Hexagon Hotend requires much higher temperature for PLA?

I got a Hexagon hotend replacing my Budaschnozzle hotend from lulzbot but it seems like if i am using the temperature setting when i was using Budaschnozzle on this new hotend it will severely under-extrude and eventually clog. I used to use 200 degrees for Lulzbot eSun PLA and now i need 250(230 is still underextruding) in order to extrude properly. Did i get a faulty unit or its the property of this hotend? I havent try other materials yet.

Wow, firstly it really sounds like you might have a mismatched thermistor (in firmware) or a temp calibration issue. At 250°C PLA will do very very bad things (char). So I doubt that you are actually seeing that temp. Do you have an external thermocouple that you can measure the temp at the nozzle? It’s a useful tool to have.

To answer your question, no, you should not see this type of variability in temp to extrude the same PLA filament. True, if each of the hot ends uses a different thermistor your temps might be off by a few degrees from each other but not that much. If you measured the temp at the nozzle (with a thermocouple) they should both extrude fine at the same actual setting.

The other difference will be in the PID tuning - they will be different but given enough time to stabilize the temp, you shouldn’t have a problem with that and it is not likely to be the cause here.

I believe you have to reconfigure Marlin’s thermistor when you move to the Hexagon, did you do that?

A loose thermistor and/or loose heater cartridge can be a culprit too, make sure these are installed correctly and tightly.

Hello mhackney,

Thank you so much for your quick reply!!! Actually i just bought the 3D printer for 2 weeks and i think it’s probably my incompetence that caused it. I was wondering when you are talking about reconfigure Marlin’s thermistor do you mean by upadating the firm ware to Taz 5? I already upadated it but in the instruction it didn’t tell us to reconfigure the thermistor. I will check the thermistor as soon as i go home. But it seems the temperature reads and response perfectly to the printer. Do you think it’s just a calibration issue like you said?

Also, i tried checking thermocouple on amazon and it only shows me probes with no temperature display, is there a special device i need to read the temperature?


Yes, update to TAZ 5 is probably sufficient. The TAZ 5 comes with the Hexagon hot end so it would be configured properly for it. You should be all set.

Something like this is perfect: http://www.ebay.com/itm/TM-902C-K-Type-Digital-LCD-Thermometer-Thermodetector-Meter-Thermocouple-Probe-/251402845720?pt=LH_DefaultDomain_2&hash=item3a88c6fe18

TM-902C probe.

Thank you!!! I went home today and checked the connection. it seems its fine and i checked the firmware with no problem too. I doubt is it possible i am using the fast print slic3r profile and the extruder moves too fast so it cools down? Anyway i am buying the thermometer and check it up later this week~!!

Very fast rapids do slightly cool the hot end but not by that much. I also meant to make sure the heat cartridge (or resistor?) and thermistor are firmly seated in the heater block. Check that too.

I see! I will wait for the thermometer to come and hopefully diagnose the issue. I am guessing its a faulty thermistor and i already starting contacting Lulzbot. Thank you so much for your quick replies and that has been very helpful! :smiley:

Just wanted to add that I’m seeing the same issue on my TAZ 4 upgraded with the hexagon. Can’t extrude PLA at all at 200C and it won’t print reliably below 230C. It is running the TAZ 5 firmware. I double checked that the right thermistor is set in Configuration.h. It is set to #5, the ATC Semitec 104GT-2. The Reprapdiscount version of the hexagon apparently uses the EPCOS B57560G104F, but everything I have found seems to indicate that the Semitec is correct for the Lulzbot version.

That is suspect then. Someone needs to get a thermocouple and measure the actual temperature. I’ve found that all-metal hotends (I’ve used quite a few but not the Hexagon) can run at slightly (5° or so) lower temperature. I find it strange that this one is needing these significantly higher temperatures. We need data!

I have a Fluke contact thermometer and the new hotend kit installed.

Here are some sample numbers taken with the thermocouple clamped to the heater block

LCD Fluke
180 164
190 172
200 182
210 190
220 199
230 207
240 215
250 222

WOW, that is way off. I have only printed ABS and I have been printing at 250-260 and it’s been working but it looks like that’s on the low end.

I have the probe attached on the opposite side as the heater cartridge and I waited a good 30 seconds after the temperatures were reached to let them settle. I am pretty sure my meter is dead on as it even does ambient air compensation.

