temperature – MakerBlock

WWMWD?

Welp. I guess this is a good time to dust off this little gem from the book, “The Martian.”

I’ve been trying to get consistent readings inside the house for a little over a week now. The infrared thermometer was helpful, but was too manual and to variable in readings despite trying to control by checking at wider intervals and taking measurements in very specific sections of the floor, wall, and ceiling. The XAIO board and thermistors were a great first step, but required too many wires and it was also having trouble broadcasting data. ¹ The Wemos D1 Mini, while an underpowered board, took a lot of fiddling to get running and a fair bit of soldering, but has worked very well.

Until external factors cropped up.

Yesterday, at the absolute peak of outside heat, our AC unit stopped working. I’m pretty sure the sound of it turning off yesterday was the last time it was working. The temperature inside reached about 86 degrees upstairs based on the home thermostat and stayed at that level until about midnight when we started up the whole house fan.²

If I were comparing a given day’s temperature to a different day’s temperature, all the readings would be basically useless. However, I’m actually more interested in figuring out if a single sunscreen can soften or blunt the increases in internal house temperatures. The data from yesterday is going to be useless for looking at absolute changes in temperature, but it certainly shows what would happen if we don’t have a working AC unit on a very hot day.³

Yeah, having the AC go out is a hassle – but on the bright side, at least it happened during a time when I was running some science experiments.

But, with about a week left to go, I’m less certain I’m going to be able to present the findings and associated original project I was planning on.

Summer Science - Testing Effects of Window Coverings on Interior Temperatures

Though, now that I think about it, this might have been improved if I attached the antenna to it? [↩]
86 degrees inside sounds comparable to Italian AC [↩]
Though, it shouldn’t take a rocket scientist to realize it’ll get warmer here without AC. [↩]

How are you printing with PLA?

I’d like to print in PLA, I really would. No warping? No rafts? Smells like syrup? Makes kittens and rainbows? Sign me up!

Rick from MakerGear has the following suggestions for printing in PLA:

Have a 150-160 C degree temperature for the entry of the barrel
He notes that the nozzle temperature is roughly 190 C degrees
However, later he suggests printing at 220-235 was possible
He suggests not to worry overmuch about PLA in the threads – its just one of those things

Nick McCoy offered several pieces of wisdom:

He found that 10W-30 oil added lightly to the PLA as it entered the extruder, by adding oil to a piece of cotton wrapped around the filament, helped it print without jamming
He noticed that pausing the extruder for more than a few seconds would jam the barrel
He found he could print at 180-210 degrees (I assume he’s measuring the nozzle temperature as you would with an ABS setup)

Nick’s results suggesting a nozzle temperature of 180-210 seem to match up with Rick’s findings of 190 or so. I think I’ll give Polly another shot and see if I can extrude at those temperatures.

An idea for checking the temperature of an extruder at the barrel entry

Several people have suggested that the temperature at the entry of the barrel is very important to printing with PLA. This makes sense. If the temperature at the barrel entry is above the melting point for PLA, it can melt right there and ooze down around the threads.

Maybe I should assembly my extruder with just the thermistor on the barrel entry, and heat it until it is just below the melting point of PLA – then check the temperature at the nozzle.

Or, I could get a second thermistor and use it at the top of the barrel while keeping the original thermistor at the nozzle. I could only use one set at a time (since I don’t know how to hack the electronics/extruder board), but that shouldn’t be an issue.

How to diagnose and fix a burned out thermistor

Unfortunately, Bender just stopped working. As I was keeping the nozzle warm while I was working on a new model, I looked up to see a flash of fire/spark shoot out from the nozzle area, ricochet off the build platform, and disappear. Looking at the RepG control panel I discovered that I wasn’t getting any readings from the thermistor. Not good.

The RepG control panel showed 0.0 as the temperature, so I shut the plastruder down, not wanting the heater to burn out of control. I restarted Bender and RepG – but I discovered that while I could control all three axes very slugishly, I could not move the extruder motor or detect temperature. I’m guess I couldn’t have increased the temperature either, but I didn’t want to try it since I couldn’t monitor the temperature. That about covers the symptoms.

In order to diagnose the problem I tried to isolate the various parts. I pulled all of the wires out of the extruder board. Then, while the wires were still out I tested the nichrome for resistance – still around 6ohms. Then I tested the thermistor – no connectivity. Again, not good. I tested the motor for continuity, and it was fine. Since the nichrome and motor seemed fine, that left the thermistor and extruder board. I popped a random resistor into the thermistor ports, but still couldn’t get a reading on it. Unfortunately, after several resets of the motherboard and extruder board, I still couldn’t get the motor to move or a reading from the thermistor. Also, I was getting an error message that the Payload was not big enough.

Rick Pollack of MakerGear suggested on the MakerBot Operators group that I reflash the extruder firmware. After several failed attempts, I finally figured out how to flash my extruder firmware from the Arduino environment by holding down the extruder reset button. This got rid of the payload error message as well as the avrdude errors and let me reflash the extruder.

I pulled the entire extruder apart and did a little maintenance. I flossed the extruder pulley teeth, pulled all the stray bits of plastic out of the idler pulley wheel area, removed the old thermistor, unwrapped the nichrome (which was wound down and then doubled over itself as the original pictures in the wiki suggested) and rewrapped the nichrome (a single layer from the nozzle up the barrel following closely in the threads to make good contact everywhere) as suggested by several people in the MakerBot operators group. I then tested the nichrome again once it had been taped down for the proper resistance, check.

Once I pulled the thermistor out of the heater assembly, I tested the thermistor at its own leads, rather than at the wires soldered to it (in case the thermistor had come apart from the wires). Still nothing. I plugged a random resistor into the thermistor ports and was now able to get a reading off the extruder (as well as move the extruder motor). Concluding my problem was the thermistor, I forged ahead with a plan to replace it.

Luckily, I had placed an order for some PLA and nearly every single part needed for a secondary extruder (or what would be needed to fix a broken extruder) including a new thermistor. If you haven’t picked up backup parts, I highly recommend it.

I clipped the old thermistor off the wires, pulled out the new thermistor and taped it to a white piece of paper immediately, putting the tape across the leads just below the bead. I then bent the leads upwards, tinned them, soldered them to the wires, taped down the wires, pulled up the original piece of tape, and then sandwiched the thermistor in tape as per the instructions. I then plugged the heater, the motor, and the thermistor back into the extruder board – and was able to get a temperature reading, apply a little heat to the barrel, and move the extruder motor. I also noticed that this removed the sluggishness from the 3 axes stepper motors.

With the heater, motor, and thermistor working separately I put everything back together and reassembled the plastruder, plugged it back into the board and tested it again – readings, heat, and extruder motor working. I then popped it back into the dinos, did a test extrusion, and starting printing again.

“Rock on completely with some brand new components”