Tube between drybox and Nextruder?  

RE: Tube between drybox and Nextruder?

The hole where the filament goes into the Nextruder is threaded and there should have been a matching PTFE connector in the accessories that came with your MK4. If it is not, you need this: a fitting of type QSM-M5.

RE: Tube between drybox and Nextruder?

I have been using a reverse bowden tube with my MK4 for a few months, and it works fine. I did it mostly to prevent the Z homing problem that can occur when the extruder pulls the filament down and there is too much resistance, falsely triggering the load cell.

My biggest problem was finding the correct QSM-M5 fitting. You can get them from many different places, but most of them have flat surfaces and sharp edges on the inside, and the filament can get stuck on them when you try to push it through. The one that finally worked for me without problems is the one Prusa sells as a spare part for the MMU2/MMU3 (called "Festo fitting QSM-M5" on their web site). It has beveled edges, so filament passes easily. It is listed as not compatible with MK4, but it does actually fit into the Nextruder just fine. Not surprising, really, since Prusa ships two of them with the MMU3 kit, and one of them goes into the Nextruder. For PTFE tubing I recommend you use 4mm outer diameter and 2.5mm inner diameter. Same as the MMU3 tubing.

RE: Tube between drybox and Nextruder?

@efvee AFAIR, the PTFE fitting for the Nextruder on my build came with the enclosure (I bought both the MK4 kit and the Prusa Enclosure at the same time with the bundle discount that Prusa was offering when I placed my order). You might want to check the Prusa store for replacement parts for the enclosure to find the right piece. Or call support and ask them about how to source the PTFE connector that goes onto the Nextruder. If you are in the states, contact PrintedSolid.

RE:

I just did a little research. The Prusa store page for Enclosure parts also lists the same Festo fitting QSM-M5 as used on the MMU units. I went to Festo's web page and found that part number is incomplete, as they have several QSM-M5 part numbers for different diameter tubing. It appears (my guess) that the full Festo part number required is QSM-M5-4 for the 4mm OD PTFE tubes used on Prusa products. I didn't bother trying to get a price directly from Festo because they seem to want one to login to provide prices, also the minimum order seems to be 10 pieces. I didn't bother to look up their published distributors.

I did, however, check prices at both Prusa and PrintedSolid in USD. Prusa has them listed at $3.77 (plus shipping), and PrintedSolid has them listed at $6.99 (plus shipping). Other 3D printer shops may carry the same part, but I'll leave that research exercise up to the reader.

RE:

Thanks all. I found the internal M5 thread. I will try to source a connector locally, along with some tubing or experiment with printed terminals, or drill-thru M5 bolt. Transport cost between Prague and my place drive that decision. M5 fitting is not as common though as M6 fitting.

RE: Tube between drybox and Nextruder?

When you buy the tubes, make sure to get the ones with 4mm outer and 3mm inner diameter. Typical would be 2mm inner diameter, but in my experience, this adds quite some friction and can even clog when the tip of your filament is a bit chunky.

RE: Tube between drybox and Nextruder?

In the end I just ordered the terminals and the tube from Prusa. The M5 terminals proved hard to find; M6 being much more common. Same for the tube. The narrow (Bowden) tube is common, the wider tube not so much. On top of that, those who sell the terminals do not sell them tube (or any tube), and vice versa. 

The wider tube can be found in the spare parts for the XL. Price is reasonable.