It's not so much a structural error as a questionable choice... by putting all the diagonal members in compression, they have to be stout enough to resist buckling. Not a big problem on a 25 or 30 ton truck, but sure to rear its head as cars went to first 40, then 50 tons. Of course, as late as 1892 a gentleman named William Voss flatly stated in Railway Car Construction that four axle cars would never exceed 40 tons capacity because the maximum carrying capacity of wrought iron axles had been reached, and he illustrated his work with a proposal for a three truck coal gondola. Within the next decade steel became relatively cheap and plentiful, and that changed everything.

Meanwhile, caboose cars didn't get appreciably heavier, so the older design trucks still gave adequate service. As an aside, even diamond archbar trucks suffered from having the top bar in compression, and so as 50 ton cars became common, so did cast sideframe designs.

By the way, the truck that Robbie found illustrated in the 1888 Car Builder's Dictionary is you missing rigid (non swing motion) version of this truck.

Yes, that one on page 315 of Car Builder’s Dictionary (1888) is quite interesting and somewhat puzzling as well. The term, “continuous frame” must refer to the cross members that tie the side frames together at each end. There seems to be no acknowledgement of the side frame design as anything unique.

But it appears as though the center bearing is bolted to the pair of iron transom beams, and that they are bolted solid to the side frames. I don’t see how springs would come into play in any suspension carrying the load on the center bearing. It looks like a rigid connection.

I can’t quite tell from the drawing, but there appear to be rather elaborate side bearing assemblies. Do you suppose those side bearings are riding on the apparent springs just to cushion and dampen rocking, but there is no spring suspension for the center bearing that carries the end of the car? I can almost interpret a vertical sliding sort of crosshead between the apparent coil spring and the top of the side bearing mechanism. If that is what is happening with this truck, it is extraordinarily unusual. But I don’t know how else to interpret that drawing.

Interesting. The truck shown on page 315 is also a swing motion truck.

http://books.google.com/books?id=Jv7VAAAAMAAJ&lpg=PA311&ots=4PoU8o01r2&dq=diamond%20swing-hanger%20trucks&pg=PA315#v=onepage&q=diamond%20swing-hanger%20trucks&f=false

If you look carefully at the traverse section in Fig 1953 you'll notice what look like the ends of swing links below the journal box, and you can see them in the sectional portion of Fig. 1952, flanking the journal box, also in side elevation Fig. 1951. Note these links are drawn as if they pass outside the bottom bars of the side frame. It appears the entire truck frame hangs from eight short swing links that hang on bosses cast on the sides of the boxes. Note the links don't have any inclination, so aren't self centering... well, I suppose weight will bring them to center, but they aren't self damping.

I agree with you that the centerplate is rigidly attached to the transoms, so must just be a pivot, and not bear any weight. Each side bearing sits on top of a spring and slides up and down between gibs bolted to the transoms. The lower end of the springs sit in castings hung from the transoms, maybe part of the same casting that forms the gibs. There does not appear to be any spring plank, because in Fig 1953 I can see the brake lever pivot attached to the brake beam at the far end of the truck.

That's what is so neat about stuff from this period. Nobody knew how it was supposed to look, or how it worked, so they just tried things; improved what showed promise, and discarded what didn't. It's a shame there is so little actual equipment from this period preserved.

The problem is to know how many were built and how long they lasted. There are lots of failures out there.

David,

When I first encountered this “mystery truck” with the photo of the 1904 wreck of M&StL caboose #12, I wondered if this was just something concocted by the M&StL shops, or was a standard design of that era produced by a manufacturer. I am amazed that so much of the mystery has been unraveled by further inquiry, and particularly in this thread. I see this as a sort of railroad archeology. Looking at the coverage in books such as John White’s The American Railroad Freight Car, it is fascinating to see how much variety of ideas there were in the 1800s. Railroading surely attracted the mechanically inclined, ranging from the practical to the bizarre.

This mystery truck genre with the four-bar side frames seems to have been used from 1856 to 1950. One unresolved question that might still be answered is whether any examples currently exist in preservation. I am particularly interested in car and diesel locomotive trucks because they are such dense and clever concentrations of mechanism. I am doing some work to model early car trucks in Solidworks 3D cad. This renders their structure and mechanism in easily understandable terms, and preserves their history.

Dennis,

I am pondering the drawing of the “continuous frame” truck on page 315 of Car Builder’s Dictionary (1888), and what you mentioned about the details and it being swing motion.

In the meantime, as to the sprung side bearings, your description fits exactly what I am seeing, although interpreting the drawing is not an exact science. But it does seem that the side bearings move up and down on top of coil springs.

That reminds me of another “mystery truck” that I brought up a couple years ago. That was the tender trucks of the late 1800s that have the load carried from the side sills, though big leaf springs, down to the tops of the journal boxes. They have a rigid bolster, and the center bearing telescopes up and down so as to not carry any load while accommodating the up and down movement through the big leaf springs. So the center bearings only have the purpose of maintaining the pivot axis, but not to carry any weight.

When I saw the apparent spring side bearings of this truck on page 315, I wondered if it could be doing the same thing as those tender trucks. But the truck on page 315 appears to have just a shallow center bearing plate, so there would be not provision for telescoping. I would expect a telescoping center bearing to have the bearing plate with tall flanges, maybe something like 6-8” tall.

If it does not telescope, then it carries the load. If it carries the load and the side bearings are sprung, then the side bearings only deflect when the car rocks. If the side bearings are sprung, that would be the first I have ever seen conventional side bearings that were sprung to cushion and dampen rocking. It would seem really strange to spring the side bearings, but leave the main load un-sprung.

