MK3S part melted  

RE: MK3S part melted

Is that a part you printed or a factory S part?

RE: MK3S part melted

I'm not sure, but I think it is one of the self-printed parts. I don't have a second printer to compare and I don't remember how it looked before, but something definitely looks wrong. As I said, the printer still works perfectly well. I noticed this by accident the other day.

Unfortunately the editor didn't insert the full-size image I uploaded. Here it is again, at full resolution so you can see where something is missing.

RE: MK3S part melted

Maybe this is the problem:

After a print , let the printer cool down, before you switch the printer off.

RE: MK3S part melted

Thanks! So this is a known issue then?

Maybe I should print some of your parts before my printer breaks down. As long as it works I don't really care, but once it fails I better have the replacement parts ready.

RE: MK3S part melted

Unless you have a backup printer, it's a good idea to have a full set of plastic spares for your printer. 

Another strategy if you don't wish to print high temp material hot fins, do a couple sets in PETG. You can unbolt and replace the fins when they deform. Caution: One report included the melted, bend down part knocking a print job loose.

Personally, I don't use the R4, rather a BNBSX Short Ears for its superior uniformity. That has the Bear airflow pattern which does not suffer this issue. Admittedly, it is an advanced extruder build. Maybe later for you. Meanwhile, get one set of spare parts printed - which may as well be a hot finned version.

RE: MK3S part melted

Thanks for your hints! I printed your extruder body and the separate hot fins in PETG. I also tried to print the hot fins in ABS but they deformed rather badly during the process. I did quite a couple of ABS prints before, but never so fine and delicate parts.

Now I just need to find some time to disassemble the extruder to exchange the melted parts. Since it still works, I'm not really in a hurry for that.

As for the alternative BNBSX Short Ears extruder, this certainly looks great, but I'm afraid I don't have the expertise nor the time for this kind of tuning.

RE: MK3S part melted

Posted by: peter.m26

Maybe this is the problem:

After a print , let the printer cool down, before you switch the printer off.

 

Sorry I didn't respond to you before. It is possible that I did this a couple of times, but I'm not sure if this can really cause the hot fins to melt. I'll try not to switch the printer off before it is properly cooled down in future. Thanks!

RE: MK3S part melted

I can confirm this is a problem. I had the exact same part melt on my MK3S kit after printing multiple 20h parts  in HIPS at 250C extruder and 110C bed. The printer is also in an enclosure with a stable 45C temperature.

My supposition is that this happens while the hotend is slowly moving on the first layer with the part fan off and high bed temperature (in my case the first layer took 1h+.). The PINDA temp sensor showed a 70C peak temperature at the end of the first layer.

While this does not seem to have impacted the print quality, the real problem stand in the fact that the PINDA mount started sagging as well, throwing off all live-z calibration between prints and risking to get caught in the print. 

I suppose this means i have to take apart the entire extruder to change the backplate on which the PINDA sensor is mounted and the extruder cover?

This parts should really be made in a more heat resistant plastic than PETG.

RE: MK3S part melted

Is that sagging plastic fin on the bottom really needed?  At this point, the extruder-cooling air is exiting from the "wind tunnel" around the extruder fins, but what benefit is derived from the little plastic fin keeping the airflow up? 

On the other hand, it's very important to keep the PINDA probe positioned accurately.  I wonder if a bit of aluminum foil, properly shaped and placed, would keep the hot air away from the PINDA support.

RE: MK3S part melted

 alessandro-v7, those are some demanding temperature needs. I'm amazed the R4 is holding up as well as it did.

Bear and Bear derived extruders should be a bit more resistant to the PINDA mount sag. 

1. Their closet PINDA clamp surfaces are several mm farther from heat block.

2. Rather than being supported only at the rear of the extruder body, they also have a vertical support rail near the end of the clamp.

Together they should make the PINDA clamp less likely to sag. However, reducing radiated heat would be desirable. You're at temperatures above normal heat sock tolerance. Maybe add a high temp, custom heat sock and/or change to Bear derivative with hot fins for that kind of working environment?

