Filament feeder slipping

Hi guys,

Lately my Ormerod has started to develop some extruder drive slipping, when feeding filament. Very annoying ofcourse, and I can't quite figure out why this is.. As it's getting a little worse over time I have to fix it asap, or it will soon affect my printquality.
The filament itself is within 0.1mm from the spec. I have maybe printed a total of 500 grams of filament, so parts shouln't be worn out already, right? I'm currently in the middle of a 3-4 hour long print so I dont want to take things apart just now to check hobbed insert etc.

I seems that it's more frequent in the beginning of a print. I raised nozzle temp to 210C to ensure a bit more oozing plastic (Mostly printing PLA) but it doesn't really seem to help much. When it starts to slip, I can remedy it some by putting a little force on the large extruder gear helping it to feed filament. Also when everything is feeding fine, I could also get it to slip by just slightly create some drag with my finger on large gear.


Check out the: Video
(Streaming does not work on mobile devices I believe)

I'm leaning towards stepper motor.. Maybe just some dirt/dust inside, or it's starting to give in? I guess Ormerods had sold by the thousands by now so someone else should have similar experience?

Any ideas would be greatly appreciated!

Regards,

[Edit, typo]

Edited 1 time(s). Last edit at 03/08/2014 07:24PM by groneorm.

I presume you mean that the extruder motor slips back a few steps from time to time. Probably the most common cause of extruder slipping is an obstruction just below the nozzle, for example when starting a print and the nozzle is too low or bed compensation has gone wrong, or when the z-drive isn't raising by the correct amount between layers. If you raise the nozzle well above the bed and try to extrude filament, does the motor slip?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks for the prompt reply :-)

If you have the possibilty, videolink above says it all.. But yes, extruder motor slips back. Will check out Z-height and bed compensation as soon as my long print is finished.
But.. it has been working almost perfect up until recently.

Is it just on the first layer? It may be your head is too low and the nozzle is "sealed' by the kapton - try raising it a little and see if it goes OK

Ray

No, it's throughout the entire print, so it's not the kapton sealing the nozzle. Slipping is much more frequent in the beginning of a print, and almost nothing towards the end. Yep, will check out the Z-hight zeroing. Appreciate the input.

If you are using a temp for the HotEnd of 185 and above and it's happening then it sounds like you might have some debri from the PTFE tube carried down to the nozzle. If it was me, I'd remove the Nozzle, burn the plastic out on the kitchen stove, then clean it out till it was clean inside the nozzle.
Burning the plastic out should make it brittle enough for you to use a pin and a drill with your fingers to clear it. Don't go running an electric drill throu it, just tease it out, else you'll spoil the nozzle. Some people have said that doing a retract with a temp of around 160' drags the rubbish out, then you disconnect the feeder tube and feed the filament thou, and cut off the end of the filament before connecting back up.

Good Luck... It's a pain when thing don't go right.

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Please send me a PM if you have suggestions, or problems with Big Blue 360.
I won't see comments in threads, as I move around to much.
Working Link to Big Blue 360 Complete

Another possibility which I suffered from initially is the extruder gears rubbing on the side of the extruder body. This can be made worse if the gears are not quite concentric as that can drive them down harder onto the body.
I fixed mine by putting an extra washer between the larger gear and the body.

Hi groneorm,

It may also be worth cleaning the hobbled insert inside the extruder body, the little grooves can often get filled with dust and plastic, which further impedes the amount extruded due to the lack of grip

Matt

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Limited Edition Red RS Ormerod 1 #144 of 200 - RRP 1.09fw
iamburnys Ormerod Upgrades Github
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Higher current for the extruder motor might solve the problem but not help you find the cause of the problem, standard Ormerod is E800

You can change that by sending this command in pronterface or edit your config.g as to make it permanent

M906 X800 Y800 Z800 E1200

Erik

Thanks for all suggestions. It turns out that feedermotor is slipping even when HotEnd's not near the glass/kapton/print if I feed at faster rate. Using default current and feeding at 240mm/min (@200C HE) it's slipping even when off the glass. Maybe that's normal at this rate? Trying to feed that much plastic through the nozzle seems to require higher current. @ E1200 it seems to feed just fine, at this rate. Is there any drawback using E1200 as default value?? Overheating? Decreasing motor lifespan?

