Stringy build

[Captain Starfish]

I've finally managed to spend a day with my new beloved.

Started off with some good pieces that only died when I got a centimetre high on the piece and the extruder head popped it off the bed.

Read the forum. Kapton, check. ABS juice? Ok. Et voila! No more lifting.

Started some more complicated pieces and after a little while the extruder started clunking and I get a stringy output. The first time is happened it choked out so bad (230º on the struder, 85º on the bed) that the output string petered out entirely. Glad I bought a couple of spare nozzles, old one into acetone bath overnight and a new one in the unit.

Nup, same problem, just not quite as bad.

[img]http://www.simonlockwood.net/linky/3dp/stringy.jpg[/img]

And that abs juice got me good - I couldn't get the bloody thing off the Kapton! I ended up lifting the tape thinking "Jeez, I'm glad I didn't drop this straight on the glass!". So the stringy piece ended up looking more like these when I took it off:
[img]http://www.simonlockwood.net/linky/3dp/stringystuck.jpg[/img]
[img]http://www.simonlockwood.net/linky/3dp/ ... splode.jpg[/img]

Everything's set for 30mm/s(?) and layer is 0.3mm on a 0.35mm nozzle.

Help, please: what stoopid n00bie dumbo thing have I done wrong to get this happening?

[geneb]

Have you verified the thermistor reading with a thermocouple yet? You want them to agree within a few degrees.

It seems to me that you're a bit under temp due to the thunking you're hearing from the extruder (it's skipping).

Can you "free extrude" 100mm of filament at 100mm/min when at 230C?

g.

[cope413]

Yep, it looks under temp. If strands of ABS aren't adhering to other ABS, it's not hot enough.

[Eaglezsoar]

Have you verified the thermistor reading with a thermocouple yet? You want them to agree within a few degrees.

It seems to me that you're a bit under temp due to the thunking you're hearing from the extruder (it's skipping).

Can you "free extrude" 100mm of filament at 100mm/min when at 230C?

g.

I think once he measures with the thermocouple he is going to see a significant difference. That filament doesn't look close to 230C.

[geneb]

I wish that these printers used thermocouples. Manufacturing tolerances on thermistors can make a person crazy.

g.

[Eaglezsoar]

I wish that these printers used thermocouples. Manufacturing tolerances on thermistors can make a person crazy.

g.

Be like me (crazy already) and one thing less to worry about!

[geneb]

You've obviously not seen my workshop. "Crazy" is the _least_ of my ills.

g.

[Captain Starfish]

Thanks, folks, will look at getting a thermocouple.

Is an IR contactless jobbie good enough for this? Seems it would make a more versatile tool for a few different jobs if it would fit this application too...

[Eaglezsoar]

Thanks, folks, will look at getting a thermocouple.

Is an IR contactless jobbie good enough for this? Seems it would make a more versatile tool for a few different jobs if it would fit this application too...

The infrared will not work properly for Hotends because of the reflectivity of the Hotend, you must use a thermocouple.

[Captain Starfish]

Drat.

Presumably I remove the bowden tube end, then feed the thermocouple down to the hot end? Or bog it onto the aluminium block with spare Permatex and leave it there?

[Eaglezsoar]

Drat.

Presumably I remove the bowden tube end, then feed the thermocouple down to the hot end? Or bog it onto the aluminium block with spare Permatex and leave it there?

Remove the bowden tube end, then feed the thermocouple down to the hot end is correct.

[Captain Starfish]

cheers birdy.

Now annoying all my nerd mates to find who has a funny wire thing and a ºC position on their multimeter dial for loansies until my eBay special turns up in about a month.

[Captain Starfish]

Roight.

Done and did, and this is what I get:

[img]http://www.simonlockwood.net/linky/3dp/ ... rssuck.jpg[/img]

In fairness I'm measuring the block temp with one and the back of nozzle temp with the other, so it won't be exact. But still... is there any calibration process that I can go through with Repetier and the Rambo board?

Thanks for the feedback so far, keep it up folks!

[cope413]

So the multimeter temp is reading from where?

Why don't you try printing something small - like a calibration cube - with your temp up to 245C? I have a feeling your temp is right (or close to it) but the filament you have needs to be printed a bit hotter.

