Project: Building Your Own 4th Axis

Previously, we looked at a rotary axis for your 3018 that was commercially produced. However, we may want to create our own with its own particular features, including the ability to hold components much like you would on a lathe. Rather than depending on the symmetry of the object being machined so that it rotates evenly on rollers, you may want to work on parts that would otherwise not sit on a store-bought 4th axis in a stable fashion. An example might be a narrow cylinder shape, or one that doesn’t have a consistent diameter (such as a bottle). To that end, we will look at building such a unit for your 3018 based on work by ZenziWerken. You can have a look at his original design here: https://www.thingiverse.com/thing:2344975. In this chapter, we will look at the design and update it as necessary for our purposes.

As part of this project, we will develop a few skills and recycle what we have learned with the store-bought 4th axis:

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Design is the starting point

The design presented is made up of several components, mostly fashioned out of flat stock. Originally planned to be made out of 6.5mm plywood, your 4th axis structure will be fine with 6 mm (1/4”) plywood from your local hardware store. If you decide to make yours using the 3018, you can use the original design, but you will have to find exactly the same components the original demands. However, in my case, I was unable to find the same parts and I had to improvise. I was also concerned that the gears in the original design would not hold up to extended wear. Because I needed to experiment, I converted the design to STL files so that I could 3D-print the parts as part of my prototyping effort. To that end, I had to modify the design by uploading the SVG file provided to TinkerCAD and make my modifications there. Also, because I needed to do some quick prototyping, I 3D-printed my parts. Let’s start with what the original SVG file looks like...

Fabrication

After several iterations, I was able to settle on a set of components for the project. Here is an image of all my attempts to get this right.

Figure 9.8 – Parts from the prototyping effort

Once you have all the parts fabricated, you can go ahead and do some test fitting before assembly. Here is my frame (I decided I don’t need the “tail stock” portion of this for my purposes).

Figure 9.9 – Test-fitting the axis frame

You can see how I had to do a lot of filing to get everything to fit properly, but that’s only because the tolerances are so tight. You can always experiment by changing the scaling to go down by fractions of a percent, but that seemed like a long and drawn-out process when I could get things done faster with some post-fabrication trimming.

Here is a parts list for the 4th axis. You should be able to use any NEMA 17 stepper motor, and you are likely to have...

The final assembly

We now can proceed to complete the assembly of the 4th axis (again, note, that I don’t need the tail stock, but if you need it because you have a very long cylinder to machine, you should build it in exactly the same way we did the main component).

We start first by mounting the pulleys on the motor and the chuck shaft. We also need to install the 8 mm collar on the chuck’s shaft, between the plates. Do not tighten the grub screws on the collar just yet. As an option, if you have enough shaft clearance, you can put a collar on either side of the plate to hold the chuck securely against the bearing, even though you have glued it into the bearing’s bore. Here’s how the 60-tooth pulley and collar fit on the chuck. This is just for illustration; you will need to assemble this element with the plates in place.

Figure 9.15 – The chuck and pulley assembly (without the front and rear plates)

Next, secure...

Installation and settings

Note that in the original post by ZenziWerken, his gear reduction is 6:1, while ours is 3:1 (60 teeth against 20 teeth). When you add in the circumference of your workpiece, you will be able to determine how much linear travel in the 3018’s X axis each revolution produces. For example, using ZenziWerken’s 40 mm wheel, we can use the following formula:

40 x π (or 3.1415) = 125.66 mm

Taken against a 3:1 gear ratio, it’s 125.66 / 3 = 41.89 mm

Just as before, the motor plugs in place of the existing X-axis motor on the CNC machine, and just as before, the 3018 will think your round object is really flat and cut into it as such. Remember, if it seems like your axis is rotating backward, simply flip the plug on the 3018 board.

Whether you use your end mill or your laser, you can now fabricate on round surfaces that can be suspended above the work table.

Summary

We learned a number of things in this chapter. We, again, learned how to adapt a design for our own purposes and use some basic ideas to use parts we could find in place of parts we could not. We also had a sneak peek at what it takes to convert a CNC-ed part to a 3D-printed part. Finally, we assembled a 4th axis that we can now use to machine or engrave cylinders of various sizes. One thing we did not take into account in this chapter is nonlinear cylinders, and this project is really meant for surfaces that are consistent – that is, the cylinder’s work area does not have a changing diameter. However, there is nothing stopping you from working on a cylindrical surface that does have a changing diameter – you just would have to set the CNC machine to work each linear segment separately.

Let us now move on to the next chapter and look at creating a “poor man’s 4th axis” for our 3018. This will allow our 3018 to cut things such as...