Full CNC Workflow with Different Materials

We are ready to move forward with milling various materials beyond simple testing. It is important at this point to have our machines calibrated and able to accept G-Code on an ongoing basis. As mentioned several times before, the type of material and the nature of the shape dictate the settings and how well our cuts come out. For every project there will be common and specific settings, tweaks, and other attributes that may be unique to the material, the machine, or the project itself.

Here’s where we will focus our attention in this chapter:

• Converting a non-CAD drawing into something your 3018 can process – a full workflow
• Working with soft wood that requires a delicate touch since the resulting parts may be fragile
• Working with soft metal, such as aluminum
• Working with hardwood (our example will involve attempting to engrave/carve a piece of 2x4 or some similar material)
• Understanding how to work...

Technical requirements

In this section, we are going to use several tools. You are not constrained to these tools specifically, but the idea is to apply what is out there to your needs. I generally like to have the following:

• Something that will convert an image to a vector graphic. This helps me make use of hand-drawn or scanned images that I would otherwise have to re-work. You would need to gauge whether the amount of re-work you must do is worth the effort or whether it is better to just redraw an object. I particularly use this kind of tool whenever dimensions are in short supply, or the scale is not clear or workable. For my BD-1 project, the drawing arrived scanned but also with some smudging on the lines.
• If you work with CNC, you will eventually have to learn how to use CAD to either create or change existing drawings. There are several free applications out there. I primarily use TinkerCAD, but there are others (free and not free), such as FreeCAD, Fusion 360...

Getting to G-Code from a drawing

One of my other hobbies is model airplane building and while I have mostly focused on static scale models, I also enjoy building RC airplanes, but I like to do so from plans, and most of the airplanes I like are not readily available in kit form and the plans themselves are not always clear or easy to read. A substantial effort has to be made to transfer the drawing to electronic form, scale it correctly, and then reliably pass it on to the automation to cut the part. One common class of parts are fuselage bulkheads. For small-scale models, balsa is called for, while larger models would do fine with plywood.

Here’s the bulkhead from the scanned BD-1 blueprints. Note that there are no measurements, so you would have to use a ruler to take your own – assuming your drawing will print properly at full scale.

Figure 5.1 – BD-1 scale model bulkhead

The first (full-sized) airplane I ever owned was a Grumman...

Cutting softwoods such as balsa and light plywood

For our purposes, I am using 3 mm plywood to cut out my bulkhead because most of the balsa wood in my shop is smaller planks for park-flyer-type (i.e., smaller scale) airplanes. I use the same plywood for model rocket fins, and while light and easy to mill and machine, it is very durable.

Both balsa and plywood are going to chip on the “bottom” surface (the surface facing the wasteboard) if we are not careful with what endmill we use. To prevent the “tearing out” that would happen with plywood, I recommend a flat-head downcut endmill. I am using a single-flute flat-nosed endmill with a 1/8” shank. These are commonly available from various vendors, and you should take into account that you will likely break a few as a matter of course. I like to keep my feed rate slow, at or below 1000 mm/s for thicker plywood and 2000 mm/s or less for thicker material. For the spindle, keep it below 24,000 RPM.

...

Cutting hardwood

Late this summer, my wife decided that the wooden table we had on our deck had outlived its purpose. Even though it was meant to be an outdoor table, it made it all of 2 years before the wood started to rot in some areas. Consequently, it had to go. So, I got to take it apart and since I did not really want it to go to the dump, I cut it up into pieces small enough to put into the trash or recycling. This is when I discovered the table’s legs were made of this exquisite and still good hardwood. Naturally, they encountered my miter saw and now, slices of the table’s legs are workpieces for my CNC machine and laser cutter.

The denser the material you cut, the more your machine needs to be rigid and your axes precise. As you gain more experience with various materials, you will find the feed rate for the denser materials, such as hardwood, will have to be slower and require multiple passes. As before, we are going to use a downcut bit because we want...

Cutting and engraving soft metals

Metals present a similar challenge to cutting hardwoods. Your endmill has to go through stronger material with the added problem that the metal-on-metal contact can generate lots of heat (you will generate heat with hardwood too, but more so with metal). When you cut metal, you can use air assist to keep your bit cool or keep spreading lubricant on your workpiece. Either way, if you thought cutting wood created a mess, cutting metal creates an even bigger mess. This is why I use a 3018 with a dust shoe hooked up to my shop vacuum whenever I am cutting metal. The 3018 is not really suited to cut large pieces of metal, but you can cut small parts so long as you go slow and make enough passes. For my purposes here, I am cutting a part to replace a plastic part on BumbleBee. The larger BumbleBee is meant to machine larger parts, but because some of its critical parts are made of plastic, it can’t really handle metal. However, I can have the 3018...

Working with foam

There is a type of dense foam material you can buy at your local DIY store that is typically used for insulation but is an absolute boon if you are an RC airplane or model enthusiast. The foam is typically called extruded polystyrene and comes either in pink or blue sheets. I am not a fan of milling styrofoam. This is not because it is not possible, it’s just that it is much messier because bits of foam cling to everything. However, all foams generate dust that is very bad for your health. So, it is doubly important to have a vacuum dust collector on your machine and to operate the machine wearing a respirator. Make sure you clean up thoroughly afterwards. You might even consider keeping your machine inside an enclosure while it is cutting foam to maintain control over all the dust. Here’s what dense foam sheet looks like:

Figure 5.11 – A sheet of dense blue foam used to form fiberglass parts for my airplane. Note the...

Engraving your workpiece and setting depths

Let’s now tackle engraving your workpiece. Maybe you have cut your part on the 3018 and it looks awesome, and you’d like to mark it in some way. Here are some engraving use cases:

• Decorative purposes
• Adding a logo or some sort of identifying mark tying the part to you
• Inventory and serial numbers – so that you can tag a certain part
• Graduation markings (for example, ruler notches for measurement)
• Labeling (for example, to indicate the function of a control that might later be attached to the finished product, such as an indicator of where the on/off detents are)

If you are working with opaque materials, letting paint (or for wood, stain) seep into the engraved areas will enhance the visual attributes of the marking. On/off marks can be marked in red on a white surface, while ruler notches might be in black on a metallic piece. Engraving need not be done with an endmill, and in fact, I generally...

Summary

We’ve covered a lot of ground in this chapter. We invented a workflow to go from a scanned or hand-rendered drawing to a physical object. Congratulations! You now know how to turn a picture, or even just an idea, into something you can hold in your hand and actually do something with.

We also did some hands-on investigation into the effects of cutting different materials and saw what we needed to do to successfully complete a project, including doing some prototyping. At this point, you should be fairly comfortable using your machine to finish your projects. This is important because in the coming chapters, we will be exploring enhancements to our 3018s as well as investigating how we might CNC on a 4th axis.