Apart from reasons of practicality, is there any reason for not using
coach screws instead of coach bolts for fixing large timber sections -
ie is the strength and longetivity of the fixing the same?

dg

dg wrote:
Apart from reasons of practicality, is there any reason for not using
coach screws instead of coach bolts for fixing large timber sections -
ie is the strength and longetivity of the fixing the same?

dg

Personally I prefer bolts,, but screws are pretty damned good. Screws
CAN pull out..rare but possible...Bolts OTOH..

On 29 May, 15:41, dg wrote:
Apart from reasons of practicality, is there any reason for not using
coach screws instead of coach bolts for fixing large timber sections -

They're entirely different devices, for different purposes. One's a
bolt, one's a screw.

Bolts are plain-shanked dowels used to resist shearing (sideways)
forces. For convenience in installation compared to a plain dowel, the
ends are threaded so that a locking nut can be attached.

Screws are compression fasteners intended to compress two pieces
together. They shouldn't be loaded sideways in shear, as they're
relatively thin and poorly attached, thus unable to resist this well.

Obviously there's some crossover: bolts in particular can apply
tensile forces, although screws are much less happy in shear. In
principle though, use each for its intended purpose and don't confuse
them. This applies equally to design in wood or metal, although wood
is usually a little less fussy about applying shear to screws than
metal would be.

On 29 May, 16:47, Andy Dingley wrote:
On 29 May, 15:41, dg wrote:

Apart from reasons of practicality, is there any reason for not using
coachscrewsinstead ofcoachboltsfor fixing large timber sections -

They're entirely different devices, for different purposes. One's a
bolt, one's a screw.

Boltsare plain-shanked dowels used to resist shearing (sideways)
forces. For convenience in installation compared to a plain dowel, the
ends are threaded so that a locking nut can be attached.

Screwsare compression fasteners intended to compress two pieces
together. They shouldn't be loaded sideways in shear, as they're
relatively thin and poorly attached, thus unable to resist this well.

Obviously there's some crossover:boltsin particular can apply
tensile forces, althoughscrewsare much less happy in shear. In
principle though, use each for its intended purpose and don't confuse
them. This applies equally to design in wood or metal, although wood
is usually a little less fussy about applying shear toscrewsthan
metal would be.

I would have thought that say a 100mm long 10mm dia coach screw would
have an almost equal shear strength to a similar sized coach bolt?

I can see how a coach bolt with washers would resist being pulled out,
and coach screw could potentially be weaker in this respect
(limitations of the timber not the screw), but for lateral shear, both
would seem equally adequate.

dg

On 29 May, 15:41, dg wrote:
Apart from reasons of practicality, is there any reason for not using
coach screws instead of coach bolts for fixing large timber sections -
ie is the strength and longetivity of the fixing the same?

dg

For a start lets do the pedant thing and at least get them called by
their right names - they are "coach bolts" and "carriage screws".

The argument on sheer and tensile is cobblers as diameter for diameter
the sheer strength is going to be the same. On the other hand the
tensile strength of a bolted joint with a suitable load spreading
plate is clearly always going to be greater than a screw into the
wood. The choice is related to whether you can get at both sides of
the joint - if you can then its a bolt - if you can't it's a screw.
Can't really be simpler can it?

Rob

On 29 May, 15:41, dg wrote:
Apart from reasons of practicality, is there any reason for not using
coach screws instead of coach bolts for fixing large timber sections -
ie is the strength and longetivity of the fixing the same?

dg

Basically screws are for fixing a thing TO a thing, bolts for fixing
things TOGETHER.

cheers
Jacob

On 29 May, 17:10, dg wrote:

I would have thought that say a 100mm long 10mm dia coach screw would
have an almost equal shear strength to a similar sized coach bolt?

Perhaps, but a screw in a hole has much less _overall_ shear strength
than a similar bolt. It's not about the screw being weaker, or even
the core of the screw being smaller than the overall diameter, it's
more about the relative strength against shear of screwthreads vs.
plain shanked dowels.

For wood it's less of a problem as wood isn't especially strong
against any shear force applied to a narrow steel dowel. For metal
it's significantly different -- no competent design shear-loads a
screwthread when it ought to be using a plain-shanked bolt, often in a
reamed and tightly fitting hole.

In an earlier contribution to this discussion,
Andy Dingley wrote:

On 29 May, 17:10, dg wrote:

I would have thought that say a 100mm long 10mm dia coach screw would
have an almost equal shear strength to a similar sized coach bolt?

