Are there gradual failure modes for thermistors? First,

3D Printing
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1

Are there gradual failure modes for thermistors?

First, I have a cheap Chinese i3 clone, so my expectation of quality is small. The exact printer is a @Monoprice Maker Select Plus, which is a re-branded @Wanhao_Duplicator i3 Plus. Short version is, this is cheaper, it works well enough, and is not as good as a Prusa.

I have done quite a lot of printing since I got the printer in April. Worked my way up the CAD / FDM learning curve. Every new spool is a different material, or from a different manufacturer. I have attempted some fairly challenging prints, and had a lot of failures - as expected. Adjusted the parameters used for every spool, to get better results.

Ordered a couple spools of known-good filament (for my printer and uses - natural PLA from 3D Solutech). And … could not load the filament.

I could force the filament through the extruder with considerable manual force, but the drive could not. What??

Used the wire/tool to push any remaining filament through the hotend - which took rather a lot of force. Used the nozzle cleaning tool to make sure there were not any blockage. Took apart the extruder, cleaned the gear - but found nothing else clearly out of sort.

Tried some scraps left over from older spools, and they also will not feed through the extruder (at the default 200C). What?

With each successive print, I have needed to use higher print temperatures, but thought that was more about the particular spool and the somewhat challenging objects I was attempting. My last good print was with @MatterHackers Pro PLA … at 252C … which is far in excess of their recommended range.

Started to suspect that the hotend was not in fact that hot.

Reloaded the known/good PLA. Started a print, with the temperature bumped up to 245C … and it seems to be working (only just?).

I suspect the temperature reported is not the actual temperature of the hotend.

Searched online, and I do not see reports of this sort of gradual failure.

Is this a possible failure mode for a thermistor … or something else?

2

Do you have one of those digital/laser thermometers? Just wondering if you can get a reading from the nozzle as it heats up and see how it compares to what the printer is reporting?

3

It sounds like a heat leak, I built my machine 5 years ago and it still runs with the original parts. Thermistors don’t quite change but perhaps You should check for thermal paste to make sure you are measuring metal and not the air around the hotend. Good luck!

4

@Martin_Dolan Nope. Have kitchen thermometer for cooking, but doubt that is a good application. Any recommendations?

5

Are you hearing any faint snaps and pops during extrusion? Maybe the filament has absorbed moisture over time and more heat is needed to drive off the moisture before the plastic will flow smoothly. I have no proof, just an idea…

6

@Alan_Thomason Pretty sure this has nothing to do with moisture in the filament. Printing with a spool from a just-opened package.

I have never seen the steam / pops as described by others. Have got “popcorn” prints, that improved after drying the filament overnight in the oven (at 170F).

7

Poor hotend design can cause problems like this. PLA sticks to metal quite. What often happens is that the filament heats up near the cold zone, which will make it practically stuck.
But since you’ve had an issue with temp since the beginning, it’s likely that the thermistor is of cheap quality or is not setup properly in the firmware. They don’t typically fail, unless the glass breaks or you drive them with too much voltage.

8

+Preston Bannister
I know this is crazy cheap however I have one and it works rather well. Not sure exactly how accurate it is but even if it’s within a few degrees…
New Laser LCD Digital IR Infrared Thermometer GM320 Temperature Meter Gun Point -50~380 Degree Non-Contact Thermometer
http://s.aliexpress.com/qmU7Rrey

Can’t really go wrong for $9

If you use it for your printer or not, they are handy to have around.

The next step up is an infrared camera, or a module for your phone, but those are $200+

9

Use a cheap thermocouple probe thermometer . They are quite accurate. The infrared ones are a bit of as it depends on the focus of the sensor. I have both and the thermocouple works much better

10

is your hotend ptfe lined or all metal stainless heat break. The cheap all metal ones just dont work well with pla.

11

@Stephanie_A This seems to be a progressive problem, as when I got the printer the first prints worked just fine at 190C / 200C. Seemed that every week I was using slightly higher temperatures for my prints.

Trying a different filament with every new spool made the progression less obvious … and of course my learning curve.

Now that I have returned to a filament I used in the first few weeks (and got good result at lower temperatures), it becomes clear that the printer has changed and requires a much higher set temperature … somehow.

Perhaps a failing controller board? Did send a support request to the vendor. No response as yet. Will order an appropriate thermometer.

