Installing a Bondtech QR extruder on my Rostock MAX V3

It's no secret that I'm a big fan of the Bondtech QR extruder. The big advantage these extruders have over others is that they use driven counter-rotating drive gears to push the filament. That simply means that the filament is being pushed from two sides, powerfully, unlike most extruders that have a single drive gear attached to a stepper shaft and a pressure idler on the opposite side of the filament. This dual drive gear system generates a huge amount of torque and the geared (standard 5.18:1 geared Nema 17) stepper provides better than 450 steps/mm extrusion resolution.

It was only a matter of time before I installed a Bondtech QR on my new SeeMeCNC Rostock MAX V3. The install was straight forward and almost a drop-in replacement for the stock EZRstruder using the simple Bondtech QR Rostock MAX V3 mount I designed (get a copy of the STL here).

Preparing the Printed Mount

Print the mount with three perimeter and three shells (top and bottom) with 50% infill. The hole in the narrow edge is tapped for an M3 cap head screw to secure the stepper motor. Make sure your stepper fits into the large round hole and sand or scrape the bore until it fits if not.

Installing the Bondtech Q3

Turn off your printer the remove the top cover and disconnect the EZRstruder connector from the RAMBo. Then remove the side plate that the EZRstruder is mounted to, the entire plate and extruder should come right off. Remove the EZRstruder and save the two mounting screws and nuts. Attach the printed mount using these screws as shown here:

Install the new geared stepper, make sure its connector is facing down as shown:

Secure the stepper with an M3x12mm socket head screw inserted into the recess and hole you tapped earlier. Don't over tighten.

Now reassemble the Bondtech QR to the stepper motor following Bondtech's Assembly & Installation Guide.

The Bondtech QR rotates in the opposite direction from the EZRstruder if wired the same way. This can be corrected either in firmware or in the wiring. Unfortunately, changing the stepper direction in Repetier firmware requires recompiling and uploading new firmware, so let's simply change the wiring to accommodate the direction change.

On the right is the original EZRstruder connector. Note the BLUE-YELLOW-GREEN-RED wires from left to right. On the left is the connector for the new stepper, note the BLUE and YELLOW wires are reversed, this changes the direction of the stepper. Your Rostock MAX V3 kit came with extra connectors and pins in the RAMBo box. The photo shows the bag that came with mine. If you don't have those or don't want to crimp new pins, you can cut and splice the old stepper harness with the new one, just make sure to connect BLUE to YELLOW and YELLOW to BLUE wires.

Install the side plate with the new Bondtech QR and route the wiring to the RAMBo.

(Here's looking at you, Bondtech QR!)

Now connect the stepper to your RAMBo as shown here:

And that's it for the installation.

Configuring and Calibrating

The only thing you need to change in Repetier is the "extruder 1" steps/mm. The good news is, this can be done in EEPROM so no recompilation is necessary. You do need to use a control program that allows you to edit the EEPROM. MatterControl, Repetier Host and OctoPrint with a special plug-in all do. I use OctoPrint here.

Here's what you are looking for: Extruder 1 steps per mm, this is the default EZRstruder value (92.4mm/s) that you most likely have in your EEPROM.

Change that to a target default value, I typically start with this:

That should get you in the ballpark, now it's time to test the Bondtech QR and calibrate the extruder. Martin (Bondtech inventor) shared a quick technique to do this:

Insert a short piece of PFTE tubing (2-4") in the output side of the Bondtech QR, make sure it is pressed in all the way. Next feed apiece of filament in from the top of the extruder and push about 1" out the bottom of the tube. Score the filament with a sharp hobby knife right at the end of the tube and snap it off - PLA works well for this.

Turn on your printer and warm the hotend up to 170°C or so - the firmware will not allow you to test the extruder unless the hotend is hot! Once up to temperature, use your control program's jog controls to feed 100mm of filament.

If you wired things properly, about 100mm of filament should have extruded from the end of the tube. Use digital calipers to measure the actual length. It helps to start with straight filament! In my case, the amount extruded was 99.20mm, a little less than the 100mm I requested. So a quick calculation will fix that:

(100mm / 99.2 mm) * 458.55 steps/mm = 462.25 steps/mm

The 458.55 steps/mm is the default value we entered in EEPROM. The calibrated calculated value is 462.25 steps/mm so enter that into EEPROM any you have a calibrated Bondtech QR ready to print on your Rostock MAX V3.

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