The Walking Beam Project

Ladies and Gentlemen,

It is my honor to present the crown achievement of Pawel’s 3d printing craftsmanship so far! The Walking Beam project! Brace yourselves- a long post is coming!

It would be good at the beginning to explain what is a walking beam and how did I get the idea to make one? I am working in sales of steel industry at the moment. We are dealing with lifting of steel coils that weight tens of tons. A coil can be sometimes 2 meters in diameter and weight for example 35 t. In order to speed up feeding of processing lines, the coils are put on “saddles” and then transported by special cars or by walking beams. A picture tells a thousand words, so here is a scheme of walking beam in action.

The coil rests on a saddle (1). The beam is lifted with the coil resting on it (2). Then it moves to next position and is lowered (3). The coil now rests on next saddle and the beam moves back to the starting position (4). It is easy to imagine that the beam can be longer than 3 saddles, and that it can transport more coils at the same time- smart and very effective.

I decided to make a model of such a machine that would transport wine corks.

The big industrial walking beams are driven by powerful hydraulic cylinders. My goal was to make everything mechanic (gears). I also wanted to have only one “power source”- a single rotating handle that would go in one direction and allow for all the cycle to take place. Furthermore it would be fun to rotate the handle several times before the cycle was done. The target were 3 handle rotations to lift/lower the beam and 5 rotations to move it left/right.

The question was: how do we make the machine first to lift the beam (keeping it still in horizontal direction), then move it only left, then down and then right? I needed two systems: lifting and transverse. Each needed to have its “action phase” (move or lift) and a “pause phase” (when the second system would be working). They should also be able to automatically switch between each other. And of course all had to be driven by one handle going rotating in one direction :)

First let’s talk about the lifting system. The heart of the mechanism I used looks the following:

I divided 360 deg into 3/16, 5/16, 3/16 and 5/16, that is 67.5 deg, 112.5 deg , 67.5 deg and 112.5 deg (three rotations for lifting and five for transverse, remember?). The 5/16’s are parts of two circles representing “pauses”. Their radius difference is equal to desired lifting distance. The 3/16’s are the lifter’s “action phases”. The beam is resting on the top of the lifter, which is rotating with constant speed. The animation below demonstrates how it works.

Now it is time for transverse movement. How to make it go left, pause, then right and pause when the drive is rotating in the same way? At first I thought about some particular half-gears with reducers and different number of intermediate gears. This seemed a bit complicated though- it will do nicely as another project. For my walking beam I used a simpler solution. I fixed the transverse drive gear (TDG) in one spot and made it rotate with constant speed in one direction. Then a frame was put “around it” with teeth on the top and bottom. Depending on whether the TDG is touching top or bottom teeth, the frame would move left or right. The lifting system was used to change which teeth are touched. I got the “action phase”, “pause”, “action” and “pause”. In addition, to prevent unwanted movement, final teeth in the frame were removed. The schematic animation below shows the idea in action:

This system has one big flaw- it can only transport the corks in one direction. At the same time it is simpler to implement and more robust to inaccurate synchronization.

Having the idea fixed I started designing the machine. I calculated gear reductions, movement distances, general overlay- well, some theoretical stuff. Then it was FreeCAD time. Finally I had an excuse to learn a bit Python. It was not very tempting to make every gear or spiral “by hand”, and having a nice procedure that could do it for me made my life much easier. Especially that there were lots of different gears to be done.

I was advised by the organ between my ears to first allocate the moving elements in space and then think how to make the supports and frames. The machine was supposed to be compact and should allow for easy dismounting and access to the parts. And of course each element was to be designed in a way that would allow printing it. It took quite a few evenings, few weekends and finally I got the design ready:

Doesn't it look awesome already?

One could ask: “why didn't you start printing when you had some parts of the design ready”? Well I did. At least few gears that I knew that were in their “final” form were printed during FreeCAD period. The rest was being modified a lot on the way. Fixing any shape by printing it puts a big constraint on other part’s shape. Being perfectly honest- I made one or two design mistakes on the way but in the end the errors were insignificant. I was able to repair them with few moves of a file and a tiny bit of glue.

In general all the parts were printed in their desired final shape and required only surface cleaning from the printing residual trash. Most important elements’ surfaces were additionally treated with acetone to get a nice smooth finish. Also due to 3d printing limits five parts were intended to be made of several elements glued together.

OK enough talking! Here are all the elements of the “Walking Beam”! Next pictures show the assembly of the whole machine. Isn't it even more awesome?

I am particularly proud of the spirals. If you take a closer look, they have different slopes and one is a single helix while the other is a double helix. For the double helix system I also had to make the gear with inclined teeth so it could fit within the gap. Here are some close-up pictures.

Finally I present to you the movie with the Walking Beam in action!

Thanks for sticking this long. I do hope you (or at least your inner-geek) enjoyed the content. I had great fun making this project and am looking forward to doing some more. Your “views”, “likes” and “shares” are an awesome recognition to all this effort and for sure will boost my engines to spend more time on 3d printing. Thank you!