Bridge Crane build

[rabler]

Plus, that failure isn't catastrophic in this design.

Ran the numbers. As long as I keep at least 2 1/2 inches below the truck saddle using 3/8" plate, I'm the below the 1:5 overbuild criteria generally associated with metal fatigue. Since that plan calls for 3" I could run the same truck for a 3-4 ton crane.

 

[rabler]

Here's a CAD drawing of the side roller assembly to go with the trucks previously drawn. Green is a R12 roller bearing. Bolted to the outside of the truck frame these will extend through the slots just enough to provide guidance. The bearing is 7/16 thick, the slot is 5/8 wide, so some washers can be used to adjust the bearing height fractionally. I'll do some chamfering on the blocks to make them a little nicer, just not worth trying to wrestle FreeCad for cosmetic features. The offset (flats) on the shaft help extend the bearing through the sidewall. An R12 bearing is 3/4" shaft, 1 5/8" OD, so 7/16" radius from shaft to outside. Since I'm looking at 3/8" thick truck sides, that would leave the bearing only reaching in by 1/16". The 1/8" flat gives me a whopping 3/16".

These don't need to run "tight" against the side of the rails, they're effectively frictionless bumpers. So I'll probably target .25" total gap on each side from the edge of the rail to the inside of the truck. That leaves 1/16" of play (bearing face to rail edge) on either side if everything is perfectly centered. That should be enough to let the truck set onto the rail -- keeping in mind that the trucks will be loosely attached to the bridge beam and all set in place as one assembly. Although what'll make the most sense is to set them in place without these blocks attached and bolt the blocks on after the trucks are hung. Also bolt the retainers on.

 

[rabler]

Yeah, I'm just playing around in CAD while recovering from last weeks misadventures. But here's the roller assembly as currently conceived for the truck on the edge of the bridge. I threw in another copy of the truck picture for reference.



The picture on the left (or first picture depending on your window size) is the exploded diagram of the roller. I'd like to keep the roller fairly large as that minimizes the tendency of imperfections in the rail to cause catching, i.e., it rolls smoother. Using tapered roller bearings means needing adjustment to get the right preload. So the leftmost piece is essentially a fine thread nut with an internal lip to preload the bearing. (I didn't include threads in the CAD image as that creates a rendering challenge). Generally for a bearing pre-load you want fairly fine threads, much finer than the 2.25" ID of the nut would normally entail. This allows the preload to be set without having to turn the nut to sub-degree accuracy.

Lots of little features not shown, like grease fittings, etc. This is just playing with ideas.

The purple and yellow endplates are what bolt from the outside to the truck body. Note that these are intended to have an inner lip that registers in the hole in the side of the truck body, so that the load is carried by the lip, and the bolts are in tension only. Basically the bolts hold the axial force while the lip holds the radial force which is the actual weight of the lifted load plus bridge.

Since the roller is meant to be driven by the axle, it is means they are either a single piece, or they are bolted/pinned together. Or I suppose you could shrink fit the roller to the axle.

Pinning/bolting has the advantage that the roller doesn't need to fit through the side hole of the truck, it could be placed in first through the bottom, and then the axle and bearings inserted. That would reduce the hole size in the truck from ~4.5 to roughly 2.5", which matters little, but more importantly the bearing plates (purple and yellow in the first image above) could be made from smaller material, probably 4" diameter stock rather than 6", which is a significant difference in cost.

 

[rabler]

Here's another rendition of the truck based on a pinned axle design (see the last paragraph above).

The plate on the lower left (pinkish?) is the fixed plate. The upper right is a threaded plate and nut (threads not illustrated in CAD). Obviously this would be a fixed and threaded plate on either side of each axle. The little orange parts are grease seals.

 

[extropic]

I didn't notice any question marks in your last two replies so I prefer to ask if you are interested in reading an alternative design approach for the rollers/bearings/shafts/retainers?

 

[rabler]

I didn't notice any question marks in your last two replies so I prefer to ask if you are interested in reading an alternative design approach for the rollers/bearings/shafts/retainers?

Sure

 

[extropic]

What bearing P/N are you depicting?

 

[rabler]

What bearing P/N are you depicting?

Ray
Does that matter? Tapered roller bearings. I’m open to ideas but lets not play 20 questions.

 

[rabler]

Here's the latest CAD rendition. This design would require putting the roller in the truck through the bottom and then pinning the axle into it, probably with spring pins. Bearings are blue. Grease seals are orange. Side "guide" bearing on the lower right. The orange strip on the right side going out of the frame on top is the retainer strip to keep the truck on the rail in case of earthquake

I'm leaning toward this version over the through-the-side version. I may shift the entire side plate down another 1/2" relative to the top rail face.

 

[extropic]

Sorry. I shouldn't have bothered you. Disregard.