Any R&D exercise is only as good as its test environment and I have previously written on the modifications carried out to the baseline Wanhao Duplicator i3 that I use for materials development testing.
First thing to say is that I chose this model for several reasons that go beyond simple cost and include the ability to modify the machine component by component. Only by changing hardware parameters can we explore how a wide variety of customers will experience the end-product. That could be done through recruiting a test panel with access to a wide variety of printer hardware but in the first instance we need to be able to provide a performance envelope so that we are not asking that panel to take too many risks with their machines.
The first mod that I carried out was to build the printer a cabinet. This was a cheap Chinese server cabinet, so 100% metal-built and flameproof, but more salient is its ability to block drafts and maintain a constant temperature.
Second mod was the replacement of the hot-end with and all-metal product from Micro-Swiss. This was done to simulate higher-end printers but also on the assumption that it would allow more reliable printing at the elevated temperatures that the Fishy Filaments recycled nylon requires. Actually it didn’t perform well at all. I found that the aluminium barrel (the piece that replaces the PTFE tube found in most hot-ends) promoted deposition of nylon rather than preventing it. I can’t say whether that is due to friction, surface scoring due to repeated cleaning, heat distribution or any other reason, but what is apparent is that the PTFE system works better overall, even at 275°C. I have now swapped back to the original hot-end, albeit with a new heating element and thermister.
However it isn’t perfect and at that temperature, probably due to differential expansion, the fit between individual components of the hot-end isn’t really close enough, so it allows leaks of molten nylon to seap through threads.
The third mod is relatively minor and is difficult to assess definitely. I replaced the plastic extruder plate and spring loaded lever arm with a machined metal version, again from Micro-Swiss. I was concerned about filament slip as the extruder assembly heated up and could see the possibility of flex within that component contributing to that issue. I can’t say whether the replacement is much better or any worse on its own, but I don’t intend to swap it out at present.
The fourth mod was removal of all cooling fans from the extruder assembly. Which on the face of things sounds crazy given the other issues and modifications carried out. Why would I deliberately make the extruder assembly cooling less efficient. Well, its difficult to get a machine rated to 260°C to operate at 275°C reliably and the fans just get in the way. Airflow fluctuates as the extruder travels around the bed, heat is sucked away from the surface of the hot-end and the leaky material flow needs frequent attention to keep print quality high. All in all its just easier not to have fans getting in the way. Most makers of printers rated for nylon recommend no cooling on the print itself as a means to promote inter-layer adhesion, so I’m just taking that advice a step further.
The fifth mod is swapping out the covering on the aluminium bed for a borosilicate glass bed. I noticed that bed levelling was getting increasingly difficult through testing as I pushed the existing system to 110°C. Bed warping is not unknown, especially at the lower end of printer specification, as the cheaper bed heating elements are close to being a point under the centre of the bed rather than a trace element covering the whole bed. You end up with a central hot spot with bed levelling adjustment screws located as far away from that spot as possible. Getting a true level surface becomes a bit like juggling jelly as you try to balance the bed temperature at the time of adjustment with the inevitable finger burn of levelling a bed running at over 100°C.
Covering the bed with a glass surface provides a means to avoid that warping, reducing levelling time and reducing the frequency of levelling. It also provides the opportunity to remove the surface from the printer, making printed form removal and tape renewal far easier, especially when you have a cabinet around the printer.
None of this will greatly shock the 3D printing officionados out there. All the techniques have been tried and tested by others but what I’ve ended up with is a test rig that simulates aspects of printer design that different printer makers have addressed in different ways. Only by fully understanding the design decisions made printer makers can we provide advice on how to cope with variations away from the manufacturers nominal use profile. If there were any field of manufacturing where deviation from the equipment maker’s instructions were likely it is 3D printing, so to me this attention to detail lies at the heart of being a good materials supplier; anticipating the issues that your customers might encounter and finding potential solutions before they get there. Or if you prefer, this is the old adage ‘Walk a mile in another person’s shoes’ at work in defining a customer experience.