Coach bolts - best practise?

[bugbear]

Is it best to square up the hole for the head of a coach bolt, or just just let it force its way in?

It's in sort-of-hard-wood (33 mm of stacked plywood), as a vice mount.

BugBear

 

[Billy Flitch]

If its a hex head drill the hole and then put the bolt in and tap it with a hammer you will have the shape to chisel out.
If its a square cup head drill the hole smack it with a hammer and let the nut pull it home.

 

[sunnybob]

Use the bottom nut to pull the coach bolt into the wood. Put a big washer under the nut to stop the nut being pulled into the wood.
The compression around the square helps to stop movement.

Tighten untill you see the coach bolt head touch the wood, then just a small extra nip, being careful to stop if you see any sign of the wood starting to deform.

 

[Beau]

Second what Bob said

 

[bugbear]

Good info, and a consensus. Thanks to all.

BugBear

 

[SammyQ]

Use the bottom nut to pull the coach bolt into the wood. Put a big washer under the nut to stop the nut being pulled into the wood.
The compression around the square helps to stop movement.

Tighten until you see the coach bolt head touch the wood, then just a small extra nip, being careful to stop if you see any sign of the wood starting to deform.

What Saint Bob (Wearing) of Wem said in many of his articles/books was that that you could crush any bolt head into a hole where the diameter of the hole for it was the same as the narrowest 'across the flats' for the head or nut; the angles would cut their own furrow. He also wrote if you mark the bolt head of conventional bolts onto the timber, then cut -with a sloping downward cut - just inside (0.1mm) the crushed outline to approx the depth of the head. Forcing it into the hole subsequently with the washer/nut regime seated the head firmly, without creating unwanted tension forces around the head and made it look nice, flush with the surface.

Bob also described 'rounding' a bolt head or nut in a lathe - or even, drill press - with a file, then drawing the bolt head/nut into a slightly small hole, bored with an appropriately smaller bit, concentric to the shaft hole. The 'grip' of the wood - as the head/nut was bigger than its hole - was good he reckoned.

Sam, revering the Great Man.