Filamemnt feed at hot-end?

[savak001 0]

HI All

Almost everytime I start a print on our UM2 the filament does not extrude even after having just printede a model.

I find I have to 'Move Material' remove the Bowden Tube at the nozzle end advance the filament and cut off the end of the filament that comes out looking like this:

Then when I start the print it works ok.

So how can I avoid this process?

Regards

Graeme

Edited May 21, 2015 by Guest

[gr5 2,170]

Is the 3rd head fan working on your printer? The one in the back? If not you will get these exact symptoms. Another possibility is that the filament is expanding into some part of the head path - perhaps your isolator (the white teflon part you can see with the spring pushing down on it) as deformed (shrunk) enough for filament to get in there and melt/expand and get stuck when it is solid. Replacing the isolator might fix your problem. Have you printed several hundred hours yet? Do you tend to print hotter than 240C? The teflon part can warp/burn slowly and it happens especially fast at 250C and hotter.

[savak001 0]

Thanks for the reply

Yes the thrid fan is working.

We have 8 of the UM2's and they all show the same problem and most have printed over 200 hours.

[DidierKlein 729]

What is the firmware installed on the machines?

If i remember well an older firmware used to retract the filament too much after a print, it might come from there?

And what brand of filament are you using?

[savak001 0]

We are using the latest firmware as installed from Cura 15.02.1.

Filament is Colorfabb PLA used at a temperature of no more than 230c.

[DidierKlein 729]

Then @gr5 might be right about the Teflon.

Can you show us pictures of one of them? (the inside part seen from top, and the bottom). I'm puzzled to why this happens on 8 printers though, 200 hours of printing is not that much.

Is there anything modified on all printers? Head? Teflon? Feeder? Bowden?

[swordriff 119]

It works i the beginning before the (weakened) Teflon gets hot, and then afer 10-30 minutes the Teflon implodes onto the filament restricting movement. 200h is it an estimate or did you read in advanced menu? Sounds shortish...

Like gr5 says, at higher temp it is consumed fast. But 200 would be contiuously at 240+++, in my estimation.

Totally agree with @gr5 and @DidierKlein.

You can possibly save the day ( if we are right ), by loosening the 4 vertical head assembly screws a little. Are they very tight?

Tighten with force of "the hand of a female".. But then again, there is not always a female around when you really need one, a german or swiss guy in the forum once said...

[savak001 0]

Yes I did read the hours direct from the printer they cover between 210 and 340 hours which is not a long time.

There are no modifications to the printer in any way.

The four main screws holding the print head together are only slightly hand tight if that makes sense.

As in the main picture above the PLA bulges and retracts slghtly into the bowden tube and seems a little tight when I move the material forward. Is this normal?

I can disassemble the print head as far as removing the spring from the teflon part but is there a way of getting the teflon bit out from the nozzle assembly?

[DidierKlein 729]

The teflon should come off easily if not you can use some tweezers to pull it out (it's not glued or anything)

[gr5 2,170]

I will typically heat up the head to 180C in case there is PLA holding it in and then if it doesn't come out easily after 1 minute at that temp I will use a large screwdriver or something similar to pry it out.

[savak001 0]

Here are the pictures as requested, taken under a zoom microscope so excuse the lighting!

Edited May 21, 2015 by Guest

[DidierKlein 729]

I'm surprised to see such bad state after only 200 hours

What you can do is drill gently with a 3mm drill (by hand should do it).

You can also take the black burned stuff away with a putty knife this should make it work again for now

[gr5 2,170]

Nice photos. In the bottom picture something looks wrong - the inside of the isolator doesn't look like a cylinder anymore. Is that true or is it some kind of illusion? Having a place for hot filament to bulge out into is a serious problem and would explain your issues. There may have been too much pressure or you may have been printing rather hot. 200 hours at 260C wouldn't surprise me but 200 hours at 210C should be not so bad.

Also in your profile settings please post what country you are located in. This affects many things related to our answers and advice. Also please mark that you own a UM2 while you are in there.

You can get free isolators (that white teflon part) from Ultimaker or you can buy them from 3dsolex.com, fbrc8.com, gr5.org/store/ and other locations depending what country you are in. Didier where do french people get teflon isolators? Do you have a store or do they email you?

[savak001 0]

At what number of hours should the teflon bit be replaced?

[gr5 2,170]

I read this forum every day and don't know the answer. I have heard "500 hours" but at what temperature? I get the feeling it's around 500 hours at 220C but much shorter at 250C and longer at cooler temps. Also the tension on the isolator can vary quite a bit depending on who assembled your printer. I've seen UM2's fresh from UM where if you grab the bowden on top of the head you can move it up and down a mm or two. And other's where that's nice and tight, and other's where that's too tight. Also the spring pushing down on the white isolator part is pretty strong and depending on how high the nozzle is positioned (it's adjustable on purpose) the spring can be pushing harder or less hard. That spring tension, combined with the bowden tension, combined with printing temperatures will all cause this to vary quite a bit.

Now I see you are in the UK so I recommend buying an i2k from 3solex.com for half your machines and getting new isolators from UM and see if the machines with the i2k do any better. The i2k will keep the isolator at 100C even if you print at 260C but only if you have zero retractions. With retractions it's unknown what the temp is at the base of the isolator.

Did your printers come with extra isolators? UM started shipping 2 spare isolators with each printer I believe. If you got your printers before they started doing that they will usually give you at least one for free. Or you can get them at a decent price also at 3dsolex.com. The tolerances on this part are very very tight so don't get this part through ebay or china.

[savak001 0]

We've had the machines about 9 months or so puchased from Creat3d, so will try them.