Before this test I cleaned out the nozzle with the "retract filament at 100C method" described in the ormerod troubleshooting guide and elsewere. Could not se any debris at all. Also the hobbed nut was clean as a whistle. Added 2 extra washer to large gear assembly just for good measure, although not seeing any wear from large gear rubbing off on extruder housing.

Could it be that my PLA isn't good? Doesn't flow right at ~200C?

Will now try a print with E1200 and se how it goes..

Hi again groneorm, well worth checking the hobbed nut teeth anyway, but if they're clogged the symptom is that the wheels turn fine, but no filament moves - what your video shows is that your extruder gears and the hobbed nut are pushing against a big resistance, and eventually slipping backwards with the back pressure , which is indeed what would normally happen if the nozzle is blocked, or the filament isn't melting fast enough. It looks like you've gone out of your way to establish that the nozzle isn't blocked - have you checked that the hot-end temperature is right? (on top of your PLA not being right as you suggest, it could be that there's a problem with your thermistor or its serial resistor - and the nozzle isn't being held at the right temperature because the temperature is being over-reported). From memory I can't swear what my machine does when I feed at 240mm/min, but I've got a hunch that it does fedd without problem (I'll check tomorrow if no-one else feeds back on that question)


Ray

Printing with extruder motor current set to E1200 solved the feeding slippage. But it might also introduce a sligtly hotter steppermotor. I didnt take any reaing with the default values unfortunately. I would say it is at 40-45C after ~10 minutes of printing.

I have tried and measure the nozzle temp but I find it quite hard. Used first a IR-Thermometer gun, witch naild the hotbeds 60C on kapton but i have avery hard time getting any relevant temps from the hotheadarea. Also tried a digital stakethermometer, only got up to 170-180C reading so when head was set for 240.

Does anyone have a reliable method for checking the hotend temperature? wuold be great.

Quote
rayhicks
....have you checked that the hot-end temperature is right? (on top of your PLA not being right as you suggest, it could be that there's a problem with your thermistor or its serial resistor - and the nozzle isn't being held at the right temperature because the temperature is being over-reported)....
Ray

Good point, as shown in dc42's test the agreement between bed and hot end thermister could be 10 off

[forums.reprap.org]

Erik

Quote
groneorm
Added 2 extra washer to large gear assembly just for good measure, although not seeing any wear from large gear rubbing off on extruder housing.
.

For me, the problems were: the small gear rubbing against the extruder body (you could see a 45 degree arc being worn), and the motor spindle rubbing against the extruder body.

I filed the area around the spindle, pulled the small gear back a little from the face of the extruder, and applied some graphite lubricant behind the small gear

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Ormerod #17

Quote
groneorm
Printing with extruder motor current set to E1200 solved the feeding slippage. But it might also introduce a sligtly hotter steppermotor. I didnt take any reaing with the default values unfortunately. I would say it is at 40-45C after ~10 minutes of printing.

I have tried and measure the nozzle temp but I find it quite hard. Used first a IR-Thermometer gun, witch naild the hotbeds 60C on kapton but i have avery hard time getting any relevant temps from the hotheadarea. Also tried a digital stakethermometer, only got up to 170-180C reading so when head was set for 240.

Does anyone have a reliable method for checking the hotend temperature? wuold be great.

I used a thermocouple thermometer (RS part number 206-3722) The K type thermocouple that comes with the instrument has a lead that is long enough and thin enough to fit down the bowden tube. I removed the filament, took the bowden tube out of the extruder and fed the thermocouple down the tube till it bottomed in the molten plastic left in the nozzle, so the reading is about as accurate as you could get. IR thermometers are not going to be reliable because (1) the target area is a lot smaller than the spot size for most instruments and (2) the aluminium has poor IR emissivity, which is going to give extremely unreliable readings unless you know exactly what correction factor to apply.