Perhaps, but a screw in a hole has much less _overall_ shear strength
than a similar bolt. It's not about the screw being weaker, or even
the core of the screw being smaller than the overall diameter, it's
more about the relative strength against shear of screwthreads vs.
plain shanked dowels.

For wood it's less of a problem as wood isn't especially strong
against any shear force applied to a narrow steel dowel. For metal
it's significantly different -- no competent design shear-loads a
screwthread when it ought to be using a plain-shanked bolt, often in a
reamed and tightly fitting hole.

It's all a bit academic anyway, because if you hold two bits of wood tightly
together - be it with a bolt or screw - any shear force if provided by the
friction between the mating surfaces rather than by the bolt or screw.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On 29 May, 17:59, robgraham wrote:

The argument on sheer and tensile is cobblers as diameter for diameter
the sheer strength is going to be the same.

I'll take Machinery's Handbook as authoritative here, over someone who
confuses "shear" and "sheer".

The choice is related to whether you can get at both sides of
the joint - if you can then its a bolt - if you can't it's a screw.

That's a question as to whether you're using a loose nut or not, not
what type of fastener you've used.

A bolt (albeit not a coach bolt) can use a fixed nutplate or a tapped
hole and be inserted by rotating the bolt from one side. Conversely a
parallel-threaded screw can have a nut applied to it.

On 29 May, 19:00, "Roger Mills" wrote:

It's all a bit academic anyway, because if you hold two bits of wood tightly
together - be it with a bolt or screw - any shear force if provided by the
friction between the mating surfaces rather than by the bolt or screw.

Not good design though. It's very dificult (i.e. impossibly
impractical) to maintain compressive forces and thus friction in a
design of bolted timber. Moisture or thermal movement, then
compressive yield in the timber, cause such a joint to go loose and
fail after a few seasons.

In an earlier contribution to this discussion,
Andy Dingley wrote:

On 29 May, 19:00, "Roger Mills" wrote:

It's all a bit academic anyway, because if you hold two bits of wood
tightly together - be it with a bolt or screw - any shear force if
provided by the friction between the mating surfaces rather than by
the bolt or screw.

Not good design though. It's very dificult (i.e. impossibly
impractical) to maintain compressive forces and thus friction in a
design of bolted timber. Moisture or thermal movement, then
compressive yield in the timber, cause such a joint to go loose and
fail after a few seasons.

True, but you can mitigate against that by using a 'spikey plate'[1] between
the 2 bits of wood. That will keep the shear force away from the bolt even
if the full compressive force isn't maintained.

[1] Not sure of the technical term!
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

Roger Mills wrote:
In an earlier contribution to this discussion,
Andy Dingley wrote:

On 29 May, 17:10, dg wrote:

I would have thought that say a 100mm long 10mm dia coach screw
would have an almost equal shear strength to a similar sized coach
bolt?

Perhaps, but a screw in a hole has much less _overall_ shear strength
than a similar bolt. It's not about the screw being weaker, or even
the core of the screw being smaller than the overall diameter, it's
more about the relative strength against shear of screwthreads vs.
plain shanked dowels.

For wood it's less of a problem as wood isn't especially strong
against any shear force applied to a narrow steel dowel. For metal
it's significantly different -- no competent design shear-loads a
screwthread when it ought to be using a plain-shanked bolt, often in
a reamed and tightly fitting hole.

It's all a bit academic anyway, because if you hold two bits of wood
tightly together - be it with a bolt or screw - any shear force if
provided by the friction between the mating surfaces rather than by
the bolt or screw.

Too true Roger - eveybody forgets that bit.


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257

robgraham wrote:
On 29 May, 15:41, dg wrote:
Apart from reasons of practicality, is there any reason for not using
coach screws instead of coach bolts for fixing large timber sections
- ie is the strength and longetivity of the fixing the same?

dg

For a start lets do the pedant thing and at least get them called by
their right names - they are "coach bolts" and "carriage screws".

The argument on sheer and tensile is cobblers as diameter for diameter
the sheer strength is going to be the same. On the other hand the
tensile strength of a bolted joint with a suitable load spreading
plate is clearly always going to be greater than a screw into the
wood. The choice is related to whether you can get at both sides of
the joint - if you can then its a bolt - if you can't it's a screw.
Can't really be simpler can it?

And you can't easily use a bolt to make a tee joint.


