Overwriting max temperature setting

I got a role of ABS filament today.

After replacing the PLA filament with this ABS filament, I set the hot end temperature at 230C and fed the filament in a little bit. I saw some extrusion at the bottom of the hot end (my old PLA was blank and this ABS is white, so I could tell it was the ABS coming out the nozzle for sure), then thought I'm ready to print some simple test piece.

After the heated bed reached 110C, the printer started printing but nothing was coming out!

So, I stopped the printing, and looked into the extruder and the filament wasn't moving. Hobbed bolt already digged into the filament. So, I took the filament out, cut out the ruined portion, and fed it to the extruder gears and hot end body again, and then ran the extruder 5 mm using Pronterface. This time, I put a little dot on the filament with a fine point sharpie, so that I can see if it's moving or not.

I tried it for a couple times, and each time, the filament starts moving, and I see a small amount of extrusion at the bottom of the nozzle tip, then the filament moves backward every so slightly, like it was bounced back, then no more extrusion and advancement of the filament.

I tried to feed the filament in by hand, and it's very hard. I cannot squeeze out any.

I wonder if my hot end is not hot enough to melt the ABS. I actually have other reasons to be suspicious about the accuracy of the temperature reading with my previous experience with PLA (I have to set the hot end temperature at 210C to make ti work and at "normal" printing temperature of PLA, the extruder cannot push the filament in and starts digging into it).

So, naturally, I would like to try printing with higher temperature... but there seems to be some kind of maximum temperature settings somewhere. Pronterface lets me set temperature higher than 230C, but when the temperature reading gets to 234-235C then I get an error message and the temperature resets to 0C.

Is there any way to overwrite or change this setting?

Thank you.

Hold the phone! If you can heat the hotend up to 230C and you can't push any through by hand, bypassing temperature limits and setting to a higher temperature is not the way to go about it. Your problems are likely either:

1) you are using the wrong thermistor table in your firmware

or

2) your filament is not going all the way down into your hotend

or

3) your hotend is jammed

As a test, clip off a piece of filament. When you get your hotend up to temperature, push the filament against the outside of the hotend and see if it melts. If it does not, check that your thermistor setting is correct. If it does melt, then you likely are not pushing the filament enough into the hotend or you have a serious clog.

I don't think my hot end is jammed. Well, at least not jammed completed. As I have said I've just switched from black PLA to white ABS, and the small amount of extrusion I can get with hand push is all white. I've cleaned up the hot end several time to make sure it's not jammed (I think I have become a semi-expert on hot end cleaning, thanks to the jamming issue I have had all week long ).

What do you mean by my thermistor setting? I'm guessing there are different types of thermistors, and the firmware should have proper setting in order to interpret the electrical signal from the thermisotr into temperature properly, right? I wonder how to check this settings, let alone changing them. Any tips on that?

By the way, FWIW, when I am not using the printer, the temperature reading from both hot end and heated bed on LCD are usually 23-25C, which seem to be correct for the room temperature where it is in. Also, both temperature readings are usually the same, sometimes off by one - but when they are off by one, usually one of them keeps going back and forth between the same temperature and 1C off. I wonder these are enough evidences which I can conclude the thermistor settings are correct. I guess it's still possible the thermistor reading can get off at higher temperature range.

I need to head out soon, but I will definitely try to melt the filament from outside of the hot end. However, as I have said I do have other reasons to believe my hot end is not as hot as what the temperature reading says, so I expect not to be able to melt the ABS filament at 230C setting - I probably will be able to make it soft, but not melted.

