Orcinus' Build Log (was: Thermistor insanity)

Topics Related to the ORD Bot Printer

Re: Thermistor insanity

Postby orcinus » Thu Jun 28, 2012 3:39 pm

Well, this was a spectacular fail... :(

My 'bot started extruding, i've let it extrude into air for a while, to see how it's behaving.
Then zeroed in the Z axis (i've got the end switch at the MAX end of Z, so the procedure consists of homing Z, then lowering it until it's a paper-width away from the glass plate and issuing a G92 Z0).
Then retracted the filament a little and let 'er print the 0.5mm thin-wall calibration object.

So it starts extruding the skirt and it dots around a little in corners but then starts extruding nicely, moves towards the center, does the first layer...

All hell breaks loose.
It manages to extrude the first layer, starts the second, makes a tangled stringy mess, at which point the extruder gets stuck, so i kill the print.
I extrude a little manually, only to find out the bolt unscrewed itself out of the locknut. I try to tighten it (retracting then tightening the bolt with a wrench does the trick), but it unscrews itself again the moment i try to extrude. I realize at this point the filament is well and truly stuck in the nozzle, so i lift the Z up so i can have better access to the extruder and one of the Z axis rods pops out of the coupler (i was experimenting with "soft" coupling, by sleeving the Z rod in cable sleeve, then inserting that in the coupler).

As if that's not enough, i try to retract the filament out of the extruder completely, except it gets stuck inside. I wait for the hotend to cool down a bit, disconnect everything and remove the extruder from the bot, but getting that filament out is a no go. I finally separate the hotend and manage to get the filament out, clean the head with acetone and poke the nozzle with a needle and it finally seems clear. Except i look through it and find out there's still a chunk of filament in the SS barel that connects the nozzle/block to the cold end.

BLARGH.
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Re: Thermistor insanity

Postby Medel » Thu Jun 28, 2012 5:49 pm

As weird as it sounds, you can use a blowtorch....
http://www.youtube.com/watch?v=6bTfl35zlHE

It totally works.
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Re: Thermistor insanity

Postby orcinus » Thu Jun 28, 2012 6:17 pm

I was briefly considering torching the hotend with a jet lighter, but it sounded too aggressive even by my (slightly pyromaniac) standards :lol:

I'll give it a try, thanks.

As an update - i've hooked everything back up and reassembled it, minus the hotend, plus the threadlocker on locknuts. And lo and behold - the extruder stepper starts just jerking back and forth. My first thought is "oh, crap, i lost've lost a phase". I swap drivers just in case, then driver sockets, then unplug the stepper and shove the multimeter probes in the connector. And, of course, it turns out one phase is out. I yank on the connector a little and get left with one wire loose.

So i set out to replace the connector and realize i'm out of 4-pole ones. No matter, it's 19:30, the nearby electronic parts shop is open till 20:00. I get there 20 minutes before closing time and - realize it's closed.

Just one of those days... :roll:
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Re: Thermistor insanity

Postby orcinus » Thu Jun 28, 2012 7:18 pm

I've pushed a filament through the heated hotend manually and it started extruding just fine. So no blockage (well, no permanent blockage).
At least something :)

Seems like my problems were caused exclusively by the extruder failure (i.e. nut coming loose, probably combined with a bad connection on the wire that eventually came loose after taking the extruder off the gantry).

Dammit, now i've got no more excuses to procrastinate and have to get back to work... :cry:
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Re: Thermistor insanity

Postby Liberty4Ever » Thu Jun 28, 2012 8:18 pm

http://youtu.be/vZzZDFdALqY
(1:27 video)

From the video comments:

Okay the first thing you should know is never unplug an energized stepper motor. The feedback from the coils can ruin your stepper driver. I wonder if you have the coils wired up correctly? If while having the motor disconnected you short the two coil wires together the motor should become hard to turn. If you have a matching pair. If you short the second set the motor will be even harder to turn. Or it could be your power ref is turned down to low. The driver could be damaged.


Not unplugging a powered stepper motor is common advice in the 3D printing community.

Having a motor lead failure is identical to unplugging a powered stepper motor.

