Build a Structure - Peter Bowen - RGS Timber Trestle

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Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Sun Nov 23, 2014 12:42 pm

OK I'm up for a challenge and will (scratch) build a Rio Grande Southern (RGS) timber trestle according to specifications and research of actual construction methods and materials in 1/48 scale for my eventual ON30 D&RGW layout in a spare bedroom.

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OK - maybe not as big as this.... !

Peter
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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Fri Nov 28, 2014 6:35 pm

Prototype Rio Grande Trestle details

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Construction Methods 
This sketch below shows the method used by the RGS to tie the bridge bents together. This style of construction has been observed at all of the major bridge sites on the railroad that contain enough material for examination. It is also evident in the water towers still standing.

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A cap was attached to the posts underneath it by driving a round steel pin down through the cap and into the post. This was done for each post and for each story of every bent. Anywhere from one to three small bridge nails (9" long with 3/8" shaft) were used to attach the sway braces to the posts. These sway braces ran from the lower left to upper right. This unit or story was often assembled off to the side and then moved into position on the bridge.

Each storey was attached to the one below by toe nailing several full sized bridge nails through the post and into the cap of the story underneath. In the bottom story, the mud sill would probably be attached before the story was moved into place. As each storey was positioned and attached to the storey below, girts were added between the bents to stabilise them.

When finished these bridges were strong and stable. The bridge at Ames, (43A), which was built in a very precarious location, stood for almost thirty years with no maintenance whatsoever.

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Rio Grande Southern Railroad had 142 bridges scattered along it's 162 miles of track . The most spectacular bridge was 9A. This wooden trestle was 836 feet long and had a 202 foot Howe deck truss in the centre. It was 134 feet high, prompting the early crews to call it the high bridge. The original 9A strained the capabilities of wooden bridge building to their limits and, as a result, it was never really successful. The crews didn't like it or trust it, and neither did management. Unsurprisingly it was among the first of the bridges to be replaced. 9A was removed and replaced with an earthen fill and box culvert in 1903. When this culvert washed away in 1908, it was replaced with the second 9A, which was a more typical curved open deck trestle.

Like 9A, almost all of the original bridges were rebuilt or replaced at one time or another. Most of the Howe trusses were replaced with simple open deck trestles, and many of the smaller bridges were replaced with earthen fills and culverts. By the end of operations, 111 bridges were left on the railroad; virtually none were original. The reasons for replacing a bridge were many, but for the most part, the arrival of heavier motive power or damage caused by weather and high water resulted in replacement.

At a glance, most of the bridges appear to be alike, a closer look however, shows that all differ in detail. The RGS built their bridges following accepted and proven engineering practices. Thus, all of the bridges look similar in overall design.

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A Robert W. Richardson view of the Butterfly, Colorado trestle Bridge 44A from November 7, 1952

Detail differences in the bridges occurred due to unusual circumstances in placement or geography. Changes also occured when the bridges were repaired. Thus, over time, all of the bridges slowly changed.

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462 crossing trestle at Ophir, Colo., October 41, 1947
Last edited by PeterBowen on Thu Dec 04, 2014 9:44 pm, edited 3 times in total.
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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Mon Dec 01, 2014 8:57 pm

The challenge has started, but first things first - need a plan to follow.

Rio Grande Southern Trestle drawing based on ON30

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One of the challenges facing scratch builders is having a good set of plans with scale dimensions.
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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Mon Dec 01, 2014 9:34 pm

The bass stripwood arrived and the first challenge is to cut all of the components needed...!

ImageThe stripwood bundles of different dimension basswood

ImageBass stripwood components cut to approximate size and ready for staining.

I have used a combination of a modified NWSL Chopper and a razor saw and mitre box.
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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Thu Dec 04, 2014 9:30 pm

50 Shades of Grey

The effects of age and weathering on wood even if it has been treated in some way will result in a grey or silver grey colour. Even cedar which is used in north America for tiling roofs often called cedar shakes will eventually turn from golden brown to silver grey over time. A closer inspection of wood ties (sleepers) used on north American railroads shows various shades of grey as the wood dries out and begins to decay. At one time ties had "date nails" driven into them to indicate when they were placed - the earliest I have is 1937...!

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I have used the leather shoe dye and alcohol method of staining wood for years and it always produces a nice natural weather wood look and in my opinion is the perfect staining process that produces a variety of different shades of weathered grey wood. I use a dilution ratio of 1:20 - 1 part black dye to 20 parts Alcohol + 1/2 part of Dark Brown. The Black dye has a blue tint to it and the Dark Brown just warms it up a bit. The result is a muddy black looking solution that is quite thin.

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I use an aluminium roasting tin the type that is inexpensive from Tesco's as a bath into which I dump the cut stripwood lengths. Leaving them to soak for various lengths of time - typically 20 to 120 seconds seems to work quite well.

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It is a good idea to test a strip before you dump the whole load into the bath just in case you don't like the depth of staining. Remember you can always make it darker by repeating the staining process BUT you can NEVER make it lighter...!

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I use long tipped tweezers to "pick" the pieces out of the staining bath and place them on drying racks and paper kitchen towel. As the wood dries it turns colour from the overall green look as shown in the photo above to a dark grey colour as shown below.

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The finished look is shown below and the "50 Shades of Grey" - which is exactly what you want... no two pieces are identical.

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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterLJ » Fri Dec 05, 2014 9:09 am

Hi Peter

This would make a very good article.

