Lattice Girder Deck Truss Bridge - Kit bashing

[zr2498]

The plan:

To add a single span, lattice girder deck truss bridge to left side of the stone viaduct as seen towards the back in the photo below. The stone viaduct was constructed using the 'Townstreet' range. The pier and abutments are kit bashed, again using the Townstreet castings.

 

 

 

 

 

The deck truss bridge will be based on the marvelous Findhorn viaduct. Unfortunately there is only space for one span - it will be 530mm long.

 

 

 

 

I will try to use as many components as possible from bridge kits produced by CVMW, plus various bridge girder and kit components that the same company supply separately.

No doubt there will be a great deal of additional styrene profile, and perhaps some details etches to add as I go along.

A picture of finished bridge kits below are very much different to the deck truss bridge, but some components, especially for the deck can be readily adapted.

 

 

 

The exact detail of the Findhorn viaduct cannot easily be copied. Even if I were to get construction drawings, I would need to start from scratch with photoetch design. So being pragmatic, I guess as long as the bridge is of the same proportion, has a similar basic layout and elements of the Findhorn viaduct, I will be satisfied.

One big change though, will be to convert the bridge to double track (to suit my layout). The other requirement is to ensure that the bridge looks British rather than American (as intended for the CVMW kit). The deck will be plated and ballasted unlike the open deck, and lets face it the bridge will end up looking completely different with the truss frames underneath.

Planning and construction has started and I will give an update on progress later this week.

Dave

 

Edited May 25, 2022 by zr2498
Updated. Reload of photos

[zr2498]

Below is the basic frame layout of the truss sections. There will be 4 frames (2 per track).

The number of sections per frame has been reduced from 8 (Findhorn) to 6. By scaling from coach lengths, the bridge span and depth could be estimated, but it will be reduced to 6 sections to align with the pitch of the cross bearers and stringers supplied with the CVMW kit deck arrangement.

 

 

 

Starting with the deck:

Initially, parts are used from the Central Valley Model Works bridge kit

 

 

 

These will include the cross bearers, splice/joiners and stringer plates.

Unlike the kit instructions, in the case of a deck truss bridge, the splice joiners will be flush with the bottom of the cross bearers as both the cross bearers and the stringer will rest on the truss framework.

 

 

 

The assembly is connected (glued) at the pins of the stringers and the holes of the splice joiners only at this stage.

This will allow squaring of the deck to be done after further parts have been added.

 

 

 

 

 

The assembly is 6 sections long instead of the 8 of the Parker truss. The end plates for the deck were subsequently replaced with cross bearers as per the mid sections. This will enable the fixing of the outer part of the deck plate and the handrails to be the same over the entire length (as on the Findhorn).

The splice joiners at the ends were trimmed to give just a small extension on the outside of the cross bearer.

 

 

 

 

 

The deck assembly has been taken as far as possible for now, as I'm waiting for some styrene profiles to make rail bearers, intermediate cross bearers and supports / stiffeners for the deck plate.

 

 

 

Next will be preparation of parts for the truss frames.

 

Edited April 1, 2022 by zr2498
Detail added. Photos reloaded

[zr2498]

The truss framework:

The construction of the basic elements of the Findhorn viaduct girders are varied and complex.

a) The outer beams are plates with attached angle making outward facing flanges. These are either plated, left open with internal gusset strengtheners or laced.

b) The diagonals mostly have inward facing channel sections, with lacing joining the flanges. What is rather strange is that some of the diagonals have different designs which vary as you move between the ends and the centre of each span. Double laced, single laced and simple straps are evident.

The photo below might give some impression.

 

The bridge kit girder components consist of outward facing channel sections connected by full plates, gusset plates or by lacing.

So, some more compromise. A design will be needed to get as close as possible to the prototype.

 

First, the box section girders on the outer part of each frame.

Lower and upper beams

The closest copy is to use the gusseted girders with 'open' design at the lower beam, and closed (outer side fully plated) for the upper beam.

