# My new Howe truss bridge



## peter bunce (Dec 29, 2007)

Hi,

Bridge number 3 has been started – I will have 3 bridges, all different on my railroad; two I have made myself and one in Aluminum was made for me as a kit from Frank Neher in Germany. 





The first is a pony truss and has a slight mistake (which I won’t be correcting), and is made from wood strip; the present bridge is being made out of PVC solid foam and some scrap plastic called Altuglass which is very hard and quite rigid. The bridge is a 4 foot long Howe Truss bridge, which is 4 foot long, just over a foot high and will be 9 inches wide – nothing like variety! 





The first attempt foundered on my lack of bridge knowledge – they have to have an odd number of side panels (shaped like a ‘X’) otherwise they will not work! Mark 2 is much better, one side has been made, and still needs the tension rods adding (those need some nuts fixing to them – they have not yet been ordered! But I can now make the other side to a viable pattern: then the cross pieces top & bottom are due to be made, needless to say they are both different. 



Here are a couple of photos of the side panel ) most things are in threes; so plenty of work has been done with myn the big circular saw – still more to do, but I am getting there!










a side view, which gives a good view of the center opf the bridge - the important bit is getting this correct, and is why an odd number of panels are needed










a diagonal view showuiin the two and one design for thecentral 'X's - missing at the meoment are the tension rods, which need some nuts soldering onto one end to start with, and then fittin - I have bough a kilogram (just under 2 lbs) of 2.4mm silicon bronze rods for the bridge and expect to user the lot! 










More to follow ---


----------



## Steve Stockham (Jan 2, 2008)

Wow! Looking good Peter. Can't wait to see it finished!


----------



## Richard Smith (Jan 2, 2008)

Nifty Peter! Always enjoy seeing your projects.


----------



## peter bunce (Dec 29, 2007)

Hi, 

The main framework has been completed now, and I estimate that about half of the work involved on the whole bridgei has been done. Still to do are al; the tension rods (from welding rod) that need nuts soldeing on one end then fitting and threalock for fixing the upper nut in position, then the cross rods are to be added, and some extra detailing done after that.

Meanwhile though here are a couple more photos of the bridge roughly located in its postion. Still after the brideg are a 6 foot long approach trestle, on the left hand side, to it - so lots more to do!










A view of the top of the bridge, showing the cross framing (which needed to be offset from the side framing, - here the bridge is dumped onto some stacked bricks, but is virtually the correct alignment for it. At the right hand side is the custom made 90 degrre crossing, and tyhe crossing keepers hut.













A side view (with a clothes line (closed up) and one of the garden chairs as well - the lawn is a still a 'work area'! At the back is the aluminium bridge and the track base(wall) swinging round into my 'horseshoe curve'.


----------



## peter bunce (Dec 29, 2007)

Hi,


The bridge I have been building is virtually finished and here a some photos (above) of it – its 4 foot long (a scale 80 feet) 13” tall, and 9.5 inches wide. Most of it is PVC solid foam, with some stiffening from a more rigid plastic as well. I have used welding rods for the ironwork, and trim from plasticard, and ait has consumed a large amount of paint! 










The ladder at the side is one of two that will be fitted to the ends, I am still deciding if I can fit some water barrell stands (which as they will stick out past the sides will be a bit fragile).










A view from the other end.










Finally a top view of the bridge.



It will be fitted at the end of a series of trestle bents, they will be a total of 6 feet long, with 10 of them to build and join together, and they are to be made from redwood from an old greehhouse that has been awaiting its new use (of its timber)


----------



## jimtyp (Jan 2, 2008)

WOW! Can you show a close up of how you did the truss rods?


----------



## Steve Stockham (Jan 2, 2008)

Excellent work....as usual Peter!


----------



## peter bunce (Dec 29, 2007)

Posted By jimtyp on 30 Jun 2010 11:11 AM 
WOW! Can you show a close up of how you did the truss rods? 


Hi Jim, A photo no, BUT here is a drawing, of the top & bottom chords and how the truss rods fit into them: 












and a bit more about the construction as the truss rods are central to the construction; as a result there is a lot of text to help. 


First there is a drawing of a standard gauge bridge, that was over the Truckee River in the July/August 2009 issue of the Narrow Gauge & Short Line Gazette magazine. That gave me a lot of information, and was modified for narrow gauge and shortened as well.

