Metal hole size for a 10mm bolt?

boardtc

I have to bolt something in my shed roof which takes a 10mm bolt. I used my impact driver to make a pilot hole with a metal screw. I then enlarged the hole with a 8mm drill bit and then further with a 10mm, but the bolt still does not fit. Is the best thing now to buy aa 11mm HSS SDS drill bit and do the same? Not finding it easy to find.

seamus

Yeah, I'd get the 11mm bit. A 12mm would do fine as well. Not as neat, but the head of the bolt will be well wider then 12mm so no biggie. You can also use a washer to be sure.

Before you go traipsing across the city looking for a new drill bit, it might worth trying to gently tap the bolt through. The hole you drilled might be a little bit at an angle or there's a tiny piece of metal in the way.

cruizer101

If is is an M10 bolt the shaft should be no more than 10mm so should fit, maybe a tight fit but should fit, you could stick the 10mm drill on and give it small wiggle when in hole to make it a bit bigger, what are you drilling through and how deep is hole.

jack of all

If you have a large triangular ("three square") file you could use the (blunt) end to ream out the hole to size, working from both sides of the steel.

Lumen

A step drill bit is a useful tool to have in the box.

Melodeon

As you say you made "a pilot hole with a metal screw", I suspect this hole it through the tin sheeting of the shed roof rather than the structural steel?

If so, it's very likely that the hole isn't actually a nice neat 10mm circle, but a vaguely 10mm rounded-triangular shape. This is a well known issue with 2-flute drills hand-held through thin materials.

As already suggested above, stir the drill around in the hole a bit, or run it the whole way through past the flutes to where the shank is a proper circular 10mm.

boardtc

More info: I am drilling through the beam structural steel which is hollow in the middle, so two sheets to get through, and drilling from both sides as it's a beam. I have 8 holes to make, all have the pilot hole made. My existing 10mm hole is a nice neat circle on the exposed side.

Lumen

The hole doesn't need to be super precise if you're using washers (which you should).

As I wrote above, I would use a step drill bit to enlarge the holes, assuming you have direct access to the holes on both sides.

boardtc

Great Lumen, step-bit, so glad I asked, perfect solution, I found this one https://www.amazon.co.uk/dp/B01M97Z7QM, there's also this option https://www.amazon.co.uk/dp/B07XXWCPB7, what you think?

Lumen

Haven't used that brand myself. They smell suspiciously cheap.

The Erbauer stuff I have used (though not this particular bit) and they're OK for the money.

https://www.screwfix.ie/p/erbauer-step-drill-bit-4-20mm/3656v

boardtc

Thanks! Not finding a SDS on there....

Lumen

https://www.boards.ie/discussion/comment/117946358#Comment_117946358

Not sure why you'd use an SDS (or an impact driver) on metal.

Centre punch, lube with oil, then normal drill, nice and slow with decent pressure, goes through metal in the few jobs I've done.

boardtc

I use my impact driver all the time to attach metal to metal with a screw, is there a better way? The installers of my shed used an impact driver.

My drill is SDS, that's the only reason. But I think I still have an old drill that does not have the legs to get through masonary anymore that I can use, thanks.

Lumen

I meant for drilling metal, but I see you were using a screw for drilling, which confused me. Whatever works I guess!

2011

SDS is normally for masonry drill bits. A chuck can be added to SDS drills which allows standard steel drill bits to be used.

jack of all

https://www.boards.ie/discussion/comment/117945671#Comment_117945671

Thanks Lumen, prompted by your advice I decided I NEED a step drill for my own toolbox, so I went out and bought that very one from Screwfix. Yes, it is cheap but seems nicely machined and worked well on a few scraps of mild steel, so I'd say it's well worth the money and certainly suitable for drilling material up to 4 mm thick or thereabouts. Sorry to be dragging this off topic..

boardtc

Lumen, I picked up that Erbauer step drill bit and got around to the job over the weekend. OMG, the satisfaction when you have the right tool for the job, amazing. A step drill but was so the way to go, superb bit of kit, thanks a million!!