 

 

The end (vertical) beams can be constructed very close to the Findhorn original using

 

 

Just managed to spot the end verticals on this photo.

 

Each of the girder sections is supplied on the sprue in two halves which have to be joined and then cut to length at the optimum position.

To estimate the number needed a few assembled girders are lined up against the original template (6 out of 8 spacings are used for the new bridge).

 

The two diagonals will meet at the lower beam. Note that there are no verticals in the centre portion of the new truss arrangement.

 

Gusset plates will be removed to allow the diagonals to enter the beam.

 

Method for joining and aligning the two halves of the top and bottom gussetted beams

 

Drill bit size No 26 (9/64")

 

Cleaning up following adhesive (showing the 3 types of girders)

 

I reckon 2 pints of outer beams cleaned and ready for cutting after a new template is produced

 

 

Next, to prepare the diagonals

Dave

 

 

 

 

Edited April 26, 2022 by zr2498
One photo removed and detail added / corrected. Photos reloaded second time

[zr2498]

Preparation of the diagonals

It is not easy to see from photographs, but the construction of the diagonals vary across the span.

 

 

 

Although the model will only have 6 sections the different designs can be accommodated.

Here is a schematic of the layout:

 

 

Type A are made by joining the two halves of the narrow size of standard lattice girders

 

 

 

Type B diagonals are made from the larger standard lattice girders but to get a 'finer' rectangular section they are trimmed to give 2.5mm extension below the lattice face. This was done on a Proxxon table saw

 

 

 

The trimmed halves can be joined to form type B. When this is done some of the lacing will be removed (where the diagonals cross).

Type C will be made in a similar way to type B by trimming the section but there will be lacing on one side only.

In this case a plain strip will be added to the laced half at 2.5mm depth to make a channel section.

Fortunately the off cuts from trimming can be reduced in depth to the required 2.5mm. I will show how this is done later.

Type D are simple straps which will be made from lengths with 5.3mm depth. It can be seen from the photographs that these are wider than the other diagonals. This was estimated from a photograph.

 

 

 

Here are some of the prepared parts

 

 

 

 

The parts in the dish above (96 of them), are gusset stay plates which have been cut and shaped from gussetted girder components.

These will be used at the diagonal cross over positions and at the diagonal ends prior to connection into the outer beams.

 

 

 

That's all for now. I plan to continue with the diagonal preparation before moving to the construction of the the outer framework for each truss.

Dave

 

 

 

 

 

Edited April 1, 2022 by zr2498
Diagram and notes correction. Photos reloaded

[zr2498]

A little more preparation done.

The CAD drawing now has the diagonals with measured thickness included. This will enable the cut angles to be made via a template.

 

 

This has been printed out (1:1 scale) and attached to a work board.

 

 

The single laced diagonals need the offcuts, (from the reduced depth laced beams) to be accurately reduced to 2.5mm depth over the length.

This has been achieved by placing the styrene offcut between two 2.5mm square section brass pieces. Held together by hand and a scalpel blade run along it until the brass is reached. Finished with sander.

 

 

This will be attached to one half of a laced beam profile to form a laced open channel section.

By placing a 3.5mm brass square section onto the inside of the profile, the distance can be set accurately over the length for the offcut to be glued.

 

The double laced diagonal beams (which have the reduced rectangular section), will be joined by placing a 3.5mm X 2mm brass section between the two halves. Similar to the halves joined with the drill bits between (described earlier).

 

 

Construction of the diagonals with the rivetted passing plates and stay gusset plates next. This will be time consuming, especially the careful removal of lacing from the beam profiles.

 

Edited April 26, 2022 by zr2498
Photos reloaded second time

[zr2498]

Some more preparation of the diagonals:

Two laces from each side are removed from each, first by snipping the bulk out (carefully so as not to cause distortion), and then cleaned up with various sanders.

