Bed temperature reading low - ABS lifting

Hi,
I'm having problems with ABS parts lifting.. I've tried blue tape / glue / hairspray etc.. however I believe that my bed temperature may be low... Measuring on a Fluke 187 it reads only around 70 degrees at the highest setting (120 degrees) That's measuring the aluminium at several points.. from the top. When in simplify3d.. I can set 140 degrees and switch the bed on, and I can then read around the 90 degree mark..
Testing this theory I printed something while at the same time blowing a hot air gun on to the bed.. and it was the only print that actually stuck and came out well..

I've also covered the sides/front and a little of the top with foil and ambient temperature is around 40/50

Has anyone else had an issue like this?

I'm considering buying some Buildtak but if there's a problem with the bed temperature then I'd like to fix that first.. The parts that have been lifted have all been printed with rafts too.. I've not tried without rafts yet..

Any help. greatly appreciated!

I Gave-up Fighting the ABS and now use PLA only !
I know that's probably not what you want to hear,
but why continue fighting a Loosing-battle ?

Note: I have about 8 partial-spools of ABS that I will Sell Cheap ;)

I print in ABS with my FFCP on glass and hairspray without any real problem. I set my bed temp to 100c for the first 5 layers and then move down to 90c. So it sounds like a possible bed temp sensor problem?

Ah.. yes I wonder if it's a sensor error.. as a "quick fix" is there a way that I can set it to higher than 120 degrees? (which I'll measure with a probe to check real temperature) Whenever I set it to 140 with simplify3d, it shows up as 120 on the onboard LCD.. I'm still running the onboard firmware 7.2

Sorry, I do not know.

I got my CTC Dual from superinksupply on EBAY. I wrote them about this problem wanting my heatbed replaced, They have a one year warranty that appears to be complete BS. They said that the heat dissipates throughout the heatbed, so my 87C measured temp. is normal when the printer says it's 110C. If you look at various forums throughout the internet this is not an uncommon problem with all sorts of printers.
I've read many posts where people use heavier wiring from the PSU to the heater assembly. Then I read that doing this can hasten the failure of the ramps board, this makes sense. Some people install a relay to protect the ramps board when installing the heavy gauge wire. Others change the value of a resister I have yet to locate in the bed assembly, and others, install some insulation below the heatbed.
I bought a dual head CTC in order to print with multiple filament meaterials and that's what I intend to do. There are too many applications of object to be limited to PLA. I've given up on any sort of useful warranty from my seller. I will be disassembling my heated bed and solving this problem, if I succeed, I will report my findings here.

Cheap printer means cheap thermisters. They are not very accurate.

When it comes to setting temps you have to guess it really.

eg I cannot print ABS at 230C I have to set it at 255C in order for it to melt.
This doesnt mean the nozzle is at 255C, it means my thermisters read 25C higher than the real temperature.
It is a huge inaccuracy, but that's what happens with cheap parts.


As for sticking to the bed, add a glass plate then use ABS juice in a spray bottle and spray a layer of it on the glass.
All of my prints, ABS and even PLA stick to it pretty well and not has a single warping issue yet!

Quote:

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Originally Posted by bigo93

Cheap printer means cheap thermisters. They are not very accurate.

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The CTC-bizer does not use 'thermistors' at hot-ends.
It has Thermocouple-wires, which are usually more accurate, over a wider range of temps, than thermistors.

(But temp accuracy is also determined by the circuit on Mobo, not just the sensor)

The heatbed has a wrong thermistor mounted, mine is off by 1/3 too. That's a well documented issue, i ordered one with 100kohm at room temperature as soon as it arrives i will change it and the problem should be gone.
Cheap bits are not that worse a you may think, half of all consumer electronics are based on the same china parts - for the price we pay we don't get a Siemens board inside :cool:

Even in the cold the minimum my bed reads is 40 degrees.. the two nozzles read the same 20 degrees that the room is.


@bigo93 - I've tested the nozzles with my thermocoupler and they seem to read correct. What do yours read when cold?

Under the heatbed, when I test on the thermistor body itself on the PCB, it reads around the same as my bed.. so definitely something awry. I'd say it's a manufacturer error more than a cheap parts type thing because even a bog standard 10p thermistor is 5% tolerance. Mine is way off that. I think they might just have used the wrong value.


@Jprtist - that value doesn't sound too bad.. The way to confirm for sure is to read the body of the thermistor under the heatbed to confirm what it's seeing. If it's reading correct, then a little insulation under the heatbed, and an enclosure, and I'd say the bed would start to read correct. Also does the aluminium make good contact with the PCB? What does it read when cold?


@Noa - Let us know how you get on once you've replaced the thermistor. I've heard others have done this successfully.. so hopefully all will be well. Do you have a link to what thermistor you bought? Also, what resistance does your original one read? Does yours also read high when just sat in the cold?

If you're getting dodgy readings when the bed is cold then I think a sensor replacement is in order.

Just reporting: I replaced the thermistor on the heated bed, my temperature reading is now much more accurate and within the expected 5%.

Quote:

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Originally Posted by noa

Just reporting: I replaced the thermistor on the heated bed, my temperature reading is now much more accurate and within the expected 5%.

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Awesome! Good work.
Do you have a link to the thermistor you used?

I used this one: Cantherm MF58104F3950, got mine from ebay but digikey should have them too.

Digi-Key Part Number 317-1380-ND
Resistance in Ohms @ 25°C 100k
B25/50 3950K
Operating Temperature -55°C ~ 200°C
Mounting Type Through Hole
Package / Case Bead, Glass

The original was at 64kOhm while the new one was at 110kOhm. I took the readings on the fly, that's far away from a trustworthy measurement - but shows for me that the original one is clearly the wrong part.

If it helps anyone, I wrote up what I did to mine, and why, at http://www.thingiverse.com/thing:1403267

Awesome.. thanks for letting us know.. I'll get ordering a thermistor and replacing mine..

I wonder why they did that.. Hard to believe it's an oversight.. I wonder if it was an easy way to ensure no one was having the bed too hot?