I should expand on that previous statement a bit.....
By "gut feel" I think I'd be swayed towards "I ain't gonna drill that
size hole in that size joist!", even if it looked as though it ought
to be okay.
Some things aren't worth taking chances with.
So basically I can drill up to a 25mm hole in a 100mm joist.
But not necessarily the 35 mm I require for a kitchen waste output.
Is there a regulation minimum for a kitchen waste pipe, thanx again.
Will this run and run ???
"Dave D" wrote
| Cheers All...
| So basically I can drill up to a 25mm hole in a 100mm joist.
| But not necessarily the 35 mm I require for a kitchen waste output.
| Is there a regulation minimum for a kitchen waste pipe, thanx again.
| Will this run and run ???
If you get the fall on the pipe wrong it won't run at all :-)
Not quite. 30% of the strength when unloaded maybe. But when the
joist is in place and loaded then the stresses are carried in the top
and bottom of the joist leaving the centre zone with little load. So
you can make bigger holes - and that's why notches in the top and
bottom have to be much smaller.
Simple thinking always produces apparently simple results that are
"A 10x4 joist will break at 3 tons"
Ok, so if I get a 10x4 joist and put it across the Mersey, I can drive a
mini over it right?
I wonder why all those engineers bother with all those thousands of tons
of steel and concete, when a simple bit of wood would work just as well?
No, and it takes a HECK of a lot of maths to determine limits in any
sort of accurate way.
However plumbers have been driving holes through joists ecver since they
were invented, and hardly any grand pianos have crashed into the living
room as a result.
Not really. The compresive and tensile stresses are disproportionally taken
up at the top and bottom edges of the joist. The middle plays comparitively
little part in providing the strength. Having the top and bottom further
apart is what makes the joist strong, not the additional material in
between. This is why steel joists often have many holes cast in the middle.
It reduces weight without much effect on strength.
Notching is far more detrimental to joist strength, particularly if done in
the middle. However, notching the top of the joist at the ends has little
effect, because not much of the stress is expressed there.
IIRc the hole must not be more than 20% of the joist depth which means
that the joist must be at least a 7x2. The hole edges should be at least
50mm from the bottom and 50mm from the top of the joist.
Also the hole position should be between 10% and 20 (or 80-90% at the
other end) of the span length .
Boring the hole between joists that are square to the joist requires
some seriously good tools which I'm going to have to buy for a current
job. I need to get a 22mm gas pipe through - the pipe will be fed in
from the outside.
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
I've been looking at those side-on drilling tools as well. There don't
seem to be any bargain-basement versions unfortunately.
Bit of a pity really because if there was a Ferm or Nutool version of
such a beast then I imagine it might do reasonably well in terms of
sales. It's the sort of tool you need in the back of the wagon for the
odd occasion when you need it, but the cost most likely doesn't lend
itself to acquiring one for most people.
I bought the one illustrated here some two years ago and its proved its
worth many times over. There is a cheaper version, but the price isn't
listed on that page, but afair, it was around the 25 quid mark.
On Sat, 11 Oct 2003 17:39:29 +0100, Grimly Curmudgeon
Thanks for the link. Obviously a bolt-on accessory for a drill is a
reasonable substitute, but I was referring to a drill which had its
gearbox arranged in the appropriate fashion (bolt-on accessories for
electric drills sort-of died a death about 30 years ago as I recall
I recently bought a Screwfix biscuit jointer for 35 quid. Does a great
job for the sorts of things I need a biscuit jointer for and I really
don't need to spend several hundred quid for a badged version which
could produce broadly similar results (can't see the justification
myself, but perhaps others with more knowledge of this might be able
I'm surprised that Ferm/Nutool haven't yet spotted an opportunity in
the bargain-basement tool line for a drill with a right-angle drive.
Agreed; the bolt-on drill attachments used to be 'orrible things, doing
nothing particularly well, but the AEG right angle drive unit,
permanently coupled to an old Blue Bosch is quite a tough piece of kit.
Solid cast body with proper gears, it's got. No cheapo nylon crap
inside. Stick on a decently sharp stubby auger and you're through a
joist in seconds.
That point is valid, as e.g. a chpiboard floor will form a stressd skin
and reduce flexure, however, one of teh chippies will always manage to
nail through the pipe if you have em laying in the top.
Its something to do with the away magnetic descalers work. Pipes full of
water attract nails. :-)
That site is a load of ballcocks, to keep on-topic. The problem
with the Liberty ships was design/welded construction. The
problem with the Titanic was sloppy procedure.
Try an experiment. Get two nails, and two pairs of pliers.
Take a nail at room temperature in the pliers, and bend it.
Put the other nail and the pliers in the freezer for 1/2 an
hour, then put on gloves, pick up the pliers, and bend the
nail. It won't snap.
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