Pilot Hole Size

[Rick Hughes]

I need to fix some 12mm diam coach screws into wood.

Normal pilot hole rules may not apply to such screws .... these do not have
a tapered shaft ... the main shaft is parallel (8.9mm)

Overall thread diam is 11.6mm

Initial thought are that I could use an 8.5mm pilot hole ..... don't want to
put in too big a hole or it won't provide the fixing load .... and too small
a hole will risk splitting of the wood.

Anybody any guide on this ?

[dave]

On 16/07/2010 23:05, Rick Hughes wrote:
> I need to fix some 12mm diam coach screws into wood.
>
> Normal pilot hole rules may not apply to such screws .... these do not
> have a tapered shaft ... the main shaft is parallel (8.9mm)

As near as dammit to 3/8 of an inch. Use that as a pilot drill.

> Overall thread diam is 11.6mm
>
> Initial thought are that I could use an 8.5mm pilot hole

You could get away with that.

Dave

[brass monkey]

"Rick Hughes" <rick_hughes@remove_me.btconnect.com> wrote in message
news:mZadnVkAuasiSt3R...@bt.com...

Nothing tabular but I fitted a decent sized vice to a ~40mm chipboard
worktop with similar bolts, maybe 10mm. Obviously the material and depth
will make a difference but I think you're not far away with your 8.5mm hole.
I measured the shaft and drilled a size or two down then tried to screw in
the bolt and increased the size as necessary. You'll soon feel if it's gonna
get too tight (remember butter/candle wax on the thread). Admittedly,
chipboard is fairly forgiving.

[NT]

On Jul 16, 11:05 pm, "Rick Hughes"

Driling a hole thats the inner diameter of the shank should work ok.
If the bolt gets too tight on the way it you can always enlarge it
very slightly.

NT

[Dave Baker]

"Rick Hughes" <rick_hughes@remove_me.btconnect.com> wrote in message
news:mZadnVkAuasiSt3R...@bt.com...

Assuming this is not hardwood you can go a little smaller than the core
diameter but not by more than 1mm I would say so your 8.5mm looks fine. You
will however need a clearance hole for any unthreaded length of screw under
the head. If you mark your drill bits with masking tape as depth guides you
can drill the pilot hole for the full length and then the clearance hole for
the top part.

If I were you I'd test the fitment on a bit of scrap wood first and make
sure that your chosen pilot hole size doesn't require too much force to fit
a screw.
--
Dave Baker

[John Rumm]

On 16/07/2010 23:05, Rick Hughes wrote:

> I need to fix some 12mm diam coach screws into wood.

What kind of wood, and how close to the edge?

> Normal pilot hole rules may not apply to such screws .... these do not
> have a tapered shaft ... the main shaft is parallel (8.9mm)
>
> Overall thread diam is 11.6mm
>
> Initial thought are that I could use an 8.5mm pilot hole ..... don't
> want to put in too big a hole or it won't provide the fixing load ....
> and too small a hole will risk splitting of the wood.
>
> Anybody any guide on this ?

The hole (if required at all - you could for example drive those screws
into a softwood joist without a hole and little risk of splitting),
wants to be core size or just under. So 8.5 sounds fine in this case.
The more forgiving the wood, the smaller the hole you can use.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
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| John Rumm - john(at)internode(dot)co(dot)uk |
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[Osprey]

Going into 2" thick marine plywood ...... so reasonably tough wood.

[The Medway Handyman]

Rick Hughes wrote:
> I need to fix some 12mm diam coach screws into wood.

Use Turbogold coach screws
http://www.screwfix.com/search.do;jsessionid=U0A5RDKWBLXDWCSTHZOSFFQ?_dyncharset=UTF-8&fh_search=turbo+coach+screw

No need for a pilot hole. Only go up to M10 though.

--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

[Rick Hughes]

"The Medway Handyman" <davi...@no-spam-blueyonder.co.uk> wrote in message
news:_8i0o.34099$qv.1...@newsfe17.ams2...

That is not an option .... for 2 valid reasons ... they don't do 12mm and
they don't do them in 40mm length.
This is to go in existing fittings which are pre-drilled in steel plates for
1/2" coach screws .... and they can't be longer than 40mm or they would
pierce through the 2" plywood.

[Rick Hughes]

"Rick Hughes" <rick_hughes@remove_me.btconnect.com> wrote in message
news:mZadnVkAuasiSt3R...@bt.com...

update - I used 8mm pilot and it worked a treat, easy enough to start, and
pulled up really tight ..... used Vaseline on threads as per normal
practice into wood.

[Styx Lawyer]

In article <_fmdnbg3F-6M8N7R...@bt.com>, rick_hughes@remove_me.btconnect.com
says...

I prefer to use a vegetable based lubricant, such as olive oil, with coach screwws into wood;
rather than a petroleum based product.

[frankk...@btinternet.com]

Poor advice all round really, There are PROPER charts for pilot hole in all sorts of woods, I suggest you look at them.

[Dave Plowman (News)]

In article <977317b8-3717-4656...@googlegroups.com>,

I'd suggest you look at the date of the post you've replied to.

--
*The older you get, the better you realize you were.

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.