Loose Heater Block after changing nozzles  

RE: Loose Heater Block after changing nozzles

@gavin-b5

"NO it does not stop rotating, you are simply lucky if it does not rotate. There is nothing from stopping the heatbreak from turning further in, when the nozzle butts up against the heatbreak as it turns in, it could start turning the heatbreak as it rotates and butts up against it whilst tightening. If your heatbreak has remained static then you are simply lucky, there is no engineering reason why the heatbreak should remain static, the heatbreak has not tightened up against anything nor is there anything holding it in place before you start tightening the nozzle against the heatbreak." The  heatbreak is threaded on both end, one end screws into the block and the other into the heatsink.

Perhaps there is some confusion over terminology, certainly there is nothing to stop the whole assembly (in order, nozzle, block, heatbreak and heatsink) turning freely. 

RE: Loose Heater Block after changing nozzles

Posted by: @towlerg

@gavin-b5

 

Perhaps there is some confusion over terminology, certainly there is nothing to stop the whole assembly (in order, nozzle, block, heatbreak and heatsink) turning freely. 

E3D is pretty clear that you should be holding the block with a wrench. I've never had the entire hotend spin like a top as you've described.

RE: Loose Heater Block after changing nozzles

Sigh, so I discovered this thread after I replaced my nozzle.  I followed the instructions given by Prusa for changing my nozzle and now my print quality has decreased and there's a leak between the heat block and the nozzle.  Ironically, I was switching to a tungsten carbide nozzle so I'd never have to bother changing the nozzle for ages but I totally regret bothering as there was no leak before and the print quality is worse.  

When I changed the nozzle, I made sure the heat block didn't move.  But the new nozzle doesn't meet the heat break no matter how far in I screw the nozzle (and yes, the nozzles were the same dimensions).  Indeed, the nozzle recently nearly fell out it was so loose; only realised what was happening when I started a print and found it had gouged the print bed because the nozzle was low compared to the PINDA height.  So I'm kinda with Gavin on this, has been a nightmare and I don't have the luxury of time to take the whole hot end apart and rebuild it (and am now wary as to whether I'd just make things worse by doing that).

RE: Loose Heater Block after changing nozzles

@johndoe-3

sorry to hear about what has happened, the same thing happened to me.
No one warns us that if you loosen the nozzle that also this chaos will be unleashed, took me half a day of tearing down my printer and rebuilding it to fix it. I had to order decent thermal compound that can cope with he high temperatures.
the heat break is effectively a threaded tube that only butts up against the nozzle to lock it in place. Once you loosen the nozzle the heatbreak is then free to turn and you cannot lock it in place in anyway, when you then try to screw the nozzle back in, the rotating force and the nozzle butting up against the heatbreak at the same time cause it to screw in as you tighten the nozzle. Once the heatbreak has gone further in, mechanically I cannot work out how you would solve this, if someone can please put it in this post. I am never changing my nozzle again. Maybe a different type of extruded like mosquito etc has a way of overcoming this ?

RE: Loose Heater Block after changing nozzles

Posted by: @gavin

[...] No one warns us that if you loosen the nozzle that also this chaos will be unleashed, took me half a day of tearing down my printer and rebuilding it to fix it.

There's nothing about the actual procedure that takes much time. There is, just like working on a bike, some degree of familiarity required to do it quickly. If you're not done it before, proceed slowly, read the documentation, and ask for help when in doubt. This applies to anything much more complicated than a toaster.

I had to order decent thermal compound that can cope with he high temperatures.

The only part of the entire hotend that requires thermal paste is the top interface between the heat sink and heatbreak. That is the "cold zone" of the assembly and does NOT require high-temperature thermal paste. You should not be applying thermal paste in the "hot zone" bottom part of the assembly between the heatbreak and heater block. If you are doing this, you are not following the directions. You do NOT want improved heat transfer between the block and heatbreak. It is, after all, intended to PREVENT the transfer of heat.

