, so you
can take them afterwards and replace them, just like a machine screw.
Cross-thread them in the hole though and you'll strip the threads out.

Some self-tappers are even self-drilling - they have a sharp point.
Others like the "Taptite" series are less aggressive and really are
thread-forming machine screws. They're less prone to wearing their
threaded holes out if re-used, but they also need accurately drilled
holes and soft metal.

"Modern" woodscrews, like the Screwfix Goldscrews, are somewhere
between the two. They look like coarse self-tappers. In use they cut a
thread into wood that's coarse pitch, yet regular enough to work all
along its length.

In the modern world of high speed bodging, just use Goldscrews for
everything.


Can they be used in place of wood screws?

More or less - depending on the size and thread pitch. For soft
materials (softwoods, plastic wallplugs), go with a coarse pitch and
think about using traditional woodscrews. For modern materials (MDF,
UPVC, sof aluminium) go with the modern parallel woodscrew.

Use a self tapper in wood and it will just drill a hole. Too fine a
pitch.

Use a soft screw in hard steel and the material will re-shape the
screw, not the other way round. This is sometimes a problem with
stainless self tappers, as they're a bit soft.


What about with wall plugs?

You can set wall plugs perfectly well into a wall just by using a
nail. All they need is a wedge in the middle. To hold into the plug
itself, your screw needs a moderately coarse pitch.

There are many sorts of wallplug. If your holes are drilled parallel,
use a parallel plug and a parallel screw (modern woodscrew). The
older plugs sometimes had thin walls and solid noses, so as to be more
compatible with the old tapered screws. Avoid these today, as they're
harder to drive in and fussier about getting the depth right.


For example, is an A2 stainless steel self tapper suitable for attaching
downpipe clips to an external brick wall? (With suitable wall plug of
course).

So long as it has a reasonably coarse pitch (Screwfix's do), it's
perfect.
--
Smert' spamionam

Andy Dingley wrote:
On Sat, 04 Sep 2004 21:32:05 +0100, Steve Jones
wrote:

What is the purpose of a self tapper screw, and when would one use such
a screw?

Machine screws go into ready-threaded holes, cut with a separate tool.

Traditional woodscrews are quite crude things that cut their own way
in, usually with a thread that tapers in diameter considerably.
snip
In the modern world of high speed bodging, just use Goldscrews for
everything.

The exception is where you want to screw planks or other bits of wood
securely to something.
With the plain shank, it will pull through lots easier, to pull the
two bits flush.
With a screw threaded all the way to the top, you have to apply enough
torque to break the thread formed in the wood, before the screw will continue
to turn and bring the two bits of wood flush.

In article ,
says...
Andy Dingley wrote:
On Sat, 04 Sep 2004 21:32:05 +0100, Steve Jones
wrote:

What is the purpose of a self tapper screw, and when would one use such
a screw?

Machine screws go into ready-threaded holes, cut with a separate tool.

Traditional woodscrews are quite crude things that cut their own way
in, usually with a thread that tapers in diameter considerably.
snip
In the modern world of high speed bodging, just use Goldscrews for
everything.

The exception is where you want to screw planks or other bits of wood
securely to something.
With the plain shank, it will pull through lots easier, to pull the
two bits flush.
With a screw threaded all the way to the top, you have to apply enough
torque to break the thread formed in the wood, before the screw will continue
to turn and bring the two bits of wood flush.

...........or by pre-drilling a clearance hole in the top plank. Much
easier and more precise, imho.
--
Paul Mc Cann

Paul Mc Cann wrote:
In article ,
says...
Andy Dingley wrote:
On Sat, 04 Sep 2004 21:32:05 +0100, Steve Jones
wrote:

What is the purpose of a self tapper screw, and when would one use such
a screw?

Machine screws go into ready-threaded holes, cut with a separate tool.

Traditional woodscrews are quite crude things that cut their own way
in, usually with a thread that tapers in diameter considerably.
snip
In the modern world of high speed bodging, just use Goldscrews for
everything.

