I need to screw 100 to 120mm, gauge 12 (5.5 mm diam) screws onto plywood on top of hardwood (joists)

The dewalt no. 10 screwdigger that I have drills a pilot hole of 3.5 mm which seems to be appropriate for gauge 12.

The problem is the length of the screwdigger; the available length is about 65mm including the countersink. This means that the last 35mm (for the 100 mm screws, 55mm for the 120mm) will not have pilot hole. Is this a problem? Isn't it too hard to drive in the screws in this situation?

Are there any longer 3.5 or 5mm wood dril bits or screwdiggers? I have not found them?

The general question is, how does one prepare the hole for long screws on hard wood?

In my case, one option is to lift the plywood and make deeper the holes on the joists, I don't like this very much because it will be difficult to replace the board with the pilot holes perfectly aligned.

asalcedo wrote:

I need to screw 100 to 120mm, gauge 12 (5.5 mm diam) screws onto plywood
on top of hardwood (joists)

Why such long screws? I'd use 50mm or so (and probably an 8 or 10
gauge) for this.

All the load is being held by the joists. The screws are mainly
stopping the ply floating around. Slightly different if you're building
a box section, but even then I can't see that longer screws add much.

Or am I missing something?

IanC

In article ,
says...


asalcedo wrote:

I need to screw 100 to 120mm, gauge 12 (5.5 mm diam) screws onto plywood
on top of hardwood (joists)

Why such long screws? I'd use 50mm or so (and probably an 8 or 10
gauge) for this.

All the load is being held by the joists. The screws are mainly
stopping the ply floating around. Slightly different if you're building
a box section, but even then I can't see that longer screws add much.

I was a bit surprised by hardwood joists too.

"asalcedo" wrote in message
...

I need to screw 100 to 120mm, gauge 12 (5.5 mm diam) screws onto plywood
on top of hardwood (joists)

The dewalt no. 10 screwdigger that I have drills a pilot hole of 3.5 mm
which seems to be appropriate for gauge 12.

The problem is the length of the screwdigger; the available length is
about 65mm including the countersink. This means that the last 35mm
(for the 100 mm screws, 55mm for the 120mm) will not have pilot hole.
Is this a problem? Isn't it too hard to drive in the screws in this
situation?

Are there any longer 3.5 or 5mm wood dril bits or screwdiggers? I have
not found them?

The general question is, how does one prepare the hole for long screws
on hard wood?

In my case, one option is to lift the plywood and make deeper the holes
on the joists, I don't like this very much because it will be difficult
to replace the board with the pilot holes perfectly aligned.


you can get long series drills from screwfix and engineering shops, the
screwfix ones are about 120mm long, obviously treat them carefully as such a
small, long drill may be snapped easily if you are careless.

mrcheerful

36mm for the top plywood board (two 18mm panels)
28mm for a suplement on top of the joist to level it out
36mm into the joist (the same as the nails fixing the floorboards penetrated into the joists).

That adds up to 100mm

I was thinking of 120mm because the first 36mm into the joists has already many holes and the screws may not grab as well.

The joist is about 230mm tall and is certainly not pine, it is harder and redder.

Does it make sense?

If so, should I drill the pilot down to the full depth?

Thanks,

Antonio

The long screws are also because the area is going to support a 94kg washing machine (that produces 160kg vertical forces with strong vibrations) and a 55kg dryer on top.

The manufacturer recommends bolting into the joists, rather than screwing

Rob Morley wrote:

I was a bit surprised by hardwood joists too.

Hi Rob

I'm guessing this fits in with the perfectly machined packers required
from the 'Thicknessing' thread.

Some type of exposed roof timber/mezzanine type construction?

It might be helpful to know all the parts, the general dimensions and
desired effect so we can conceptualise the finished construction.

IanC

asalcedo wrote:

I need to screw 100 to 120mm, gauge 12 (5.5 mm diam) screws onto plywood
on top of hardwood (joists)


OK, I reread the other Thicknesser thread.

In the 'worst case' you have 2x18mm ply, then 27mm packer and you need
to secure this to the base joist in an asthetic manner?

I'd probably use 50-60mm screws with glue to secure the packer to the
joist, and then the same to attach the ply to the packed joists.

Will there be any/much sheer force (ie, pushing things along the top
surface of the beam) and potentially shifting the packer from the
joist? If not I think the above will do it.

If there will be much sheer force I'd consider building it up layer by
layer using 60mm screws (and possibly 40mm for the last sheet of ply).

HTH
IanC

asalcedo wrote:
I was thinking of 120mm because the first 36mm into the joists has
already many holes and the screws may not grab as well.

The joist is about 230mm tall and is certainly not pine, it is harder
and redder.

Does it make sense?

If so, should I drill the pilot down to the full depth?

