How often to replace various parts on the MINI? (a proposed regular part replacement schedule)
How often to replace various parts on the MINI?
I have three MINIs and have logged 7,000 print hours on each. During that time, I've had to replace parts (e.g., nozzle, various PTFE tubes) and a resource I would have found (and would continue to find) useful is a recommended replacement schedule for various parts. Basically, after how many print hours should each part (that needs to be replaced) be replaced?
Of course, this depends on the filament you're using and perhaps other factors but just having a schedule for printing entirely with PLA would be a helpful benchmark. People have mentioned in various places on the forum how often they replace parts but hardly anyone gives the time in print hours. Usually people reply with some number of weeks or months; this is meaningless without knowing how many hours they're running their printers per day. I've suggested that Prusa add this to their regular maintenance page for the MINI but I don't see it there yet so I thought I'd create one here based on my own experience with three MINIs.
Regular part replacement schedule
Here is my regular part replacement schedule in progress (I emphasize in progress because, in some cases, I have noticed a part needs replacement well after it should have been replaced...). I am developing this schedule printing only with PLA. So if you're printing with a more abrasive filament, obviously you might want to replace certain parts more frequently. I'm also using MINIs without any modifications; all the parts are standard parts (same type as when I originally purchased the printer). For each part, I've linked to the product page on the Prusa website in case you're unsure which part I'm referring to. I've added a "(?)" to parts where I'm still unsure of the best replacement interval.
- Standard brass nozzle (0.4 mm ): Approximately every 500 print hours
- Hotend PTFE tube: Approximately every 500 print hours
- Hotend-Extruder PTFE tube: Approximately every 3,000 print hours (?) (I had filament break through the tube at 6,400 hours... see 5th post)
- Filament sensor PTFE 4x2x15: Approximately every 3,000 print hours (?)
- Heatbed thermistor set: This is probably not a part that needs to be regularly replaced. I've had to replace this on two of my three MINIs, one at 1,400 print hours and the other at 2,800 print hours; my third MINI has been printing for 7,000 hours with the original. It seems that in some cases the originally installed set breaks because of a sharp bend in the wire where it passes between the heatbed heater cable ends/attachments. When I replace this part, I wrap that portion of the cable in electrical tape to give it some extra protection; this seems to work because I've not had to replace any of the replacement (non original) heatbed thermistor sets.
But aren't there too many variables to have a schedule like this?
In anticipation of those who might respond that the replacement schedule depends on so many factors that it's useless to even have recommended hours, I'll just say I think having some number of print hours, even if it is very approximate, would be helpful. I have found these numbers to be useful in my printing, perhaps because I'm printing entirely with PLA so there's less variability in wear. If you don't think this would be useful for you, that's totally fine! All I can say is that I personally find it useful.
Anyone else have print hours to share?
If you've developed your own part replacement schedule, please reply with what time intervals have worked well for you! Please only give times in print hours and only give times if you print entirely with PLA. If you use other filaments, it might be best to start a new topic to keep this topic dedicated to a PLA benchmark standard.
Best Answer by Aaron O:
Here's a follow-up on the above replacement schedule with some photos on how to recognize when parts should be replaced. For the nozzle, I personally can't see a difference in the nozzle itself indicating that it should be replaced. Rather it's just a general decrease in print quality (vague and not particularly helpful, I know).
Hotend PTFE tube
For me, the only problem I've ever had with the hotend PTFE tube is that the end of the tube closest to the nozzle (the downward pointing end) dilates.You can see this dilation if you hold the tube up to a light with the light behind the tube (i.e., the tube is backlit so that the light passes through the tube toward you). This is a bit hard to photograph but I've included a photo of this below.
I only replace the PTFE tube if I see this dilation. I've found that I can actually flip the hotend PTFE tube upside down and continue using the same tube for another several hundred hours without any issue. That way I can get twice as much use from the same tube! An added bonus is that when I flip the tube upside down I don't have to loosen and retighten the hotend grub screws since the length of the tube hasn't changed.
You may also see this dilation more directly if filament balls up and gets stuck in this dilated portion of the tube. Here's a photo I took of that (see the ball of white filament at the right end of the tube.
This dilation doesn't occur at super regular intervals. Sometimes it happens after ~200 print hours; sometimes after ~500 print hours. I think it depends on what I'm printing, perhaps how much the filament gets pushed back into the hotend with retraction?
