If you’re a fan of 3D printed RC cars, then you’ve got at least one thing in common with September designer of the month, Brett Turnage! Brett has contributed a lot to the 3D printing and RC community including his RS-LM 2014 Audie R18 E-Tron Quattro RC car and adjustable suspension chassis. He’s also interested in CNC milling and is here to talk about how you can use 3D printing and CNC milling together.
If you are on Pinshape, then you most likely know how 3D printing works. What you may not know is that there are now desktop CNC milling machines which can also create 3D objects. I want to explain the differences between 3D printing and milling while showing how they can work together. I will also describe my experience with using a desktop CNC mill.
What is Additive and Subtractive Manufacturing?
3D printing is an additive process where you start with a blank bed. Objects are created with melted filament, with one layer at a time building on top of the last until you create your final shape.
Addictive Manufacturing, Simplify3d slicing
CNC milling is the reverse, instead of starting with a blank bed, you start with a base form called a “stock.” This stock can be a block of wood, plastic, or metal (or a variety of other materials) that the machine cuts down—layer by layer until you have carved your final shape.
Subtractive Manufacturing, Fusion360 CAM (Computer Aided Manufacturing), water block for 3d printer.
Available Desktop CNCs
CNCs are usually large industrial machines that can cost the same price as a car—some as much as a supercar. They are not known for being something that an untrained person can use, let alone something that will fit on a desktop next to your computer. Today, there are three options that fit that criteria: Othermachine Company’s Othermill Pro, Carbide 3d‘s Nomad 883 Pro, and Inventables Carvey. All three of these mills are enclosed, small enough to put on a desk, and are aimed at making milling easy. They all have their own software program that can handle 2D items or engraving, and all come with a one-year commercial subscription to Autodesk’s Fusion360 for its CAD/CAM program for designing and milling more complex items. Students and hobbyists also have unlimited free access to use Fusion 360.
CNC mills do vary in weight: the Othermill Pro is portable weighing only 16 lbs where its counterparts are near 70 lbs. The weight difference is due to the Nomad 883 Pro and Carvey’s frame being made of steel, where the Othermill’s innovative construction achieves a rigid frame while using lightweight materials. These mills range in price from $2200 to $4000. They all use a 1/8” er-11 collet and require endmills (a tool that is similar to a drill bit, but is designed to cut laterally instead of just vertically). Since these mills are small, they lack the horsepower of larger machines so milling has to be done in small layers with the tool moving at high rpm.
Benefits of Desktop CNC
The benefits of desktop CNC are that they are able to make a billet part. Billet means that the item is carved out of a solid material. Solid parts are stronger than parts that are made in subsequent layers. The other benefit is the wide variety of materials that they can cut. The general rule for these machines, is that they can mill anything softer than steel because they do not have coolant being sprayed on the cutting tool and the workpiece. Harder materials like steel require coolant to prevent overheating of the cutting tool.
Assembled water block made with Othermill
3D Printing and Milling working together
3D printing is great for quick parts when figuring out a final shape. It used to be known as rapid prototyping and it shines at making and testing new designs of parts inexpensively. When I make my RC cars, every part is tested multiple times before I get to the final part. This constant testing and refining is invaluable, and the fact that 3D printing does this cheaply means that I can keep testing different designs until I finally find the one that I like. This would be impractical if I was using the mill for this task, but the mill can take over when the 3D printer is done, making a final part out of solid materials like metal. So in this way, they can work together, with one doing the prototyping with inexpensive materials, and the other making the final part out of more expensive materials.
Water block that was milled with the Othermill installed on printer
My Experience with Othermill Pro
I have an Othermill Pro. It was originally a Version 2, but was recently upgraded and rebranded by Othermachine. The Othermill is primarily marketed as a PCB (printed circuit board) prototyping machine. I believe that does not fully characterize the machine capabilities because it is a powerful mill that can cut any material including aluminum while being lightweight and portable. I exclusively use it to make aluminum brackets for printers and for cars. It works for many other tasks and projects that are non-PCB related.
Othermill Pro milling 6061 Aluminum
Setting up the machine was extremely easy: you place it on a table, plug in the power to an outlet, attach a USB to your computer, and download the host software, Otherplan. The software walks you through the initial setups of locating the bed and any brackets, and locating the tool (which automatically sets the z-height). It also comes assembled, unlike some 3D printers that may need some setup or modifications to start working reliably. All you need to supply are endmills and materials to cut. It has windows on all sides, which are attached with magnets. If the windows are removed while the machine is in operation, it automatically stops the tool.
Using a mill requires you to think differently than when using a 3D printer. The cutting tool only moves down, so any overhangs and bridges cannot be done in one pass. To do this, you will need to run one cutting path, and then re-orientate the stock to run a second procedure. I exclusively use Fusion360 for designing my parts and figuring out my cutting paths because I mill complex designs. Unlike Otherplan that makes it very easy to figure out things like facing and clearing, Fusion takes some trial and error in determining which tool path looks the best and produces your desired result.
The Pro, offers a custom designed motor that can spin the tool to 26,000 rpm. The faster the speed, the faster I can cut. The Version 2 only had a top rpm of 16500 rpm, so although it was no slouch, I had to keep my federate down because my tool might stall if it hits a rough patch in the material that I was cutting.
Close up of milling 6061 aluminum
The Othermill has become essential to my workflow. It is so amazing to now be able to make intricate parts out of aluminum or plastic—parts that I can use on vehicles or printers. It has opened up a new world of possibilities for things that I can make and avoids the extra cost and wait times it would take if I subcontracted to a CNC shop.
Although I love the mill, its small size does mean that I am restricted from making very large parts in one piece. It has a build area of 5.5” x 4.5 x .1.6 so it is great for small parts.
The main downside to milling is all the cleaning. If you are a person who hates to clean then owning a mill will be a challenge because every time you use it, you will have to clean up the mess. A shopvac and a tiny brush are a must.
Final Thoughts on 3D Printing and Milling
I have read articles that suggest milling is superior to 3d printing, and that it can deliver what so many articles of 3D printing once promised. However, I do not see it as so black and white. I think that if you know that you need a mill then you should buy a mill, but if you are on the fence and struggling between whether you should buy a 3D printer or a mill, here’s some things to consider. If you don’t know how to use a CAD program, then you might want to choose a 3D printer because you don’t have to learn a CAD program to make 3D printed parts. However, if you already have a 3D printer and you love making stuff, then adding a mill can give you a lot more options and capabilities. In this way, I think it is not a question of whether desktop subtractive manufacturing will overtake additive manufacturing, but how they can compliment each other and enrich the lives of makers and fabricators alike.
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