Rostock Max went insane last night.

[Brian]

I was printing a large print and there was about an hour left to go when I went to sleep. When I woke up at 6:30AM to go to work, I could hear the printer still working and I went to see what was happening. When I checked, there were just over 5 minutes left in the job. Huh? 7 hours before, there was one hour left!

Then I looked at the print, and I saw that the top few millimeters were missing, but the extruder was still working away in the air a few mm above the top of the object, with no filament coming out. I thought my spool ran out or there was a jam or a break but then I discovered that both the bed and extruder temperatures were set to 0 on the LCD screen.

Is this a bug or something? I have no idea what happened. I know the gcode is good because I had previously just printed the exact same item. Oh yeah. I was printing over USB if that makes a difference.

Any ideas?

[Jimustanguitar]

Depending on your slice, I've found that "cool head lift" isn't taken into consideration when the firmware calculates time remaining. If you've got a high minimum layer time and the print is pausing to let things cool between layers it can really add up.

I *think* that the ETA on the display is just an estimate based on how many lines of GCode are left, not necessarily how long the commands in those lines take to execute.

[Brian]

I'm really not doing any pausing between layers. I am trying to get really solid layer adhesion for strength, so I am running as hot as I can and accepting the stringing that comes from the high temp. So that's not it.

The thing is that I previously ran the same job with no issues, and it completed in the estimated time (about 4 hours). I started a second print of the same part and went to bed 3 hours later, so I know it really had one hour left based on the previous print.

The thing is that the software must have gotten confused because it shut off the heaters and continued to move the extruder like it was printing. The filament solidified in the extruder and stopped coming out. The job also took several additional hours to finish.

I think it must have gone crazy. Every so often I get odd behavior from the software, like starting a print and the extruder homes and then prints without going to Z=0, so the filament just comes out in mid air.

I thinkl this is just weird bugs.

[Jimustanguitar]

Might have been USB related then, try the same code on SD and I bet it'll go without a snag.

I've noticed that MatterControl will stop working when my computer times out, and I failed a couple prints that way. I've since changed my power settings to never do anything based on a timer and it's helped a lot.

[Brian]

I have more information now.

I was going to do the print from SD as you suggested, but when I got it all ready to go I noticed that there was a huge blob of extruded plastic on the nozzle of the extruder. I thought maybe a clog or a jam was the problem, so I fired it up to get the ABS off and the temperature ramped up to 139 and just sat there.

I assume what happened was the hot end resistor(s) are failing and the controller was unable to heat the extruder enough and the ABS formed a big wad until the temperature got so low it jammed. It looks like a failsafe in the firmware shut off the heaters or something when the hot end failed.

I hope it's the resistors, and not the Ramb0.

[Brian]

Update:

I checked the hot end with a multimeter and found that across the resistors I see 7.9 Ohms, which is slightly WRONG. I then dismantled the hot end for a closer look.

I see that my High-Temp "Copper" RTV was pretty crunchy on one side, and the other side it was somewhat more flexible, but still seemed dry to me. I cut the leads and measured the resistors, and the crunchy one measured 7.9 Ohms and the other one was Infinity.

So, apparently, one of the resistors failed at some point, and the other one was doing the work of both, and probably cooked the RTV and over time it became brittle and cracked and lost thermal contact with the metal.

A few weeks ago, I mentioned I was having issues with the hot end varying in temperature a lot during the course of a print, and I attributed it to the heat being drawn away by the extruded plastic. I suppose this may truly have been the case but was only a problem because my resistors were failing and the RTV was not making good thermal contact with the metal.

I will replace the resistors, this time I will try and improve the mounting using the aluminum foil wrap technique, so I get better contact and less RTV filling the gap. I suspect this will help.

[Eaglezsoar]

Brian, this is just a suggestion. You can get the 12V 40Watt cartridge heaters on Ebay.
They replace the resistors and you only need one of them. They have been proven to be very reliable.

[Brian]

Hi Eaglezsoar,

Is there a specific size or shape that I need to purchase? I want to get one that fits. Does it slot into the hole for the resistors, and what holds it in place? It sounds like a good option.

[Eaglezsoar]

Hi Eaglezsoar,

Is there a specific size or shape that I need to purchase? I want to get one that fits. Does it slot into the hole for the resistors, and what holds it in place? It sounds like a good option.

They are available in a 6mm Diameter and a length of 20mm or 30mm.
If it fits too loosely in the hole it can be wrapped in a small piece of foil.

Ebay is the best place to find them I will provide a link for the 6mm x 30mm you can check the US vendors and search for the heater cartridge 6mm x 20mm
http://www.ebay.com/itm/Reprap-12V-40W- ... 338bc2919b

[Brian]

Hi Eaglezsoar,
Ebay is the best place to find them I will provide a link for the 6mm x 30mm you can check the US vendors and search for the heater cartridge 6mm x 20mm
http://www.ebay.com/itm/Reprap-12V-40W- ... 338bc2919b

Awesome! Thanks, Eaglezsoar!

[Holy1]

Damn Eaglezsoar, where were you last week when I asked about the cartridge heaters? Just replaced the resistors in mine today. Just kidding about the " damn". Thanks for posting the eBay link, I"ll get a couple for spare.

[Eaglezsoar]

Damn Eaglezsoar, where were you last week when I asked about the cartridge heaters? Just replaced the resistors in mine today. Just kidding about the " damn". Thanks for posting the eBay link, I"ll get a couple for spare.

So Sorry!

[nitewatchman]

Hi Eaglezsoar,

Is there a specific size or shape that I need to purchase? I want to get one that fits. Does it slot into the hole for the resistors, and what holds it in place? It sounds like a good option.

I use a single 6mm x 20mm cartridge. Put it in either resistor hole. Much easier to shim using a thin strip cut from a Coke Can even if it takes part of a wrap.

Mind is held in by wrapping the Hot End with a strip of Silicon "Repair" Tape.

Consider a Srew-In Thermistor while you are into it.

nitewatchman

[Brian]

Thanks for the info guys! I have ordered the heater Eaglezsoar recommended. I do have another question:

Do I need to change the wiring for the 40W heater, or is the stock wiring good enough for this heater?

Thanks!

[Eaglezsoar]

Thanks for the info guys! I have ordered the heater Eaglezsoar recommended. I do have another question:

Do I need to change the wiring for the 40W heater, or is the stock wiring good enough for this heater?

Thanks!

The wires you had running to the resistors will work fine for the cartridge also.
I do recommend using a 2 pin connector as indicated in the assembly manual for the Max.