[Captain Starfish]

Sorry, wasn't clear: I took the bowden clip off the back of the head, took the nozzle out, took the double tube out, put the nozzle back in and dropped the thermistor down the filament path as far as it would go. It was sitting against the back of the nozzle where the inner tube pushes in.

I have noticed that printing PLA is fine, and printing flat ABS is looking good too - just that as I move away from the bed on taller objects this starts happening.

Is it worth coating the thread of the nozzle with heatsink compound before reassembling to get a bit better thermal transfer?

Or just crank up the heat a bit?

Cheers!

[ccavanaugh]

I see similar issues latter into a PLA print.. normally after about 2 hours.

I suspect the stock peek cooling fan or the #70766 fan shroud for the peek fan is limiting the cooling and eventually causes the PLA melt zone to creep up. Short PLA prints and ABS are never a problem.

I hope to make some time over the holiday break to tweak the shroud a bit. I suspect it's causing some of the hot air to be recirculated around the peek insulator instead of fully exhausting cool air around it. Coupled with a low CFM fan and it eventually catches up.

[Captain Starfish]

No shroud yet, still messing about with calibration prints mostly - the part in the photos was something I wanted in a hurry and had a shot at, ended up making do without it.

I am finding that when the filament starts petering out during a run, if I retract the filament back into the bowden tube and remove the tube, then tear down the head, there's a 1cm long slug of plastic sitting in the bottom of the double liner. Presumably it's melted back there and solidified when everything cools down.

Normal?

[ccavanaugh]

Normal if you do not have a peek fan. I eventually had to use a peek fan with ABS on my H1-1 using the 2nd generation SeeMeCNC hot end. It's not limited to PLA only.

If you don't have a peek fan installed, I suspect that is the root of your issues.

[Captain Starfish]

I have a PEEK fan installed, just not the shroud.

Nestled in the head (only just, so it doesn't foul and tick against its own shroud), M42 P6 S255 is built into the startup on my G-Code and the fan is running during the extrude.

So. Does this change things? Am I just needing to run it up to 245 or do I have a different issue? Bear in mind the EZStruder is skipping, too, when this is going on. So I'm wondering whether the cool 0.35mm nozzle means I can't get filament through fast enough, which means cranking up the temperature on the block, which means regardless of fan I'm getting a melt zone too far back. IE peek fan ain't my problem, but your issue shares symptoms with a symptom (not cause) of mine...

[ccavanaugh]

I had to drop back to a .5mm nozzle with PLA to solve my EZStruder issue which was grinding up the PLA. Extrusion pressure was too high even feeding by hand with the .35mm nozzle.

ABS and .35mm was not an issue, so I think it may be my spool of PLA (UltiMachine Blue). Next order of PLA will be from SeeMeCNC with the assumption it is better tested with their hotend.

I would make sure your hotend temp is calibrated in firmware before going too crazy. The recommendation was to lightly clamp the top between the aluminum body and the brass tip. I used the generic thermistor table and adjusted the beta value until I was within .5C at 220C. A closer temp calibration is only going to help dial in good PID control and minimize your temp swings during prints.

Personally, I think the PEEK fan without the shroud may be more effective.

[Captain Starfish]

Damn I hate work.

6 hours of <not tinkering> until I can go give this a try.

But, in 6 hours, that's what I'll do. Thanks!

One thing - any easy link to temp calibration guide? Or easy enough to wade through configuration.h and spot the obvious?

[ccavanaugh]

My setting below..
Make sure you define your sensor at type 97. Adjust the Beta value to match your real value. You will need to recompile, upload, test etc...

I calibrated at 220 as my reference temperature.

