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Bed temperatures

peterb8f15b29
(@peterb8f15b29)
Famed Member

I Have a Geeetech A10T with the Geeetech SuperPlate glass bed. It was noted that in Adams Training session Module 1 Episode 4 that the the glass is a bad transmitter of heat. Given that should I set the bed temperature higher to compensate for this. I used a Covid 19 thermometer gun and got in the region of 40C for a setting of 50C.

I am using PLA but bed temperatures will be more critical for other materials. Your advice please

Thanks

Peter

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Topic starter Posted : 17/08/2021 9:25 am
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Peter,

You're correct - the low thermal conductivity of glass means that the surface temperature is going to be lower than what you set the bed temperature to. This is because the thermistor that senses bed temperature (which is used by the printer uses to gauge whether it should add more heat to the bed) is located on the bottom of the metal plate under your glass bed. When the bottom of the metal plate reaches the target temperature, the printer stops heating the bed. Naturally since the glass doesn't transfer heat energy very effectively, the temperature at the top of its surface will be somewhat lower than programmed, and the disparity will grow the higher the temperature (so it might be a 10°C disparity at PLA temperatures of 40-50°C, but you might find a 15°C disparity at PETG temperatures of 70-80°C).

Now to answer your question. An infrared thermometer gun like you describe will work well - it basically measures the level of infrared radiation emitted by a surface (the level of infrared radiation is proportional to an object's temperature) - however the exact reading depends on the emissivity of the surface (some materials emit more or less infrared for a given temperature). You can confirm this by measuring a couple of different surfaces in the room - assuming everything in the room is at the exact same temperature (i.e. room temperature), you will see different readings depending on if you point at the thermometer at, say, a wooden table top compared to a painted wall or a glass table top. This is because wood, paint and glass all have different emissivities. Having said that the effect is quite small (usuall a few degrees), but if you want to obtain maximum accuracy, use a matte black surface for your measurements. One useful trick is to stick a small piece of electrical tape to the glass bed then measure the temperature of the tape.

You will indeed have to set a higher temperature with a glass bed. Anecdotally I can tell you that I had best results printing PLA on glass when I set by CR-10 mini to 60°C (which gave real measurements of just under 55°C at the center of the bed and 50°C at the edges). The best way to find the optimum is to run some experiments - try printing a calibration cube at setpoints of 50°C, 60°C and 70°C and see which one has the best adhesion without excessive elephant-footing (collapsing outwards where the print touches the bed). Once you've zeroed-in on the best decade then you can refine further (eg. if 60°C performed best, try 55°C and 65°C, then choose between 55, 60 and 65C).

If in doubt (very similar performance across multiple different temperatures), choose the lowest satisfactory temperature, as this gives the quickest warm-up time and the lowest energy consumption (since the bed is the single component on the printer that uses the most power, in the region of 250 watts for a standard-sized printer). Do be aware that setting a temperature on the low side increases the risk of the print detaching from the bed - especially if it has fine lines or features in the first layer (since prints tend to peel off at the corners first). In that case, you might want to bump the temperature up by 5­-10°C when printing a challenging print (one with small sections on the first layer) to achieve better adhesion (at the expense of longer warmup time and higher electricity consumption).

Hope this helps! Let us know how it goes! 🙂

 

Regards,
Luke

ReplyQuote
Posted : 17/08/2021 7:57 pm
Pablo liked
peterb8f15b29
(@peterb8f15b29)
Famed Member

@lmf5000

Hi Luke,

Thanks for that. I have already raised my bed temperature to 55C but will try 60C next. I liked your comment about the emissivity and will try a black electrical tape to see what the temperature difference is between that and the glass that will give a better feel to what the Bed setting should be.

I will update with my findings.

Regards

Peter

 

ReplyQuote
Topic starter Posted : 18/08/2021 9:36 am
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