12

@ekaggrat_singh_kalsi Can you provide an example of what you use?

13

After checking the temperature, you may want to check / replace the heat break. It is likely Teflon lined, the Teflon degrades over time and can collapse. If your temperature is truly wrong the sensor may be bad, I have never seen a board fail in that way.

14

FYI, still getting passable prints, with the set-temperature in excess of 250F (though I suspect to actual temperature is much less). The ~$7 infrared thermometer recommended by @Martin_Dolan is ordered and shipped.

Doing prints for the Z-motion, enclosure, and electronics.

No response from Monoprice support, as yet.

Hoping for some sort of resolution before the printer gives out.

… and I have a seven-year-old grandson climbing on my lap …

15

sorry i skipped this… use this :https://www.aliexpress.com/item/tm-902c-temperature-meter-tm902c-digital-Thermometer-Thermocouple-Probe-Thermocouple-Needle-Probe-0-1300-degree/32731425958.html?spm=2114.search0104.3.34.F9Aq4s&ws_ab_test=searchweb0_0,searchweb201602_5_5570020_10152_10065_10151_10130_5490020_10068_10344_10342_10343_10340_10341_10307_10137_10060_10155_10154_10056_10055_10054_5470020_10059_100031_10099_5460020_10338_10339_10103_10102_440_10052_10053_10107_10050_10142_10051_10324_10325_5380020_10326_10084_513_10083_10080_10082_10081_10178_10110_10111_10112_10113_10114_143_10312_10313_10314_5560020_10078_10079_10073_5550011,searchweb201603_2,ppcSwitch_3&btsid=9abdc74a-d371-4235-a814-926513698607&algo_expid=019fd631-e472-43d9-afb2-9fd8e022223d-4&algo_pvid=019fd631-e472-43d9-afb2-9fd8e022223d

the infrared ones wont work

https://www.aliexpress.com/item/tm-902c-temperature-meter-tm902c-digital-Thermometer-Thermocouple-Probe-Thermocouple-Needle-Probe-0-1300-degree/32731425958.html?spm=2114.search0104.3.34.F9Aq4s&ws_ab_test=searchweb0_0,searchweb201602_5_5570020_10152_10065_10151_10130_5490020_10068_10344_10342_10343_10340_10341_10307_10137_10060_10155_10154_10056_10055_10054_5470020_10059_100031_10099_5460020_10338_10339_10103_10102_440_10052_10053_10107_10050_10142_10051_10324_10325_5380020_10326_10084_513_10083_10080_10082_10081_10178_10110_10111_10112_10113_10114_143_10312_10313_10314_5560020_10078_10079_10073_5550011,searchweb201603_2,ppcSwitch_3&btsid=9abdc74a-d371-4235-a814-926513698607&algo_expid=019fd631-e472-43d9-afb2-9fd8e022223d-4&algo_pvid=019fd631-e472-43d9-afb2-9fd8e022223d

16

FWIW, on reflection, I seem to have run across posts from folk using higher print temperatures, which others described as far too excessive. While this could be written off as new-user mistakes, this might be a not-well-diagnosed failure case.

@ekaggrat_singh_kalsi Ordered the product you recommended (though the post seems to have disappeared).

Should be able to get measures in a week or so.

17

you need to check two points on the hot end , one the nozzle tip and two the gap between the first two fins. If the fin temperature is above the glass point of the filament ( 50 for pla and 80 for abs ) you will get a excessive force on the extruded. This is a indication of a failing fan .

18

Somewhat similar story, and timing:

19

Just got my printer back from an RMA. Took a couple weeks to get response and RMA from Monoprice, plus another week (roughly) to get the unit.

The returned unit has been cleaned (lots of plastic fragments from prints when sent), and a new print surface (mine was quite scarred).

However resolved (new controller board?), the printer seems to now be working properly. I have a print running with the extruder temperature set to a (normal) 200C, which looks just fine. (Before, with the extruder temperature setting at 254C, the prints were marginal, and any lower setting was hopeless.)

Oh. The set screws for the Y rails were loose. (Checked for loose screws when re-assembling the printer.) Easily fixed.

Wondering if the Chinese manufacturer shipped a batch of bad printers, as the Monoprice folk are coping with a suddenly overwhelming support load, and the USA distributor for Wanhao went out of business.