pilot hole for long screws

[asalcedo]

I need to screw 100 to 120mm, gauge 12 (5.5 mm diam) screws onto plywoo

on top of hardwood (joists)

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

The problem is the length of the screwdigger; the available length i about 65mm including the countersink. This means that the last 35m (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 thi situation?

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

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

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

-- asalcedo

[Ian Clowes]

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

[Rob Morley]

I was a bit surprised by hardwood joists too.

[mrcheerful]

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

[asalcedo]

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 floorboard penetrated into the joists).

That adds up to 100mm

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

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

Does it make sense?

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

Thanks,

Antoni

-- asalcedo

[asalcedo]

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

The manufacturer recommends bolting into the joists, rather tha screwin

-- asalcedo

[Ian Clowes]

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

[Ian Clowes]

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

[Chris Bacon]

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).

[usenet]

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.

[asalcedo]

Hi Chris,

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

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

Thanks,

Antoni

-- asalcedo

[asalcedo]

Hi Chris,

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

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

Thanks,

Antoni

-- asalcedo

[Rob Morley]

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.

[david lang]

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

[Doctor Drivel]

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

[Fitz]

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

[asalcedo]

Hi Rob,

Thank you for your thinking.

I agree with you now. I will glue the packing pieces, put everything i place and then drill with the bit that I have. Then remove the ply an deepen the holes. I really did not want to screw too many times and t 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 stron vertical ones.

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

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

Thanks,

Antoni

-- asalcedo

[asalcedo]

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

-- asalcedo