1 Topic by elmoret

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Topic: Jamming only after idle

So, I upgraded my hotend to one from qu-bd:

http://store.qu-bd.com/img/p/22-74-large.jpg

And things seemed to work fine for a while. Now, if the extruder is idle for 5+ seconds, it will do nothing but skip steps when it attempts to restart. If I push on the filament while the motor is skipping steps, it will eventually start moving, and extrudes fine at 400mm/min in Repetier. As soon as it stops for anything more than a few seconds, it will jam on restart - plastic comes out while it's skipping steps, but much more slowly.

I've checked motor voltage: 0.18v, though I've tried up to 0.40v. It seems like there's a gap or void, and plastic is melting into it, then catching and preventing feeding or something.

Any ideas? I'm losing my mind.

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2 Reply by lawsy

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Re: Jamming only after idle

The positioning of the thermistor on the standard hot end causes it to under read.

Try experimenting with higher temps, going up a few degrees each time.

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3 Reply by vince7c95

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Re: Jamming only after idle

Is it possible that the barrel isn't screwed in completely into the peek? I read something about plugs occurring when the parts aren't completely screwed together.

4 Reply by elmoret

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Re: Jamming only after idle

I've tried up to 250C.

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5 Reply by jooshs (edited by jooshs 2013-01-24 02:01:21)

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Re: Jamming only after idle

I wonder if the PEEK has inconsistencies in the point at which it softens. I've been through 4 hotends since August and some of them just started melting out at lower temperatures. I could always tell it was about to happen because of what you were describing. It would start with that, and then a little portion of the seal at the bottom of the PEEK would start to soften and ABS would start oozing. As soon as it softens at all, you're toast. I've also read the ABS tends to have back flow issues and expand at the top of the PEEK barrel. This is supposed to happen between the top of the heater barrel and the bottom of the Teflon disk. Any nozzle from SD I took apart did not get anywhere near the Teflon disk. The pressure builds and it has to work its way into the threads of the PEEK and or expand up where it cools, hardens, and impedes the filament.

6 Reply by elmoret (edited by elmoret 2013-01-24 02:39:18)

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Re: Jamming only after idle

A few more words...

I have the thermister in the smaller of the two holes above, perpendicular to the barrel. It won't extrude under about 220C. 220C-250C it extrudes fine once it's gotten going.

If I back the filament all the way out and back in again, it will extrude fine.

Four hot ends? At $60/ each? This is becoming an expensive hobby...

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7 Reply by jooshs

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Re: Jamming only after idle

For the amount of prints I get, it's still a good deal. I wish there was a more reliable solution but I haven't invented one yet, so I won't complain too much. I'm still pretty convinced there were issues with the black filament causing one problem and that wire bundle just broke down over time causing inconsistent connections for the thermistor and hot end. If you can get the heater barrel out, you should be able to tell if the PEEK threads started melting.

Also sounds like the filament might be softening above the hot end if you can back it out and then put it back in and it extrudes fine. May be time to try the cold end of the hot end cooling.

8 Reply by elmoret

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Re: Jamming only after idle

I tightened the barrel with respect to the PEEK about 2 full turns, took the temperature to 270C, been doing ok so far.

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9 Reply by Tomek

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Re: Jamming only after idle

elmoret wrote:

I tightened the barrel with respect to the PEEK about 2 full turns, took the temperature to 270C, been doing ok so far.


What are you doing..?

If your temp is at 270C you are doing something wrong, and/or have a very poorly calibrated thermistor. 270C is substantially above PEAK's melting point.


Am I missing something? I just came back from running outside so I might have skimmed too much

10 Reply by elmoret (edited by elmoret 2013-01-24 05:04:51)

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Re: Jamming only after idle

PEEK's melting point is 343C.

The thermistor is no longer located on the outside of the nozzle. Not even on the outside of the heater block (which would run hotter than the nozzle, by necessity), but buried in the heater block, right up next to the brass barrel. It'd be like wrapping the thermistor inside of the nichrome wire when making the sold style Solidoodle hot ends.

It's quite possible that the thermister is not calibrated well anymore. The batteries in my Fluke are dead, so I can't check it. Anyone know where to get a new one? Everything I've read says they're EPCOS 100k, but there are many models of that.

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11 Reply by jooshs (edited by jooshs 2013-01-24 05:14:36)

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Re: Jamming only after idle

It has a melting point of ~343, but a glass transition at 185 and only retains its mechanical properties at 250 continuously.

http://www.boedeker.com/peek_p.htm

Thermistors are usually here, but sold out right now. I have several extra if you're in a bind.

http://www.panucatt.com/Azteeg_X3_repra … ax33dp.htm

12 Reply by elmoret (edited by elmoret 2013-01-24 05:21:20)

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Re: Jamming only after idle

Occasionally skipping steps again. Gonna throw this thing out the window soon.

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13 Reply by elmoret

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Re: Jamming only after idle

jooshs wrote:

Thermistors are usually here, but sold out right now. I have several extra if you're in a bind.

http://www.panucatt.com/Azteeg_X3_repra … ax33dp.htm

What'd they run you? I'd be happy to take one off your hands, shoot me a PM.

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14 Reply by devilman2075

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Re: Jamming only after idle

Qubd offers thermisters a dollar a pop. Should have looked around on the site, you can get basically everything you'd need right from them.

15 Reply by elmoret

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Re: Jamming only after idle

devilman2075 wrote:

Qubd offers thermisters a dollar a pop. Should have looked around on the site, you can get basically everything you'd need right from them.

Didn't know I needed another one until now!

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16 Reply by jon_bondy

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Re: Jamming only after idle

elmoret wrote:

Occasionally skipping steps again. Gonna throw this thing out the window soon.

When it skips, is it cutting a divot in the filament?  What kind of pressure setting do you have on the idler bearing?

17 Reply by elmoret

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Re: Jamming only after idle

No divot that I can see - the motor is skipping, but not slipping against the filament. No dust on the idler wheel.

I can see one thread poking out from the thumbnut on the spring tensioner.

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18 Reply by elmoret

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Re: Jamming only after idle

Alright, it seems I had two issues:

1.) Skipping steps only on restart - this was because the brass barrel was not tight enough into the PEEK, I think
2.) Occasional missed steps when printing - this was because my filament diameter in slic3r was set to like 1.7x, and my filament was 1.8x. I slowed down the feedrate, and it's not missing steps anymore. Need to do another single wall calibration.

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19 Reply by solijohn

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Re: Jamming only after idle

jooshs wrote:

It has a melting point of ~343, but a glass transition at 185 and only retains its mechanical properties at 250 continuously.

http://www.boedeker.com/peek_p.htm

Thermistors are usually here, but sold out right now. I have several extra if you're in a bind.

http://www.panucatt.com/Azteeg_X3_repra … ax33dp.htm

You've nailed it on the head there. Lots of printers seem to have the peek insulator issue, and
even some premium hot ends use it. There are some alternatives (I think I've seen cermaic,
believe it or not) but they are somewhat less practical.

Former Solidoodle employee, no longer associated with the company.