Pilot holes with Coach Screws

[RickH]

Been some years since I used Coach screws (as per DIN571)
I have to fit a number of M12 x 60 screws into the edge of 50mm thick timber studs & wall plates.

These have a shaft diam of 12mm which is also the diam of the lands for most of the length, only aprox the first 15mm is tapered.
The core diam of threaded section is aprox 8.5mm


This will obviously necessitate pilot holes ... Should I aim to use a pilot hole to match the core diameter, i.e 8.5mm ? .. that does not seem to give much meat left for thread to grip ... but perhaps that is enough

 

[xerxes]

I don't use coach screws myself, but I assume the same principles apply as for smaller gauge woodscrews.

The pilot hole should generally be around half the clearance hole for the shank, when fixing into softwood. If screwing into hardwood, make the pilot hole a tad bigger.

See here for a helpful table (imperial only).

 

[^woody^]

I'm a fan of coach screws ..... and impact drivers!

When I've used 8 and 10mm for first fixing, they fly in with the impact driver - with no pilot and no splitting

But for a pilot, a 5 or 6mm bit will do for normal constructional softwood

 

[RickH]

Thanks...

I have a pneumatic impact driver ... didn't think of using that.

Normally just think of it for removing rusted nuts etc.

I'll couple it with a 5mm pilot hole to make sure they go in straight.

This is a 2 part job ... I am using some purpose made 10mm thick galvanised 'L straps' - today I resin fixed in the M16mm steel studs to fix the straps to reinforced concrete slab ...
Tomorrow will be time to fix straps to wall plate and vertical studs.

There is separate post on this :
//www.diynot.com/forums/viewtopic.php?t=162288