Is the H-Series Like a Duck?

One that does many things can’t be exceptional at anything.

As Joris from 3Dprint.com put it:

A desktop CNC and 3D Printer. . .that is kind of the maker version of a washer dryer? As we say in Dutch Not meat nor fish, as in not good at either of them?

Or compliments of Argentina:

Probably like a duck. Can’t walk well, can’t fly well.

This criticism is often warranted for multi-functional products, but not always. What good is a pickup truck? It’s not a passenger vehicle or a piece of construction equipment. That’s the snarky response, but we’ve heard this question enough times that it’s probably worth taking the time to give a serious answer.

“Good” is a loaded term in that question. For machine tool performance, people generally are interested in speed and accuracy…or more precisely throughput and accuracy.

For 3D printers, the question is: how fast can the machine put down material at what accuracy (and with what minimum feature size)? An important addition to this measure of good is: With what material properties? FDM is a slower form of 3D printing, but the speed limits are not entirely set by the motion control system. Layer adhesion generally suffers as you increase linear speed of the printhead. Elastomeric materials provide higher layer adhesion, but they have their own limits defined by the viscous flow at the orifice. At high rates of shear, the flow becomes irregular and the extruded bead starts to ball up. Each material has its own limiting factors. Considering that standard FDM speeds haven’t changed much in a decade, the question becomes: How does the H-Series compare to existing FDM printers?

A 3D printer can be broken into 2 main systems: deposition and motion control.

1. Regarding deposition, the Flexion Extruder is a well-proven product (it has funded our company for the entire H-Series development), so we don’t need to make a case for it here.

2. The question for motion control is: how well does the mechanical system maintain fidelity to the control signal as you increase rates? Tool loads are insignificant for FDM, so the system forces are all due to accelerations of the toolhead and/or workpiece. The design of the H-Series reflects the need for the mechanical system to withstand higher loads than a typical printer. The X and Y axes are low profile and are mounted to locations on the base casting where it is bolted to the table. This way, resultant loads from XY accelerations are not transferred thru the machine so they generate negligible relative motion between the printhead and workpiece. For the H-Series Additive machine, the mass of the saddle/Y-axis/bed assembly is minimized. It is comparable to the mass of a typical dual extruder gantry assembly. The Y-axis only moves the bed and linear rail assembly, so it is driven with a high torque Nema 17 stepper motor and a properly tensioned 6mm wide GT2 belt. The X-axis moves the full assembly, so it is driven with a higher torque Nema 23 stepper and 9mm GT2 belt. The sizing of the linear rods also reflects the loading condition of each axis (8mm diameter for Y and 16mm for X). The turret/arm assembly only moves in the Z-direction, and the high mass of this assembly is negated with a counterweight in the column. The Z-axis is driven on 16mm shafts with a Nema 23 stepper motor and 5mm pitch preloaded ballscrew. With this setup, we can perform quick Z-movements with very little deflection. All of this to say that the H-Series Additive machine measures up well to the best printers in its class.

If the question is: how good is the H-Series Hybrid Machine compared to typical FDM printers? That is no comparison. The Hybrid machine is beefed up to handle both machine accelerations and cutting tool loads. Supported linear shafts are used on X and Z, and the Y-axis shafts are increased to 16mm diameter. The X and Y axes are driven by preloaded high-lead ballscrews and Nema 23 steppers. The resulting drive ratio allows for fast travel speeds (in the 250~300 mm/s range), quick accelerations (1000 mm/s2 range), and high instantaneous speed changes (10~20 mm/s). Deflections are not a problem, but moving around a higher mass is more expensive in terms of electrical power. The relationship between mass and work is linear though, so the increase in energy consumption is not drastic.

The comparison of the Hybrid machine to typical FDM printers breaks down when you look at surface finish, accuracy, and minimum feature size (not to mention many other benefits). Milling operations far exceed extrusion printing in all of these categories. The only question is: how much time is added to a typical build for the subtractive operations. Depending on the geometry of the part and what surface finish you’re going for (defined by tool radius and stepover), subtractive toolpaths will likely be 5-15% of the total build. However, given that you can use larger nozzles and more coarse layer heights for the “near net shape” additive portion of the build, total build times often actually decrease.

The other end of the question is how “good” is the H-Series at machining? In this case we could frame the question as: What surface finish can the H-Series maintain at what chip load at what feedrate in what material? We will give a more quantitative answer to this question as we work through the testing matrix. But in the meantime, a qualitative answer is that the machine is more rigid than typical CNC routers in its price range, but less rigid and lower mass than a typical small milling machine. It is designed specifically for the machining of thermoplastics which do not tolerate excessive speeds and feeds, so the spindles are lower power than a typical router. (12W and 60W versions are available). Soft metals can also be cut at low chip loads, but this is not the target application for the machine. Metal chips create a host of other problems. We will build out capabilities in this direction as the market demands. (That goes for other functionalities as well.) The benefits of the H-Series Hybrid machine overlap with milling machines and routers, but they are different. With routers or machining centers, many parts can be quickly milled out of solid stock, but the material is usually more expensive and more of it is wasted. The H-Series also has the benefits of additive manufacturing: the ability to create parts with multiple materials and with complex internal geometries.

In summary, it is a good machine. A different kind of machine.