Pilot hole size

[DIY_novice01]

Need to get some drill bits for making pilot holes to suit a 3.5mmx50mm screw. Dont know what type of wood it is yet but does 2mm for softwood and 2.5mm for hardwood sound correct?

Oh, any suggestions for drill bit brand?

The job is to redo a few loose floorboards upstairs.

Cheers

 

[johnny2007]

2mm will be fine for both soft and hardwood, unless you're going very close to the edge.

 

[DIY_novice01]

Just noticed that the 2mm drill bits for sale look is shorter than the screw so will not be able to fully pilot the joist. Does that particulary matter?

Or rather the part of the bit that cuts is shorter than 50mm

 

[rsgaz]

3.5mmx50mm screw

That's quite thin, get some number 8 screws instead (4.2mm) and use a 3mm pilot.

Oh, any suggestions for drill bit brand?

Bosch, Heller, DeWalt, ideally cobalt (HSS-Co) for extra hardness, rather than HSS-G. Don't get HSS-R.

shorter than the screw so will not be able to fully pilot the joist. Does that particulary matter?

Yes, you are more likely to snap/shear the drill bit when the flutes are shorter than the drilling depth. To counteract that, drill down to 10mm, then fully withdraw the drill whilst still spinning. Then down to 20mm and withdraw again, etc, in 10mm steps until you reach full depth. This allows the swarf/chips to escape, preventing overheating(and shearing off the bit) from the clogging of the chips.

loose floorboards

I hope you are certain you know where the pipes/cables/etc are! For the boards to pull tight against the joists, you also need to drill a clearance hole(slightly larger than the screw diameter)...

...but, the drill will bite and suddenly pull down and ruin your pilot hole, so, a small piece of wood(wine cork?) over the drill bit as a depth stop is a very good idea...

 

[foxhole]

The joist needs no pilot hole. Never needed to pilot hole floorboards either.

 

[DIY_novice01]

That's quite thin, get some number 8 screws instead (4.2mm) and use a 3mm pilot.

If they are too small how about these which are 5x50mm and then use a 4mm pilot? Have them left over from a different project. Save another trip to the shops for something in between.

With regards knowing whats under the boards. I was going to lift the problematic boards out fully and have a gander underneath. No chance am I risking screwing into existing nail holes. I trust thats the right approach? Or is there anything else to consider?

 

[Jakg]

My suggestion would be to use proper flooring screws.

 

[big-all]

i use thousands off no6x2" inch screws into 12mm mdf and 3/3.2even 3.5mm pilot holes will fully grip so would expect 3.5mm screws [no7 equivalent] would be happy with 3mm in pine???
just experiment screw into timber leave 10mm sticking out and claw hammer under the head and lever out [if you can]??

 

[johnny2007]

i use thousands off no6x2" inch screws into 12mm mdf and 3/3.2even 3.5mm pilot holes will fully grip so would expect 3.5mm screws [no7 equivalent] would be happy with 3mm in pine???
just experiment screw into timber leave 10mm sticking out and claw hammer under the head and lever out [if you can]??

Mind your eyes when you do that.
Screw heads can fly like bullets.

 

[big-all]

Mind your eyes when you do that.
Screw heads can fly like bullets.

thinking more gentle up to full load rather than yank as hard as you can

 

[johnny2007]

Was dismantling a shed once and pulling nails off some timber at shoulder height.
One of the nail was a screw, fortunately I had goggles on or they'd have changed my name from johnny foreigner to popeye.
That's how I know...

 

[big-all]

Was dismantling a shed once and pulling nails off some timber at shoulder height.
One of the nail was a screw, fortunately I had goggles on or they'd have changed my name from johnny foreigner to popeye.
That's how I know...

yes indeed we all get caught out when we think we know better and dont take the correct precautions

 

[johnny2007]

yes indeed we all get caught out when we think we know better and dont take the correct precautions

Done that a lot in my younger days.
Stupidity was rife then

 

[cdbe]

Go to Toolstation and buy an assortment of sizes of Draper HSS Jobber drill bits, they are unbelievable cheap (20-30p per bit) they will be fine for floorboards (they'll also go through 12mm RSJs quite well). Find the size that works best and add the rest to your tool collection.

 

[DIY_novice01]

Go to Toolstation and buy an assortment of sizes of Draper HSS Jobber drill bits, they are unbelievable cheap (20-30p per bit) they will be fine for floorboards (they'll also go through 12mm RSJs quite well). Find the size that works best and add the rest to your tool collection.

They are cheap thanks for the tip.
Is everybody else of the opinion 3.5mm spax screws are too thin? Is so will pick up a bag of these too.