I am building a viaduct (OO).  I have some scale drawings from the
ECML and a reasonable idea of the geometry, but it needs to be
curved.  Building this is non-trivial.  I have hit upon an idea: I
will build the trackbed from 6mm ply, cut to the 4' radius curve I
want, then make a template for the front faces of the pillars and
arches out of 6mm hardboard, which bends easily.  This I can then
put in place, butt 100mm PAR timber behind to form the core of the
pillars and take the weight.  I think I'll use the 15' prototype
radius for the arches and not worry about the rear arches being
wider, the rear will have a scenic backdrop and won't really be
visible.  The calculations are easier if I stick with the 15'
radius.

So, the hardboard will also form the retaining walls, and the
trackbed board will be approximately the scale width between the
walls on the prototype, which is 25'6" scaled at 4mm which is of
course wrong for the track gauge, but this is not finescale.
Actually the bed will be 6mm over as the total width of the parapets
on the prototype is 4'6" (2'3" each, according to my measurements
from the drawings); this leaves a convenient 3mm to make up with art
board which will conceal both the inner textured face of the
hardboard and the joint between hardboard and plywood.

I think that should do it.  I will work out the brick finishing
detail later, I don't think I will be using chads or embossed
finish, as the arches are all headers arranged radially, although I
guess I could score the hardboard or even cut a fine groove with a
suitable lino cutting tool.  Anyone tried anything like that?  I'm
guessing it would take a loooooong time!

Guy
-- 
May contain traces of irony.  Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

Just zis Guy, you know? wrote:
> I am building a viaduct (OO).  I have some scale drawings from the
> ECML and a reasonable idea of the geometry, but it needs to be
> curved.  Building this is non-trivial.  I have hit upon an idea: I
> will build the trackbed from 6mm ply, cut to the 4' radius curve I
> want, then make a template for the front faces of the pillars and
> arches out of 6mm hardboard, which bends easily.  This I can then
> put in place, butt 100mm PAR timber behind to form the core of the
> pillars and take the weight. ................
>
> So, the hardboard will also form the retaining walls, and the
> trackbed board will be approximately the scale width between the
> walls on the prototype, which is 25'6" scaled at 4mm which is of
> course wrong for the track gauge, but this is not finescale.
> Actually the bed will be 6mm over as the total width of the parapets
> on the prototype is 4'6" (2'3" each, according to my measurements
> from the drawings); this leaves a convenient 3mm to make up with art
> board which will conceal both the inner textured face of the
> hardboard and the joint between hardboard and plywood.
>
> I think that should do it.  I will work out the brick finishing
> detail later, I don't think I will be using chads or embossed
> finish, as the arches are all headers arranged radially, although I
> guess I could score the hardboard or even cut a fine groove with a
> suitable lino cutting tool.  Anyone tried anything like that?  I'm
> guessing it would take a loooooong time!

Things which I'd think about:

1) Vehicle overhangs means that they might strike the viaduct walls.  On a 
fairly tight corner the overhangs on vehicles can be considerable. I would 
measure this carefully (both inside and outside overhang), and then allow a 
bit more because models sometimes come out over-scale(*), and stock will 
"hunt" on the track and within sloppy journals to some extent.   4ft radius 
is fairly generous, but you'll still have some overhang.

2) Front face.  I dislike hardboard. Its cheap, but that's about it. You can 
get very thin plywood (1mm!) which curves easily.  I might use foamboard (a 
bit thick for the above trackbed walls), which can be bought from art shops 
(expensive) and sometimes scrounged from old shop window displays (free).

3) Stone/brickwork. If planning to scribe it, then usual technique is to 
apply DAS modelling clay in very thin layer to front face (often with aid of 
PVA to help sticking). Then scribe with dental probe, old shaped nail in 
block of wood, or similar.  Some of the very very best models are made this 
way.  Alternative might be large acres of plasticard embossed brick, or even 
printed brick papers if the viewing distance is appropriate (could always 
write software to generate brick patterns and fill colours in Corel Draw (or 
similar) and produce any pattern required on home printer).



(* I have a friend who built a beautiful small bridge who now has to cut it 
down the middle and widen by about a milimetre to clear the stock he built 
for the model. )

- Nigel


-- 
Nigel Cliffe,
Webmaster at http://www.2mm.org.uk/

On Sun, 15 Jun 2008 19:36:52 +0100, "Nigel Cliffe" 
said in <g33ne7$ree$1@news.albasani.net>:

>1) Vehicle overhangs means that they might strike the viaduct walls.

Yup, the curves are being double-checked as we speak.  This is one
reason I decided to stick with double and not quadruple track round
some of the layout, the overhangs are a pestilential nuisance.
Luckily 4' is the smallest radius on the layout, the old one had 3'
curves which were much more of a problem.