Ron,

Yes, I remember that discussion, and was thinking the same thing. Apparently, with the light equipment of the time, they found it acceptable to use load carrying side bearings. I wonder exactly when they fell out of favor.

I disagree with your characterization of the center plate. Unfortunately, they have not provided a sectional view. However, if it was a load bearing bowl like a modern center plate, I would expect to see a raised rim, then a smaller central hole for the kingpin, which kept the body over the truck if it should get displaced. Not seeing a hole indicated, I'm interpenetrating the entire center as a hole, maybe 4" or 5" in diameter, which would allow deep engagement of a mating pin, essentially the telescoping arrangement you are looking for. I note that every other truck illustrated does show the central hole for what they call the "king bolt or center pin".

Dennis,

I see what you mean about the center bearing. There is no small hole for a pin, but rather, just an apparent flange ring raised maybe an inch above the mounting plate. But that ring may actually be a cylinder that also extends below the mounting plate by 5-8”. It may just have an open bottom. The end view is not in section through the center bearing, so the lower part of the cylinder could just be hidden by the iron transom channels.

If this truck carries the load on side bearings like those tender trucks did, I assume the point was to reduce rocking. Normal side bearings have some clearance before they engage the rocking car body. So the rocking can run free and gather momentum until it uses up that clearance. Then it dampens out that energy by pressing the side bearing and bolster end down onto the spring nest. Carrying the entire load fulltime on both side bearings eliminates that free play before they engage during rocking. So that would reduce rocking for better stability. The whole load of the car end would still be fully sprung, as both side bearings work either one at a time or in unison.

It would identical to the principle of those unique tender trucks, but with a different detail arrangement. I have never seen trucks with the design of those tender trucks under any rolling stock besides tenders. If that is what these trucks on page 315 are doing, that indicates that the principle of those unique tender trucks was indeed applied to freight cars.

For lack of any known historical designation, I am not sure how to label this design. They are side-bearing trucks, but all trucks have side bearings. In any case, this outboard suspension with a non-loaded, telescoping center bearing, as a design category, is the most unique departure in the entire realm of truck design and construction. It is counterintuitive because trucks need to pivot, and that seems to dictate that the load must be transferred through a pivot connection between the truck and car.

Ron,

Of course, we don't know how extensively these trucks were used, if at all. The truck illustrated on the preceding page is also a Boston & Albany "continuous frame" truck of a different pattern; a sprung pedestal truck with a normal looking center plate that shows the center hole. By the way, it appears the "continuous frame" refers to the fact that these trucks have end frames, like a traction motor truck, possibly intended more for the containment of broken axles than any structural purpose.

I actually scanned through the whole Google Books version of the 1888 Car Builder's Dictionary, looking for the mating part for this center plate; didn't find one, nor any car illustrations of a car so equipped. So it begs the question how extensively they were used.

While the full contact sprung side bearings might arrest rocking, they are going to increase the racking of the car bodies. Wood freight cars were never very resistant to racking, or "weaving" as was the term used to describe it. While the sides were well trussed, the roofs were not, and became parallelogram shaped, the leading edge changing sides alternately as the car twisted one way, then the other. It wasn't a huge problem as long as board roofs were used; they loosened up enough to accommodate the motion. When sheet metal became popular for roofs after the turn of the twentieth century, the trade press had continual complaints about leaky roofs. By the twenties, all the vendors sold "flexible" metal roof systems that solved the problem by allowing enough movement to accommodate the weaving without tearing the metal. The "all steel" roof products of the thirties were a continuation of the same philosophy, with interlocking panels connected with large pins. The problem didn't go away until the adoption of the "rigid steel" or "solid steel" roofs used on the standard design steel boxcars; these had heavier gauge steel panels riveted together to form one large shear panel. But all this came decades after sprung side bearings were tried and discarded.

Dennis,

The end bars of the continuous frame may also be to help keep it square. Those transom beams seem to be at quite a structural disadvantage for maintaining square tracking. However, the continuous frame, being fundamentally rigid right to the axles, has no way to equalize the four wheels. But I suppose the frame can equalize by the flexing of the cross bars at the ends. That may be why they are only single bars laid flatwise to the ground. I see what you mean about the side-load-bearing trucks increasing the body racking. The whole car body would tend to get involved with the truck suspension.

One issue with having the side bearings carry the load is that they must allow shifting in the horizontal plane as the truck pivots. Even the conventional side bearings, with only part time contact, have rollers to accommodate that horizontal shifting between the two elements of contact. I don’t exactly see rollers in the drawing on page 315. The same question applies to the tender trucks with these side-load-bearing features, although they are mounted closer together between truck centers on tenders. Maybe the components of these loaded side bearings simply slipped with friction surfaces to allow the truck to pivot. In a normal truck, even the center bearing has friction as the truck pivots. These side-load-bearing trucks are like a normal truck with a 3-4 ft. diameter center bearing.

If our speculation about the operation of this truck design is accurate, it may have been very limited in application, but the same side-load-bearing principle used in the tender trucks was extremely common, going back apparently to at least 1860. The latest application of that principle that I know of was on the tender trucks for the CMStP&O 4-6-0 class I-1 locomotives built in 1903. Those trucks appear to still use the arch bar frames, but use some extra beefy castings around the big leaf springs standing on the journal boxes.

There is an article about these engines in North Western Lines Vol. 22, No. 4. The article says that the I-1s were twins of the C&NW class R-1s except for the tender trucks. It comments that the I-1s retained the tender truck design from earlier locomotive design practice.