Peter L-J

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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Thu Dec 11, 2014 7:49 pm

A word about cutting 1/4″ x 1/4″ basswood – using a mitre saw or a NWSL Chopper.

I had to modify the NWSL Chopper to accommodate larger stock see below:

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After cutting pieces they are then cut and sanded further to fit using a Minicraft Sander and 180 grit 75mm sanding discs. It is important to get all of the cut ends perfectly square and this is the only method that I know of to accomplish that.

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Building the trestle bents on top of a plan. I started using a copy of a plan and soon realised that it was not square and was slightly distorted.

I drew up a new plan to the exact scale and I have included it elsewhere in these postings.

Laying out the components using ‘T” pins.

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Last edited by PeterBowen on Thu Dec 11, 2014 8:01 pm, edited 2 times in total.
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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Thu Dec 11, 2014 7:59 pm

Bent construction continued...

When I started thinking about this project I knew that it would take a lot of time as each component has to be cut and sanded to fit and it is almost impossible to mass produce items – well it is impossible because I tried grouping a number of pieces together and sanding them all at once – a disaster for one reason or another the only way is to make each one separately and be patient about the outcome and thus a very time consuming job.

Each joint must be a perfect fit or it just will not glue together plus it will look wrong!

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Completed two storey trestle bent complete with cross bracing and sway braces.

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You can also follow this construction articleand see more prototypical information about the D&RGW RR and RGS on my website that is devoted to collecting historical information.
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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Sat Dec 13, 2014 1:55 pm

Production of trestle bents has been moving along slowly in recent days, using weights to hold components while they set is time consuming.

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Patience is the name of the game here, however the results are starting to show...

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It is interesting to note the various shades of staining which in my opinion produce the most natural effects of wood weathering.

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Above close-up detail showing joints and cross bracing. Note the attempts at showing the graining of the wood which was done with a wire brush prior to staining.

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One and Two storey bents completed with bracing on one side.
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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Thu Dec 18, 2014 3:12 pm

A word or two about size and proportion in relation to building the components of a trestle. Bear in mind that the size of timbers used in the construction process are huge and have to carry enormous loads and weight.

The main support posts for instance are 12" x 12" square and can weigh as much as 35 lbs. per foot of length.

When placed next to scale size people, freight cars and locomotives you start to realise how they will look when completed.

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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Fri Dec 19, 2014 5:33 pm

Time for some Nuts N Bolts ...!!!

Attaching NBW's - nut, bolt, washer castings - in this case they are 2.5 inch hex nut on a bolt with 4.5 inch washer. These are plastic castings from EDM Models aka Paul Martin at NG Trains www.ngtrains.com/Pages/Details/NBW/nbw.html

Each small bent requires 24 front and back, each of the larger bents require 40 ...!

Use a pin vice to drill a 0.8mm hole through. I pre paint the castings with Vallejo Model Colour #337 Highlight German Black and dry brush over with #70818 Red Leather for that well worn and rusty look.

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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Sat Dec 20, 2014 1:42 pm

Weathering and Bridge sub-structure

There is a requirement for the trestle to bridge a road or other right of way and therefore the trestle bents would cause an obstruction, so a raised section is required to allow vertical and horizontal clearance.

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This is achieved by bridging between two existing bents about halfway way along the overall length of the trestle. At this point the bents are doubled up see photo above, ie., two are bolted together to provide the additional strength and stability required to support a laminated bridge beam shown in the photos below.

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The laminated bridge beam is bolted together and NBW's applied as shown below.

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Detail showing well rusted bridge bolts. These are painted with Vallejo Panzer Aces #337 Highlight German Black - I like this instead of black as it is a green grey black that looks like well weathered steel plus a dry brushing of Vallejo Model Color #79818 Red Leather which in my opinion is a good rust colour when mixed with a little of the colour above. I have also used this combination for weathering locomotives and freight cars.

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The individual beams are 12" x 12" (.25" x .25") and the NBW's are a scale 2.5" hex nut on a bolt with 4.5" round washer part #8080 available from EDM Models aka Paul Martin. Currently priced at £2.75 for 96 pcs that's 3p each...!!!

This article also available on my website DRGWRR.co.uk
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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Mon Dec 22, 2014 8:01 pm

Assembling the two laminated bridge beams on to the two doubled trestle bents requires weights and clamps and a lot of patience to ensure that the components are square and aligned correctly. It is at this point that the structure begins to take shape and great care has to be exercised to avoid damaging the pre-built sub-assemblies. You can never have enough weights and clamps to hold everything in place while the glue dries.

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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by PeterBowen » Tue Dec 23, 2014 11:06 pm

Last minute construction prior to Christmas festivities and a well deserved break from squinting . . . !!!

The deck stringers consist of 3 - 8" x 24" x 32' sections with 2" x 6" x 24" spacers. These spacers were added on the prototype to assist in drainage of surface water so that it drains away. The deck ties will eventually be laid at right angles to the deck stringers.

It is important to lay these stringer laminated sections on a level surface with many weights and clamps as shown below.

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Re: Build a Structure - Peter Bowen - RGS Timber Trestle

Post by el_capitan » Mon Dec 29, 2014 1:04 pm

Hi Peter,

Great How-to article on building a trestle
so long

Alain Kap

It’s fun to ride the train today … when the train you ride is Santa Fe!
(Wording of a Santa Fe ad back in 1962, the year I was born)

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