Solved Needing higher and higher print temps to print. Turned out to be a clog not bad thermister.

I've been printing fine with a E3D v6 for a number of months. I noticed that the temperatures I was printing at started to change and then got to be too high to risk (according to the thermistor). This pointed to a Thermistor failure. I replaced the thermistor with a stud type thermistor and recompiled the arduino firmware (sensor type 5 changed to sensor type 1). The Sensor printed PLA at 220 so things seemed off, knowning the bolt was 1mm too long I cut it to make it fit better and then it went to 240c and then 260c to print PLA. I found that the crimp was bad on the wire so instead of replacing the JST with another crimp on (since crimping isn't something I've good at) I soldiered a premade JST connector after rerunning the wire. The checked each solder point. It has a round trip Ohms of 3 Ohms. Which at low temps won't make a difference but at 260c that could make a difference. The stud sensor seems to be reading 106 kohms at 25c using an oregon scientific room thermometer it read 2c higher then the heat beds thermometer.

So here is my question, is the stud sensor bad, my wire too resistant, need heat paste or is there something wrong like the Arduino?

 

If it reads around 100k at room temperture it's probably not any damage to the thermistor. A jump to high temps indicates a short of some form.

 

Ok so if sensor read higher than actual temp it would suggest the ohm level is too low suggesting short. Thanks would that be in the ramps or arduino since I rewired the sensor completely?

 

Temps didn't "jump" they just register higher then they really are.

 

2C is negligible difference for a thermistor.

 

My bed temperature is showing 70 in MC, but by IR thermometer it's 63.8
I haven't yet tried to measure the extruder.

 

Temperature is one of those "fun" measurements. All you ever really know is the temperature of the sensor.
Look at the NWS spec for measuring air temperature. They specify what kind of grass the little white house (painted with a particular kind of paint and built in a specific way) is sitting on.

 

Right. The IR gun is reading the surface of the glass. The thermistor is in direct contact with the heating element.

 

OK I was able to prove it was a short. I pulled the sensor connection from the ramps board and temperature dropped to 17c which means it is still measuring resistance somewhere. I'll have to check the wiring to make sure nothing is stray. Is the assembly using the Arduino 10 bit Analog pin? I wouldn't think that would be accurate enough for this based on my use in robotics. Is it using a better Analog to Digital sensor on the Ramps board? I'm trying to figure out which part would be replaced if it's not a stray wire.

 

Here's the circuit diagram for the ramps: http://reprap.org/mediawiki/images/f/f6/RAMPS1.4schematic.png

Check here for more info: http://reprap.org/wiki/RAMPS_1.4

 

OK I had a short (when I disconnected the sensor the temp dropped to 17c). I have rerouted it to pin 15 after a recompile and tested at room temp, at room temp its working, and if I disconnect the sensor it gets no reading - so this pin isn't shorted. However, when I heat it up, it's not hot enough to melt the filament. I'm borrowing a fluke inferred sensor later today to check the real temp. If it is not getting up to temp and it's still reading wrong then it will mean the sensor is likely bad also.

 

You won't get an accurate reading with a IR sensor since the internal temperature is what the thermistor is measuring. The external temperature will be significantly lower.

 

If that is the case then my only other option at this point is replace the sensor. I have parts on the way to experiment in making a stud sensor but it will be a bit before they arrive.

 

You can measure the resistance at temp and compare it to the thermistor table as well.

 

OK after testing 2 more thermistors, I'm thinking it's actually a clogged print head. I pulled it apart and it had a clog past the heat break. I bought some chemical to desolve the PLA, it softened but didn't seem to desolve after 48 hours. I'll reassemble with the new thermistor and give it a try. This makes me concerned about this in the future. What do you use to desolve Nylon and XT (PET)?

 

Is your hotend fan running?

 

Fan is running. The issue was that when it was not printing before I raised the temp and then it printed. I went through the cycle a couple of times thinking it was my sensor. End end result was the temp went high enough that PLA melted above the heatbreak. Once the chemical broke it down enough I was able to disassemble the pieces and clean them. I didn't realize it was getting worse and worse over the course of a year. I put it back together and it prints like new now. Problem solved.

 

The fan is important. It keeps the heat from rising and melting the filament above the hot end heated area. If the heat gets up there, it clogs after a cooling. Just a thought. Frank