Heat bed temperature drop
I observed a strange behaviour of the heat bed temperature. As an example I mention here printing a benchy with Prusament PETG (orange) and using the system preset print file:
Heated temp for 1st layer is 85 C. After this it will raise to 90 C: temperature was reached after ~1 min of the change. Then the temperature dropped to 86 C within ~4 min. Then started to raise again to 90 C within ~5 min. The bed temperature keeps then stable for the rest of the print. More pronounced is this effect when printing nylon or PC. Consequence is, that I observed warping with these filaments and also with PETG when printing larger objects. Increasing the temperature using tune will give a preheat error (code 26201).
I contacted support and received a replacement for the heat bed. Too badly, this didn't make any difference.
Any ideas what may be the cause?
Printer MK4S kit (1 year old). Firmware 6.2.0 (newest).
RE: Heat bed temperature drop
Hi,
I experience the same when printing a temp tower, close to the middle of the sheet. The temperature drops more then 10 degrees and i get an error. When i measusre the temp around the object with an ir thermometer i measure the board is way above the set value. My analysis is that the ventilator cools the spot above the temp sensor way to good. I tested by decreasing the rpm of the vent. and the indicated temp went up again. I have no solution yet. maybe install more temp sensors on more places under the bed? anoying....
RE: Heat bed temperature drop
Hi pa3cw.
Many thanks for sharing your experiences. Based on your findings, I made two additional test prints with PETG:
- moved benchy to the front-left corner (far away from the thermistor).
- disabled the cooling print fan and printing benchy in the middle of the bed, where I've seen the highest temperature drop.
In both cases the heat bed temperature changed less than 0.2 C, which is absolutely fine.
Conclusion: It may not have been worth to upgrade from MK4 to MK4S, because the print fan on the MK4S is much more powerful for enabling higher print speeds. I'm considering to moving back to the MK4 extruder design.
RE: Heat bed temperature drop
Hi, I have MK4S and recently got several failed prints.
Initially I thought it is the thermistor going bad and sending the wrong values, but then I changed it and still noticed some temp fluctuations when printing PETG and the bed is set on 90 degrees.
After some testing here is what I have found:
- if the filament profile is set to run the print fan with higher speed above 35% to 60% and the temp of the bed of the first layer is set to be 85 degrees. After the first layer is done the temp of the bed is set to go to 90 degrees and starts heating. If the object is small the next 2 layers are printed fast and the fan starts to blow much harder and depending in the object can go 40-60-%. That causes the bed above the thermistor to start cooling faster and it can't catch up to reach 90 degrees.
- It happens only with smaller parts in the centre or centre-left\top-left. Essentially close to the thermistor area.
- if you print large part above the thermistor, the plastic acts as temperature insulator and it is less likely to happen
So what I did to fix it:
- first I changed the thermistor with new original part. My concerns was that is faulty. That was not exactly the case. The old thermistor had some small fluctuations but not massive. Anyway that was done after 2years of printing so not big deal.
- updated the filament profile for PETG not to go over 40% print fan speed for cooling. I think the MK4S fan is quite powerful and the lack of 2-3 thermistor readings to average the temperature of the bed it may easily cause cold spots.
- print small parts towards right\bottom part of the print plate.
I am not sure if that is common problem or people just do not print small parts that often and their fan speed is set to be quite low. Also there is some chance that my bed is going bad and not working as it is supposed to. That part is hard to test if you have one printer of that model so, I am just guessing.
A way to simulate the issue is to print a small PETG part on MK4S, placed on the centre or slightly on the left and upper part of the plate. Start printing and wait the first two layers to finish, then manually set the print fan to go to 50 or 60% and see if the bed can bring the temperature from 85 to 90 degrees. The room temperature for my test was 22-23 degrees ( Not a hot or cold day).