PROJECT: Prusa i3 MK3S + MMU2S

So... a couple of months ago we got the MMU2S (multi-material) upgrade for our Prusa i3 MK3S, and boy oh boy has it been a wild ride trying to get the thing calibrated... 
The process reminded me of our old Prusa i3v, as it too required a bit of work to get a print up and running, which in the end you still had to keep an eye on to make sure everything was ok

Calibration Troubles

As you might have guessed, the MMU2S did not work out of the box for us. This was mostly due to stringy tips during unloading, which eventually lead to load blockages
I tried numerous things to improve the tip shape, from adjusting the number cooling moves/unload speed/printing temperature, to varying the unload temperature using a Python script. Sadly, none of this helped as much as changing to PrusaSlicer 2.2.0 DRIBBLING by antimix. Which is a custom slicer that adds a "dribbling" motion (think basketball) during the unload

Here is a snapshot of the 30 tests I did trying to improve the tip shape:
Default PrusaSlicer Settings (with & with out the Python script)

HCD profile (with & with out the Python script)

Reliability Mods

I soon found that using a custom slicer was not enough, as I constantly ran into unload issues even when the tips were nice and pointy. The culprit turned out to be the PTFE tube running from the MMU2S to the extruder, which had too small an inner diameter (2mm ID) for the tips to travel freely
Why? Well it turns out that the PTFE tube inside the hotend (different to the one above) expands over time, and this tube also controls the tip diameter (think molten tips being squished into a cylinder). This results in the unloaded tips being 2-2.5mm in diameter which believe it or not have trouble fitting through a 2mm hole ;^)

With that said, here is a list of mods I installed to improve reliably:
  1. Stock (2mm ID) PTFE tube replaced with 3mm ID PTFE tube
  2. Stock MMU2S selector replaced with magnet variant
  3. Chamfered inner edge of Festo fitting (PTFE holder) at extruder to help with flat tips
  4. Replaced stock filament buffer with "gravity assisted buffer" (using M16 nuts as weights). I found that the stock buffer & long PTFE tubes added too much resistance to filament movement, which made printing finer details that much harder (as in areas where small amounts of plastic was meant to be deposited were nearly cavities)

Printing Profile

After heaps (o_o) of tests here is what I settled on:
  1. PrusaSlicer 2.2.0 DRIBBLING kby antimix
  2. Dribbling temperature -15°C of normal print temperature. For example, if your printing temperature is 200°C then I would suggest setting the dribbling temperature to 185°C
  3. Minimum temperature same as dribbling temperature
  4. Maximum temperature same as printing temperature
  5. Number of dribbling moves to 3

The Outcome

Our first successful print!!!
  • Smiling owl by cipis
  • 5 colours
  • 448 tool changes with only 2 issues requiring intervention:
    • Once due to filament debris from previous print
    • Other due to bad tip with glow in the dark filament (load error)


UPDATE: Kobo N647 Replacement Button Cover

Wife has a Kobo N647 which is still going strong, but recently the rubber button cover has began to disintegrate. So I designed a replacement in SolidWorks and 3D printed it with out Prusa i3 MK3S + MMU2S

This was my first successful "soluble support" MMU2S print, where the body was printed in PETG while the "soluble supports" were PLA. If you have not heard of using PLA/PETG like this, well it turns out that the two adhere reasonably well to each other when printing, and once the model is printed and cooled the two are easy enough to separate. Hence why you can use one with the other to make a "soluble" interface 

As always, you can find all files here


UPDATE: New Etsy Items

My Etsy store has grown a bit :D

3D Printed Muji Gel-Ink Pen Holder

I have been wanting reusable pens for quite some time and a few of weeks ago managed to get some decent fine tip gel pens from Muji. To keep these organised I designed a compact vertical case that the pens "clip" into like so:

Also here are some fancy renders from SolidWorks Visualize. These were rendered in 2018 SP5 using "glass fiber" as the material to mimic the clear PETG look:

3D Printed Christmas Tree

This model was on my backlog for ages, and now it has finally materialised:


PROJECT: Half-Life 2 AR2, Update #4 - Receiver & Barrel Test


Exciting news, I have combined the receiver & barrel assemblies to get a better idea of how things will be functioning together :D

