Printing Instructions

• Before the first print
• Materials
• Parts list
• Slicer settings
• Calibration test
• Part orientation
• Printer Upgrades
• Filament drying and storage

Before the first print

Some Robak 3D printed parts are designed be compatible with off-the-shelf components such as bearings, differentials, nuts and screws. These require finer tolerances to work properly.

1. Extrusion

Assuming there is no printer movement errors I highly recommend to calculate these two parameters:

• E-steps
• Flow rate

This will save you a lot of time during the assembly and make Robak mechanical elements last longer.

Different materials may require different flow rates. Repeat the process for every material you’re going to use for best results.

Here’s the video showing how to calibrate the extruder step by step.

2. Material shrinkage

Even if the extrusion is tuned well you may get an undersized component because the part’s going to get smaller as it cools. The shrinkage ratio is different for different materials.

Use this table as a quick reference. Always refer to the datasheet provided by the filament manufacturer or measure it with a test print.

You should compensate for the material shrinkage simply scaling the model upwards.

Scaling 1.5% upwards (for PA12) in Cura

Here’s a great video about that.

3. Hole size

If all the dimensions except the holes are spot on, you can use the Holes horizontal expansion setting to fine tune it.

This video shows how to calculate the Holes horizontal expansion value using the test print.

Materials

Option 1. For beginners

Use the material you like and have already printed with.

Don’t spend money on expensive materials and upgrades. Try to master slicer settnigs for some basic material and improve the dimmensional accuracy of your prints to the maximum.

Good quality PLA is enough to start because it’s easy to print and doesn’t require printer upgrades. On the other hand it is too brittle to unlock the full potential of the Robak. If you decide to go for a more extreme build you will have to replace breakable parts with something tougher.

Option 2. My recommendation

• Use PA12 or PA12+GF for steering components*
• Print other parts with PCTG or PETG

*check3DPartsList for part names

Option 3. Cost-effective

• Use whatever you have on hand
• or print all parts with PETG

Option 4. Most durable

• Use PA12 for steering components and Arms
• Print the Body with PCTG
• For other parts use fiber filled PA12

PC and PP seems to be good alternatives as well.

Parts list

3DPartsList contains .stl filenames, number of copies to print and the recommended material for each part.

You can also find 3DPartsList.csv in the robak-x.x.x.zip package

Slicer settings

Walls

Recommended Wall Line Count is from 4 to 6.

Temperature

Set the temperature closer to the higher limit for better layer adhesion and to compensate for worse heat conductivity of a steel nozzle.

Infill

No need to go above 50%. For most parts 35% is enough.

Part cooling

In theory fast cooldown lowers layer adhesion which is bad. No cooling may lead to other problems meaning that the sweet spot is somwhere in the middle. It depends on the material being printed and the cooling system of your printer.

• avoid 100% fan speed and no cooling at all
• start with 30% or 50% fan spped and adjust if needed

Other

Slicing the Body:

• change Z Seam Alignment to Sharpest Corner
• set Fill Gaps Between Walls to Nowhere

This ensures a smooth printing process without any unnecessary nozzle travel which could distort this quite thin part.

Calibration test

This is the ultimate Robak 2 calibration test.

• 15.1mm and 10.1mm - bearings should fit tightly
• 5.65mm - M3 square nuts can be easily placed in
• 3.15mm - hinge pins revolve freely
• 3mm - M3 bolts loosely go through the hole
• 2.5mm - a hex key needed for cutting an M3 thread

Calibration.stl and CalibrationDrawing.pdf you can find in the release package under ROBAKv2/CAL

Part orientation

Printer Upgrades

All metal hotend (for printing above 240°C)

The maximum safe temperature for PTFE-lined hotends is around 230-245°C depending on the quality of the PTFE.

That means printing PETG for an extended period of time may degrade your PTFE tube and release toxic fumes. For higher-temp filaments such as PCTG or PA an all metal hotend is necessary.

TriangleLab Dragon Hotend

Hardened steel nozzle (for abbrasive filaments)

Filaments with added particles such as carbon or glass fiber will damage a brass nozzle quicker causing unreliable print results. Once you upgrade to the hardened steel one, you most probably won’t need to use brass nozzles anymore.

Steel has different thermal properties from brass so you may want to try adjusting your printing temps a little bit from what you used to use. Increasing nozzle temperature for 5°C usually solves all problems.

TriangleLab .6mm hardened steel nozzle

Printbed surface (for convenience)

The most common choice for printing Nylon is mirror glass with thin PVA glue layer on it. The downside of using mirrors is when switching to PETG it’s likely you’ll have to replace the print surface as well. That’s because PETG sticks to glass so hard you wouldn’t be able to release larger prints without damaging the surface (or the print). Alternatively you can keep using PVA glue which separates PETG from the glass, but cleaning and applying glue every couple of prints can be really annoying.

G10 (aka Garolite) is an excellent print surface. Nylon sticks to it pretty well even without glue. PETG and other materials hold well, but at the same time they don’t weld into the surface making parts self release after the bed cools down.

235x235mm G10 surface cut from 1000x1000mm sheet

Filament drying and storage

This applies mainly to Nylon, but there is a chance your PETG/PCTG spool needs drying because of poor storing conditions.

If you notice a popping sound while extruding it is (steam bubbles going away) , the filament definitely needs to be dried out.

• Follow the manufacturer’s drying recommendation.
• Keep filament in an airtight container to protect from moisture.

I dry all PA12, PA12+GF/CF, PETG, PCTG filaments in an oven before the first use. After that I place spools in containers and print directly from a dry box.

dry box: IKEA 365+ 10l (358oz) food container with silica gel