Filament is slipping / 1.75mm mod

Hello ,

And first sorry for my english

I’ve finished my Mendel90 2 weeks ago and started printing some small pieces, it’s working really good.

I’m having problem to print large pieces, filament is slipping. Printing speed is about 50mm which seems to be not to fast for me ?

BUT, I’m using 1.75 filament. My Hotend is JHead MKV-B with 0.35 nozzle, PLA is used (and is good quality). Printing at 190°C

Of course I have a PTFE 1.75mm tube in the hotend. Some people reported that it was working fine like this (http://forums.reprap.org/read.php?292,278497,330504#msg-330504) but not for me, as I said on large pieces. It’s randomely slipping, the hobbed bolt is not dirty.

So In the extruder block, you have a 4mm hole for the filament, I thought that it was too big and the filament was too loose in it.

I designed a new extruder block with 2.3mm hole (3mm filament and 4mm hole which is 33% difference, so 1.75mm + 33% gives 2.3). I took Nophead original .scad file and made the mod (somewhere in the code “r=4/2” changed to “r=7/6”).

I tried last night and the result is worse. It’s almost always slipping now even at low speed. So my guess is that the hobbed bolt is now too far from the filament and the filament does not go into the hobbing even with the springs at their max. With the 4mm hole maybe it was better because the filament could be curved as the hole was bigger ?

So now before I plan to buy an EZ Struder, I’m thinking to mod the extruder block again, to shift the hobbed bolt 1mm more close from the filament, what do you think ? Is there another mod to do ?

Thanks for your answers !

Yes the extruder will not grip 1.75mm filament because the idler will not close far enough onto the hobbed bolt. Shifting the bolt forward won't help because the bearings and so the front wall of the bearing block will move as well and it is the idler axle hitting the bearing block that prevents it closing completely. It is deliberately like that as it makes loading (3mm) filament easier.

You could try cutting away the thin plastic walls that cover the front of the bearings or grind flats on the ends of the idler axle to allow it to close a bit further. It is hardened steel so you can't file it. If you don't have a grinder you could replace it with a softer metal rod, such as mild steel or brass.

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[www.hydraraptor.blogspot.com]

Here are some updates I used a lime to flat the axle, It was not hardened as I used a rod from a HP printer for this part, so it was quite easy. But again it was not enough, because as I said I changed the input and output holes for the filament to 2.3mm, and the filament is too hard do bend , so simple mod was to make bigger holes (5mm) with a drill, so that the filament is touching the hobbing without - bending/curving ? - it.

It seems to be perfect now I will try to print and let you know

Well I thought it was ok but it started again and I am wondering if it was a hotend problem.

Here are some pics the resistor is really burned color is it normal ?

Also the nozzle is full is plastic just to the top ...

It looks like it has been leaking. Was it sealed with PTFE plumbers tape?

If you get burnt plastic on the thermistor wires it can cause it to read high so the temperature drops.

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[www.hydraraptor.blogspot.com]

Yes it was sealed with self almagating silicone tape (rated to 280C)


It is more the resistor which is burned rather the thermistor. but maybe it's the exhaust paste which is burned like this.

Edited 1 time(s). Last edit at 06/07/2014 08:07AM by The_ccm.

No I meant the thread of the nozzle where it goes into the PEEK. That should be sealed with plumbers tape. That is what stops the plastic leaking out as straight threads on their own do not form a seal.

The exhaust putty I use does not burn at these temperatures, it remains cement coloured unless contaminated with something that burns, but perhaps you used something different.

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[www.hydraraptor.blogspot.com]

Here are some updates... you were right, I made 2 things wrong when building the hotend :

- PTFE tube was not deep inside and didn't touch the nozzle
- missing plumbers tape
=> it was leaking, that's why after printing there was always parts of plastic around the nozzle.

I also changed my Z_HOME_POS because I think it was too close from the plate, and the PLA was not able to go out from the nozzle for the first layers, that's another reason why the filament was sliping.

with the hotend fixed, flat made on the idle axle, this is almost perfect now. I tried ABS for the first time and it gave a good result.

thanks for your help.