Prusa i3 MK3 Extruder with Bondtech gears

I really like the the new bondtech extruder being used by Prusa I3 MK3 .

I am considering creating an adapter to add to the MP3DP

Just curious if this has been done already and if there is interest.

The extruder supports a probe and a filament sensor.

How hard would it be to modify the rambo firmware to take advantage of these additional features


[attachment file=108800]

If you clamp to the stepper body it probably already fits.

Thanks for the quick response, Ryan.

If I understand your suggestion you would have me just place the Prusa extruder on the MP3DP??

The vertical distance between the X Rails are not the same.

I believe I would need to modify your X gantry, to receive the extruder body of the Prusa I3 MK3.

Additionally does Marilyn have native support for the z probe and the filament sensor??

Marlin does have support for Z probe and filament sensors. It’s definitely an intermediate customization though, unless you’re blindly following a tutorial.

Ryan is saying his mount just holds onto the motor. If you can just let his mount hold the motor on this extruder, then you’re good to go.

My favorite part of the MK3 extruder is the part fan, actually. Ryan’s has some very neat compound curves, but this one is just so simple (sorry Ryan).

Not sure the motor mount could be rotated 90 degrees. By design the Prusa motor sticks strait out. In order to get the clamp around the motor it would need to be rotated 90 degrees left or right. Not sure either would work. I will try this tonight and show what I have come up with.

Thanks for the clarification Jeff :slight_smile:

OK been thinking about this all day.

Checked when I got home, absolutely know way to get the motor mount around the Prusa assembly:-(

So time to do a little design work.

I have include the A redesign of Ryans XCarriage

I have modified it to have the receiver holes need to connect the Prusa Extruder in the same orientation as the I3 MK3

print is going as I type.

I will send pictures Thursday:-)

See Ya

1 Like

OK just pulled the gantry off the printer

[attachment file=108886]
forgot the image

I need to angle the overhang you can see the drip but it is still structurally fine by the time the upper nema 17 hole is printed. Also including top view showing the receiver m3 hex nuts embedded in the belt pass-through

[attachment file=108890]


If I may suggest. I have the Prusa MK3s and it is great but not perfect. If you are planning to make some changes to your MP3DP then you might want to make an even better upgrade. On thingiverse there is an extender assembly that uses a lot of parts from the Prusa but it improves the design a lot. I mean ALOT. The Prusa can’t do flexible filament very well. But this mod can. This mod also suggests other mods to use to get the X carriage to fit and be easy to work with. Check into it. It may be more work than you want to do but it is the path I am choosing to take. Just check the long list of advantages.


Just glanced looked really cool. Thanks. Why does this support flexible filament and the Prusa does not is it the extra torch on the extruder that makes the difference.

FYI I also have a Prusa and an Ultimaker I am amazed by the quality of the Prusa as a factor of {Return On Investment} litterally 1/5 the price of my ultimaker.

Sorry for the long reply. I tend to give more details than necessary.

I have a Prusa is MK3s with MMU2s at work and one at home.

I love the print quality of these things!!! But …

… they both suffer from three problems when I try to use TPU 95 (hardness) or Ninja flex 85 (hardness) The first problem is the filament path from the top of the extruder body to the bond-tech gears. On the MK3s with the MMU2s there are 3 separate plastic pieces that make up the walls to the filament path. The only way to tune the IR sensor is to shift the position of some of these pieces. So they don’t line up perfectly. That makes it very difficult to load a filament because it can get stuck before it even gets to the gears.


The second problem is the IR sensor that detects when the filament is loaded to the Bond-tech gears. The MK3s uses a magnet lever that the filament pushes out of the way to trip the sensor. The MMU2 upgrade swapped the lever with one that only moves when the filament pushes the two bond-tech gears apart.

With the MMU2 the IR sensor can’t be tuned very much. and the plastic pieces have poor tolerances. They literally rattle on the 3M bolt holding them into place. So the printer has a very hard time knowing when the IR sensor is actually triggered or not. That gets even more complicated with Flexible filament because the magnet on the lever or the spring on the bond-tech gears will flex the filament so it is less likely to trigger the sensor.

The purpose of this sensor when loading filament is to know when the gears should slow down during the loading process. Flexible filament usually needs to be loaded into the nozzle a little slower to prevent a jam. Well… when the sensor doesn’t detect the filament the gears continue to spin full speed during the load. Then it causes a jam.

I admit both of these previous problems are worse for people with the MMU2 upgrade. But this last problem applies to the MK3s with or without the MMU.

The third and last problem is horrible! The tolerance for the gap between the gear and the sides is not so good. So here is what usually happens. The filament goes down into the PTFE tube and into the nozzle. Then it stops because its a nozzle and it will take more pressure to melt and force the material through the tiny hole. THe gears continue to spin. The filament can’t go down into the nozzle anymore so it goes sideways. I have seen it get wrapped around the main drive gear more than a dozen times. It usually takes me five or six startup attempts to get a print started with TPU. with each failure I have to get the filament unwrapped around the main drive gear.

[attachment file=109001]

There isn’t much room in there. I don’t know how it does that. But there must be a gap.

I have tried to tighten the tension screw and loosen it. I get better results with it a little loose. Prusa official documentation suggests to use it with the tension screw a little loose as well. It also says TPU is supported (for advanced users) and they hope to be able to support Nijaflex in the future. But it is not supported now.

In any case. This extruder that I suggested is built off of the Skelestruder upgrade for the Prusa MK3. If you watch some of the videos they have here you can see them running TPU 95, Ninja flex 85 and some crazy stuff that is super flexible 65 through it at crazy fast speeds. I am not exactly sure how they did it but I have chatted online with people that all say the upgrade made it so they can print with flexible filaments.

So I will be making this upgrade on my printers when I have time.


1 Like

Thanks your amazing, the details are truly appreciated.

I have only had my Prusa for a few months, but I have had problems with the IR Sensor I have been manually loading my plastic. This has worked well for me. The print quality is what I have been really happy with.

With respect to the problems you described with the Prusa when using Ninja Flex. Would a manual load of the filament solve the clogging issue of the extruder advancing to fast. The assumption is that the root cause of the clog is the continual turning of the BondTech gears without the associated flow be supported by the head.

Does this problem go away if we manage the extrusion speed??


The problem will … not entirely go away. I have created filament and print settings profiles that work … better. I started by using the semi flex filament settings and slowed everything down. Also slowed down the print speed settings. I also manually load the filament to the nozzle. Then I start the print. If I sit there and hold it so I know the IR sensor is triggered it will usually start printing. About 1 in 4 attempts works for me. But when it gets started it usually just keeps on working.

Not fully operational yet but the head is built and attached to the Printer:-)

[attachment file=109292]

1 Like

That looks awesome.

1 Like

That looks great!

I decided to come back here and share something that I found that may have solved my flexible filament problem without rebuilding the entire tool head. This little PTFE cut guide can be used to shape the PTFE tube so it will prevent flexible filaments from jamming in the bondtech gears. I wish I had seen this before I tore my tool head apart. Oh well. I will test this on the other printer then decide if I want to continue my rebuild or return to the Original Prusa design.

I know this thread is several months old but I wanted to give you an update. I switched to another extruder on my Mk3s with the MMU2s. This thing is great. It handles flexible filaments really easily. The IR sensor works great. But this one is intended to be used with an MMU.