The bridge is mainly 5mm thick PVC solid foam (I think that the name in the USA is Sintra board? http://www.sintrapvc.com/) you would have to use the 6mm thickness; and Evostik (a latex based contact type possibly like Walther's and others 'Goo'?) The tie rods are made from 2.4mm (3/32") welding rod that can be soldered - mine is silcon bronze. To that are soldered 2.5mm brass nuts on one end of cut to size rods. 

The portal ends are thicker than most of the rest of the bridge to give some strength and stiffness there - I use two laters of 5mm faced up with thin styrene sheet. Add a couple of stiffening braces at the upper corners. 

The top and bottom chords of the side panels are 3 pieces each as above, held part by spacers mine are 1.5mm styrene card - all glued up, and then the 'X' frames that fill the void of the frame (carefully work them out - I did it twice the first was wrong!) are made and fitted again in threes; to the top & bottom of the chords leaving the gaps clear. 

Into those gaps go the tie rods but first the gaps are not wide enough so they are drilled to allow the rods to go through, but with close tolerances (=tight!). Now make the top and bottom strips of .020 black styrene which each have two holes to allow the rods to pass through, and fit one to each rod above the soldered nut.

Now take the rods with nuts soldered to one end, and the strips and fit them up through the holes to the top chord where they go through the corresponding holes - they should be vertical. Alternate the end at which the (soldered) nut is, and add at the other end fit the strips again. Both strips can be glued down to the outside horizontal faces of the top & bottom chords. The non-nut end can now have a nut threadlocked onto it tight can get it. That keeps the side panels tight and in compression. 

Now you need more hands! the bottom of my bridge is 9.5 inches wide - cut out some cross ties (mine are in units of 4 per set), these give you the width of the bridge: first find some room a bench (it will need to be big this bridge if 4 foot long) the cross ties (which are made 7.5mm thick) are fitted to both the top and bottom to keep both sides in position.

Add all the bottom ones; the top ones will be removed, and replaced in due course. The top has a series of horizontal 'X' frames but not at the same centres as the sides - my sides have 9 and 2 half frames and the top has 10 and 2 half frames. These have half lap joints at the point where they cross, and the ends are fitted to pillows - these are little pent roof shapes that allow the ends to be cut straight, these can also be used for the sides but will have to be drilled through for the vertical rods. 

I made and fitted a non prototypical shelf that the top 'x' frames sit onto to assist in placing them: when all is dry, more welding rod is need for the cross rods that hold the sides together, again work out how many (add one for each end just inside the upper cross pieces) solder on more nuts to one end and drill through the pillow blocks centers on both sides the should line up. Fit the rods as before with styrene card stress distributor plates - rectangular bits with a central hole! 

Back to the bottom; totally non prototypical here to allow for two end to end square steel tubes that are glued under the cross ties; they are 12mm (1/2") so cannot be seen from the sides as the side bottom chords are 15mm deep; they are 3 foot long so are joined with a inner plug to make them 4 foot long, and fitted with end plugs at the same time.They were well painted before fitting. The bottom should be a twin of the top; I added some short pieces of rod to tie the sides to the tubes though. Add at ethe ends some pads that held the bridge in position in reality - these extended from the abutments and the bridge was bolted to them. These are faced underneath with some thin aluminium sheet for protection.

On top of the cross ties I added, above the steel tubes, a double thickness pair of strips that are spaced for under the rails, and an outer (single thickness) pair located for the end of the ties of my Peco track, these will accept the screws to hold the track in position.

Now the bridge can be painted and detailed as you want:I added some stiffening plates and also lots of nuts and bolts - I make my own - this bridge has lots - the main brass nuts - I bought 140, there are two left!



This bridge was somewhat difficult to paint my hands and wrists just fitted between the open triangles of the sides to get at the inside, the long handled 'kids/artists' bristle brushes were a great help here. The length is about the maximum for my arm (evidently 2 foot long) to get to the middle whilst painting, it was not really possible to paint it in sections before assembly. It took an amazing amount of paint!


----------



## SE18 (Feb 21, 2008)

looks great


----------



## up9018 (Jan 4, 2008)

Great looking Bridge Peter!!! 

Chris


----------



## jimtyp (Jan 2, 2008)

Peter, thanks for the great info. 

A few questions: 

Do the strips on the top chord wrap around. They looked triangular shaped? I really like that look, how did you do that? 

On the top it looks like you built a ledge of sorts for the top X frames to rest on? How did you do that? 

The bottom ends of the bridge, where it would rest on an abutment, what did you do there? 

I see the width is 9.5", what is the height? 

What angle and how wide are the vertical X frames? 

Any chance of getting a link to a bigger picture? I really, really like this bridge, it's the best Howe Truss I've seen.


----------