 

 

 

I find the sanding sticks from Flory Models excellent for this

 

 

 

Now the rather crazy part. To allow the small laced diagonals to pass through the outer larger laced diagonals, the wall thickness needs to be reduced where they pass. This will be disguised and will be shown later. But for now all of the larger diagonals are cut into two and stay gusset plates added

 

 

 

Awaiting more styrene strip which has been ordered for the diagonals,  so for now I can get on with the truss outer beam preparation

 

 

Edited April 1, 2022 by zr2498
Extra detail. Photos reloaded

[zr2498]

Longitudinal beam preparation:

The beams were prepared by removal of gusset plates from the beams. Either two or three plates were removed where the diagonals enter the beam.

5 pieces were need over the length to achieve the correct spacing (4 lengths shown in previous photographs).

 

 

 

The plates are removed by cutting out with razor saw, trimming back to the 'wall' with a scalpel blade, and finishing with sanders

 

 

 

 

At this point I went back to CAD as the pitch of the gusset plates was too tight between double diagonal entry positions.

To overcome this the depth of the trusses were increased from 65mm to 70mm, thereby reducing the angle and allowing some clearance.

The CAD drawing was revised and plotted.

 

 

 

Now all of the longitudinal beam sections were cut, and accurately sanded square as they will be joined to give the overall length

 

 

I have recently purchased a DSPIAE multi angle sander which gives superb end faces, and I am sure will be a worthwhile investment

 

 

 

So here we have the parts for the 8 beams (4 upper and 4 lower).

 

 

 

The corner detail which will connect the laced beams (shown on the left) to the longitudinals, has yet to be determined as these will also be the location for the bridge feet.

What have I started!

 

Edited April 1, 2022 by zr2498
Spelling. Photos reloaded

[zr2498]

Assembly of the truss frame outer beams:

Each of the longitudinal beam sections were positioned on the diagram such that the diagonals would fit beteen the gusset plates.

They were numbered, cut to length, sanded and joined. 8 over-length beams were then ready to trim to the truss section length.

 

 

To get the same beam length and a frame which was square, a jig was set up as shown below. The two 70mm pieces are made from styrene square tube.

 

 

After each length was finished, the gusset plates at the ends of each beam were removed so that the laced verticals would sit flush.

 

 

Next, the laced verticals were made to length. 9 laced crosses fitted between the diagonal entry locations. The outer laces were removed. With practice, this was found to be the  easiest by removing the bulk with the snips and then a sharp scalpel to carve away the excess. This gave a much cleaner edge and was better than trying to position sanders.

Each of the verticals were cut to length and then sanded until there was a sliding fit into the jig.

 

 

A little more preparation of the longitudinals. Where the diagonals will interface, the left over parts of the gusset plates would need to be removed.

Again with practice, this was found to be easiest by first using a larger file, a trim with the scalpel on the inside of the beam and finally sanders.

 

 

At each of the joins a splice plates are added (from the CVMW single truss bridge kit).

 

 

The 4 sides of each truss have not been glued at this stage as I'm not sure if the diagonals can be fitted into the frame if this is fixed.

So, now for some experimentation with making up diagonals. This is the first bash with overlength pieces . The interface with the outer beam is the next decision. Whether to fit into the beams or to fix to external gusset plates.

 

 

The space between the flanges has been filled with a thin styrene strip to better represent the Findhorn viaduct design which combines channel sections

 

 

Edited April 1, 2022 by zr2498
Spelling correction. Photos reloaded

[zr2498]

A small design change was needed to remove the 'step' in the wall of the larger diagonal (as seen in photo above of the last post), at the position where the smaller diagonal passes through.

But first, the 24 small diagonals are prepared

 

 

 

The white styrene strip was sitting slightly proud of the flanges of the black styrene so some filing and sanding back was needed so that a level surface is obtained (prior to rivets!)

Now back to the more complex diagonals. They had all been cut in half so that extra parts could be fitted between them.

Made from the parts as below. Lengths 6.4mm

 

 

 

 

 

The assembly sequence for the 8 double laced diagonals as below. Add styrene strip between flanges first.

 

 

 

Add parts to widen and thicken the wall at the 'pass through' location.

 

 

Then the two halves are joined.

