Drilling 5mm pilot hole x150mm deep through oak sleepers - drill bit recommendations please!

[Temmy]

Hello,

I need to drill a bunch of pilot holes through my oak sleepers at 5mm, and 150mm depth. I got a drill bit off Amazon that snapped on the 4th hole, so totally open to some recommendations.

Thanks.

 

[Deleted member 174758]

If you could go to 6mm (the smallest size auger bits normally come in) you could change to a proper auger bit rather than trying to use a metalworking bit for the job. If so you need to look for a machine auger bit circa 210 to 260mm long and ideally from a decent manufacturer (e.g. Armeg, Bahco, Bosch, Fisch, Irwin, Makita, Milwaukee, Wurth, etc) and get yourself a file (ideally an auger bit file, but failing that a 4in flat needle file with a handle with one safe edge, i.e. one edge with no teeth on it) because you will probably need to sharpen the auger bit at some point. Avoid bits with 1/4in hex drives as they can snap off if over-stressed. Auger bits of 6mm need to be run at 500 to 900rpm and no faster. The threaded nose of an auger should pull the drill bit through the wood without the need to push hard providing it isn't over revved. Another common mistake is not to clear the build-up of waste in the auger bit from time to time - this will clog any bit and you might snap the drill bit if the lands get clogged.

BTW the reason I avoid cheapo no-name Chinese auger bits is because they often arrive blunt, they aren't always straight and they won't always resharpen (some of my decent bits are more than 20 years old and have been resharpened mutiple times). On eBay a decent bit won't cost you a fortune - just looked at an Irwin (only 190mm long, though) at under £11 and a Bahco 6 x 460mm at £18.27. Not as cheap as carp, but you get what you pay for

 

[foxhole]

https://ffx.co.uk/product/Get/Irwin-Irw10502738-5709131135579-Auger-Drill-Bit-5Mm-X-150Mm.

?

 

[Deleted member 174758]

150mm will be too short to drill a 150mm deep hole, @foxhole, the actual cutting length of that will be around 100 to 110mm

 

[Temmy]

https://ffx.co.uk/product/Get/Irwin-Irw10502738-5709131135579-Auger-Drill-Bit-5Mm-X-150Mm.

?

Ha, snap! Just ordered this - https://www.amazon.co.uk/Irwin-1050...9295925&s=diy&sprefix=5mm+auger,diy,57&sr=1-3

 

[Temmy]

150mm will be too short to drill a 150mm deep hole, @foxhole, the actual cutting length of that will be around 100 to 110mm

I'll give it a go. I'm using a spade bit to open up a hole first (dowel pegs going on top) so the length + impact driver for the screws might be enough for what I need it to do.

 

[Deleted member 174758]

Thought you wanted a 150mm deep hole. And why 5mm? (odd size for a dowel) Surely you'd just want to drill a single clean hole? (and an auger bit is far better at that)

 

[foxhole]

150mm will be too short to drill a 150mm deep hole, @foxhole, the actual cutting length of that will be around 100 to 110mm

Bits 180mm , 20mm in chuck so will do 150mm holes .

 

[Deleted member 174758]

The one you posted a link to is total length 150mm working length 73mm. Auger bits aren't sold on depth of cut. My 235mm augers cut about 150 to 180mm depth - so not 20mm in the chuck. AFAIK this is the norm

 

[foxhole]

OP link shows 180mm length.

 

[Deleted member 174758]

It says "Dimensions: 12 x 180 x 12mm" which is the size of the packaging (tube or box) it comes in. The auger bit size at the top of the page is clearly stated as "Irwin 105027385 5 x 150mm Auger Drill Bit", or the dimension is a typical misleading Amazon description. BtW how does a 5mm diameter hole get drilled by an 8mm bit? As the FFX site states, "Length 150mm, working length 73mm"...

 

[Temmy]

150mm will be too short to drill a 150mm deep hole, @foxhole, the actual cutting length of that will be around 100 to 110mm

@JobAndKnock you were totally right. It wasn't deep enough at all to get the screw in.
The screw I'm using is 6.7 x 150. My understanding was the pilot hole needs to be a few mm smaller for the screw to have something to bite into. In this case would you still suggest a 6mm auger?

 

[Deleted member 174758]

I'm always a bit leary of Amazon descriptions, but equally machine auger bits have always seemed to start at 6mm in the past. Hand auger bits, designed to be used in a bit brace, used to start at 3/16in or 4.8mm, but they are increasingly difficult to get hold of and TBH they aren't designed to be used in a power tool

You are right about the pilot hole needing to be a bit smaller, but if it's too small with such a long screw the screw can wind-up (twist) and snap off like a carrot, especially with softer screw materials like stainless steel or brass. And that is certainly a very long screw! TBH I didn't realise anyone did stainless steel screws of that size. Why so long?

If the screw thread extends for only a short distance in that 150mm (e.g. 40mm) you might need a smaller pilot, but for 100mm of thread length into timber 6mm should suffice

Anyway, try this £3.29 clearance offer from Toolstation - 6mm diameter, 235mm long, working length 160mm. It's a Heller brand. I have a few Heller auger bits in my auger bit roll and they're reasonable quality (i.e straight, reasonably sharp, more or less the size they say they are and they can be re-sharpened). Alternatively, on eBay, there's this Bosch 6mm auger bit, 235mm long x 160mm working length. Cheapest for this item on Amazon is nearly 3 times the price, at £12.79!

 

[Temmy]

I'm always a bit leary of Amazon descriptions, but equally machine auger bits have always seemed to start at 6mm in the past. Hand auger bits, designed to be used in a bit brace, used to start at 3/16in or 4.8mm, but they are increasingly difficult to get hold of and TBH they aren't designed to be used in a power tool

You are right about the pilot hole needing to be a bit smaller, but if it's two small with such a long screw the screw can wind-up (twist) and snap off like a carrot, especially with softer screw materials like stainless steel or brass. That is certainly a very long screw! TBH I didn't think anyone did stainless steel screws of that size. Why so long?

If the screw thread extends for only a short distance in that 150mm (e.g. 40mm) you might need a smaller pilot, but for 100mm of thread length into timber 6mm should suffice

Anyway, try this £3.29 clearance offer from Toolstation - 6mm diameter, 235mm long, working length 160mm. It's a Heller brand. I have a few Heller auger bits in my auger bit roll and they're reasonable quality (i.e straight, reasonably sharp, more or less the size they say they are and they can be re-sharpened). Alternatively, on eBay, there's this Bosch 6mm auger bit, 235mm long x 160mm working length. Cheapest for this item on Amazon is nearly 3 times the price, at £12.79!

The screw is for attaching two courses of horizontally flat oak sleepers together, which total 200mm in height. Here's the screw on Amazon. The dimensions of the thread are probably better shown in this photo:

 

[foxhole]

Too long , you only need 120mm for 200mm total , 30mm deep 12mm hole on top sleeper to allow the head to sink in giving you 50mm into the bottom sleeper .Stainless steel can be weaker and snap easier .