Lesson: Make sure your motor wiring is secure.

I'm not saying that's necessarily your problem, but it might be a good place to look, and yet another warning to those following in your footsteps.
Apparently, I didn't build that! :-)
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Re: Thermistor insanity

Postby orcinus » Thu Jun 28, 2012 8:58 pm

Yes, yes, i know :/
That's why my first instinct was to check if the driver after the motor started behaving erratically.

Also, whenever i mess with the steppers / am testing them out, i keep them non-energized when not moving.
It doesn't guarantee i won't burn out a stepper if a wire gets snagged or cut, but it reduces the chances.

Edit: Oh, and like i wrote, the driver is fine and the stepper coils are intact as well... it's just the connector that failed, and the reason it failed is, i'm using Molex-micro-fit-like connectors made for 9A max, that are really really badly suited (i.e. too wide) for the wire gauges involved.
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Re: Thermistor insanity

Postby Liberty4Ever » Thu Jun 28, 2012 9:30 pm

orcinus wrote:i'm using Molex-micro-fit-like connectors made for 9A max, that are really really badly suited (i.e. too wide) for the wire gauges involved.

I want to buy a controller with 3.5mm spacing removable screw terminals. The best of both worlds. Screw terminals, so no doing the smash and solder technique because your $600 worth of crimpers don't include the one you need for the micro connectors, and you can still unplug an entire block of connectors (all stepper motors, all limit switches, all extruder components, the heated build platform heater and thermistor, etc.) A board with the screw terminals along the outer edges would be a little bigger, but it'd still easily fit on an ORD Bot electronics plate.
Apparently, I didn't build that! :-)
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Re: Thermistor insanity

Postby orcinus » Fri Jun 29, 2012 12:16 pm

That sounds pretty much like Frobz' ORDuino:
Image

Not removable terminals, but screw terminals nonetheless. Plus, you can solder the removable blocks instead yourself, if the need arises. And yeah, i'm with you there, i'm getting fed up with crimping these...
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Re: Thermistor insanity

Postby orcinus » Fri Jun 29, 2012 6:07 pm

Okay, i've repaired the connector, removed my little Z-axis experimental sleeve thing (there's more wobble now, but at least the Z axis isn't getting unsleeved from the coupler mid-move) and made sure the extruder bolt is threadlocked to the nuts (there's no taking it off now, i've used the green Loctite for mounting bearings - if i ever decide to take it off, i'll have to cut the bolt).

Aaaaand - well, after extruding a few millimeters, another failure. The extruder stripped the filament. So i tried pushing the filament and can barely move it. I try retracting the filament and it's not going out. I heat up the hot end to 210 deg C and push, hold then pull (manually) and manage to extract the filament. Rinse, repeat, same thing happens.

So i try extruding some filament by pushing it into the hotend manually and it starts fine, then goes to a full stop. A-HA!
Seems like the heat isn't getting to the nozzle fast enough - i.e. there's more heat being carried away by the filament and the steel tube than is transfered to the head by the block. I.e. i was right with my instincts regarding PTFE tape on the nozzle.

It's a bad idea.

Have to go to work now, so dismantling the hot-end and removing the PTFE will going to have to wait...
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Re: Thermistor insanity

Postby orcinus » Sun Jul 01, 2012 9:39 pm

Long story short...

I've replaced PTFE with a thermal compound. It worked.
For a while. Then the filament got stuck in the nozzle and the SS tube (which acts as the thermal barrier).

At first, i thought it's due to lack of cooling on the cold end, but the temp at the top of the SS tube / radiator fins is about 60 deg C.
The temp in the middle of the tube is around 100 deg C. According to Laszlo, the melt zone is in the SS tube and that's normal, although cooling is advised if the temperature of the radiator is above the pain threshold.

Dismantling the hot end, i found that the PLA had leaked between the SS tube end block and the nozzle.
There were two separate bits of PLA stuck in there. One was at the very bottom of the nozzle:

Image

... the other in the SS tube itself:

Image

It's quite possible they were a single piece that snapped when i've unscrewed the two.
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