>2) Front face.  I dislike hardboard. Its cheap, but that's about it. You can 
>get very thin plywood (1mm!) which curves easily.  

I'll see if I can find that at my woodyard, but the HB is OK in my
experience, stable as long as you seal it properly.  This is in an
outbuilding, though, so may get damper than I'd like.  

Looking around, I can find 3mm flexible ply in 8 x 4 sheets for a
reasonable price, that's the way to go I think.  I kind of wish I'd
built the main curves with that, I used 6mm because it's what I had
(and what the local timber yard sells) and it does work, but it was
hard work curving it.

>3) Stone/brickwork. If planning to scribe it, then usual technique is to 
>apply DAS modelling clay in very thin layer to front face (often with aid of 
>PVA to help sticking). Then scribe with dental probe, old shaped nail in 
>block of wood, or similar.  

I'd forgotten this trick, which is perfect for the job.  Thanks.  I
remember now that you can roll the clay really thin, onto board, and
then roll it for the inside of the arches.  I've found some
instructions for that.  A massive improvement over what I was
thinking of doing!

Great tips, thanks.

Guy
-- 
May contain traces of irony.  Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

On Jun 15, 7:05 pm, "Just zis Guy, you know?"  wrote:
> I am building a viaduct (OO).  I have some scale drawings from the
> ECML and a reasonable idea of the geometry, but it needs to be
> curved.  Building this is non-trivial.  I have hit upon an idea: I
> will build the trackbed from 6mm ply, cut to the 4' radius curve I
> want, then make a template for the front faces of the pillars and
> arches out of 6mm hardboard, which bends easily.  This I can then
> put in place, butt 100mm PAR timber behind to form the core of the
> pillars and take the weight.  I think I'll use the 15' prototype
> radius for the arches and not worry about the rear arches being
> wider, the rear will have a scenic backdrop and won't really be
> visible.  The calculations are easier if I stick with the 15'
> radius.
>
> So, the hardboard will also form the retaining walls, and the
> trackbed board will be approximately the scale width between the
> walls on the prototype, which is 25'6" scaled at 4mm which is of
> course wrong for the track gauge, but this is not finescale.
> Actually the bed will be 6mm over as the total width of the parapets
> on the prototype is 4'6" (2'3" each, according to my measurements
> from the drawings); this leaves a convenient 3mm to make up with art
> board which will conceal both the inner textured face of the
> hardboard and the joint between hardboard and plywood.
>
> I think that should do it.  I will work out the brick finishing
> detail later, I don't think I will be using chads or embossed
> finish, as the arches are all headers arranged radially, although I
> guess I could score the hardboard or even cut a fine groove with a
> suitable lino cutting tool.  Anyone tried anything like that?  I'm
> guessing it would take a loooooong time!
>
> Guy
> --
> May contain traces of irony.  Contents liable to settle after posting.http://www.chapmancentral.co.uk
>
> 85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

I built a bridge which needed a curved exit ( it was removable for
access to other parts).  I quickly discovered the need for retaining
walls to prevent major damage due to accidents and the clearance
problem ( 1M radius).  The thing which really caused grief was the
entry/exit to the curved end . This eventually came good when I banked
the track in a more prototypical manner. This eventually cured
problems in other places too.
The main lesson was not to "finish" the job until thoroughly tested
( it is still not decorated!)

Regards

"Just zis Guy, you know?"  wrote in message 
news:ipha54ha5d8tiovj520bcing8mqgfdq3h2@4ax.com...
>I am building a viaduct (OO).  I have some scale drawings from the
> ECML and a reasonable idea of the geometry, but it needs to be
> curved.  Building this is non-trivial.  I have hit upon an idea: I
> will build the trackbed from 6mm ply, cut to the 4' radius curve I
> want, then make a template for the front faces of the pillars and
> arches out of 6mm hardboard, which bends easily.  This I can then
> put in place, butt 100mm PAR timber behind to form the core of the
> pillars and take the weight.  I think I'll use the 15' prototype
> radius for the arches and not worry about the rear arches being
> wider, the rear will have a scenic backdrop and won't really be
> visible.  The calculations are easier if I stick with the 15'
> radius.
>
> So, the hardboard will also form the retaining walls, and the
> trackbed board will be approximately the scale width between the
> walls on the prototype, which is 25'6" scaled at 4mm which is of
> course wrong for the track gauge, but this is not finescale.
> Actually the bed will be 6mm over as the total width of the parapets
> on the prototype is 4'6" (2'3" each, according to my measurements
> from the drawings); this leaves a convenient 3mm to make up with art
> board which will conceal both the inner textured face of the
> hardboard and the joint between hardboard and plywood.
>
> I think that should do it.  I will work out the brick finishing
> detail later, I don't think I will be using chads or embossed
> finish, as the arches are all headers arranged radially, although I
> guess I could score the hardboard or even cut a fine groove with a
> suitable lino cutting tool.  Anyone tried anything like that?  I'm
> guessing it would take a loooooong time!
>
> Guy
> -- 
> May contain traces of irony.  Contents liable to settle after posting.
> http://www.chapmancentral.co.uk
>
> 85% of helmet statistics are made up, 69% of them at CHS, Puget Sound


