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Bondtech Extruder Upgrade - Design Error?  

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lantis
(@lantis)
Active Member
Bondtech Extruder Upgrade - Design Error?

I equipped my Prusa Mini with an E3D Revo Micro Hotend and a BondTech dual drive extruder because I get much better print results with PETG with it. However, since then I've had problems printing PLA, the extrusion is very erratic.

After days of trying and disassembling and reassembling, I finally found the cause: The BondTech Drivegear can only be turned with a lot of force and very choppy and the Prusa extruder motor can therefore not dose the filament exactly enough and it constantly alternates between over- and under-extrusion.

The BondTech extruder has two rollers that grip and feed the filament from both sides. These rollers are connected by gears. The problem now is that the tensioning screw, which determines the force between the two rollers, also changes the force on the gears. The harder you grip the filament, the harder the gears are pressed against each other and therefore harder to move.

That means you have to adjust the tension so that the filament just doesn't slip through, but the gears can still be turned without too much force. I think that's an odd design decision. In my opinion, it would be ideal if the gears always ran smoothly and the full tension force was transferred to the filament instead.

How is your experience with it? Can this be optimized somehow? Even though I've solved my extruding problem by fine-tuning, I still know that the extruder motor is put under more unnecessary load and may not work as precisely as it could.

Posted : 19/05/2022 6:29 am
rinkel
(@rinkel)
Trusted Member
RE: Bondtech Extruder Upgrade - Design Error?

I Don't use the Bondtech extruder, but i do use the same drivegear in a MK3-mini extruder.
Although i see your point, and agree. 
I think there is enough room for the gears to grip when filament is pressed. I don't need to fully squeeze the gears together before the filement gets enough grip. In my case there is enough grip on the filament and i still have enough room for more squeeze.

 

Posted : 19/05/2022 10:08 am
fuchsr liked
fuchsr
(@fuchsr)
Noble Member
RE: Bondtech Extruder Upgrade - Design Error?

I have Trianglelab extruders on my Minis, same design. Never had any issues with them. In fact, I never had to change the tension, PLA, PETG, ABS, TPU, whatever brand, all good with the same setting for the screw. And thankfully I stayed away from installing the Revo I bought, considering all the issues people are reporting.

Posted : 19/05/2022 11:26 am
Chris Laudermilk
(@chris-laudermilk)
Estimable Member
RE: Bondtech Extruder Upgrade - Design Error?

I think we are seeing the squeaky wheel effect on the Revos. The people with issues are going to make the most noise. I now have two Revos (Voron edition in my Trident and Micro in my Mini). I love them; for me they have just worked. The Trident is now at nearly 350 hours printing, 99% of that on the Micro now residing in my Mini. The Mini still needs some tuning, but it's working well with the new hot end.

While I don't have the Bondtech gears on the Mini, I do on the Trident, and gear mesh between the driven and idler gears has not been an issue. The thing is, you tighten just enough to have filament not slip and no more.

Mini+ (kit) - Revo Micro

Posted : 19/05/2022 1:52 pm
fuchsr liked
lantis
(@lantis)
Active Member
Topic starter answered:
RE:
Posted by: @chris-laudermilk

The thing is, you tighten just enough to have filament not slip and no more.

I did that, but then the gear resists to move. And it does that too without filament, so there is no pressure on the filament, the main pressure is on the gears. And if I turn the tension screw tighter, the filament isn't compressed any tighter either. The grooves on the filament are always the same depth. The only thing i change with the tension screw is the amount of force pressed on the gears. The more tension, the harder it is for the gears to turn. With or without filament, it doesn't matter.

This post was modified 2 months ago 2 times by lantis
Posted : 19/05/2022 2:00 pm
fuchsr
(@fuchsr)
Noble Member
RE: Bondtech Extruder Upgrade - Design Error?

I think we are seeing the squeaky wheel effect on the Revos

Of course. In fact, by definition forums like these are there to help people with problems so they represent a very biased view of the world. Like for every person with a heatbreak issue on their Mini. there's probably 10+ (like myself) who have never seen it.  With the Revo we're also witnessing the usual "first generation" issues, hopefully they will all be worked out soon and then the Revo will be a very fine choice. Of course, hopefully before long we're going to see "fist generation issues" again with the new Prusa XL 🙂 ☹️🙂

 

To bring this back to the thread's original topic, I'm not sure I would call this a design flaw. I can break anything if I want, with enough force  🔨. With the extruder, there should be enough grip to move the filament nicely without getting to the point of deforming the gears. If not, I would be tempted to dis- and re-assemble the extruder to make sure the gear alignment is correct. And if that doesn't fix it, maybe contact Bondtech support, in case you received a defective unit.

Posted : 19/05/2022 3:30 pm
lantis
(@lantis)
Active Member
Topic starter answered:
RE: Bondtech Extruder Upgrade - Design Error?

Maybe I'm just misunderstanding the concept of an extruder and it's all as it should be. It's my first 3D printer and I have little experience with 3D printing.

It just feels wrong to me that so much force has to be expended just to drive the gears. And that the gears are not free to rotate continuously, but rather "stepped" based on the individual gear teeth. So it is not possible to transport the filament very finely. Or is that not necessary at all?

Posted : 19/05/2022 4:06 pm
rinkel
(@rinkel)
Trusted Member
RE: Bondtech Extruder Upgrade - Design Error?

you should not have to apply such amount of force. My idler is arount half way it's path.

Posted : 19/05/2022 8:19 pm
rinkel
(@rinkel)
Trusted Member
RE:

Although i understand what you're saying, the grip-part should be large enough to have sufficient grip at the start. 
I really don't have any issues with the gears and the filament flows fluently and i haven't heard many people complaining about this either. 
There must be something wrong with the gears, or with the filament.

Posted : 19/05/2022 8:26 pm
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