# size of tension rods on Howe truss bridges?



## peter bunce (Dec 29, 2007)

Hi,

I hope to be building possibly 3 bridges that will be about 3 or 4 foot long each; these will be left out in the all weathers, and not brought in when it is bad.

They will be 'through' Howe Trusses, (one may be a pony truss) and so far I have had a lot of help ( for which grateful thanks) from MLS members but am still not quite there yet. 

We did not have such bridges in the UK so I profess to being quite ignorant re the finer points of them! This ignorance has been reduced by various books and publications though, but I still feel to be short on 'knowledge' of them, and I do like to make a good, and correct version, if possible, though I will incorporate a pair of stiffening longitudinals under the bridge(s) to hopefully keep them horizontally straight over time. 

They use vertical tension rods, that will be used with PVC solid foam 'timbers'.- we have terribly poor (at a reasonable price) timber and our wet (UK) climate will rot the stuff in no time! 

I have looked at aluminum 3/32" rod for the rods, but wonder if this is a bit thick, and possibly 1/16" would be better. Hopefully I (and am still looking for a supplier) will be able to find them from 'Brazing Rod' suppliers. The aluminum is welding rod, though copper plated steel is available the copper coat is not very thick thick, as its real use is to promote the steel to 'flow'. 

Aluminum is not going to work for one method - from David Fletcher who soldered nuts to brass wire for the top & bottom of the rods, for his bridges, but the UK to Australia is a bit far to go for a look at them! So ins the UK to the USA for that matter! This method holds up to the weather better than glue, which I can understand.

So my query mainly is which diameter of rod - 1/16 (= a scale 1.5") or 3/32 (= about 2.2")? I agree not much difference but they are painted black so will look to be thicker, and there is a lot of them. 

I know that there are many very good bridgebuilders in MLS, and any help is always appreciated.


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## Bruce Chandler (Jan 2, 2008)

Peter,

Here's one I made with 3/32" rods:









I don't think that they look too thick, but what do I know?









From normal viewing, they DO blend in...









I think I'd be just looking for availability and going with what I could find; as long as it's not too expensive.

I've also heard of folks using bicycle spokes, as they are already threaded. 


I did use glue when building these, but I really felt that it almost wasn't needed as the sides were held in place very nicely by the rods.


I'm looking forward to your progress.


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## John J (Dec 29, 2007)

What do you know? You sure know how to grow beautiful flowers. Have you submitted that one for the Calender?


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## Rod Hayward (Jan 2, 2008)

I used bike spokes mate


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## peter bunce (Dec 29, 2007)

Hi Rod, 

Thanks for the thought; I looked at those and I do not think they are long enough; I have a D&RG 1/20th (scratch built) D&RG caboose with cuploa - that is tall as it has the signal light on the top. 

That is why the spokes look to be (& after some web checking) somewhat short for what I want, which is a pity as I like using them..


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## Dean Whipple (Jan 2, 2008)

Pete, 
Check out my "*6' Howe truss bridge*" page, I used 3/32 brass welding rod, threaded with #3-56 brass nuts, unpainted and in a short time the brass aged to a nice "_rusty" _ brown color....


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## tj-lee (Jan 2, 2008)

For my bridge, I purchased rods from Micro Fasteners but they are steel not brass and rust up nicely which is the look I was going for. Part number TR0256 threaded rod, 2-56 x 12 inches. The threads are cut 2 inches on each end.










The hexnuts are brass 2-56 (5/32x.052), part number HNBM0256. 

Best,
TJ


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## Rod Hayward (Jan 2, 2008)

Troo, that is a 1.22.5 effort up there...


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## Don Howard (Jan 2, 2008)

RGS in western Colordo used various sizes across the Howe trusses.

Bridge 9A 202' panels used from 1 1/2 up to 2 1/4.
Bridge 45A in Ophir Colorado: a modeler of O-scale used 2 1/4.

I have cut some wood for bridge 45A but am holding off on more cutting until I can either get a copy of the actual plan, or someone can confirm various sizes of the components.
[url]http://picasaweb.google.com/RGSNorth [/url]

Bridge 9A in those pictures used the same size rods all the way across.
The wooden diagonals were also made uniform, even though the builder knew the sizes varied-done for strength. 


I have seen bridge 45A bottom chord depths vary from 14" to 15", and the chord widths vary from 7", 8", 8", 7" in one reference to 8", 8", 8", 8" in another. 9A used the 8,8,8,8.


Unless someone here or on the RGS forum on Yahoo disuades me, I'll be using 3/32" brazing rod.

Thanks for your question, as it has helped clarify how I will proceed.
Please document your build as you have done with your lovely buildings and rolling stock.


Don Howard


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## xo18thfa (Jan 2, 2008)

Hi Peter: I used 1/8" brass rod with #5 x 40 TPI thread for a 1:20.3 bridge. In narrow gauge it looks pretty good, in standard gauge they would be way to big.


http://1stclass.mylargescale.com/xo...ed%202.JPG


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