I'm creating a series of documents on restoration best practices for the Friends of the Cumbres and Toltec.

For truss rods on wooden cars, I've found some tidbits of information here and elsewhere, but never have I seen any comprehensive set of information. What if I am restoring a car that has cracks in the truss rods, or threads are damaged, or even they are missing completely?

There doesn't seem to be any current regulations on truss rods. I have the 1892 Railway Car Construction reprint and there's basically one sentence in the book on them.

So in 20 years a kid comes to me and asks "how do I fix this car. The truss rods are all messed up?" What can we tell him?

Bill Kepner

Like everything else in restoration, make it back like it was originally.

The great thing about metal is your can weld it up or grind it down ask much as you like. If the originals (in this case truss rods) have with held the test of time and pass FRA inspections then you should keep using that original design. If the threads are worn or gone then you can weld them up and re-cut them using a die. Pretty tedious job involving a welder, grinder, and straight edge to check thread height.

Of course it's always a good idea to just replace the old material with new material. In your case threaded rod stock is very common and inexpensive. You would need a brake press to make some bends but once it is done you will never have to worry about replacing it again.

I would always check old threads by putting a bolt in the hole, tightening it good and tight, then finding out what that torque is with a torque wrench, then going 20% over that torque. If it didn't strip it was a good hole.

A lot of the truss rods on older cars are wrought iron, not steel, your mileage may vary. This can make welding difficult. Torque wrench? Torque spec? in 1879?

In most general terms, the truss rods will have lasted far better than the wooden components and probably won't need attention provided you restore the wooden components properly. Adjustment is enough that the sills are abut straight and level, not so much that the middle humps up. Jacking the frame and then following with tightening the truss rods can make for an easier and more controlled adjustment.

Understanding the entire trussed structure is far more important than dealing with just one part of it.

My experience is same as Dave’s, truss rods are wrought iron and are not weldable. We stretch a wire from bolster to bolster and jack the car up until it has a slight arch. When it is lowered it might actually be straight. Hardest part of the job is cleaning the threads so the turnbuckle will move. Sometime heat maybe required. Do not try to straighten the car by turning the turnbuckle, it must be jacked at the queen posts first. I would not try to take more than 1/2” sag out of a car per year. There are a number of trusses in a typical car and they all have to be correctly adjusted so they work together. The anchor points at the other ends of the rods have to be in good condition or they may fail when the truss rod is adjusted. I would recommend agains completely unscrewing the turnbuckle. It can be difficult to get both ends lined up and started at the same time. I back off the turnbuckle far enough to expose the rod threads that will be inside the turnbuckle when adjusted. Then these threads are coated with a lead based anti-seize compound.

New turnbuckles with upset threaded rod ends are available. These would have to be welded into appropriate steel rods to make new truss rods.

Since the era that truss rod underframes were used pretty much coincides with the production of wrought iron, it's almost a foregone conclusion that the truss rods and various other tie rods are going to be wrought iron and therefore not weldable. I cut some wood elevated car bodies years ago, cars dating to 1907 IIRC, and was surprised just how much of the metal hardware was W.I., which doesn't cut any better than it welds. It seems that most the structural shapes were steel, but the round sections were W.I. Round stock must have been the last bastion of wrought iron production.

This is likely a blessing, given the way the truss rods on a freight car typically are routed through holes in the wooden end sill; if the rods were steel I'd expect them to be rusted down to little pencil thin sections where they are buried in the wood but W.I. seems to hold up much better in this situation.

If the threads are stripped off the ends of the rods, I would suspect some hand forging could increase the diameter of the upset at the expense of some length, but truss rods often have an extra inch or two of threads inside the turnbuckle that could be put to use. Of course it will take a skillful smith to do the job, and the rod is going to have to come off the car, but if it can't be saved it will have to come out anyway, and once out it can serve as the pattern for a steel replica.

Rough iron is weldable and it is not that difficult even for a someone who isn't a professional welder. Like any type of skill you need proper prep work, the right equipment, and a basic understanding of metals.

Links http://modernwelding.net/welding-wrought-iron/

https://forum.millerwelds.com/forum/wel ... ought-iron

For a very in depth look at wrough iron including welding

http://digital.auraria.edu/AA00000072/00001

I'm going to take exception to that statement. That may be true if the welding is to repair a decorative grill or the like, but the original question was about a cracked truss rod. Truss rods are the tension member of a truss, and therefore are highly stressed. The references I find, some of which you cited, typiically state that wrought iron should not be welded if the weld is to be highly stressed. Here is a quote:

"If mechanical working of the wrought iron has not been thorough and the slag stringers are large in volume and extent, welding can be difficult as large slag inclusions form in the weld and at the fusion boundary. Those at the fusion boundary may be oriented normal to the direction of stress and could lead to premature failure if the structure is subjected to alternating stresses. Welding that results in a through thickness stress must be approached with great caution since the wrought iron can be very weak in this direction and a form of lamellar tearing can easily occur."

The problem is wrought iron has a grain structure, with thin threads of slag running along its length. In the melt pool these can coalesce into large slag inclusions, which would be classified as weld defects. I don't think anyone should be suggesting welded repairs on truss rods, whether for crack repair or to build up threads.

