woensdag 23 mei 2018

3D Eksperten Silky Gold and Copper PLA review

I have been looking for a gold-like filament for a while, and it proves difficult to find one that has a convincing metallic appearance. Many filaments with ‘gold’ in their name are merely a yellow or orange colour with perhaps a hint of metallic additives. For instance I bought a spool of Polaroid ‘gold’ PLA and even though it is overall a good material, it proved to be merely a deep yellow with only under ideal lighting conditions a very slight metallic sheen.

A while ago I saw some makes on Thingiverse that looked quite promising, and the author was friendly enough to tell me that the filament was ‘Silky Gold’ from a Danish manufacturer called 3D Eksperten (3DE). At that time 3DE didn't ship to my home country and only offered expensive express shipping. I checked out the store again after a few months and they did ship to my country with an option of more reasonably-priced shipping, hence I ordered both a spool of the Silky Gold as well as Silky Copper. I added the latter not only to reduce the relative shipping cost, but also because it looks stunning on photos. The total cost was about €60, which means €30 per 1 kg spool which is reasonable for a specialty filament. In hindsight I should also have added a spool of Silver to have a full set of shiny metals, so I know what to buy the next time.

Despite the cheaper shipping it still arrived within a mere 3 days with tracking information. The filament comes in stylish boxes and is packaged in resealable plastic bags with of course a packet of silica gel contained within. This is nice but I have learnt that all plain plastic bags are only weak barriers against moisture: they will only slow down the rate at which moisture can reach the spool. For this reason one should refresh the desiccant in such bags at regular intervals, and for longer-term storage it is recommended to use mylar bags instead. Those have a metallic layer that is much better at stopping moisture (this is why all foodstuffs sensitive to humidity are packaged in metallic bags). The desiccant inside these particular bags proved to have absorbed near their saturation level of moisture, so I dried the filament in an oven to be absolutely certain it was in optimal condition. A weight comparison however showed that it hadn't taken up any noticeable amount of moisture.

The spools themselves sure do look promising out of the box, especially the copper one which looks like a big transformer coil. I have never seen such a convincing plastic simulation of a metal. The gold is very nice as well, still obvious it is merely plastic but it comes closer than any other attempt I have seen so far. It wouldn't be the first time that printed objects lose the appearance of the raw spooled material however, so the proof is in the pudding and it's time to load up this stuff and get printing.

The tolerances on the filament are within the typical ±0.05 mm range. On the gold I measured an average diameter of 1.77 mm, on the copper 1.72 mm. These diameters remained consistent over the length of material I have used so far. The filament also appears well wrapped without risk of tangling, something that cannot always be said from the cheaper brands. I used my typical PLA settings of 200°C extrusion and 60°C bed temperature, on a glass bed with 3DLac and moderate cooling fan speed. Adhesion is excellent even with only a thin layer of hairspray. There is no obvious odour during prints, not even the typical popcorn-like smell of regular PLA.

I started out with my traditional test print, a variation on the classic 20 mm calibration cube printed at 0.2 mm layers. This already looked very promising: the surfaces are shiny enough to reflect light like actual metal albeit with a matte finish (a true mirror it ain't). I then printed the 3DHubs Marvin (or rather my ‘improved crotch’ remix, which is a good test for overhangs and rounded surfaces. These looked even better, especially the copper one which from a distance could easily fool someone into believing it is made from actual metal.

The Marvin prints do show it is even more essential to avoid visible seams with these filaments than with most other materials. The glossy effect is visibly disturbed at the places where an outer contour starts. To understand why, we need to make at least a good guess at how the metallic effect is achieved.

Left: piece of free-air extrusion, right: normal printed extrusion
Close-up view
A close-up view reveals the usual trick of mixing in little metallic specks is not being used. Instead, there is a shiny effect that varies with extrusion direction. How does it work? There are two important observations: one, both the spools and the printed results reflect light only at angles perpendicular to the direction of extrusion. Second, the filament tends to contract very quickly in the direction of extrusion when extruding in free air, and the end result loses its shiny appearance altogether and becomes a plain dull yellow or orange strand. I can only explain this by assuming that the plastic contains a kind of elastic fibres that become glossy when stretched (like silk indeed). During normal extrusion the material is not allowed to contract, which ensures that the fibres remain stretched. For the same reason you should not print this filament too slowly: if the extruder keeps heating the same part for too long, the shiny material gets too much time to lose its ordering and gloss.

