MK6+ to QU-BD Extruder upgrade

[Herón Ordóñez Guillén]

Well, it's done, I upgraded my ToM with a QU-BD extruder and I thought I should share some of the problems/solutions I had.

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TLDR: Use parts from the MK6 to complete the extruder, you may need to drill open the little tube if you are using PLA and you should print a bearing+spring filament drive now that you still have a working printer.
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My original setup was a MK6+ with Jag's bearing filament drive printed in ABS. This upgrade uses 2 bearings, and greatly reduces the drag on the filament. I was using 3mm filament with this setup.

I got a dual extrusion - heater cartridge - no motors kit from QU-BD. I found that 1 screw was missing from both extruders, which makes me think that maybe the instructions are incorrect, or that I did't find the right screws in the package. If you are doing this upgrade, you have the required screw in your MK6, no worries.

Note that I could have gone with a single extruder kit, but I got the dual just in case I need spare parts or for another future printer. Also, I made the mistake of ordering the "universal" mounting accessories, instead of the Makerbot style one. don't do that.

Finally, what I did was use the MK6 as a donor for the missing parts for the new extruder.

Preparation:

1.- Print a bearing+spring filament drive.

The filament drive from the QU-BD has too much drag, even after sanding and polishing the little set screw that pushes the filament.

I printed this one: http://www.thingiverse.com/thing:32315 AFTER I had the new extruder working, don't make the same mistake, print it beforehand if you can.

2.- If you want to go with the included filament drive, you need to cut or otherwise shorten the set screw on the MK6 filament drive gear. There's no space in the plastic block for a protruding setscrew. I used one of those stones that you use for sharpening knives to remove material from the tip of the setscrew. You can also go the easy route and just swap it with the set screw of the included drive gear. I think they are both M3.

I really, really, really encourage you to use the printed filament drive. It will work much better and you will probably upgrade later, so, do it now that you still have a working extruder.

The actual steps:

3.- Disasemble the MK6 and disconnect the thermocouple, heater and motor from the electronics.
The parts that you will need from he donor MK6 are:

-Motor
-Filament drive gear
-thermocouple ( very important! don't break it while disassembling the hot end)
-the little M3 and washer that holds the thermocouple to the thermal core (this is the screw __I think__ is missing from the kit)

4.- Asemble the extruder according to the instruction _videos_. There's some things that you need to do differently:

-Use your thermocouple instead of the thermistor included in the kit. Use the short M3 bolt and washer you took from the MK6 to hold it in position.

-Use the MK6 filament drive gear, not the included one. It won't fit the motor shaft. You will need to move the gear all the way to the bottom of the shaft, the set screw won't be on the flat cut of the shaft anymore.

-Use your printed filament drive instead of the included plastic block.

-You don't need to mount the heater cartridge until you are about to test the extruder. It's easy enough to slide in place when everything else is set, so don't risk breaking the wires, skip this step and place it last. Place the heater set screw, so you don't lose it.

4a.- You may want to assemble and disassemble the extruder with the original parts a few times, it's easy but you need to be familiar with the process so you can troubleshoot later.

5.- Mount the extruder. There's included hardware.
6.- Connect everything, slide the heater cartridge in place and tighten its set screw lightly.

7.- Test! Heat up and you should be able to push the filament by hand or from RepG's control panel.
8.- Print. Since you are using the same motor and drive gear, you should be able to print with your current settings, just make sure you adjust your filament diameter as the QU-BD is 1.75mm only. Maybe tune your retraction settings a bit as the filament is more fragile and too much retraction may break it.

Conclusion: Great upgrade!

This extruder is extremely nice, once I got it to work, it has worked great without a problem. You can push a lot more plastic through and you can go to higher temps as it doesn't have any PTFE to release toxic fumes.

Also, the thing is tiny, your ToM will feel roomy compared to bulky MK6. It makes a big difference in looks. Using the MK6 as donor has the advantage of making this upgrade really cheap and you don't have to reconfigure anything software wise (aside from the filament diameter and maybe retraction)

As a final warning, if you are going to use PLA, you __may__ have problems with the filament expanding in the little tube and jamming. The solution is to drill the the tube open with a 3/32" (2.38mm) bit. The "default" opening of the tube is 2mm, so it's a little tight for PLA that is not very consistent or has absorbed moisture, specially after being deformed with the drive gear.

I only got the extruder to operate after I did this modification, and it's a known solution to this problem in the QU-BD support forums. But don't take my word for it, test it without the modification and if it works, you are set, if not drill it open. If you actually use a printed filament drive, you may not even find this problem at all.

Hope you guys find this useful.

Regards!

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Herón Ordóñez

[Michael Cook]

I had the same setup as you, but I upgraded to a single QU-BD extruder. I bought the full kit from them (motor and all) and it works quite well. It's amazing how much smaller it is than the MK6s. I knew to keep the old thermocouple, so I didn't have any issues there. For what it's worth my kit wasn't missing anything.

I tried their drive gear for a little bit, but I didn't like the amount of pressure it took to make it work. I replaced it with a MK7/8 gear from Makerbot and now things work great. Their extruder block actually works pretty well in that configuration. I used a minimalistic MK8 for a little bit which worked great until I snapped it in half trying to get the spring back in after some tinkering. I haven't printed another yet.