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257

The Natural Philosopher wrote:
dg wrote:
Apart from reasons of practicality, is there any reason for not using
coach screws instead of coach bolts for fixing large timber sections
- ie is the strength and longetivity of the fixing the same?

dg

Personally I prefer bolts,, but screws are pretty damned good. Screws
CAN pull out..rare but possible...Bolts OTOH..

I use loads of the Screwfix Turbo Coach Screws
https://www.screwfix.com/app/sfd/cat...67177&id=46700

2 or 3 of those in 6 x 2 timber and it aint not going anywhere. Incredibly
strong joint.


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257

In an earlier contribution to this discussion,
The Medway Handyman wrote:

The Natural Philosopher wrote:
dg wrote:
Apart from reasons of practicality, is there any reason for not
using coach screws instead of coach bolts for fixing large timber
sections - ie is the strength and longetivity of the fixing the
same? dg

Personally I prefer bolts,, but screws are pretty damned good. Screws
CAN pull out..rare but possible...Bolts OTOH..

I use loads of the Screwfix Turbo Coach Screws
https://www.screwfix.com/app/sfd/cat...67177&id=46700

2 or 3 of those in 6 x 2 timber and it aint not going anywhere. Incredibly
strong joint.


Yes, they're good.

Pity that even Screwfix doesn't know the difference between a *coach* bolt
and a *carriage* screw! g
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Tue, 29 May 2007 19:58:59 +0100, "Roger Mills"
wrote:

True, but you can mitigate against that by using a 'spikey plate'[1] between
the 2 bits of wood.

You'll see me using "spikey plates" after they pry my twybill from my
cold, dead fingers....

On 29 May, 19:58, "Roger Mills" wrote:
In an earlier contribution to this discussion,
Andy Dingley wrote:

On 29 May, 19:00, "Roger Mills" wrote:

It's all a bit academic anyway, because if you hold two bits of wood
tightly together - be it with a bolt or screw - any shear force if
provided by the friction between the mating surfaces rather than by
the bolt or screw.

Not good design though. It's very dificult (i.e. impossibly
impractical) to maintain compressive forces and thus friction in a
design of bolted timber. Moisture or thermal movement, then
compressive yield in the timber, cause such a joint to go loose and
fail after a few seasons.

True, but you can mitigate against that by using a 'spikey plate'[1] between
the 2 bits of wood. That will keep the shear force away from the bolt even
if the full compressive force isn't maintained.

[1] Not sure of the technical term!
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

Timber connectors

dg

On 29 May, 17:59, robgraham wrote:


For a start lets do the pedant thing and at least get them called by
their right names - they are "coach bolts" and "carriage screws".


I thought they were just different words for the same thing - after
all isn't a carriage a coach?

Tomatoes, tomartoes?

dg

On 29 May 2007 16:08:41 -0700, dg mused:

On 29 May, 17:59, robgraham wrote:


For a start lets do the pedant thing and at least get them called by
their right names - they are "coach bolts" and "carriage screws".


I thought they were just different words for the same thing - after
all isn't a carriage a coach?

Tomatoes, tomartoes?

You see, one of those is a made up word and one isn't, that's a
different thing altogether.
--
Regards,
Stuart.

Bolt or screw?

http://www.screwfix.com/app/sfd/cat/...20300&id=83889

robgraham wrote:
On 29 May, 15:41, dg wrote:
Apart from reasons of practicality, is there any reason for not using
coach screws instead of coach bolts for fixing large timber sections -
ie is the strength and longetivity of the fixing the same?

dg

For a start lets do the pedant thing and at least get them called by
their right names - they are "coach bolts" and "carriage screws".

The argument on sheer and tensile is cobblers as diameter for diameter
the sheer strength is going to be the same.

This is not the case. The key difference is that the valley of the
screw threads concentrate the sheer forces on the metal at the bottom
of the vally on the loaded side. With a plain shanked bolt this
concentration does not happen and the load is distributed over a
larger area.

Guy
-- --------------------------------------------------------------------
Guy Dawson I.T. Manager Crossflight Ltd

wrote:
Bolt or screw?

http://www.screwfix.com/app/sfd/cat/...20300&id=83889

Screw!

Guy, who's not thinking run or F**K!
-- --------------------------------------------------------------------
Guy Dawson I.T. Manager Crossflight Ltd

Roger Mills wrote:

[1] Not sure of the technical term!

http://www.screwfix.com/app/sfd/cat/...99094&ts=05307

--
Cheers,

John.

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