 

For the 8 single laced diagonals the sequence is similar

 

 

 

A little more cleaning up of these to be done but for now the diagonals (except for the 8 sets of plain straps) are ready for cutting to length before fitting to the outer truss frame. This will be something of a test as the length and angles of at the joins will need to be accurate.

 

 

 

Waiting for Archer rivets to arrive for the diagonals.

 

 

 

Edited April 1, 2022 by zr2498
Extra detail. Photos reloaded

[zr2498]

Now for preparation of the plain straps positioned at each diagonal at the ends of each truss frame

Styrene strip used for these

 

 

 

 To ensure consistent widths, the initial cuts at each end were made (slightly oversize), via the 'chopper'. Then joining of cuts via a scalpel and finally sanding and checking width (5.3mm) using a micrometer.

 

 

At the end of each of the diagonals the attachment to the outer truss frame needed to be prepared.

Each of the narrower diagonals and the plain straps are to be attached by gussett plates extending to the inside the outer frame beams. The wider diagonals will have an internal gusset so that only the rivet fasteners will be visible on the outside of those diagonal beams

The gussett plates are made by cutting shapes from splice plates included on the CVMW single Pratt truss bridge sprues

 

 

 

Using the template and jig each of the diagonals were cut to length (slightly over), using a razor saw, and fine sanded using the DSPIAE angle sander set at  147 degrees until it overlayed the lines in the template

 

 

 

The gusset plates were added to each of the ends and trimmed to match the shape of the diagonals, then a final sand as above

NOTE: The narrow diagonal has to be passed through the wider one before the gussett plates are added = nearly forgot

 

Now all of the diagonals for the first of four truss frames are prepared. Small pieces of H section will be attached to the end of each to locate them into the outer beams.

 

For now, here are a few pictures of the progress

 

 

 

 

 

 

 

Guess this is building up to the great glue job when the first frame will be assembled. Hope it works!

 

 

 

Edited April 1, 2022 by zr2498
Photos reloaded

[zr2498]

To fix the diagonals to the outer beams, 'H' section is attached which loosely represents reinforced internal gusset plates sitting inside the outer truss beams.

The profile fits nicely into the slots of the beams

 

 

The H sections are fitted to the diagonals so that they will sit centrally into the beams

 

 

 

Small stay plates were cut from CVMW standard punch plate girder pack

 

 

 

These, together with the larger stay plates were added to the ends of the diagonals. Lacing was removed at these areas beforehand via snips and a scalpel

 

 

 

Before assembly, the ends of the lower beam were filed down to prepare for the bridge shoes. Easier to do at this stage

 

 

 

So now ready for assembly

 

 

 

The outer plain straps were added after the the beams and diagonals were connected

 

 

 

Need to tidy the work station!

 

 

 

One of four truss frames virtually complete. Some splice pates and additional rivets to add, and then a clean up. The remaining three are about 60% complete but at least the method is now determined.

 

 

 

These will probably get painted before the next stage of joining them via cross bracings

 

Edited April 1, 2022 by zr2498
Forgot about the rivets! Photos reloaded

[zr2498]

Two of the four truss frames nearly completed. Just to get an idea of the scale of the bridge, part of the deck is placed on top of the two outer trusses

 

 

 

 

 

With two more truss frames to fit internally to those above, and with the cross bracing plus walkways it will be pretty busy under the deck!

Findhorn (single track) underneath

 

 

Edited April 1, 2022 by zr2498
Photos reloaded

[zr2498]

Back to the deck before the remaining two truss frames are constructed.

The conversion to double track was already in place but for walkways either side of the tracks' the deck needed to be widened. This would also give a greater width (+9.5mm) between each pair of truss frames, which is a bonus as it also allows a better proportion between width and height of each set of trusses.

A bit of a cut and shove job to enable this. Two cross bearers cut and joined to give a wider version as can be seen below

 

 

The wider deck with positioning of track albeit longitudinal 'rail bearer' beams will be used finally

 

 

Edited April 1, 2022 by zr2498
Photos reloaded

[zr2498]

Some technical term information here:

Stay plates - these have been added to the ends of laced beam sections. At the diagonal ends they are located within the external or internal gusset plates.