Hotend-Extruder PTFE tube
In my experience, the only wear on the Hotend-Extruder PTFE tube comes from the filament scraping against the upper inside of the tube, especially in the middle of the tube where the filament is really pushing hard against the tube. This causes thinning of the wall of the tube but it can also causes underextrusion issues in prints. If the Hotend-Extruder PTFE tube is not replaced, the tube can get so thin in this part of the tube that the filament can literally break through the tube when it is loaded by the extruder (this happened to me after 6,000 print hours and never having replaced the tube):
Ideally you want to replace this tube before this happens. You can see the thinning in a similar way to seeing the dilation in the hotend PTFE tube. Hold a light behind the Hotend-Extruder PTFE tube so that you're looking through it. Even better is to do this with filament loaded in the printer; if your Hotend-Extruder PTFE tube has started to thin, the filament will be displaced toward the top at the midpoint inside the tube rather than running directly down the midline of the tube along its whole length.
You might be wondering how smooth PLA filament could possibly cause so much wear to the inside of a hard plastic PTFE tube. Of course, any two materials grinding against each other for a long enough time will cause wear. But my guess is that the small grooves/indentations in the filament from being pushed through the extruder "teeth" make the filament especially abrasive to the inside of the PTFE tube.
Extruder-Spool PTFE tube
Oops, I forgot to include this in my original part replacement schedule! This is the 150 mm tube that connects the filament sensor to the extruder. Just like the Hotend-Extruder PTFE tube, this tube can also get internal wear from the constant sliding of filament. You can see how much wear by looking through the tube with a light behind it, ideally with filament loaded to see if the filament deviates from the midline.
I finally replaced my Extruder-Spool PTFE tubes after 7,000 print hours. Here's a photo showing the middle of the Extruder-Spool PTFE tube in cross section (right side) and the end of the that same tube for reference (left side). Note how in the middle of the tube (again, right side in the photo below), the filament has worn the wall of the PTFE tube down to a fraction of the original width. Ideally you would want to replace this tube before the wear gets this bad. Perhaps about every 3,000-4,000 print hours?
Filament sensor PTFE 4x2x15
This is the tube through which you first insert filament to load it into the printer. I don't have a photo for this one but you'll see similar wear on the inside of this small tube just as for the Extruder-Spool PTFE and Hotend-Extruder PTFE tubes. It should be fairly easy to see this wear because it will be visible right where the filament enters the tube (no need to do the backlight viewing thing).
RE: How often to replace various parts on the MINI? (a proposed regular part replacement schedule)
Excellent info.
Next time when you are close to the replacement I suggest taking pictures of the worn out part and a new one - so people can more easily recognize the symptoms of the given wear outs. Then add pictures to the post as Add Media above editor area.
Regarding times for the items to be replaced, of course it depends on the components, especially when using custom ones - for me actually I managed to damage the thread in the aluminium block faster than anything else. Switched to another one along the heatbreak, I noticed that hotend PTFE tube is no longer experiencing wear out due to temperature, so now only the internal filament move causes the issues. This means certain components replacement may be expensive in the beginning but can save money and time in the long run.
See my GitHub and printables.com for some 3d stuff that you may like.
RE: How often to replace various parts on the MINI? (a proposed regular part replacement schedule)
Thanks for sharing! I have been wondering the same thing. I have 5 Prusa MINI's running, which have clocked similar numbers as yours (although I don't have such an exact time keeping). In principle I follow a similar regime, but I see a large variation in how long my hot-end PTFE tube lasts without issues, which seems to correlate with room temperature this summer. Are you using the standard heat break or have you replaced them?
RE: How often to replace various parts on the MINI? (a proposed regular part replacement schedule)
Thanks @_kaszpir_, photos are a great idea. What I should have done is not put the actual replacement schedule in the original post but put it in a subsequent post that I could mark as the "Best Answer." Then I could always update the "best answer" with a new post if there was something I wanted to change. I will create a new post here and mark it as the best answer with some photos that I have already.
I also seem to have had more wear on the hotend PTFE tube earlier on than I am currently. I haven't replaced any hotend components (other than the nozzle and hotend PTFE tube) so I'm not entirely sure why I'm no longer getting the same amount of wear. I did start decreasing the nozzle temperature after the first layer (to reduce stringing) at some point - maybe that helped.
RE: How often to replace various parts on the MINI? (a proposed regular part replacement schedule)
Thanks @jaap! I am using the original, standard heat breaks in all three printers; I've never replaced them.