The exception is where you want to screw planks or other bits of wood
securely to something.
With the plain shank, it will pull through lots easier, to pull the
two bits flush.
With a screw threaded all the way to the top, you have to apply enough
torque to break the thread formed in the wood, before the screw will continue
to turn and bring the two bits of wood flush.

..........or by pre-drilling a clearance hole in the top plank. Much
easier and more precise, imho.

That too.
But if you happen to have screws with the right size of plain shank,
then it means one less tool needed, which can be handy.

On Sun, 5 Sep 2004 19:55:03 +0100, Paul Mc Cann
wrote:

With a screw threaded all the way to the top, you have to apply enough
torque to break the thread formed in the wood, before the screw will continue
to turn and bring the two bits of wood flush.

..........or by pre-drilling a clearance hole in the top plank. Much
easier and more precise, imho.

Hi,

This might not be good idea for outdoor stuff like window frames
though.

cheers,
Pete.

Andy Dingley wrote:

On Sat, 04 Sep 2004 21:32:05 +0100, Steve Jones
wrote:


What is the purpose of a self tapper screw, and when would one use such
a screw?


Machine screws go into ready-threaded holes, cut with a separate tool.

Traditional woodscrews are quite crude things that cut their own way
in, usually with a thread that tapers in diameter considerably.
Because they mangle the wood so much, they usually have a plain
parallel section to the top of the shank. This locates in place like a
nail. If a long parallel woodscrew was threaded all the way long, it
would have drilled itself a clearance hole by the time you got to the
top of it.

Self tappers appeared in the '50s (they're tricky to make - took quite
a bit of steel metallurgy to make something hard enough, yet cheap).
First intended for thin, soft sheetmetal like aluminium, they're quick
and cheap to install. They also cut a reasonably neat thread, so you
can take them afterwards and replace them, just like a machine screw.
Cross-thread them in the hole though and you'll strip the threads out.

Some self-tappers are even self-drilling - they have a sharp point.
Others like the "Taptite" series are less aggressive and really are
thread-forming machine screws. They're less prone to wearing their
threaded holes out if re-used, but they also need accurately drilled
holes and soft metal.

"Modern" woodscrews, like the Screwfix Goldscrews, are somewhere
between the two. They look like coarse self-tappers. In use they cut a
thread into wood that's coarse pitch, yet regular enough to work all
along its length.

In the modern world of high speed bodging, just use Goldscrews for
everything.



I read in teh book /understanding wood' of some tests done with wiodscrews.

They actually held better when nailed in and tightened the last few turns.

Good analysis of nail to wood shear failure in there IIRC.



Can they be used in place of wood screws?


More or less - depending on the size and thread pitch. For soft
materials (softwoods, plastic wallplugs), go with a coarse pitch and
think about using traditional woodscrews. For modern materials (MDF,
UPVC, sof aluminium) go with the modern parallel woodscrew.

Use a self tapper in wood and it will just drill a hole. Too fine a
pitch.

Use a soft screw in hard steel and the material will re-shape the
screw, not the other way round. This is sometimes a problem with
stainless self tappers, as they're a bit soft.



What about with wall plugs?


You can set wall plugs perfectly well into a wall just by using a
nail. All they need is a wedge in the middle. To hold into the plug
itself, your screw needs a moderately coarse pitch.

There are many sorts of wallplug. If your holes are drilled parallel,
use a parallel plug and a parallel screw (modern woodscrew). The
older plugs sometimes had thin walls and solid noses, so as to be more
compatible with the old tapered screws. Avoid these today, as they're
harder to drive in and fussier about getting the depth right.



For example, is an A2 stainless steel self tapper suitable for attaching
downpipe clips to an external brick wall? (With suitable wall plug of
course).


So long as it has a reasonably coarse pitch (Screwfix's do), it's
perfect.

They actually held better when nailed in and tightened the last few turns.

Yes, I needed to get my "Birmingham" screwdriver out a few times when
assembling my conservatory.

Christian.

In article ,
says...
They actually held better when nailed in and tightened the last few turns.

Yes, I needed to get my "Birmingham" screwdriver out a few times when
assembling my conservatory.

Christian.





tsk tsk, thats an Irish screwdriver you're talking about
--
Paul Mc Cann