 

It is worth mentioning that all of the stay plates when cut from the beams need thinning down substantially using files.

 

 

 

When all of the truss frames have the diagonals in place, detail will be added for example further splicing plates at the joins of the longitudinal beam lengths

 

 

On constructing the frames and diagonals. First the end beams are attached to the lower beam, then the diagonal lower connections made, then upper diagonal connections to the top beam, and finally connection of the top corners of the frame.

 

 

 

It has however taken quite some time to get to this position, i.e. four truss frames

Below is a picture of the deck temporarily resting on the 4 frames. I will need to make a jig to position / space the frames accurately before cross bracing can be added

 

 

 

Starting to take shape

Edited April 1, 2022 by zr2498
Photos reloaded

[Enterprisingwestern]

 

I teks me 'at orf t'yer.

I thought I was doing well adapting/bodging/scratchbuilding an Airfix girder bridge kit to my requirements, but this knocks my efforts into a cocked hat.

Consider a season tickets worth of craftsmanship/clever suitably applied.

I note you are a user of DSPAIE tools, an excellent under used range, maybe due to the cost.

 

Mike.

[zr2498]

1 hour ago, Enterprisingwestern said:

 

I teks me 'at orf t'yer.

I thought I was doing well adapting/bodging/scratchbuilding an Airfix girder bridge kit to my requirements, but this knocks my efforts into a cocked hat.

Consider a season tickets worth of craftsmanship/clever suitably applied.

I note you are a user of DSPAIE tools, an excellent under used range, maybe due to the cost.

 

Mike.

Mike

Thanks for the kind comments, and congratulations for being the first posted reply on this thread. Yes, the DSPAIE angle sander is not cheap, but it does a great job, will last and be well used; so a good investment.

This bridge build has turned out to be a much bigger project than expected and still plenty to work out. Painting and weathering will be a challenge as I need to get into tight spaces without ruining the detail. Air brush will be needed.

Dave

[Portchullin Tatty]

That is looking very impressive.  And a great prototype too!

 

Can I suggest that it would be more realistic if this was the bridge where located where your present stone five arch bridge is than to one side of it?  Bridges are expensive to make, so they only use them when they are necessary so they don't just appear.

 

It would look rather grand with a stone arch either side and then with the truss in the middle.  Google the Boat of Brig viaduct for a bit of inspiration (one side has several arches, the other only a single arch).

 

However, your trainset and all that!

[zr2498]

1 hour ago, Portchullin Tatty said:

That is looking very impressive.  And a great prototype too!

 

Can I suggest that it would be more realistic if this was the bridge where located where your present stone five arch bridge is than to one side of it?  Bridges are expensive to make, so they only use them when they are necessary so they don't just appear.

 

It would look rather grand with a stone arch either side and then with the truss in the middle.  Google the Boat of Brig viaduct for a bit of inspiration (one side has several arches, the other only a single arch).

 

However, your trainset and all that!

Thanks for the suggestion. I did have the uncomfortable feeling that this new bridge was not in a prime position, especially with so much detail that might not be easily visible if positioned off to one side. I guess that I had not even considered the major change as the stone viaduct has been in that position for quite some time, but thanks again for prompting a rethink. 

Dave

[Enterprisingwestern]

 

Well Dave, you've just cost me thirty quid or thereabouts on a couple of packets of CVMH girders, having seen your efforts I thought I'd better up my game!

 

Mike.

[zr2498]

On 10/01/2022 at 20:13, Enterprisingwestern said:

 

Well Dave, you've just cost me thirty quid or thereabouts on a couple of packets of CVMH girders, having seen your efforts I thought I'd better up my game!

 

Mike.

Mike

Really pleased that some of the methods detailed in this build are giving you ideas for your own kit bashing. That was always the intention.

