Something’s wrong here, and I’m not sure what it is. There are a bunch of things it could be, and I’m frustrated.
Tonight, again, I watched the MakerBot plastruder push the heater barrel right out of another PTFE insulator.. First it had extruded a small amount, then the entire barrel pushed out. I should create a gallery of PTFE insulators..
I was just ready to print out the test piece that I’d read about for months. I had just tightened up all of the belts, and I was convinced everything was going to work great.
Unfortunately, the barrel is now caked in this seemingly unremovable glaze that’s practically filled the grooves to the point where it seems smooth, which is why it’s not getting a grip anymore. Actually, I don’t know that. I suspect the thermistor is giving inaccurate results, but I’m not sure which way. When I saw it push out, I’d told it to be at 220C. If it was actually colder than that, the plastic would have been tougher to push through the nozzle so the motor would have pushed the heater barrel out (I DID see it extrude some through the barrel, so at least some of it melted). Or it could be way hotter than that, and have affected the PTFE. I don’t know.
I’m burnt for a while. This is extremely frustrating. The extruder needs to be strong as steel, and there needs to be some ability to detect when we’re pushing waaay harder than we should need to, so firmware can stop the motor before it tears the extruder apart. I’m tempted to use some of my Mendel supply of brass rod and PTFE rod to create another extruder from scratch (and use kaptan tape instead of fire cement, since that’s what the MakerBot’s extruder uses), but then I also have to use more nicrome wire, which I don’t have too much of. Agh.
Frustrated. Hulk mad. RepStrap no work. 🙁
[Update: Before giving up for the night, I clamped the existing heater barrel down in a vice, and successfully ran an M6 die from my new metric tap & die kit along the barrel, completely cutting away all of that awful glaze. Later I plan to cut off another piece of PTFE, drill it on both sides, use the M6 tap, and rebuild the insulator again. I do not plan to turn anything on though until I can find our meat thermometer, borrow one from a friend, or buy one at the store, so I can see what temperature the barrel actually is when I tell it to go to 220C.]
If your setting your temperature to 220, and it’s out ( miscalibrated or whatever) by 10%, it’s possible that you are just running it to cold. I’d suggest setting your temperature to 280, and seeing what happens. At an *actual* 280degC ABS will print a REALLY solid object, with some browning/oxidisation. If you are (say) 10% cooler, you’ll be in the higher-end of the working range of temperatures, but will be guaranteed to be fully fluid. partially fluid or “stiff” ABS is really difficult to reliably work.
good luck!
Buzz.
Thanks for the advice, I’ll take all I can get. But, doesn’t PTFE do horrible toxic things around 250C? I know I read something like that somewhere – probably on the Thermoplast Extruder 2.0 page. I could try it with just the barrel (no insulator) by holding it with insulated pliers and jamming some filament in there by hand, but won’t that change the temperature somewhat too? Actually, as I write that, I can’t imagine that it would. I’ll try that (without the PTFE) – thanks.
Yeah, PTFE (Teflon) decomposes horribly above ~250C, and around that temp thermistors start failing. Kapton/cermaic insulation start wigging out if exposed to 300+ centigrade.
If you get ABS caked in (glazed/burnt/etc), just soak the affected pieces in acetone overnight. The parts will be clean as a whistle in the morning! (Also, on a side note, IIRC caustic soda dissolves PLA)
-Adam
Oops, forgot-
Kapton is a cheaper and easier way to build extruders. If you mess up/break things, you only have to peel off the tape!
-Adam
Though I may try making one out of fire cement one day for the hell of it, I think I finally agree about the Kapton tape. 🙂
Damn it.. I woke up this morning around 4:30am unable to sleep, so I came downstairs and built a new PTFE insulator. Tapped it nicely, it screwed right on the clean barrel, everything looked good. Turned on the machine, ran replicatorg, went to its control panel, and the temperature was fluctuating. Worse, it was going up (even though I didn’t tell it to – target temperature was 0). Before I turned it off I saw a small amount of ABS drip out of the nozzle (it’s still got some plastic from last time), so it actually was getting hot.
Did I just wreck the extruder controller, or the thermistor, or do I just have a correctable short somewhere? I wrapped some more kaptan tape around areas that looked suspicious but turning it on again later it had the same problem. (it’d start around 80C, seem to up very rapidly, every once in a while the number would jump to some wildly wrong # (too hot I think) but then back to what it should have been I’d the temperature was steadily increasing.
I don’t know enough about the logic in the extruder controller board but isn’t it quite troubling that the temperature is going up when software isn’t telling it to? Ok, the way that question was worded was poor – obviously that’s got to be fixed and breaks the entire machine – I mean does it indicate that the board is broken instead of just the thermistor sensor or the wires to the sensor, for instance? Or is the heater capable of heating just by a short, without the extruder controller instructing it to heat?
See if there’s an Infrared Thermometer where the RepStrap came from. That would be more accurate than a meat thermometer.
I bought one, and it’s still off by like 5-10 degrees C. 🙁
> (it’d start around 80C, seem to up very rapidly, every once in a while the number would jump to some wildly wrong # (too hot I think) but then back to what it should have been I’d the temperature was steadily increasing
This sounds like a bad connection somewhere leading to the thermistor. When there is a break, the firmware will read out its maximum temperature, but it averages 3 temperatures, so if it misses just one of three it will end up with some high number between the actual temperature and the max temperature.
As far as the PTFE insulator failing, you might want to check out this post: http://blog.reprap.org/2009/09/my-extruder-doesnt-work-what-can-i-do.html
I have a hose clamp around my PTFE insulator preventing it from deforming around the threaded part.
Hose clamps are now in the mail, whether they work or not. I also ordered a few more feet of PTFE rod, but now I’m beating myself up for not remembering that I wanted to try PEEK next.
nicrome wire, is that not also found in hair dryers??
Just a thought… That is where I plan on ‘mining’
mine from
=)
From what I’ve read you want to make sure you use insulated nichrome wire, not uninsulated, and makerbot.com sells it for 50 cents a foot (and you only want to use one foot, because you need a specific resistance which is determined by the wire length). I’ve thought about hair drier or toaster “mining” several times but I’m guessing that at the end it’d be more effort than it was worth, unless you were on some junkyard wars game show or something. 🙂
Yeah, you’ve got thermistor issues. If your temp goes above 250 deg C, you’ll melt the heater barrel out of the PTFE.
Your temp should be stable; switch to a thermocouple to make things easier. Temp sensor placement is critical too, you want to measure the barrel temp, not the nicrome temp or the insulator temp.
After my first heater melted I added some code to do a sanity check on the extruder; the ptfe has lasted for almost 20 lbs of feedstock now.
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