This also explains why seams are especially visible: the extrusion changes direction abruptly at the start of the contour and it takes about a millimetre until the fibres are fully aligned to the new direction.
Vase mode print of thing:415360 by Alphie

There is unfortunately no magic solution to hide seams. If you're lucky, the object has enough concave corners to allow your slicing program to hide the seams inside. If not, a typical strategy is to randomise the starting point of the contours but this will leave the surface littered with quite visible specks due to the effects described above. The only way to eliminate seams is to print in ‘spiral vase’ mode when possible. I have done a few vase prints and they look impressive.

Objects with many different surface orientations are the most rewarding hence I made a vase model with faceted hexagonal outer surface specifically to showcase this filament. Also when printing coin- or medal-like models the best results are obtained when keeping the special properties of the filament in mind. Top surfaces of coins should be printed as one continuous spiral in order to get a finish that has no seams and reflects light in interesting ways.

Left coin was printed with spiral top infill, right with plain rectilinear. Model by FLOWALISTIK. (Too bad these aren't worth actual Bitcoins…)
The material proves quite tough: extruded material doesn't break easily and is not easy to cut up. If my fibres theory is correct, perhaps they also contribute to strength. While I consistently have stringing problems with almost all other PLA filaments in my Micro Swiss all-metal hot-ends, these silky filaments are much less prone to stringing, perhaps again thanks to their tendency to quickly contract in free air.

There is one problem with ordering this filament and it is that the 3DE store is mostly in Danish only. The language is similar enough to my Dutch mother-tongue that I managed to get through the ordering process with the occasional help of Google Translate, but it may prove challenging for people from other countries. Also, no shipping outside the immediate surroundings of Europe. On Amazon one can find similar filaments which might come from the same source (judging from the similar hexagonal pattern on the spools), so it is worth trying if you are not able to order from the 3DE store.

To conclude, this is a great filament for decorative pieces and medaillons or coins. The copper is obviously my favourite because it comes very close to looking like the real thing. The gold may not be able to fool anyone but still it looks better than other attempts at a ‘gold’ filament I have seen.

zondag 15 april 2018

Hacking the 4th generation IXO: white instead of yellow LED

I have a 4th generation Bosch IXO screwdriver and it is pretty good, aside from the measly LED that is supposed to help light up the thing you're working on. The LED is a yellow-orange color and is not very bright. It also has an uneven circular intensity pattern. In other words, it is pretty useless. I have been planning to replace it with a white LED for a while, and it seems I am not the only one with this idea. A bag of Nichia NSPW300DS 3 mm LEDs has been sitting on my desk for more than a year and I finally decided to have a go at it. These are probably not the brightest 3 mm LEDs currently available, but they were available at the shop where I usually buy components, and 15000mcd isn't bad at all.

However, as Joken mentions on his IXO teardown post, one cannot just replace the LED: the yellow LED is only supplied with 2 V through a 68 Ω resistor. Dropping the resistor only gains about 0.7 V, and 2.7 V is still way too low for a typical white LED that requires about 3.2 V.

I have a solution though: I bought some booster circuits from AliExpress a while ago, in fact these are buck/boost circuits that provide a steady 3.3 V output from any input between 1.8 V and 5 V. They aren't terribly efficient and I don't need the buck capability here, but the PCB is tiny which makes them a good candidate. They look like the following photo:

I did some tests by connecting the booster instead of the LED+resistor, but it is unable to reach 3.3 V with the white LED on its output. This is because the circuit that drives the LED seems to be a current source, limiting the current to either 11 mA (when pressing the switch without activating the motor) or 20 mA (when the motor is active). Due to P = U⋅I and some loss due to inefficiency of the booster, it can only push either 4.5 mA or 10 mA through the white LED. However, there is a way around this: by reducing the value of the 4.7 kΩ resistor that comes before the transistor, we can make it supply more current.

I simply soldered another 4.7 kΩ on top to reduce the resistance down to 2.35 kΩ:

This shifts the current source to 17 and 36 mA respectively. The booster turns this into 7.5 mA and 17 mA, which is much closer to the nominal current for the white LED, so this is the final configuration I used. There is no series resistor for the LED, I purely rely on the limited current coming from the transistor. I removed the 68 Ω resistor and connected the booster circuit. Instead of trying to solder onto the tiny resistor pads, I picked the connected through-hole pad. The little PCB (with the 3-pin header removed) fits nicely under the battery.

The result is pretty nice, finally the LED is useful! The lighting is also a nice even area instead of ugly concentric circles. It does draw more current now, but compared to the motor, 36 mA is still pretty negligible.