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Which firmware should I use with my Bear frame and extruder?

We will always recommend using genuine Prusa firmware as it is the most tested firmware today for Prusa printers.

For MK2.5S and MK3S we recommend 3.7.1

For MK2S, MK2.5, and MK3 we recommend 3.3.1

/!\ Warning: Original Prusa firmware versions from 3.5.0 to 3.7.0 have critical issues that could make your Einsy or Rambo Mini unusable (or reduce its lifetime) and might seriously affect your printing experience. Some components can go higher than 100°C! If you are running one of these versions, immediately flash your printer with the recommended version. Here is the link to this critical issue:

Bed transistor overheating #1636

Are the Bear X-Ends compatible with the original Prusa extruders?

The Bear X-Ends are not compatible with the stock Prusa MK2.5S or MK3S extruder.

The Bear X-Ends are compatible with the Bear Extruder, MK2.5 and MK3. They are also compatible with the BondTech Prusa upgrade extruder if you use the appropriate X-Carriage.

I am using the Bear MK3S Extruder (from the dev branch on GitHub), and I cannot pass xyz calibration. How can I get it to calibrate?

This is a known issue which is caused by the difference in height between the stock Prusa MK3S extruder and the Bear MK3S extruder.

There are two workarounds for this issue. Firstly, you can flash MK3 firmware, such as 3.7.1, and perform the XYZ calibration. Ignore any messaging referring to a different machine being detected. Once calibration is passed, flash the MK3S firmware of your choice to access the full functionality of the MK3S.

The second method is to modify the firmware to account for the difference in extruder height. If you do not want to modify it yourself, there is a modded version available here:

Any links to third-party software available on this website are provided “as is” without warranty of any kind, either expressed or implied, and such software is to be used at your own risk.

Disclaimer: The use of any non-Prusa firmware linked here is provided “as is” without warranty of any kind, either expressed or implied, and is to be used at your own risk. We encourage people to use genuine products and firmware from Prusa.

I have a MK2S Bear and want to use the Bear X-Ends. Is there a MK2S version of the Bear Extruder?

There is no official version of the Bear Extruder which suits the MK2S.

However there is a community developed version, from Ringo1908, that allows you to use the MK2S hardware - hobbed drive gear, bearing idler and PINDA probe, in an extruder based on the Bear Extruder. You will need a 12V, 2-wire, 4010 fan for this extruder to replace the stock 3010 fan.

Should I use a smooth or toothed idler on the Bear x-Axis?

The Bear is designed to permit use of as much of the original hardware as possible. As such, you may use the original 20T smooth idler.

However I would recommend that you choose a Gates 2GT, 20T, toothed idler with dual bearings, to replace the Prusa supplied, 20T smooth idler with a single central bearing.

I use genuine Gates idlers from E3D.

My screws and nuts are floating, is there a problem with the design?

All Bear parts are designed to accomodate standard hex and square nuts with a snug fit. If you are finding that your nuts aren't staying secured or are spinning within their socket, this is most likely caused by under extrusion in your prints. Refer to our extrusion multiplier calibration guide here:

Extrusion multiplier and filament diameter

Is the Bear extruder compatible with the original stock X axis?

Due to a different belt path, the Bear extruder and X axis are matched to each other and cannot be used separately. As a unit, they are compatible with both Original Prusa and Bear Upgrade frames.


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