Dennis,
Don't forget there were multiple grades of wrought iron, structural wrought iron is not the same as common wrought iron. There are different levels of refinement (fining). IIRC Structural work was only done with double and triple refined or higher grade (IIRC I think they went as high as 5x), where the inclusions are drawn out so much that they are almost hair like. If you look at the advertisements in the back of the locomotive cyclopedias and trade publications you will see advertisements for Bloomery Bar, Muck bar, Merchant bar, single refined, double refined, triple refined, etc...

Basically the raw Bloom is hammered into a bar, folded and forge welded, this is repeated multiple times to refine the structure. The more times it is fined the less slag is in the material and the longer & thinner the inclusions and crystalline structure becomes. This is the reason wrought iron splinters and breaks like a branch.

The strength of Low Grade / Basic Wrought is practically cast iron, whereas highly refined wrought is closer to Low Carbon Steel, in how it reacts to strain and impact. Easier way to visualize it, Basic/Low grade wrought when snapped will look like a pine branch (heavy splinters), whereas highly refined wrought will snap like an oak branch (fine splinters).

Rich C.
------------
Note:

Bloom is the puddle of iron that comes out of the furnace as iron ore is converted to metal iron.

Finement is the term for mechanical refining of Wrought Iron, the buildings specifically built for the purpose were called Finement Forges and Finement Shops.

In the early to mid 1970s I was a welder working for a living. The "Lake Shore car" better known as MLS&W #63 looked like a farmers shed on freight car trucks. Though maybe it was some spare passenger trucks back then? I felt the car should of been taken to a field and burned as it truly was pretty far gone. Wasn't the first or last time I was wrong. Their was a young college guy who rode a BMW with side car going to UW Madison who was almost single handedly working on the car which was boarded up and again looking very sad. He was taking some sort of welding/blacksmith course and had access to a forge. The truss rods had been cut off this car when in the Potato Yard in Chicago. Always wondered if that was anywhere near the "Water Market" area on 14th pl? He forged new ends and I welded them on to the new truss rods he built. He went to great lengths to make this a solid repair and don't remember exactly what he did after I welded it up for him. There was another member who was more involved in the early stages of this incredible restoration but don't recall his name. I would credit him for the save. At that time MC restoration forces were not nearly as focused and such a driving force as they are now. So the early work in the 1970s was important. Wasn't till at least 20 years later that the car was completed. Because the steel was replaced I do not think it was wrought iron. It welded up easily with no problems as I recall. Wish I could remember exactly what he did after the welding? He may have heated it and beat it. But he was really into the blacksmithing thing. I was just a dumb welder. Our steam fitter at the time felt it was above him to do this work so I ended up doing it.

https://www.midcontinent.org/equipment- ... estern-63/

A privately owned wooden sleeper "Rhinelander" I believe is in the process of being jacked up and straightened. A very little at a time as mentioned above. Unfortunately there are no pictures of that process but here is a picture of that car. She doesn't look real bad in the picture in 2000 but she may have settled between then and a couple years ago. But slow and easy I believe is the process of tightening things up.

https://www.midcontinent.org/equipment- ... inelander/

I do very little in the wood car arena but find it very interesting how the wooden cars were built and what the restoration forces at MC do in the restoration of the coaches. Both in the restoration of ceiling panels and beautiful wood work, but also in the actual main construction. As daunting as any restoration of a steam locomotive. Obvious differences aside.

So is the OP about any car in particular or just a "need to know thing" for your project work? You might want to contact the restoration dept at MC as one of your contacts? This email should get you to the shop people eventually. I do not want to publicly put individuals emails out there. E-mail: inquiries@midcontinent.org. Obviously there are others who can help too. Good luck OP on your work. Regards, John.

Thank you all for this information. I will be incorporating some of it into my restoration docs.

Most of the restored freight cars on the C&TS used steel for their truss rods and we have been able to successfully repair by welding. The material is 1 1/8", but the threaded ends are 1 1/4". So it is necesary to weld the threaded ends. I had been wondering if that was a common repair or it substitution of 1 1/4" was used anywhere; it would have made it much harder to get those installed on some cars.

Bill Kepner

Upset ends on truss rods was common practice. I imagine the thinking was that as structural tension members the larger uncut diameter was necessary to maintain full strength for the full length of the rod (through the nuts/turnbuckles). Not too hard to find examples in old car drawings that are fully dimensioned.

The root diameter of an 1-1/4"-7 thread is a little over 1-1/16", so there is no advantage in the body of the truss rods being any larger than that. The 1-1/8" body with an 1-1/4" thread makes for a saving in material and tare weight.

Back in the day, material's cost compared to wages was way higher than today, so RR's would shave material off of all sorts of stuff to save a few bucks per car, which adds up to a substantial amount for a whole fleet.

According to a spec sheet from the Northern Pacific circa 1900, truss rods were to have the ends upset and not welded on. Now this was forge welding, but if you are unsure of exactly what kind of metal you are dealing with that would still be the best policy.
Mike N.