Category3D Printing

Calibrating the second nozzle offset

Anyone who ever built a dual x printer knows the problem, how to get the difference between the two nozzles down exactly. I tried many things myself, including printed interference patterns, and conduction. All work to some degree, but never reliably.

Then one day i saw one of those cheap USB microscopes and it was pretty clear what will work.

€12 spent on ebay later i was the proud owner of a super cheap USB microscope with the fantastic resolution of 0.3 megapixel.

USB Microscope looking at merlin hotend tip







I printed a small helper, a crosshair for the microscope

Nozzle in the crosshair








With the help of the microscope and the crosshair it was suddenly very easy to calculate the precise offset between nozzle 1 and 2. I just placed nozzle 1 in an easily recognizable place, noted down the coordinates, then switched to nozzle 2 and drove it by hand to the same visual position, et voila, the two coordinates that represent the same exact spot in X/Y. With a bit of work you can do better than 1/10mm, though that should suffice for most uses.

Another advantage of this is that it is now easy to check the repeatability of positioning in X and Y. In the past i had to flexible endstops, the microscope exposes stuff like this easily.

Another advantage is that you can now easily see if a nozzle is worn down.

Thanks to Thomas Kramm, we got this idea while presenting at the  Maxon Supermeet 2018

Merlin Set available from Protoworx

Protoworx now offers a complete Merlin Set

Merlin Hotend Sets jetzt im Shop verfügbar

Some practical stuff

A friend of mine made me these super nice countersinks with a knurled aluminum shaft. To turn them into useful tools for manual work i designed and printed some hefts for them. For fun i did one in TPU, the other in ABS. Both work fine, but the TPU heft is much smoother and it’s slight flexibility gives a nice grip. The print quality of the TPU one is seriously much better, it was printed on the DuoCube, while the white one shows the Z wobble that my old machine acquired a few months back. I have to address that at some point in time, but hey, the machine is about 7 years old now and still pretty good for that.

Black: Hard TPU, White: ABS

Cooling with compressed air

Just a short post on the current state of compressed air cooling.

I am currently testing the Merlin extruder, i decided to name it in the same way as the hotend since the two belong together, which uses compressed air from an aquarium membrane pump (bubble pump). A medium size pump is sufficient for one hotend and one part cooler.

I made the mistake of ordering a larger pump than needed, which makes the printer unnecessarily loud due to to much air hissing out of the small gaps. On the up side, i might be able to push the Merlin hotend beyond 260°C with this. 🙂


Compressed air part cooler

Merlin Extruder with compressed air hotend and part cooling

Merlin Extruder with compressed air hotend and part cooling

Merlin extruder with compressed air cooling



Dual material file heft

This is something i wanted to do for a while. A handle, in this case a file heft, that is a mix of soft but tough material on the outside and hard plastic on the inside.

Like the bottle cap it’s ABS with TPU, but this time the ABS is the bulk of the piece. There are 2 perimeter shells of TPU around a 50% ABS hexagonal infill.

The heft weighs just 24 g, but is very stable with a smooth and grip friendly surface.

You can see the ABS infill structure through the transparent TPU perimeter

Assembled file

Dual material bottle caps

After some terrible experience with TPE i tried TPU. What a difference!

TPU prints super easy and gives you high quality surfaces and it is super tough.

Today my wife needed a new cap for an expensive cleaner, so i took 10 minutes to model one in C4D and printed it in TPU. The first print worked immediately, but i wanted to try something new. I set the TPU up together with ABS and printed the cap with ABS for the infill and TPU for the perimeter.

The result is very much  worth the extra effort. The TPU gives a nice finishe and due to it’s elasticity it seals the bottle very nicely. The ABS gives the extra bit of stiffness so the cap does not deform so easily.

Next up is a file heft made up in the same way.

Printed bottlecaps as replacement











SainSmart TPU on Amazon

New GreenTec Filament from Extrudr

GreenTec 02 GreenTec 01 Greentec 03





On the left printed @0.15mm Layer height with an 0.5mm nozzle on my DuoCore @210°C. On the right printed @0.2mm Layer height with an unknown nozzle @200°C on a friends i3. What is interesting are the differences in slicing, the left was sliced using S3D, the right one with Slic3r.

I was very positively surprised by the new GreenTec filament from Extrudr, that i ordered on a whim alongside a couple of kilos of my usual ABS.

Not only does it produce a nice matte finish, it prints without any hint of warp, the stability is excellent and it is a dream to postprocess with any kind of tool.

The only two drawbacks i found so far are that it sticks so strongly to the printplate (aluminum with 3Dlac @60°C) that damage to the part or printplate are a very real threat and the current price of €56 / Kg

I hope the price goes down over time, but even at the premium it might be worth it, especially considered that i don’t have to feel so bad about producing garbage prints since GreenTec decomposes neatly, different to PLA.

biodegradable plastics

Thermal Runaway – Silicone cover to the rescue

Silicone Cover after Thermal Runaway

Silicone Cover after Thermal Runaway

As it turned out, it was a lot earlier than expected that the silicone sleaves from this posting

Silicone Sleave for Merlin made the trouble worthwhile. Some peculiar behavior of Marlin lead to a thermal runaway for a couple of seconds at full power. The silicone, that is rated for 450°C deteriorated, but the extruder remains unharmed and even the hotend survived thanks to the new cooling.

For those interested, what happened was that while homing Z Marlin stopped working completely. Everything was frozen including menu and the PID for the hotend, which got stuck with the heater switched on. I haven’t found the reason for the behavior yet, but i’ll do the homing before the heating in the foreseeable future.

Interesting differences in print quality

CloneProblem02 CloneProblem01

These two extruder bodies were printed in clone mode. The white one shows serious stribes that resemble Z wobble, but the blue one doesn’t. Since only X movement was different between the two it is either that, which i don’t believe due to the error existing on all sides, or it derives from the difference in the material. Interestingly the original setting was for the white material. If anything the blue one should show small signs of underextrusion since the filament diameter for that was smaller than for the white.



This is the difference in stepping distance when doing 0.1mm steps. This is not simple z wobble but something different again since it occurs along the z axis, not perpendicular to it.

This is the difference in stepping distance when doing 0.1mm steps. This is not simple z wobble but something different again since it occurs along the z axis, not perpendicular to it.

Interestingly the problem is uneven movement along z, not perpendicular to it.

Some images of the current cooler design

Slot Cooler 03 Slot Cooler 02 Slot Cooler 01

On the RepRap forum the question came up how the Merlinb hotend is cooled when printing Polycarbonate @ 260°C
The design i currently use is rather simple, it focuses on cooling the lower part of the PEEK and guides the airflow as far around to the backside of the hotend as possible. Ultimately i would like to be able to press all air through a small gap at the lower end of the PEEK, but that is a tight fit given that the heater block needs to be insulated.

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