You can, if you so desire, put thermal paste on the thermistor and heater cartridge to ease replacement, though use of a silicone sock makes this less of a concern. If so, you want to use something like a $15 tube of Slice Engineering's boron nitride paste, but this is entirely optional. Otherwise, any quality thermal paste (e.g., Arctic) is fine for the heatbreak-heat sink threads.

the heat break is effectively a threaded tube that only butts up against the nozzle to lock it in place.

It is a double-ended threaded tube. The other end should be hand-threaded into the heatsink. That should prevent it from rotating just from tightening the nozzle when bracing the heater block.

Once you loosen the nozzle the heatbreak is then free to turn and you cannot lock it in place in anyway, when you then try to screw the nozzle back in, the rotating force and the nozzle butting up against the heatbreak at the same time cause it to screw in as you tighten the nozzle.

If you did not follow the proscribed procedure and loosened the nozzle without bracing the heater block, this is true. If that does happen, you should tighten the heatbreak into the heatsink first, then screw the block on.

Once the heatbreak has gone further in, mechanically I cannot work out how you would solve this, if someone can please put it in this post. I am never changing my nozzle again. Maybe a different type of extruded like mosquito etc has a way of overcoming this ?

The Mosquito and others have a bracket (pillars) in place to avoid the need for bracing the block. That's the "one-handed nozzle change" procedure they advertise. 

I can understand if you're hesitant to do this yourself after a bad experience and I'm not mocking you for that. I misunderstood a few things and made more work for myself than necessary starting out. I do want to stress that you've already learned most of the hard lessons, and there's no need to fear something as simple as a nozzle change. This is particularly important as nozzles are consumables. They are not meant to last the life of the computer and they can be damaged. Just like changing a tire, changing a nozzle is sometimes required.

If you don't care, that's fine. But please don't discourage others from looking for help.

RE: Loose Heater Block after changing nozzles

I designed this to solve the problem of holding the heatblock:
https://www.prusaprinters.org/prints/41652-heatblock-clamp-for-nozle-change-mk3s

RE: Loose Heater Block after changing nozzles

@xanthe

fancy patent 👍 

I like to use this tool: https://z-catch.com/ - works properly

wbr,

Karl

RE: Loose Heater Block after changing nozzles

I think what Gavin is saying is the heatbreak can keep threading into the heatsink (eventually to disappear or least  turn in too far). I don’t see how this is possible but I have never disassembled the hot end so don’t know for sure.  If he can keep turning then something is not right and indeed he would be getting problems. 

RE: Loose Heater Block after changing nozzles

Posted by: @xanthe

I designed this to solve the problem of holding the heatblock:
https://www.prusaprinters.org/prints/41652-heatblock-clamp-for-nozle-change-mk3s

Thank you.  I'm going to give this a try.  I find it awkward and imprecise to (try to) hold the block with a wrench (spanner) while installing or removing a very hot nozzle.

RE: Loose Heater Block after changing nozzles

@jsw

I use a small pair of molegrips, it puts a bit of torque on the hotend but atleast I can't drop it on the bed.

RE: Loose Heater Block after changing nozzles

utimately the best improvment I have seen is this Pitstop modification:

https://mihaidesigns.com/pitstop

watch the 1 minute video

I am so going to build this, allows full access to your etruder in seconds, not a 7 hour rebuild

RE: Loose Heater Block after changing nozzles

@gavin

Interesting design. I am curious about your feedback 👍 

wbr,

Karl

RE: Loose Heater Block after changing nozzles

Posted by: @john-6

I think what Gavin is saying is the heatbreak can keep threading into the heatsink (eventually to disappear or least  turn in too far). I don’t see how this is possible but I have never disassembled the hot end so don’t know for sure.  If he can keep turning then something is not right and indeed he would be getting problems. 