Generally on prototype viaducts the arches were the same radius front and 
back, and the curve was taken up by the pillars being slightly wedge-shaped. 
I hope this helps your calculations.

-- 

Regards

John

In message <48564dcd$0$1026$afc38c87@news.optusnet.com.au>
          "John Nuttall"  wrote:

> "Just zis Guy, you know?"  wrote in message 
> news:ipha54ha5d8tiovj520bcing8mqgfdq3h2@4ax.com...
> >I am building a viaduct (OO).  I have some scale drawings from the
> > ECML and a reasonable idea of the geometry, but it needs to be
> > curved.  Building this is non-trivial.  I have hit upon an idea: I
> > will build the trackbed from 6mm ply, cut to the 4' radius curve I
> > want, then make a template for the front faces of the pillars and
> > arches out of 6mm hardboard, which bends easily.  This I can then
> > put in place, butt 100mm PAR timber behind to form the core of the
> > pillars and take the weight.  I think I'll use the 15' prototype
> > radius for the arches and not worry about the rear arches being
> > wider, the rear will have a scenic backdrop and won't really be
> > visible.  The calculations are easier if I stick with the 15'
> > radius.
> >
> > So, the hardboard will also form the retaining walls, and the
> > trackbed board will be approximately the scale width between the
> > walls on the prototype, which is 25'6" scaled at 4mm which is of
> > course wrong for the track gauge, but this is not finescale.
> > Actually the bed will be 6mm over as the total width of the parapets
> > on the prototype is 4'6" (2'3" each, according to my measurements
> > from the drawings); this leaves a convenient 3mm to make up with art
> > board which will conceal both the inner textured face of the
> > hardboard and the joint between hardboard and plywood.
> >
> > I think that should do it.  I will work out the brick finishing
> > detail later, I don't think I will be using chads or embossed
> > finish, as the arches are all headers arranged radially, although I
> > guess I could score the hardboard or even cut a fine groove with a
> > suitable lino cutting tool.  Anyone tried anything like that?  I'm
> > guessing it would take a loooooong time!
> >
> > Guy
> > -- 
> > May contain traces of irony.  Contents liable to settle after posting.
> > http://www.chapmancentral.co.uk
> >
> > 85% of helmet statistics are made up, 69% of them at CHS, Puget Sound
> 
> 
> Generally on prototype viaducts the arches were the same radius front and 
> back, and the curve was taken up by the pillars being slightly wedge-shaped. 
> I hope this helps your calculations.
> 

Sorry. missed the last post...

You could score the hardboard with one on those old-fashioned line
markers - with a slightly blunter point... should keep you occupied
for a day or two!
                    _
                 __|_|_<-- "locking
                |      |    key"    |
         _______|      |____________|_______
         |      |      |                    |
         |______|      |____________________|
                |______|            | <-- pointy bit
                
                   ^ movable block
                   
Cheers
Richard
         
-- 
www.beamends-lrspares.co.uk       sales@beamends-lrspares.co.uk
              I have become... comfortably numb

On Mon, 16 Jun 2008 02:29:13 -0700 (PDT), Sailor
 said in
:

>The main lesson was not to "finish" the job until thoroughly tested

Finished? Small danger of that.  I live in uk.rec.sheds.

Guy
-- 
May contain traces of irony.  Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

On Mon, 16 Jun 2008 12:44:16 +0000, beamendsltd
 said in
<bef656b04f%beamendsltd@btconnect.com>:

>You could score the hardboard with one on those old-fashioned line
>markers - with a slightly blunter point... should keep you occupied
>for a day or two!

Is a marking gauge, innit?

Guy
-- 
May contain traces of irony.  Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

In message 
          "Just zis Guy, you know?"  wrote:

> On Mon, 16 Jun 2008 12:44:16 +0000, beamendsltd
>  said in
> <bef656b04f%beamendsltd@btconnect.com>:
> 
> >You could score the hardboard with one on those old-fashioned line
> >markers - with a slightly blunter point... should keep you occupied
> >for a day or two!
> 
> Is a marking gauge, innit?
> 

Dunno - but it's the first thing we had to make in woodwork at school!

