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Prusa Mk3 problems and a fix


Ultra Member
If I sound a little bitter toward Prusa its because I am.....but hold on, it worked out in the end :)

When I got my Prusa printer I had nothing but problems, failed print after failed print Their support is awful, "have you tried rebooting" type of crap. I finally discover the problem and will explain it in case some else encounters this bit of misery.





What was happening is the hot end would jam. you couldn't reverse the plastic out of it and end it ends being a hot end disassembly to fix it. From that you discover some of serious flaws. The set screw and and clamp screw holding in the thermistor and heater are socket heads and point straight down. Straight down where they're perfectly situated to fill with plastic if a print screws up. To make matters worse, Prusa is buying the cheapest gummiest hardware possible so said screws quickly strip after a few hot jams/disassembly. The bore for the heater is so oversized that you have to visibly bend the AL block before the slit clamp tightens. With this over tightening in place, it make it easy to strip the the head when trying to loosen it


Using better hardware and a correctly size hole is a big improvement. I changed the thermistor to a cotter on the side and the heater clamp to a low profile hex head (not yet made at the time of the photo). This fixed the problem of having to drill out stripped garbage hardware to disassemble after a jam. An additional frustation is that until you can free the thermistor and heater, you constrantly the somewhat delicate wires while mucking about trying remove/drill the stipped screws...so they end up breaking occaisonally


Really though, the goal is to fix the fault not just make recovering from it easier. Prusa does not have their own hot end and instead uses the e3d end which is open source. By all accounts that seemed a reliable hotend....but no, Prusa had to muck it up. Being open source I printed some drawings and started checking. To my surprise I found the bore the Prusa made e3d differed from the e3d drawing - a stepped bore instread of straight through.

I wrote all this up like a engineering report with photos, rational, discription etc and sent to Prusa thinking I might help a lot people avoid this pain. Their reponse was "have you checked that you are using the current software version"? Lights are on but nobody was home. Very frustrating, especially after paying a premium price so I wouln't have all kinds of problems.


That's was the tragedy....here's the comedy (in the literary not Aristotelian sense lol). I ordered an after market heat break without the stepped bore and success! no more jams. Simple solution, but man, what a lot agony to arrive at it! I order new (NON Prusa) spares for the thermistor, heater, and other hot end parts just in case and haven't needed them. (i get all that stuff from aliexpress, cheaper and more selection than amazon). The sun started shining and I've been having a blast with printing all kinds shop stuff

Here's a sampling of shop projects I've used it on

Needle file/rifler trays - just a small sample, printed probably 40 of these


electronics enclosure


Sinker EDM


Pot mount for a lathe speed control (part of conversion to VFD)


A lot of the parts for this soft bearing, two plane, dynamic balancer I've making

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