It only has to screw in 1mm, thats it, how do you propose to get it to screw out again ?
It happened to me, sadly, I do not know of anyway of unscrewing it again or securing it in place so it cannot screw in.
ok to some degree it is static and can bind in place, but on my unlucky day, it screwed back in.

RE: Loose Heater Block after changing nozzles

@Gavin

 Please learn how to do a proper nozzle replacement and stop spreading misinformation. 

The process is quite simple. Once you do it successfully, you’ll understand why it really only takes a few minutes and does not leave the hot end loose, as you claim. E3D has good instructions if you’re having trouble: https://e3d-online.zendesk.com/hc/en-us/article_attachments/4404474953361/Nozzle_Changing_Guide.pdf

RE: Loose Heater Block after changing nozzles

You all realize you have shared 3 different versions of the same 'simple' process with 'critical side effects if done wrong' that all vary in their procedure while treating people disparagingly for spreading misinformation as they are confused over you insulting them with your misinformation, right?

1.  https://e3d-online.zendesk.com/hc/en-us/article_attachments/4404474953361/Nozzle_Changing_Guide.pdf E3D PDF for nozzle change Step 1 states to roate the heater block in order to loosen the heat break from the heat sink.. AFTER which you turn on the nozzle heater to 285 degrees. Re-tightening of the heat block in order to connect the break to the sink again is done after cooling. I presume their version of 'gaps' is 'don't overighten, better to be loose and get a blob ruining your heat block/thermistor than damaging parts directly'. They provide no way of knowing if you actually have contacted the nozzle to the break.

2.  https://help.prusa3d.com/en/article/changing-or-replacing-the-nozzle_2069 Prusa official instructions state to heat the nozzle to 280, hold the heater block completely in place while unscrewing and screwing back in the nozzle. Block stays heated the whole time. I suppose this is the safest as if the install was done correctly and it worked at first you should be tightening the nozzle down until it hits the break as you don't move the block at all. The 'gap' in this case is a safety check that it's in contact and nothing changed. You s hould be confident the nozle can't adjust to the block as you tighten.

3. Prusa accompanying video for their above tutorial which differentiates with the step to turn the block before nozzle removal, screw nozzle in with .5mm gap, then adjust block back. This is more aligned to the E3D document, except the timing of heating the hotend makes me wonder which is correct as to which parts are loosing or not lossening upon force when hot vs cold to cause more misalignment expectations in the proceses of nozzle-to-break contact.

E3D and Prusa video seem to be getting us into trouble when you can't tell if your turning the thread alignments around when you grip and spin the heat sink up inside it's extruder mounting. I have zero confidence on how to know by feel or sight if my nozzle is in cotact with my break based on these instructions. For example.. if my nozzle CAN screw to the base of the heat block and I back it off the gap.. then my turn of the heatblock has no guarantee I'm in contact when I aligned it back unless I then experiment with tightening the nozzle... and how do you fix it if it does...  how do I knoew what is spinning where when I apply force.. heatbreak inside heat sink? Heat block around heat break? Heat sinks within extruder? Seems the final test is screwing the nozzle and if it can go to the block you are just screwbarred having to disassemble and you really don't know what you did to cause it.

I find this crap frustrating and it appears to be more of a severe dedsign flaw that should have been figured out years ago between Mk1/M2 or Mk2/Mk3 at least. Or better yet.. a clearly congruent and well explained process including a final verification step and what to do if it fails.

Silly stuff. Very poor design and documentation. I bought a Prusa because it appeared to be the leader in design and documentation, but it seems to be a mirage on the most critical elements.

RE: Loose Heater Block after changing nozzles

Logged in just to say add me to the list of the unfortunate ones that did the mundane nozzle change and ended up with this. It'll be a long week ahead taking apart the hotend. Maybe I should just change to the RapidChange Revo system E3D released.

RE: Loose Heater Block after changing nozzles

The process is quite simple but I wished Prusa would add in the KB article and the Youtube video a big warning to brace the heatblock or else you risk going into the "bad scenario" and it isn't trivial to reverse that.