Obviously any thermocouple thermometer should work - some multimeters have a thermocouple input. Perhaps your digital stake thermometer will take other types of thermocouple in which case just get a thermocouple that will fit down the tube (such as RS 787-7709).

Dave
(#106)

OK, so I think I actually have narrowed it down to a thermistor problem and/or cartridge heater.. Seems like temperature is severly off, on the low side. I stripped one of my steak thermometers down to it's thermistor and kapton-taped it to the back of the HotEnd. (As seen from the fan) I have a few other thermometers that I calibrated the current one with. It was within 3%. Could only do this up to 120C, but still, confident enough of the readings.

Then I set of and took measurements at 50C, 70C, 100C, and then every 20C up to 300C.It was off by 14-31% The higher I went the worse it got. The fan air was deflected from the nozzle with a small sheet of plastic so it wouldn't cool the reading down more than necessary. From 140C and up, I briefly stopped the fan entirely for 10 seconds taking note of the peak value. Naturally, since I measured the temp on the outer surface of the HotEnd there are some discrepancy but I don't think that it's more than maybe 10-20C ? If thats true that would mean that my earlier PLA printing was not at 210C, rather around 170C. This would ofcourse explain the slipping feeder, since the plastic didn't flow right,

At 300C the Duet shut down the heater so I didn't get a reading there, not wanting to push it..

Finally for the big question(s).. Can I offset the reading within the software somehow to get a corrected one?? Or is the thermistor/cartridge slowly dying on me regardless?

Orm	Ext	% Off
50	43	-14,00%
70	56	-20,00%
100	86	-14,00%
120	99	-17,50%
140	114	-18,57%
160	128	-20,00%
180	140	-22,22%
200	151	-24,50%
220	164	-25,45%
240	174	-27,50%
260	184	-29,23%
280	193	-31,07%

Degrees Celsius

Thanks for all your help so far! I just printed a decent looking snowman in black PLA with a HotEnd setting of "240C" with NO slipping. Extruder stepper at default current, E800.

If you are using my latest firmware 057t - dc42 then you can reprogram the thermistor resistance at 25 C and thermistor beta. See the checkin comment for details.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

groneorm - the standard thermistor should have a resistance of 100k at 25°C - can you hold it at that temperature and measure its resistance with a multimeter? I've had three duets (original from RRP, returned because of manufacturing fault on the 5V regulator, a T3P3 duet, which I still have, and the warranty replacement from RRP which I still have), the first two both under-read hotend temperature at ambient (-4 to +4 say for a temperature of around 18 °C) and over-read at high temperature - I tabulated the results here [forums.reprap.org] a while ago. Mine actually agreed with external measurement around 100°C though, yours reads low all the way through the range that you've reported. I recently started using the warranty replacement, and this seems to be spot-on (I haven't retested over the full temperature tange, but it agrees with external measurement at ambient now). Recently dc42 raised the question of whether the series resistor (which is used in tandem with the thermocouple to give a voltage that the duet can turn into a temperature) had a close enough tolerance - it would seem in my case that there is some difference between duets (since I haven't changed anything other than duet boards - no change in thermistor or its position, or the connections between) so I would tend to think that the series resistor does vary between boards. You might have a very extreme series resistor, or your thermistor might be out of spec (which is why I suggested checking the resistance at 25°C - if this checks out then you could try taping it to an external probe and holding it in kettle steam, which should show 100 on the external and let you measure the resistance at 100°C - this will let you calculate the beta for that temperature range and check it against the "spec" beta of 4066 where beta = (T₁*T₂)/(T₂-T₁) * ln(R₁/R₂) - all temps in Kelvin (°C+273.15)- I can't find a spec sheet for the thermistor with the beta on (or what range the beta is valid for unfortunately). If the thermistor checks out the next step would be to check the series resistor and/or the voltage feeding the divider ( the series resistor is R19 and should measure 1K, one end connects to the thermistor, the other end should be at 3.3V when the duet is powered up). If the thermistor doesn't check out, you can either plug your calculated beta into the software, dc42 has recently added the feature of changing betas using gcodes, or you should be able to get a replacement from RRP.