There's no point in having a pilot hole through all
the gubbins on top of the joist, drill a clearence
hole. If you dont, you'll shear the screw off. I'd
be tempted to lubricate it anyway, to be on the
safe side (with tallow, or something more modern).

asalcedo wrote:

Ian Clowes Wrote:
asalcedo wrote:

I need to screw 100 to 120mm, gauge 12 (5.5 mm diam) screws onto
plywood
on top of hardwood (joists)

Why such long screws? I'd use 50mm or so (and probably an 8 or 10
gauge) for this.

All the load is being held by the joists. The screws are mainly
stopping the ply floating around. Slightly different if you're
building
a box section, but even then I can't see that longer screws add much.

Or am I missing something?

IanC

36mm for the top plywood board (two 18mm panels)
28mm for a suplement on top of the joist to level it out
36mm into the joist (the same as the nails fixing the floorboards
penetrated into the joists).

That adds up to 100mm

I was thinking of 120mm because the first 36mm into the joists has
already many holes and the screws may not grab as well.

The joist is about 230mm tall and is certainly not pine, it is harder
and redder.

Does it make sense?

If so, should I drill the pilot down to the full depth?

If you use modern screws such as Screwfix's Turbo Gold or Turbo Ultra
I doubt you'll need a pilot hole at all. I've not drilled a pilot
hole in years and I haven't split anything yet after driving a huge
variety of sizes (from 3 x 10mm up to 8 x 120mm) into a wide variety
of sorts of wood.

--
Chris Green

Hi Chris,

That is very reassuring, I looked into the Screwfix Turbo Gold screws and ordered them, more expensive but they seem better indeed.

I have never used screws longer than 70mm and your experience is helpful.

Thanks,

Antonio

Hi Chris,

How long do you reckon the clearance hole should be for the 100-120mm screws?

What kind of lubricant can I use? I don't know tallow, would vaseline do?

Thanks,

Antonio

In article ,
says...

Ian Clowes Wrote:
asalcedo wrote:

I need to screw 100 to 120mm, gauge 12 (5.5 mm diam) screws onto
plywood
on top of hardwood (joists)

Why such long screws? I'd use 50mm or so (and probably an 8 or 10
gauge) for this.

All the load is being held by the joists. The screws are mainly
stopping the ply floating around. Slightly different if you're
building
a box section, but even then I can't see that longer screws add much.

Or am I missing something?

IanC

36mm for the top plywood board (two 18mm panels)
28mm for a suplement on top of the joist to level it out
36mm into the joist (the same as the nails fixing the floorboards
penetrated into the joists).

That adds up to 100mm

I was thinking of 120mm because the first 36mm into the joists has
already many holes and the screws may not grab as well.

The joist is about 230mm tall and is certainly not pine, it is harder
and redder.

Does it make sense?

If so, should I drill the pilot down to the full depth?

I'd have thought it would be better to glue and screw the packing pieces
first, then add the ply as a separate operation (but I suppose you'd
have to be careful to avoid the screws you just fitted). Otherwise you
could put everything in place, drill with the bit you have then remove
the ply and deepen the holes.

wrote:

If you use modern screws such as Screwfix's Turbo Gold or Turbo Ultra
I doubt you'll need a pilot hole at all. I've not drilled a pilot
hole in years and I haven't split anything yet after driving a huge
variety of sizes (from 3 x 10mm up to 8 x 120mm) into a wide variety
of sorts of wood.

Agreed. Wickes do thier own version called Easy Drive or something. I used
80mm and 100mm ones to build a pergola, screwing straight into side & end
grain with no splitting at all. No pilot hle.

Dave

"david lang" wrote in message
. uk...
wrote:

If you use modern screws such as Screwfix's Turbo Gold or Turbo Ultra
I doubt you'll need a pilot hole at all. I've not drilled a pilot
hole in years and I haven't split anything yet after driving a huge
variety of sizes (from 3 x 10mm up to 8 x 120mm) into a wide variety
of sorts of wood.

Agreed. Wickes do thier own version called Easy Drive or something. I
used
80mm and 100mm ones to build a pergola, screwing straight into side & end
grain with no splitting at all. No pilot hle.

I find Scewfix not so cheap these days for most things. Are Wickes screws
cheaper?

mrcheerful
. wrote:
"asalcedo" wrote in message
...

snip

you can get long series drills from screwfix and engineering shops, the
screwfix ones are about 120mm long, obviously treat them carefully as such a
small, long drill may be snapped easily if you are careless.


Oh yes. And clumsy. These should be regarded as disposable items and
bought in batches in my experience. Very useful though.

--
Steve F

Hi Rob,

Thank you for your thinking.

I agree with you now. I will glue the packing pieces, put everything in place and then drill with the bit that I have. Then remove the ply and deepen the holes. I really did not want to screw too many times and to have hidden screws that I or someone else could find in the way.

It is important, I think, to screw the ply and packing to the joists. Although there will not be horizontal forces, there will be strong vertical ones.

These vertical ones will make the ply flex, the deflection will be less if the ply is screwed to the beams. I am a civil engineer and I remember that bit.

Smaller defection is exactly what I need to damp the vibrations.

Thanks,

Antonio

Can you give me a web address where I can find these long drills? I have not been able to locate them. Thanks