Currently the whole thing is controlled by 3 Arduino Nano's. This may sounds a bit overkill but doing so allows me to run time sensitive modules in parallel, which is a must for the animation sequences
Also, since the previous update the firing/cycling rate has increased to ~5Hz thanks to a stiffer spring. I can push it further but I would need to increase the PWM duty cycle, which would make the coil run hotter (think higher average current). This is something I am a bit cautions about as the body is printed in PLA which has a low glass transition temperature (~65°C)
I guess if I don't manage to reach 9Hz then we can call this the AR1.5 prototype ;^)

Couple of closing notes:
  1. I plan to print the final model in PETG which has a higher glass transition temperature (~80°C), so will have the option to push more current through the coil
  2. I want to try using a couple of sensors to get the firing pin position, this way I won't be purely reliant on PWM as I could simply switch the coil off once the firing pin has reached the end


PROJECT: Half-Life 2 AR2, Update #3 - The Waiting Game


Progress has been quite slow thanks to the hectic period we are in (I'm looking at you COVID19). You would think that working from home would give me more time to work on projects, but being stuck inside for a big portion of the day is quite mentally draining....

But getting back to progress, initial tests of the firing pin assembly were quite positive, I could get reliable cycling up to 3Hz (in the game the AR2 cycles at ~9Hz). The big limiter here is the return motion, which can be improved by using a stiffer spring. However if the spring is too stiff then the forward motion will be negatively impacted. So now I am waiting for a bunch of springs to try out

To keep myself occupied I have started working on the magazine assembly. So far I have defined the area that will house all the electronics (batteries, servo, control board...), and am now figuring out the shell movement (from magazine to barrel). Here is how the AR2 is looking so far:

Also, if you have not seen my previous post I have decided to get the multi material upgrade (MMU2S) for my 3D printer (Prusa i3 MK3S). I envision this being crazy useful as it will enable me to print soluble supports, which will make printing awkward shapes (basically everywhere on AR2) much easier


RESEARCH: SolidWorks Topology Optimization

One of the things I have come to realise with my AR2 project is that having a multi-extrusion 3D printer would be crazy useful, as all my prints to date needed support material which unfortunately is a pain to remove. However, with a multi-extrusion printer you can do fancy stuff like print all supports in PVA, which dissolves in water!

Hence, I finally bit the bullet (bad time to be spending due to COVID19...) and ordered the MMU2S upgrade for my Prusa i3 MK3S. But there is a small hurdle, the MMU2S is designed for large (and preferably flat) working areas, something I do not have. So I decided to modify my current work space with a shelf to hold the 5 rolls of filament, and to spice things up I tried using the Topology Optimization feature in SolidWorks to design the shelf brackets. Overall, this produced quite an organic shape that reduced the bracket weight and gave it the best stiffness to weight ratio

The Steps

NOTE 1: I am running SolidWorks 2018 SP5
NOTE 2: Here is an easy to follow tutorial on Topology Optimization in SolidWorks 

  1. Make a 3D model as you normally would
  2. Add a SolidWorks simulation (SOLIDWORKS Add-Ins → SOLIDWORKS Simulation)
  3. Create a new Topology Study (Simulation → New Study → Topology Study)
  4. Select body material (I went with PET as I will be printing in PETG)
  5. Define the fixtures (faces where the body will be held in place)
  6. Add a force as well as it's direction (I went with 50N as at most the shelf will hold 5 1kg rolls of filament)
  7. Add a model goal (I wanted to reduce mass by 40% while having best stiffness to weight ratio)
  8. Specify the preserved regions and depth (I selected the bracket mounting faces and went with a depth of 2.5mm)
  9. Specify De-mold direction (arrow should be pointing towards flat surface)
  10. Create a model mesh (I used a 2mm curvature-based mesh)
  11. Run the simulation
  12. Finally, adjust the target Material Mass and calculate the Smoothed Mesh

The Results

  • Original model: 
    • 74.4g
    • 210851mm³
  • Topology Optimized model: 
    • 44.5g
    • 84013mm³


UPDATE: Worth The Weight

This one is for all my mates who through the day would never come, and while it's not Half-Life 3, it's certainly a step in the right direction ;^)