If it is the wrong thermistor table setting, wouldn't setting it at a higher temperature be a quick work around? I wouldn't think the temperature reading would go up and down with a wrong firmware setting, but off by certain percentage, rather. So, to achieve the actual 230C hot end temperature, if my thermistor reading gives me a reading which is consistently 20% cooler, I just need to set the temperature at 276C and my hot end will be at 230C... Isn't that how it would work?



iquizzle Wrote:
-------------------------------------------------------
> Hold the phone! If you can heat the hotend up to
> 230C and you can't push any through by hand,
> bypassing temperature limits and setting to a
> higher temperature is not the way to go about it.
> Your problems are likely either:
>
> 1) you are using the wrong thermistor table in
> your firmware
>
> or
>
> 2) your filament is not going all the way down
> into your hotend
>
> or
>
> 3) your hotend is jammed
>
> As a test, clip off a piece of filament. When you
> get your hotend up to temperature, push the
> filament against the outside of the hotend and see
> if it melts. If it does not, check that your
> thermistor setting is correct. If it does melt,
> then you likely are not pushing the filament
> enough into the hotend or you have a serious clog.

IMO that's risky, and not the ideal solution in the end. It's better to track down the source of the problem so you don't melt anything down.

When I first started 3d printing, I was unsure of which thermistor I had with my hotend. I guessed, because I knew I had a 100k thermistor using my DMM. Well, there were several options in Marlin for 100k thermistors (epcos, honeywell...) and I chose the wrong one. For PLA, it was *mostly* fine.. when I set my hotend to 185C, in hindsight I estimate it was actually at 170-175C. Occasionally it didn't extrude due to variations along the filament(!) and would jam my extruder. Once I realized the problem, I changed the thermistor table in the firmware and it worked like a charm.

All this to say that things can mostly still work sometimes even when you have things setup incorrectly. You could turn up the max temp and use it as a work around. If you had a different problem than you expect (which happens often), then you could also experience unintended consequences and melt the PEEK on your hotend (if you are using a j-head). I just try to avoid advising people to do things that could potentially break their machines... especially in cases where there are ways to diagnose the problem without risking equipment damage.

Well, I hear you well. Also, I wasn't brave enough to go ahead and overwrite the max temperature setting, so I haven't done anything stupid and burned up my J head or anything (at least not yet)

I actually ordered another J head, with a smaller size nozzle. I could see another printer or at least another (second) extruder on my printer in my future, so I thought it would be a reasonable investment. Also, I wanted to try out a smaller nozzle size to see if I can get a better result with smaller layer height.

Maybe I will try something drastic once the second J head gets here, but until then I would try to exhaust all the other options before taking a potentially risky measure.

I've also ordered a couple of thermistors (Semitec 100K) - since I know what these new thermistors are I believe I can eliminate the chance of using a wrong temperature table. Also, I will finally be able to know if my current thermistor was reading the temperature correctly or not. My preference was Epcos or Honeywell, but Newark charges extra $20 shipping for Epcos (because they only have them on stock in UK warehouse) and the error margin seemed to be too big for Honeywell; 20% for the models which were available. Semitec thermistors I ordered have 3% tolerance, and I hope that's still good enough.

I paid about $4 for each of these thermistors after shipping charge, and I think it was money well spent.

iquizzle Wrote:
-------------------------------------------------------
> IMO that's risky, and not the ideal solution in
> the end. It's better to track down the source of
> the problem so you don't melt anything down.
>
> When I first started 3d printing, I was unsure of
> which thermistor I had with my hotend. I guessed,
> because I knew I had a 100k thermistor using my
> DMM. Well, there were several options in Marlin
> for 100k thermistors (epcos, honeywell...) and I
> chose the wrong one. For PLA, it was *mostly*
> fine.. when I set my hotend to 185C, in hindsight
> I estimate it was actually at 170-175C.
> Occasionally it didn't extrude due to variations
> along the filament(!) and would jam my extruder.
> Once I realized the problem, I changed the
> thermistor table in the firmware and it worked
> like a charm.
>
> All this to say that things can mostly still work
> sometimes even when you have things setup
> incorrectly. You could turn up the max temp and
> use it as a work around. If you had a different
> problem than you expect (which happens often),
> then you could also experience unintended
> consequences and melt the PEEK on your hotend (if
> you are using a j-head). I just try to avoid
> advising people to do things that could
> potentially break their machines... especially in
> cases where there are ways to diagnose the problem
> without risking equipment damage.