Ray
PS - it's very unlikely that the issue lies in the heater cartridge unless it's bullying the thermistor into lying to cover up its failure also, if anything, your external thermometer will be under-reading because of cooling effects, so the thermistor/duet error may be greater than you measured, but it won't be less

Edited 2 time(s). Last edit at 03/10/2014 07:46PM by rayhicks.

Quote
dc42
If you are using my latest firmware 057t - dc42 then you can reprogram the thermistor resistance at 25 C and thermistor beta. See the checkin comment for details.

Great, just what I need then! Thanks for your great effort with the firmware altogether DC, and you're also a great resource and help here at the forum for us novices and others.
I've been a bit lazy, still on 57r I believe :-) But that will change tomorrow for shure.

Quote
rayhicks
groneorm - the standard thermistor should have a resistance of 100k at 25°C - can you hold it at that temperature and measure its resistance with a multimeter? I've had three duets (original from RRP, returned because of manufacturing fault on the 5V regulator, a T3P3 duet, which I still have, and the warranty replacement from RRP which I still have), the first two both under-read hotend temperature at ambient (-4 to +4 say for a temperature of around 18 °C) and over-read at high temperature - I tabulated the results here [forums.reprap.org] a while ago. Mine actually agreed with external measurement around 100°C though, yours reads low all the way through the range that you've reported. I recently started using the warranty replacement, and this seems to be spot-on (I haven't retested over the full temperature tange, but it agrees with external measurement at ambient now). Recently dc42 raised the question of whether the series resistor (which is used in tandem with the thermocouple to give a voltage that the duet can turn into a temperature) had a close enough tolerance - it would seem in my case that there is some difference between duets (since I haven't changed anything other than duet boards - no change in thermistor or its position, or the connections between) so I would tend to think that the series resistor does vary between boards. You might have a very extreme series resistor, or your thermistor might be out of spec (which is why I suggested checking the resistance at 25°C - if this checks out then you could try taping it to an external probe and holding it in kettle steam, which should show 100 on the external and let you measure the resistance at 100°C - this will let you calculate the beta for that temperature range and check it against the "spec" beta of 4066 where beta = (T₁*T₂)/(T₂-T₁) * ln(R₁/R₂) - all temps in Kelvin (°C+273.15)- I can't find a spec sheet for the thermistor with the beta on (or what range the beta is valid for unfortunately). If the thermistor checks out the next step would be to check the series resistor and/or the voltage feeding the divider ( the series resistor is R19 and should measure 1K, one end connects to the thermistor, the other end should be at 3.3V when the duet is powered up). If the thermistor doesn't check out, you can either plug your calculated beta into the software, dc42 has recently added the feature of changing betas using gcodes, or you should be able to get a replacement from RRP.

Ray
PS - it's very unlikely that the issue lies in the heater cartridge unless it's bullying the thermistor into lying to cover up its failure also, if anything, your external thermometer will be under-reading because of cooling effects, so the thermistor/duet error may be greater than you measured, but it won't be less

Will check out the resistance tomorrow.. If I recall right it was good during comission atleast..Ill try to wrap my ahead around your info tomorrow, have to crash now since its up early tomorrov..

Thanks guys for your help, means alot to me!

BR,

I'm suffering from the same problem as groneorm here, I started a thread called nozzle blockage a while back but I don't think I explained the problem as well as groneorm has.
I'm not very electronically minded (if you can't fix something without a big hammer whats the point ?) but i'll have a go at the suggestions here tomorrow and see if I have any luck.

Note the beta I gave in my last email is actually incorrect - the beta for the extruder thermistor should be 4138 (just in case you end up going in this direction).

It may also be a bad idea to measure the resistance of R19 directly (directly probing both ends of the resistor should be OK, but might result in damaging the thermistor input pin on the chip if the input voltage is exceeded by your meter and there's a connection to ground) - a safer method of testing would be to substitute a 100K resistor (if you have one) for the thermistor which should give a reading around 25°C from pronterface, and substituting a piece of wire, which should give a reading around 5000°C (I think, I'll have to check on mine tomorrow), and can check what temperatures are reported for other resistor values if you'd like (presuming that you have a range of resistors lying around - if you do, then let me know what values you have),

Ray

Quote
dmould
..I used a thermocouple thermometer (RS part number 206-3722) The K type thermocouple that comes with the instrument has a lead that is long enough and thin enough to fit down the bowden tube. I removed the filament, took the bowden tube out of the extruder and fed the thermocouple down the tube till it bottomed in the molten plastic left in the nozzle, so the reading is about as accurate as you could get.

