Extreme Temperature Issues

Hey guys,
I've been toying around with my new Mendel for a few weeks now, and have had success printing various parts.

However, last night I ran into a bit of a strange issue. After my print completed, I let the machine stay at idle while I cleaned up the part (instead of turning it off like I usually do).
Within a few minutes I noticed a bad buring smell. The head had reached 400*C, and was starting to melt my J-Head (luckily I managed to save it).

I managed to replicate the problem a few times with the same result. Turning off the extruder temperature in the software doesn't seem to stop it from running away either. I physically have to kill the power to my PSU, to shut down the heater.


Now, I'm wondering if it's the software or the firmware. I'm leaning to firmware, as it didn't hit hardware shutdown on MAXTEMP (which by default is set to 275).
I'm running a RAMPS 1.4, with the ready to run Sprinter firmware listed on the Wiki page. The only changes I made to the firmware was the SAE z-axis calibration, and Greg's extruder calibration.
I'm interfacing with Pronterface (Mar 25/12 build).
All my print jobs are done with Slic3r, and seems to hold the temperature perfect until the job finishes.

Has anyone had this problem before?
Any ideas?

Thanks,
Tyler

Hi. I just had the same thing happen but did not save my hot end. It melted the aluminum. I'm never going to let this thing outta my sight when I print now. Or I will set it outside to print in the driveway.

Anyways, I tried installed 3 new thermisters and it did the same thing. Do you have a heated bed? Do the temps seem to be within range for that? Any other repeatable variables and might point to a culprit part?

In looking at the date of your post it looks like ours failed about the same time. My controller board came with the firmware preinstalled. Been printing okay-ish for a month or so. Mine burned up while i was letting everything warm up.

Only thing I can think of is reflashing new firmware, and I really don't want to do that.

Best of luck!
John

Hi John,

Sorry to hear about the melt down.
I agree, I feel a bit uneasy about letting it print when I'm not in the same room, or even letting it run in the house.

To answer your questions; yes I have a heated bed. I have noticed it veering off the set temp, but nothing crazy. When set at 60, I've seen it wander off to about 75.
I haven't tried any major changes. The only thing so far is reducing the safety limit, and re-flashing the firmware to see if I can atleast get it to trigger. So far no luck.

If I can't figure it out in the future, I may resort to a physical safety shutdown switch on the hot end, while printing. I may wreck some print jobs, but it will put my mind at ease knowing that I won't burn up a hot end... or worse.

I'll keep playing around with the settings and see if I can come up with a solution. I'll keep you in the loop if I figure something out.

Tyler

I've had some time to think about this and plan on building in some safety features when I get her up and running again. Firstly, to prevent the thermister or resistor on the hot end from shorting out, I'm going see if I can install them and fill the remaining hole opening with a fireplace caulk/cement. That should prevent metal on metal shorting. Assuming the caulk is non conductive. eh

An big red emergency stop button would be nice to have. I had a few times where the vertical endstop didn't work and the hot end really put some pressure onto the printing bed before I could pull the plug.

I may rig up a second set of safety thermisters to the bed and hot end, and connect them to the emergency stop and an audible buzzer. Not sure if it would be benefical to keep the fans running in that event...be nice to cool things down, but if somethings on fire, well, lol that wouldn't be good.

I really like this printer (when its working) and have some plans for some large parts with long print times. I do however, not want to sit around andd baby sit this thing for 12 hours at a time. At that time investment, I could whittle the parts faster by hand. lol. I suppose to go as far as one could, would be to build a nice lexan case to house the printer. Get a small C02 bottle (like the kind used in paintball) and rig it up for fire suppression with an easy solenoid valve. If something gets to hot, kill the power and flood the box with C02. Kinda like a poorman's halon system.

I know it probably seems uber paranoid and extreme, but I'll be danged if I'm going to catch the house on fire, and I am not giving up on this printer.

How about a coupla thermal fuses. I saw a blog where someone used one to control the bed temp, you'd just be using it to cut the temp if it goes into meltdown.

Maybe a wiki page on safety measures would be good. If these are going to be household items, it'd be a positive step.

A wiki page on safety would be an excellent addition. I don't want anyone to have any accidents with these things.

Oh man, I wish I had thought about the thermal fuse idea. Brilliant. One of those things could have saved me a alot of sanity and a couple bucks. Maybe a thermal breaker switch to avoid those 'where are the spare fuses' situations.

It would be nice to have the fuse trip in such a way that printing can be resumed after the problem is fixed and the fuse is replaced, assuming it could be fixed without moving the print head.

Maybe we need to rig up a safety board / fuse block to compliment the on board electronics. Something that can easily be added onto any machine. Hmmmmm