RE: How often to replace various parts on the MINI? (a proposed regular part replacement schedule)
That's interesting! I'll look into lowering the temperature after the first layer. I have stringing on one of my printers as well, which started after i recently replaced the nozzle. I don't quite understand what the root cause can be there, but the only thing I can think of is a thermal problem again. Maybe I need to take the print heads apart some time, and renew the thermal paste.
What are the indications that you see that you need to replace the parts above?
RE: How often to replace various parts on the MINI? (a proposed regular part replacement schedule)
Here's a follow-up on the above replacement schedule with some photos on how to recognize when parts should be replaced. For the nozzle, I personally can't see a difference in the nozzle itself indicating that it should be replaced. Rather it's just a general decrease in print quality (vague and not particularly helpful, I know).
Hotend PTFE tube
For me, the only problem I've ever had with the hotend PTFE tube is that the end of the tube closest to the nozzle (the downward pointing end) dilates.You can see this dilation if you hold the tube up to a light with the light behind the tube (i.e., the tube is backlit so that the light passes through the tube toward you). This is a bit hard to photograph but I've included a photo of this below.
I only replace the PTFE tube if I see this dilation. I've found that I can actually flip the hotend PTFE tube upside down and continue using the same tube for another several hundred hours without any issue. That way I can get twice as much use from the same tube! An added bonus is that when I flip the tube upside down I don't have to loosen and retighten the hotend grub screws since the length of the tube hasn't changed.
You may also see this dilation more directly if filament balls up and gets stuck in this dilated portion of the tube. Here's a photo I took of that (see the ball of white filament at the right end of the tube.
This dilation doesn't occur at super regular intervals. Sometimes it happens after ~200 print hours; sometimes after ~500 print hours. I think it depends on what I'm printing, perhaps how much the filament gets pushed back into the hotend with retraction?
Hotend-Extruder PTFE tube
In my experience, the only wear on the Hotend-Extruder PTFE tube comes from the filament scraping against the upper inside of the tube, especially in the middle of the tube where the filament is really pushing hard against the tube. This causes thinning of the wall of the tube but it can also causes underextrusion issues in prints. If the Hotend-Extruder PTFE tube is not replaced, the tube can get so thin in this part of the tube that the filament can literally break through the tube when it is loaded by the extruder (this happened to me after 6,000 print hours and never having replaced the tube):
Ideally you want to replace this tube before this happens. You can see the thinning in a similar way to seeing the dilation in the hotend PTFE tube. Hold a light behind the Hotend-Extruder PTFE tube so that you're looking through it. Even better is to do this with filament loaded in the printer; if your Hotend-Extruder PTFE tube has started to thin, the filament will be displaced toward the top at the midpoint inside the tube rather than running directly down the midline of the tube along its whole length.
You might be wondering how smooth PLA filament could possibly cause so much wear to the inside of a hard plastic PTFE tube. Of course, any two materials grinding against each other for a long enough time will cause wear. But my guess is that the small grooves/indentations in the filament from being pushed through the extruder "teeth" make the filament especially abrasive to the inside of the PTFE tube.
Extruder-Spool PTFE tube
Oops, I forgot to include this in my original part replacement schedule! This is the 150 mm tube that connects the filament sensor to the extruder. Just like the Hotend-Extruder PTFE tube, this tube can also get internal wear from the constant sliding of filament. You can see how much wear by looking through the tube with a light behind it, ideally with filament loaded to see if the filament deviates from the midline.
I finally replaced my Extruder-Spool PTFE tubes after 7,000 print hours. Here's a photo showing the middle of the Extruder-Spool PTFE tube in cross section (right side) and the end of the that same tube for reference (left side). Note how in the middle of the tube (again, right side in the photo below), the filament has worn the wall of the PTFE tube down to a fraction of the original width. Ideally you would want to replace this tube before the wear gets this bad. Perhaps about every 3,000-4,000 print hours?
Filament sensor PTFE 4x2x15
This is the tube through which you first insert filament to load it into the printer. I don't have a photo for this one but you'll see similar wear on the inside of this small tube just as for the Extruder-Spool PTFE and Hotend-Extruder PTFE tubes. It should be fairly easy to see this wear because it will be visible right where the filament enters the tube (no need to do the backlight viewing thing).
RE: How often to replace various parts on the MINI? (a proposed regular part replacement schedule)
Approximately every 500 print hours
Apologies, I made a mistake here. This should read "Approximately every 1,000 print hours".
RE: How often to replace various parts on the MINI? (a proposed regular part replacement schedule)
Super post!
Also much thanks to the provided photos!