Design files for this project can be found here.
Earlier this year I bought and assembled my own Prusa i3 mk3s as a quick way to iterate on various mechanical projects in the comfort of my apartment. There are plenty of reviews online for this model so I won’t be providing my own review here. I will however, say that this printer has vastly exceeded my expectations for the price. The small list of modifications that I have made to this printer so far include:
- Replacing the extruder head with a Bondtech Upgrade Kit for more consistent prints.
- Replacing the hotend components: 50W heater, PT100 w/ amplifier, titanium heat break, and copper block to support high temperature filaments.
- Installing the Bear X Extruder with the Bondtech X Carriage for the better belt tensioning mechanism.
After replacing the above components, I still encountered issues with uneven cooling on bridges and overhangs. This prompted me to try my hand at designing a better cooling shroud that evenly cools from all sides.
The design that I eventually settled upon was to use brass tubing for directing air to the nozzle and two centrifugal fans to evenly pressurize the airflow chamber for even airflow among all the airflow ducts. The brass nozzles were used to prevent the plastic shroud from melting from being in close proximity to the heater block, which was a concern even with a silicone sock installed. The metal ducts will still conduct heat from the heater block to the plastic shroud however, albeit slowly. To remedy this, firmware modifications were necessary to ensure that a minimum amount of airflow (20% fan speed) is always enabled whenever the hotend is on.
- Adding copper tape for some additional heat dissipation so that less airflow (10% fan speed) is required to prevent the plastic from melting. High thermal conductivity epoxy was used to connect the brass ducts to the copper tape.
- The plastic shroud design was modified to avoid collision with the Z lead screw with homing.
- The airflow ducts were modified at the tips to angle the airflow downwards instead of straight.
- The silicone sock was changed to a different version that doesn’t get damaged as easily.
- Add a third mounting point on the back to keep the shroud from sagging.
- Angle the airflow ducts slightly off from the nozzle tip to create a ‘tornado’ effect that pulls in more air from the surrounding. This didn’t work as it resulted in very inconsistent extrusions and poor print quality when bridging.
- Printed the shroud with Colorfabb’s HT filament (rated for 100°C).
- Added kapton tape for additional thermal insulation between the airflow ducts and the heater block.