Bondtech gear keep coming loose  

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randy.h3
(@randy-h3)
Trusted Member

I've been having an issue with my extruder gear coming loose. Is this something I can fix with some lock tight or just deal with it? As I understand I should have a replacement in my parts bag which I'll be hunting for as my current one is getting a bit stripped. Any other advice or tips? the last time I tightened it I made double sure it was on the flat part of the drive shaft.

Posted : 31/07/2019 7:15 pm
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(@-2)
Illustrious Member

The trick is to ensure the set screw is properly aligned with the flat on the motor shaft. If even slightly askew the set screw will come loose.

When setting the screw, you need to wiggle the gear to ensure the screw end, which is flat, completely contacts the flat on the shaft. Any slight angle allows the screw to come loose (it really isn't tight to begin with).

Even with LokTite, any improper set screw contact will come loose, so some resort to smearing enough goo to glue the gear on. Taking the gear off after that is a full extruder disassembly.

This post was modified 2 years ago by --
It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 31/07/2019 7:28 pm
randy.h3
(@randy-h3)
Trusted Member

Just to dot my I's do you happen to know what size hex key fits bet? Maybe I've got one a pinch too small or large.

Posted : 31/07/2019 11:59 pm
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(@-2)
Illustrious Member

No - I pick the first one that fits and hits bottom.  I think it's a M3x2 set screw, 1.5 mm hex key.

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 01/08/2019 12:24 am
peter.metselaar
(@peter-metselaar)
Active Member

having the same problem. the screw keeps getting loose.

am quite sure it's been tightened to the flat surface of the shaft.

after a few hours of printing it's loose again , any idea's to fix this issue properly ?

Posted : 28/11/2019 8:17 pm
karl-herbert
(@karl-herbert)
Illustrious Member

@peter-metselaar

Try to use a small peace of Teflon tape to save the M3x2 pin screw. Loctite could be a problem to remove the srew.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 28/11/2019 10:32 pm
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(@-2)
Illustrious Member

If the screw is coming loose, it is NOT being secured to the flat. When the screw isn't perfectly flat, it only grabs by  a portion of the round face, any vibration quickly wiggles it loose.  You may also have damaged the flat on the shaft and left a gouge, which makes correct installation impossible.  Pop the gear off the shaft and inspect; if any marks showing, use a file to clean the shaft flat and try again. 

When screwing the set screw down, I always wiggle the gear and shaft as I slowly tighten the screw, and it's pretty amazing how far off flat I can be when the screw first starts to feel "tight" ...

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 28/11/2019 10:40 pm
peter.metselaar
(@peter-metselaar)
Active Member

@karl-herbert

Could a blanc mail pollisher do the truck? (As alternative for  Loctite )

because this  is quite easy removable

Posted : 29/11/2019 11:35 am
karl-herbert
(@karl-herbert)
Illustrious Member

Generell i agree with tim-m30.

Nail pollisher? never tried this, but worth a try. In some cases i'm also working with loctite high strengh, but not in combination with such small pin screws because removing the srew (with or without heat) could be very difficult or impossible.

The best threadlocker i' have ever seen is this one: https://www.nord-lock.com/de-de/nord-lock/?gclid=Cj0KCQiAoIPvBRDgARIsAHsCw08uCy__VOKt64zPambcS3PQb3eD6KLO2l3PrEnHMni0j-VKW1mc42saAnjREALw_wcB

,but not applicable in this case. If nail pollisher is not working you could try to roughen the thread slightly with a small saw blade.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 29/11/2019 12:11 pm
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(@-2)
Illustrious Member

You can try the old trick of applying nail polish to the TOP of the set screw.  The film prevents the screw from turning, and if torque is really strong the film shatters to show the screw has loosened.

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 29/11/2019 9:06 pm
peter.metselaar
(@peter-metselaar)
Active Member

@tim-m30

did use some mail pollish, just  have to want and see.

Posted : 30/11/2019 7:26 am
royalt213
(@royalt213)
Active Member

I have the same problem.  However, my problem is that none of my allen keys fit in it properly.  I have tried 3 different 1.5mm allen keys and they are slightly too small, so when I try to tighten it down sufficiently, it will skip.  The screw head is so shallow, a ball head allen key can't be used at all.  Because of this, after a few hours, the screw works itself loose.

This little set screw is easily the weakest link of the Bondtech gear.  I'm going to try to find some non-crap set screws from somewhere else.  But if anyone else has any ideas for how to deal with my particular issue of not being able to tighten it down sufficiently in the first place, I would be very grateful.

Posted : 01/06/2020 2:43 am
karl-herbert
(@karl-herbert)
Illustrious Member

@royalt213

I'm using this tool set. Maybe this will solve your problem: https://www-de.wera.de/de/great-tools/hex-plus/

 

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 01/06/2020 3:08 am
royalt213 liked
royalt213
(@royalt213)
Active Member

Vielen dank, Karl. Das sind großartige Werkzeuge.

Posted : 01/06/2020 3:28 am
randy.h3
(@randy-h3)
Trusted Member

Very nice set! A little spendy but I may try a set when I have some extra cash. Thanks for the tip!

Posted : 01/06/2020 4:36 am
cwbullet
(@cwbullet)
Illustrious Member

Here is the set I have:  

Wera Hex-plus

They work great without stripping screw heads.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 01/06/2020 10:29 am
royalt213
(@royalt213)
Active Member

Man, almost a year later and I'm having the same problem again.  I really hate this Bondtech gear.  I wish there was a drop-in replacement.  The tiny set screw is terrible.  It looks (and feels) like it's made out of aluminum. With all the effort and crap I've had to do dealing with this, I'm almost considering just tossing my MK3S altogether.  The only other thing I can think of to deal with this is literally J-B welding the gear in place.

On an interesting side note, I contacted Bondtech about the gear and the screw and I told them how highly I thought of it.  They said that all of their gears are shipped with black screws.  Yet, the one that came with my Prusa, and all the spare ones, are all silver.  Any ideas on why that is?

Also, if anyone has any other ideas on how to tighten this piece of crap reliably without spending $50 on tools, I would appreciate it greatly.

Posted : 19/11/2020 5:43 am
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(@-2)
Illustrious Member

Most of these issues are due to simply not ensuring the set screw is perpendicular to the shaft. If off, even a tiny fraction, the screw bites, but it's face is not flat to the shaft and can't lock properly. A little bit of vibration later the assembly is loose again.

Remove the gear, check the shaft for any bite marks, dress them with a file if they are high, then reattach the gear, but take a few minutes and make sure the set screw is aligned with the middle of the shaft, flat, and slowly apply torque until the gear can no longer wiggling: and then do that last torque.  

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 19/11/2020 8:07 am
royalt213
(@royalt213)
Active Member

@-2

Thanks for your reply. Yeah, that is what I did last time around. I was as careful as I could be. I wiggled it gently while tightening it to make sure it was biting flat. I think it's a combination of problems: the sensitivity to being misaligned, not being able to get enough torque because no wrench fits snugly inside the head, etc. I'm going to try again and use some blue Loctite this time.

Thanks again.

This post was modified 5 months ago by royalt213
Posted : 21/11/2020 11:04 pm
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