If you get the Railway Modeller magazine you will see in this months' issue (Feb 22), another article on bridge building. I built the M & GNR bridge for Tony Wright. That was constructed in brass so a complete different set of skills needed.

 

 

Photo: Tony Wright

 

And here is another kit bashed bridge made a few years back. A Parker truss bridge (double track made from single track kits), before CVMW had a double kit available! Again all made from their components but I still need to build the plated deck, and get on with the layout.

 

 

 

 

 

 

Edited April 1, 2022 by zr2498
Photos reloaded

[zr2498]

Some more progress. Even though needed for accuracy it is not so 'exciting' as the beam and diagonal constructions!

Lots of detail added to the truss frames:

Beam detail a) The attachment of wide diagonals to main beams. This assumes that the plates on the outside of the diagonals extend to the outside of the longitudinal beams. This is not as the Findhorn viaduct as the diagonals are too wide to fit inside the beams. I have used an arrangement as on the Forth bridge (same builder).

 

 

 

3 different sizes of plates were needed for this and they were prepared from plates on the CVMW single track truss bridge sprues and cut to consistent sizes on the chopper as below

 

 

Cut 1 - the rule is held in place with some BlackTac

 

 

Cut 2

 

 

Cut 3

 

 

Larger piece for the end plain plate diagonals

 

 

 

An example showing how they fit onto the beams

 

 

 

Next the beam corner detail

 

Edited April 1, 2022 by zr2498
Spelling correction. Photos reloaded

[zr2498]

Beam detail b) Beam corners

I have tried to replicate that as seen on the Findhorn viaduct

 

 

 

Extra flanges

 

 

 

Rivetted angle (from double track sprue)

 

 

 

Splice plates (from single track sprue)

 

 

 

Bridge shoes (from double track kit)

 

 

 

Assembled

 

 

 

Gusset plates for cross bracing next

Edited April 1, 2022 by zr2498
Correction. Photos reloaded

[zr2498]

Beam details c) Lower cross bracing gusset plates

 

3 different types made up from parts of the CVMW double track bridge kit

 

 

 

The wider gusset plates will be used where there is a cross beam as well as cross diagonals. The 'diagonals only' are made up of two small plates butted together

The corner plates are made up from an additonal offcuts as below

 

 

 

Shown before bridge shoes fitted

 

 

 

An assembled example of two types

 

 

 

Beam detail d) Additional beam splice plates

 

These have been added to the bottom of the beams (4 splices X 4 beams), by filing down the gusset plates in the vicinity of the splice and then making up a shingled splice arrangement as below

 

 

 

On the top of the beams a splice plate is added to the flanges as below. This applies to the top beam flanges at splices as well

 

 

 

Still have some rivets to do on the diagonals. Just ordered from Archers.

For now designing and preparing the 'upper' cross bracing gusset plates. Semi-scratch build needed for those.

So far there are 339 components for each truss frame! Yes, I am keeping a count but it is hard to believe when just looking at the assembled frame?

 

 

 

Edited April 1, 2022 by zr2498
Photos reloaded

[hayfield]

There is kit bashing and then extreme kit bashing, I do take my hat off to you for the lengths you are going to

[zr2498]

On 10/01/2022 at 16:34, Portchullin Tatty said:

That is looking very impressive.  And a great prototype too!

 

Can I suggest that it would be more realistic if this was the bridge where located where your present stone five arch bridge is than to one side of it?  Bridges are expensive to make, so they only use them when they are necessary so they don't just appear.

 

It would look rather grand with a stone arch either side and then with the truss in the middle.  Google the Boat of Brig viaduct for a bit of inspiration (one side has several arches, the other only a single arch).

 

However, your trainset and all that!

Decision made.

The new bridge will take centre stage (behind the two Pony Truss bridges), and I will remake the sone viaduct with a number of stone arches either side. The existing stonework is Townstreet stonecast so not sure how easy to recover some of the parts. Probably start again with those, but relatively simple when compared with the complexity of the lattice truss bridge. Thanks for getting me to have a rethink about what would be more realistic.

Dave