Dave
(#106)

Brilliant idea!

Erik

Quote
rayhicks
Note the beta I gave in my last email is actually incorrect - the beta for the extruder thermistor should be 4138 (just in case you end up going in this direction).

It may also be a bad idea to measure the resistance of R19 directly (directly probing both ends of the resistor should be OK, but might result in damaging the thermistor input pin on the chip if the input voltage is exceeded by your meter and there's a connection to ground) - a safer method of testing would be to substitute a 100K resistor (if you have one) for the thermistor which should give a reading around 25°C from pronterface, and substituting a piece of wire, which should give a reading around 5000°C (I think, I'll have to check on mine tomorrow), and can check what temperatures are reported for other resistor values if you'd like (presuming that you have a range of resistors lying around - if you do, then let me know what values you have),

Ray

That sounds great! I have most of the common values from 0-1MOhm to compare with.. I'm not sure wich values we are lookng at here, but I can probably come up them.. :-)
Thanks!

Attached is a spreadsheet that I use to calculate thermistor resistance from temperature. Bear in mind that if you are using firmware prior to 057t-dc42 then the temperature resolution for the hot end thermistor is about 5C at room temperature.

EDIT: updated spreadsheet so that it can also calculate the temperature reading you should get using a known resistance.

Edited 2 time(s). Last edit at 03/11/2014 07:08AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
Attached is a spreadsheet that I use to calculate thermistor resistance from temperature. Bear in mind that if you are using firmware prior to 057t-dc42 then the temperature resolution for the hot end thermistor is about 5C at room temperature.

Nice, thanks! Will look in to this promptly..

Quote
dc42
If you are using my latest firmware 057t - dc42 then you can reprogram the thermistor resistance at 25 C and thermistor beta. See the checkin comment for details.

Could you point me to this info? I couldn't find it really..

I've just updated the spreadsheet in my previous post to also calculate the temperature reading you should get when you substitute a known resistance for the thermistor, both using 10-bit ADC (as in the original firmware) and 13-bit ADC (as in my 0.57t-dc42 version).

You can find 057t-dc42 and other revisions at [github.com]. From there, follow the link to the file you want, then click Raw to download it.

Edited 1 time(s). Last edit at 03/11/2014 07:12AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

@dc42 -any chance you could an export an xls or xlsx please? My excel (2008 for Mac) refuses to open .ods, I found a converter but it seems to just have values, not equations.

@groneorm, the release notes that describe setting the R₂₅ and beta values are here: [github.com] (scroll down the readme until near the end)

Ray

Ray, it's time you tried Libre Office But here is a .xls.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

just for fun, I compared my new RRP duet with the T3P3 duet with two known resistors and a short across the E0_TEMP input - I did this twice for the T3P3 which was running an older version of 0.57-dc42 (n or q I think) the results are as below (my original RRP duet behave similarly to the t3p3 one, with low readings at ambient and over-reporting at working temp, hence the comparison):

			
      Warranty t3p3? t3p3t
res	temp	temp	temp
short	-9890.8	2235.3	-9890.8
9850	84.5	82.5	82.5
99900	24	3.6	7.5

"t3p3?" is the tp3p duet running unknown firmware, "t3p3t" is running 0.57t-dc42, "Warranty" is the replacement duet running 0.57t - the resistances are as measured by my multimeter (nominally 10k and 100k), it looks like version 57t has a boundary issue maybe - causing the low voltage on short to appear as a large negative value (not that this is going to matter in normal use, but I thought I'd bring it to your attention dc42)

Ray

Quote
dc42
Ray, it's time you tried Libre Office But here is a .xls.

Will do! - thanks for the conversion in the meantime

Ray