Bed and Head not playing nice anymore

[Captain Starfish]

Isn't it great that these machines (and I suspect it's not specific to the RMax) are such dynamic beasts? Let's face it, if you could build and dial your printer in then NEVER have to touch it again, just hint the "print" button every time, it would be boring and no fun at all.

Le sigh.

After being vocal in a few threads about the combination of Elmers, low bed temperature, 120% extrusion on first layer and nice close nozzle at Z=0 and how wonderful the bed adhesion was with it, I've had a string (hurr hurr) of parts now pop and curl over the last couple of days.

Dang.

I thought I'd document the process of hunting and killing this issue, in case it helps someone else hitting the same problem. So here we go.

First off, the easy ones. I have been using my chunked glass bed, placing pieces away from the chunks, hoping to eke the last of it out and so on. So I gave up, put a new sheet of boro on the bed and re-ran the MC auto levelling calibration. No dice, still same problem.

Then I noticed that the hot-end ramps up to about 220º but then just crawls up to the setpoint at 230º - and now it's struggling to even reach 230º. During the print it's dropping to around 218º. Likely suspect, I think. If the filament is coming out too cold it's not going to stick to anything.

So my next step will be attach the thermocouple and see if that 220º instead of 230º is indeed a 220º head - indicating the heating circuit - or is 230º but only reading 220º - indicating a problem with the thermocouple, the kind that would eventually lead to a meltdown.

I'll continue my investigation but, in the meantime, has anyone hit this problem before?

[McSlappy]

I had something similar-ish... Check your temp graph and also power to your heater - are they nice and smooth or does it spike all over the place?
When mine started this, I swapped the thermistor and problem solved!

[Captain Starfish]

I've never trusted my thermistor, not from the day I bought it. Last week, just before all these shenanigans started, I bought a bundle of cartridge heaters, a screw-in thermocouple and an I2C or SPI thermocouple breakout on fleaBay. Haven't had a chance to add the thermocouple and double check things today, will do so to avoid catastrophic failure whilst I await the new toys. When the new gear arrives it will be going into the unit regardless of how well the thermistor appears to be working that particular day.

[Eaglezsoar]

I've never trusted my thermistor, not from the day I bought it. Last week, just before all these shenanigans started, I bought a bundle of cartridge heaters, a screw-in thermocouple and an I2C or SPI thermocouple breakout on fleaBay. Haven't had a chance to add the thermocouple and double check things today, will do so to avoid catastrophic failure whilst I await the new toys. When the new gear arrives it will be going into the unit regardless of how well the thermistor appears to be working that particular day.

I know that it is a pain, but could you provide a link to the thermocouple and the breakout board you purchased? The selection is vast and I am unsure which to buy.

[Captain Starfish]

No pain at all.

The thermocouple is ANY "K" type thermocouple you can find.

The chip you are looking for is the nice shiny new MAX31855 or the older, clunkier (but cheaper) MAX6675.

They both do the same thing: read and compensate etc for a K type thermocouple and spit the temperature to within a couple of degrees out on a SPI port ready to get hauled in by the the Atmel micro via one of the expansion ports.

Both on eBay.

Down here in Australia, aka "mexicans with mobiles" we had these available: http://www.ebay.com.au/itm/291148309129

Because I'm a kind, caring kinda jerk, I'll say this: hang on for a couple of days until I get mine bedded in and I will give you the <Repetier 0.91 or whatever is the latest branch> source mods required to get this working together with any photos of wiring mods required to plug it in.

Or a whole lotta swearing because I couldn't make it fly

[Eaglezsoar]

Thanks for the link, now I understand what you are trying to do, but it is going to take a small thermocouple to fit into a HotEnd.
I would love to wait and have you figure out all the hard stuff so I can steal your work

I actually meant use your work because you are a kind, caring kinda jerk.

[Captain Starfish]

*Like*

Thermocouples can be ridiculously small, my multimeter one is maybe 2.5mm across. It's just getting them in a threaded unit seems to include getting a 6mm thread.

That's fine.

The EZStruder bog standard hot ends have two heater resistor holes. One gets the lotion, whoops, I mean the 40W heater cartridge. The other gets a tap and the 6mm thermocouple block. Wins all round, until I really need to print nylon and get the new E3D v12 (or whatever they're up to) hotend.

[Eaglezsoar]

*Like*

Thermocouples can be ridiculously small, my multimeter one is maybe 2.5mm across. It's just getting them in a threaded unit seems to include getting a 6mm thread.

That's fine.

The EZStruder bog standard hot ends have two heater resistor holes. One gets the lotion, whoops, I mean the 40W heater cartridge. The other gets a tap and the 6mm thermocouple block. Wins all round, until I really need to print nylon and get the new E3D v12 (or whatever they're up to) hotend.

I caught you this time, you said lotion. Sounds like you and your HotEnd have been VERY good friends.

[Captain Starfish]

The other option was getting the hose. So yeah, good friends but possibly not the kind of relationship you had in mind

[Captain Starfish]

Well, well, well.

I went to install the thermocouple to check head temperature this morning. I ended up having to tear down my hot end because I couldn't loosen the nozzle without some serious force. Oh. It's jammed solid, the internal PTFE has melted to a plug and there's a big old plug of ABS in there to dig out.

Hmmm.

Cleaned it all up, put a new PTFE liner in and banged it back together with the thermocouple, ran up the hot end to temperature (230º). Well, it said 230º on the LCD. The thermocouple said 260º. Fortunately no visible damage to the PEEK break but not an ideal setup. No wonder the thing was struggling to reach setpoint! That's it for today but now I have to wonder whether I go through the whole re-calibration rigmarole on the thermistor tables in the firmware or whether I just wait for the proper thermocouple to turn up and be done with it.

I can /probably/ leave the printer off for a few days whilst I wait for new toys to arrive... probably.

[Eaglezsoar]

Well, well, well.

I went to install the thermocouple to check head temperature this morning. I ended up having to tear down my hot end because I couldn't loosen the nozzle without some serious force. Oh. It's jammed solid, the internal PTFE has melted to a plug and there's a big old plug of ABS in there to dig out.

Hmmm.

Cleaned it all up, put a new PTFE liner in and banged it back together with the thermocouple, ran up the hot end to temperature (230º). Well, it said 230º on the LCD. The thermocouple said 260º. Fortunately no visible damage to the PEEK break but not an ideal setup. No wonder the thing was struggling to reach setpoint! That's it for today but now I have to wonder whether I go through the whole re-calibration rigmarole on the thermistor tables in the firmware or whether I just wait for the proper thermocouple to turn up and be done with it.

I can /probably/ leave the printer off for a few days whilst I wait for new toys to arrive... probably.

I think you are going to have to calibrate any thermocouple you use. Even ones from the same manufacturer can vary. Look at it as part of the fun!

[Captain Starfish]

A big difference between a thermistor and a thermocouple (as I understand it) is that one thermistor can massively vary from the next but that a thermocouple will reliably generate a current based on the temperature difference across its dissimilar metal junction. In other words, always have to calibrate thermistors, never have to calibrate thermocouple (within the accuracy requirements of what we're doing, anyway).

Time will tell.