Interview with Stephen Heston and Austin Reid of Diabase and the Flexion Extruder

We told you a few days ago about Diabase Engineering’s new 3D printer. Intrigued by the 3D printer and the team behind it we did an interview with Stephen Heston and Austin Reid of Diabase. They make the H Series a $6900 hybrid 3D printer CNC machine with five toolheads. From the team that gave us the Flexion extruder soft material printing is, of course, a feature but so is a quick change head, active nozzle cleaning, quick change build platforms and many more. In a 3D printer world where you can hardly tell many printers apart the Diabase peoples are coming up with something very different. Whats more they have features that seem to be developed for people who actually use 3D printers rather than made by the marketing department.  These guys are 3D printer craftsmen who know their stuff.

A desktop CNC and 3D Printer isn’t that 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?

“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.  Regarding deposition, the Flexion Extruder is a well-proven product (it has funded our company for the entire H-Series development), so I won’t expend any effort stating our case there.
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 (in the 1000mm/s^2 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 generally for the machining of thermoplastics which do not tolerate excessive speeds and feeds, so the spindles are lower power than a typical router (6W and 30W 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.)

In summary, it is a good machine.

Why so many print heads?

Imagine printing a shoe sole – at a minimum, you would want a flexible material for the main body, a very-flexible material for the insole and tread, a rigid material for mechanical interfaces, and dissolvable support material. This is just a conceptual example. In reality, we often make use of all 5 heads. Also, not just print heads…tool locations. These can be additive, subtractive, measurement, or post processing tools. The H-Series is a mechanical platform. We plan to build out functionality in all of these areas.

Whose you’re ideal customer group for this machine?

For the Additive machine: Customers who have experience with multi-material FDM printing. For the Hybrid version: Customers who have experience programming and operating various types of CNC machines. This is not a machine for beginners.

Why introduce a machine?

Two reasons: to take full advantage of the existing capabilities of the Flexion extruder, and to establish a platform that will allow the use of new deposition technologies and build strategies. We have many technologies in both categories in the works and we were tired of being limited by the existing state-of-the-art.

The H even scans

Isn’t selling extruders a much better business?

We are not going to stop development or sales of extruders. The H-Series opens up the design space for us.

I’m a huge fan of the idea of a variable density insole, do you see that becoming popular?

Yes. We see footwear in general as a huge growth opportunity for this industry: including insoles, orthotics, and fully-customized shoes.

I’m just not seeing a lot of people extrude TPU and TPE materials, it is still too hard. Do you think 3D printing will change once that becomes more common?

Those people are using the wrong extruder. Printing with elastomers is actually much easier than printing with most rigid materials.

Whats a clamping mounting block?

It is a mounting block that includes a region that deforms into contact with the extruder barrel as a clamping screw is tightened. This provides better thermal performance than the common method of using a set screw to secure the barrel.

Does your Flexion HT also come with PTFE inserts? Won’t those degrade at 290?

Yes, but the PTFE liner ends at the heat break rather than extending into the hotend as it does in the standard Flexion design. So, the PTFE is not exposed to excessive temperatures.

What two tips could you give people new to 3D Printing?

1) Start slow, focusing on good bed adhesion and layer adhesion.
2) Don’t look at your machine as a black box that should make anything you desire. Learn how it works and design your parts for the process.

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