Use a spade bit for drilling holes for coach bolts?

[ToolbeltDandy]

I need to drill holes to attach newel posts (90 mm x 90 mm) to deck joists (45 mm). I think it would be ideal to clamp the post in place and then drill the holes in both the post and joist at the same time but I don't know whether the "twirly bit" (as my mum calls it) is long enough on a 10 mm wood drill bit (I don't think it is). Should I use a spade bit for this? ToolStation has this nice long one.

Also, for M10 coach bolts, I should use exactly 10 mm holes? I figure so, but sometimes I figure wrong

 

[Monkeh]

Why not measure your bits?

And yes, a spade bit will be fine. As would an auger or a long HSS or brad point. It's a hole you need, it doesn't terribly matter how you drill it.

 

[ToolbeltDandy]

I know it's not long enough on the bits I currently own, but I'll make a trip out tomorrow. I've never used a spade bit before so I thought I ought to ask in case they're not appropriate for this purpose. It would waste a lot of time and effort to find out they're not after buying and using it. :/ Thanks for your guidance

 

[Monkeh]

Spade bits will be fine for boring a hole, just beware that the exit will be messy. Clamp a spare piece of wood over the end to get a clean exit.

 

[big-all]

i personaly stop 6mm short with a spade bit and drill from the other side where the point has broken through

but as said a bit off wood in this instance clamped on as breakout could be expensive

 

[Monkeh]

I find the clamped scrap wood method easier and more accurate, personally. And I have loads of old floorboard and bits of pine board etc to sacrifice.

 

[RedHerring2]

A spade bit can easily be extended using an extension bar.

Someone advised me to use torx head bolts so that the head can be 'lost' in the timber. I don't know if it's useful in your situation. The heads are just like coach bolts but with the torx socket in the head. Also useful if removing them at a later date.

 

[opps]

The torx coach bolts will cost more but will drive in faster and with less torque. The torx bit for the drill will also be cheaper than buying a socket attachment for your drill.

the spax ones are good