Shortly before the dinosaurs died.

> Guy

Cheers
Richard

-- 
www.beamends-lrspares.co.uk       sales@beamends-lrspares.co.uk
              I have become... comfortably numb

John Nuttall wrote:
> 
> "Just zis Guy, you know?"  wrote in message
> news:ipha54ha5d8tiovj520bcing8mqgfdq3h2@4ax.com...
> >I am building a viaduct (OO).  I have some scale drawings from the
> > ECML and a reasonable idea of the geometry, but it needs to be
> > curved.  Building this is non-trivial.  I have hit upon an idea: I
> > will build the trackbed from 6mm ply, cut to the 4' radius curve I
> > want, then make a template for the front faces of the pillars and
> > arches out of 6mm hardboard, which bends easily.  This I can then
> > put in place, butt 100mm PAR timber behind to form the core of the
> > pillars and take the weight.  I think I'll use the 15' prototype
> > radius for the arches and not worry about the rear arches being
> > wider, the rear will have a scenic backdrop and won't really be
> > visible.  The calculations are easier if I stick with the 15'
> > radius.
> >
> > So, the hardboard will also form the retaining walls, and the
> > trackbed board will be approximately the scale width between the
> > walls on the prototype, which is 25'6" scaled at 4mm which is of
> > course wrong for the track gauge, but this is not finescale.
> > Actually the bed will be 6mm over as the total width of the parapets
> > on the prototype is 4'6" (2'3" each, according to my measurements
> > from the drawings); this leaves a convenient 3mm to make up with art
> > board which will conceal both the inner textured face of the
> > hardboard and the joint between hardboard and plywood.
> >
> > I think that should do it.  I will work out the brick finishing
> > detail later, I don't think I will be using chads or embossed
> > finish, as the arches are all headers arranged radially, although I
> > guess I could score the hardboard or even cut a fine groove with a
> > suitable lino cutting tool.  Anyone tried anything like that?  I'm
> > guessing it would take a loooooong time!
> >
> > Guy
> > --
> > May contain traces of irony.  Contents liable to settle after posting.
> > http://www.chapmancentral.co.uk
> >
> > 85% of helmet statistics are made up, 69% of them at CHS, Puget Sound
> 
> Generally on prototype viaducts the arches were the same radius front and
> back, and the curve was taken up by the pillars being slightly wedge-shaped.
> I hope this helps your calculations.
> 
> --
> 
> Regards
> 
> John


To make an arch that is a different radius on one side as compared to
the other, one would need fractionally tapered bricks. 
Alternatively one could make a series of narrow parallel arches, each
with a brick less than the one on it's larger side. Neither method is
really practical. 
Of course if the span of each arch differs then the height of the arch
will also differ, which introduces another geometrical difficulty.
As the required radius decreases, the difference in length of the pillar
sides becomes greater if one's arch is the same radius on both sides,
until one reaches the point where the pillar ceases to exit on one side.
I built a brick arched viaduct on 18-24" radius ("J" shaped) and
effectively foreshortened the inside as against the outside, so that the
lengths differed but the heights remained the same. The arch underside
brickpaper was a very odd shape, (edges cut in-situae)  but by making
that in two halves with the odd shaped bricks at the top of the arch it
looked ok. Luckily it was in from the edge of the baseboard so one
couldn't get one's eyelevel to a position to look up under the tighter
curved arches.

The structure of the viaduct was MDF deck and pillar faces with the
outer surfaces made of old floor lino/vinyl tacked on.

Regards,
Greg.P.

On Tue, 17 Jun 2008 08:53:56 +1200, Greg Procter
 said in :

>To make an arch that is a different radius on one side as compared to
>the other, one would need fractionally tapered bricks. 

Yes, I get this.

My plan is to build the arches parallel and bodge the far side of
the pillars which will not be visible to the operator.

Guy
-- 
May contain traces of irony.  Contents liable to settle after posting.
http://www.chapmancentral.co.uk

85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

"Just zis Guy, you know?" wrote:
> 
> On Tue, 17 Jun 2008 08:53:56 +1200, Greg Procter
>  said in :
> 
> >To make an arch that is a different radius on one side as compared to
> >the other, one would need fractionally tapered bricks.
> 
> Yes, I get this.
> 
> My plan is to build the arches parallel and bodge the far side of
> the pillars which will not be visible to the operator.
> 

The main problem with that construction is that you will always know!
=8^))))

Now that I think about it, why not do the under-arch brickwork on CAD
generated paper on a home printer?
The taper per row would be very small, but of course lots added together
creates the noticable total error.

Greg.P.