Forgot to mention I did the firmware update as well.

Thanks tmorris9,

So I suspect the thermistor is not correct. I’d try the EPCOS B57560G104F in firmware and test again. I bet it’s as simple as that. But at least it’s pretty clear that the issue is the temp calibration!

The LulzBot Hexagon hot end uses the Semitec thermistor Marlin thermistor selection #5

The hot end has a different thermistor placement than the Buda, different heater block mass and different PID response.

Ultimately, the only thing that really matters when printing with this hot end or any other hot ends, is that you can get repeatable results. We find that when printing with the hex setting the temp to a hotter temperature than you would with the Buda you’ll get more reliable, stronger and cleaner prints.

Make sure you’re using this thermistor in the firmware:
// 5 is 100K thermistor - ATC Semitec 104GT-2 (Used in ParCan & J-Head) (4.7k pullup)

#define TEMP_SENSOR_0 5
#define TEMP_SENSOR_1 5
#define TEMP_SENSOR_2 0

I still contend that there is an issue. I have 7 printers here with 3 different thermistors and one has a thermocouple. They all read within +/- 1°C of actual temperature read from an external thermocouple.

I agree that heater block mass, element type and PID tuning will all affect things BUT given time to equilibrate, these are not really contributing to actual temperature differences. I also agree that the important thing is repeatable results. I would even be ok with a 5° variation from “real” temperature. But these folks are seeing >20°C differences. That is a recipe for frustration.

I’d be more than happy to test and tune a Hexagon if you want to loan me one to test. I don’t need the full package, just the hotend.


OK I wanted to see if I could get a more accurate measurement. I took my tool head off the printer and found they have a threaded hole going all the way through the heater block, it’s got a screw and small plate on one side that is used to hold the thermistor in place. I was able to put a small thermocouple into the hole to the center of the heater block and then hook it back up. Here are a few (not wanting to do them all over) of the readings.

LCD Fluke
180 !75.5
200 195.5
230 223.4
250 241.3

So as you can see the numbers are closer and I would say that my sensor is in very close to the thermistor and center of the heater block.

They are still low (but could be better) but not nearly as bad as was measured on the outside of the heater block.

That’s much more reasonable.

I have a thought… I only have experience with 1.75mm filament and have tested more than 12 different hot ends. Once the temp is calibrated, the same filament extrudes nicely at the same temperatures on all of these. I was amazed at how BIG the 3mm filament is. It would take a fair amount of heat to melt that much mass. This happens in the hotzone of the hotend. The Budhashnozzle has a a large block for the hotend, the hexagon looks to be much smaller. Perhaps the elevated temperature is needed in order to push the larger filament through? If so, if you slow way down as a test, the 3mm filament should extrude at the normal temp.

This phenomenon comes into play as you speed up printing. When I ramp up speed to 100mm/s on my Rostock, I have to increase the hotend temp about 8°C in order to keep up. The new Volcano from E3D has a massive block precisely to provide the heat needed to melt lots of filament.

Measured both, plugged the numbers into my volume calculator and the Hexagon heater block has a higher volume by 1.2%

This of course does not account for holes.The biggest difference is the Buda is 8.2mm tall and the Hex is 17.2mm tall. The buda is a bit wider and deeper but the height makes up for the difference and then some.

Great research, thanks! Well, that does not explain it then. The height of the Hexagon should actually make it better at melting filament due to the longer melt zone.

The other difference is the heating element itself. What is used on the Hexagon?

It uses a cartridge (40w I believe) and the Buda used a resistor.

A 40W cartridge should have no problems. So, I contend that there is a thermistor mis-match or some bad firmware. Smoothie had an issue that it was doing the wrong calculation and was off by about 8°C. It’s been fixed and everyone thought their temperatures jumped.

It’s simple to check if you are willing to take the thermistor out. Simply hook it up but out of the hot end and drop it into a cup of boiling water. It should read 100°C.

I’ve used a lot of hot ends and thermistor/thermocouples and heaters of all types and a 20° variation is just not acceptable IMHO.

Your latest Fluke readings actually indicate a much smaller difference (about 5° in the PLA/ABS temp range). That is reasonable and acceptable. Now the question is, why do you need to bump the temp up so much to extrude. Has anyone actually done a controlled filament extrusion temperature test (described in the link in my signature) #9 Know Your Filament?