Code: Select all

// 97 Generic thermistor table 1
// 98 Generic thermistor table 2
// 99 Generic thermistor table 3
// 100 is AD595
// 101 is MAX6675
// 102 is MAX31855
#define EXT0_TEMPSENSOR_TYPE 97

Code: Select all

If you need the generic table, uncomment the following define.
*/
#define USE_GENERIC_THERMISTORTABLE_1

/* Some examples for different thermistors:

EPCOS B57560G104+ : R0 = 100000  T0 = 25  Beta = 4036
EPCOS 100K Thermistor (B57560G1104F) :  R0 = 100000  T0 = 25  Beta = 4092
ATC Semitec 104GT-2 : R0 = 100000  T0 = 25  Beta = 4267
Honeywell 100K Thermistor (135-104LAG-J01)  : R0 = 100000  T0 = 25  Beta = 3974

*/

/** Reference Temperature */
#define GENERIC_THERM1_T0 25
/** Resistance at reference temperature */
#define GENERIC_THERM1_R0 100000
/** Beta value of thermistor

You can use the beta from the datasheet or compute it yourself.
See http://reprap.org/wiki/MeasuringThermistorBeta for more details.
*/
#define GENERIC_THERM1_BETA 4530  // orig was 4450
/** Start temperature for generated thermistor table */
#define GENERIC_THERM1_MIN_TEMP -20
/** End Temperature for generated thermistor table */
#define GENERIC_THERM1_MAX_TEMP 300
#define GENERIC_THERM1_R1 0
#define GENERIC_THERM1_R2 4700

[Captain Starfish]

Every day's a school day.

Probably worked all this out (especially the damned #97 setting!) and had it sorted as you were typing your reply: but thanks, I do appreciate the effort!

So, thermocouple in between nozzle and block was measuring 208º when the RMax was telling me 235º, no wonder I was having issues. Got it all sorted.

:edit: FWIW I grabbed another meter with a couple of wraps of solder around each probe. Ran up to temp (230º) then switched off the RMax, pulled the thermistor lead and measured its resistance at the same time the temperature changed from 200 to 199ºC. Then let it cool to room temperature - a nice cool 35º here in sunny Western Australia - and grabbed another pair of values before calculating a Beta value and R0/T0. When I'd done that I plugged it all in, powered up and uploaded, ran up the hot end again and it was within 2ºC. Good enough.

Still had to put the two tube layers back in but noticed that, undoing the nozzle, the bottom of the block was spinning. PEEK thread loose? Not to worry, pulled the head out and the thermistor fell out completely.

Probably part of my trouble, Mr Schmartypantz here didn't realise how deep the thermistor hole was. It looked like a very shallow depression. So I'd bent the leads 90º and popped it in. Now the leads are straight, it's all the way into the hole and a good slug of copper permatex is setting to keep it in place.

So that's it for me today, going to leave it to cure until tomorrow when I'll repeat the Z calibration (head's been moved) and the thermistor calibration. Might as well have a go at the bed whilst I'm at it. CALIBRATION PARTEH!!!!

And with any luck I'll be printing perfect cal cubes tomorrow night.

Fingers crossed!

[Captain Starfish]

Ok got all that sorted tonight and did a couple of prints. Starting to look a lot better. At 240º the extruded plastic begins to discolour and I see smoke, at 220º there's string again. Somewhere in there is a sweet spot and I'll find it eventually!

I may have decent content back but having real bed lifting issues now. Tried dropping layer one back to 0.2mm but it starved of plastic. So definitely 0.3mm min for the first layer - but that lifts. Hmm - could my ABS juice be too thick? It's still flowing like water but I've just been chucking ABS into the pot for the last couple of days so it's going to be way more loaded than it was to start with. Also, my bed at 95º on the thermistor is measuring 60º on the top of the glass with the thermocouple - is that about right? What's the calibration measuring point for the bed (Onyx with borosilicate)?

[ccavanaugh]

I see a fairly large delta between reported temperature and glass temperature. I've not done much to calibrate out bed temps yet.

I made a thin aluminum heat spreader out of .020" thick material sheet I found at the hardware store. It does wonders to help distribute the heat without increasing heat time. That will help on larger prints.

I like to preheat the bed and let it sit idle for about 10-15 minutes before I heat the hot-end and start a job. It helps bring the glass closer to the heated bed temperature.

For lifting, a trick I have used on ABS is to using auto window tint on the glass along with some hair spray. After printing and cooling, I have to put the plate in the freezer to get the part to pop off the surface. I can get maybe 10 prints before I have to strip and replace the window tint. I like it better than kapton because of price and accessibility. Having a spare piece of glass is nice because of the time to let the window tint cure out (6-12 hours) after application.