Jamming question

I’ve been good at identifying and fixing problems on my P3 steel. It’s been working flawlessly until last night. The extruder starting skipping, which usually means a jam on my machine. I noticed this 2 hours after, so I cleaned out the extruder. Filament moves fine outside of the hotend. What I noticed before cleaning is that there were blobs of hard plastic on the heat bed from dripping. When I ran the filament after cleaning, it started fine then jammed again. It came out as extruded plastic and those blobs intermittently when it was extruding. I tried another color and the same problem. Jamming in the past for me was due to warm ambient room temps (PETG), so the machine is in a room with cool air. The warm air in the past caused the fins to not properly cool melting the plastic in the chamber above the heater (e3dv6).

So I’m at a loss for the reason of the jamming. I have the carttridge style thermistor. Is it possible for it to read a temp but actually be hotter or colder? I’m not sure what the blobs of plastic mean as it usually comes out like strands. The filament is dried frequently in a food dehydrator and kept in an air tight container, so it’s not full of moisture. Any help would be appreciated.

You don't mention what extruder/hotend you're using (my P3Steel runs with a Wade geared extruder and a E3D v6 hotend) but heres some things to check/try

• You say previous issues with your e3d v6 and heat creeping up the heatbreak part. Have you got a fan on the heatsink ? For me, without the fan there and on the filament quickly melts higher up and will jam.
• Could there be some contaminant in the hotend or nozzle that keeps blocking the hole ? This has certainly happened to me, and sometimes if I extrude with the extruder in mid air, if the filament comes out at an angle instead of straight down, I think thats evidence of this. I've used 'cold pulls' (google it) with some success, but sometimes need to unscrew the nozzle and using tongs and a mini blow torch carefully melt/burn everything out of the nozzle. then refit.
• How large a 'retract' have you got set. If this is too large (more than 1-2mm) it could be pulling half melted filament up into the cold part of the extruder where it jams. Try reducing the retract distance.
• As a last resort, try wiping some cooking oil on the filament. A very light coating (wipe with a tissue and a few drops) on the first 20-30cm seems to 'season' the hotend and nozzle and reduce jams.

Hope this helps.

Paul.

E3dv6 is mentioned in my body. It is a bowden style.

Yes there is a fan. It is in the front to pull in the coldest air (had it in the back which sucked). I cleared the nozzle with piano wire. My retract is 4mm, but as I've said I had no issues with this. It's PETG, so it needs more. And the bowden tube is not short (but not too long). I just checked the fins, and they are cool to the touch or at least room temp not warm or hot. So the fan is doing it's job. I also tried to push filament through with my hand. it was hard to push. Normally it flows like butter. So I wonder if this time it is a thermistor issue. I've had more issues with this hotend than I care to mention, but that is another topic.

E3dv6 is mentioned in my body. It is a bowden style.

Yes there is a fan. It is in the front to pull in the coldest air (had it in the back which sucked). I cleared the nozzle with piano wire. My retract is 4mm, but as I've said I had no issues with this. It's PETG, so it needs more. And the bowden tube is not short (but not too long). I just checked the fins, and they are cool to the touch or at least room temp not warm or hot. So the fan is doing it's job. I also tried to push filament through with my hand. it was hard to push. Normally it flows like butter. So I wonder if this time it is a thermistor issue. I've had more issues with this hotend than I care to mention, but that is another topic.

Sure enough, it is heat creep. I checked the ohms on the thermistor, and it was close to 100K. I had the original fan lying around (I had replaced it with a quieter one with close to the CFM output). The new fan must have started to fail. I can't believe this hotend is that sensitive. I'll be replacing this hotend soon.

Spoke too soon. Jammed again 1/3 of the way through a print. Not a fan of E3D.

We had a thread on here about 2 months ago where similar symptoms turned out to be partial failure of the driver transistor.
The result was poor temperature control and the occasional blocking of the nozle.
I don't think it showed up on the temperature trace. I think you have to monitor the driver output to see it.
Solution was to fit a new driver.
The driver transistor doesn't fail open or closed but has some other issue.

Do you mean the hotend transistor? I don't see how a driver would be the issue as the only driver in the mix is the extruder driver, which works fine. But if the hotend transistor was failing, I would think the thermistor would pick up the fluctuations. Do you have a link to that thread? It would be worth checking out.

I'm still thinking it is the hotend. I say this because it starts to print fine then fails. My guess is the fan is doing its job, but something (perhaps the thermal past went bad) is causing the hotend to get too hot in the non-melt zone as it prints causing the jams.

Edited 1 time(s). Last edit at 04/13/2018 02:38PM by mlaustin66.

Here is an example of what is happening. It was worse on other prints. So starts out great, jams, and limited flow out of the nozzle unlike the start. Extruder works fine when filament is outside of hotend.

Edited 1 time(s). Last edit at 04/13/2018 12:11PM by mlaustin66.