Bunnies may consider redesigning that portion of R4 to match Bear advantages, but most effort is directed towards the Short Ears.

---

That fin surround helps keep heatsink airflow from interfering with heater block. I don't know that last portion's percentage contribution.

RE: MK3S part melted

To help out those using the R4 extruder, bunny scientists added a support brace to the PINDA clamp to fight thermal sag. This is now standard feature in the R4 extruder with hot fins project.

Bunny Science Hot Fins for Prusa MK3S R4 Extruder

https://www.thingiverse.com/thing:3645975

Man. I hate how this new forum nearly always distorts image aspect ratio!

RE: MK3S part melted

@guy_k2 Thank you for your help!

I did't think this kind of temperatures were that demanding on the machine, considering it is supposed to be able to print nylon, which can reach temps of 290C at the hotend. Maybe the enclosure temperature has more effect on the general heat exposure of the plastic parts than i thought.

The electronics does not seem to mind the toasty enviroment, top temp reported on the board sensor is aroun 62C, no driver error of any kind in more than 50h of hotbox printing, the PSU is outside the enclosure, and the PETG structural parts of the carriages are holding well for now, with top temperatures of around 50C near the motor mounts (cheap IR thermometer, i guess +- 5C accuracy.) . I don't know if the plastic under tension might start to slowly creep at those temperatures, but they are fine for now. I'm more worried about the extruder motor to be honest, it's really hot to the touch with the enclosure open, and i guess even more when printing with high ambient temperature.

The modified extruder body you posted is really intresting and might be a solution for now. I might try and print it directly in grey ABS+ (will grey be fine with the filament sensor?) to cover all bases, if the printer manages to suffer another hotbox session. Other filaments i have on hand might be alloy 910 and TitanX, but i don't know if they have the required thermal resistance and material compliance. I also have some HT resin for the DLP printer that is able to resist at 200C+, but the resin is less than ideal for mechanical parts in term of weight and brittleness. Maybe the hotfins?

Does the extruder you posted retain the original, slightly misaligned filament path?

thank you again.

RE: MK3S part melted

This is NOT a user error with cooling. I almost never turn my printer off and when I do it's hours to days after being idle. 

Mine warped in under 40 hours of printing PLA Benchies, 20x20x20 cubes, and "life z" style tests. 

I had about 4000 hours on my MK3 with the prior 30 days being nonstop (maybe an hour between some prints, tops) .05mm prints. It was still pristine when I took it apart. 

This is one of the reasons I am extremely disappointed with Prusa for the MK3S downgrade. 

I found it when I had to tear it down for a jam, but with no fall back I had to reassemble it as is. I've since run off the Butterworth design options, but as my MMU start cooperating after that last rebuild I'm not messing with things until there is a problem...

RE: MK3S part melted

It has the original Prusa filament path. That project was more for users who wish to be very close to stock.

The only one that has ALL the goodies is the BNBSX Short Ears. That jumps features and extrusion uniformity forward.

Happy BNBSX doing Polycarb

Here is a BNBSX happily printing a batch of hot fins in Polymax Polycarb. Our machines SHOULD be allowed to print in materials beyond PLA and PETG without self destructing.

RE: MK3S part melted

same problem here...

RE: MK3S part melted

I went with the Bondtech upgrade and have had no issues - but I also had no issues with the original Prusa parts either.

RE: MK3S part melted

Bondtech upgrade body has a higher temperature plastic.

Bear based bodies are also OK even with PETG. Their only issue is the PINDA clamp screw gradually working loose over time. That can act a lot like the PINDA clamp sagging, but there is zero sag even after 48 hours of polycarb with 273 C nozzle.

I'll be fixing that screw issue in BNBSX B03 revision with a nylock. Screw working loose on PINDA clamp has bitten me twice.

Meanwhile, I'm hoping the R4 users are a little better off with their extra support rail.