Material feeder spring tension

[jonnybischof 60]

Hi community

I know this has been disussed before, but I've had problems with the material feeder recently so I decided to bring it up again.

The problem is that atm my material feeder always starts grinding up the filament at some point of the print (very annoying because I've got a time scale for the stuff I'm printing right now...).

In the assembly instructions (http://wiki.ultimaker.com/Ultimaker_rev.4_assembly:_Material_feed_mechanism) it says clearly that you have to use a 30 mm long screw for mounting the spring. It also says that in the end, the spring should stick out about 11 mm.

THIS IS IMPOSSIBLE.

Take a look at that picture:

It's not 100% snug on the picture, but that's because I couldn't hold the parts together and take the pic at the same time (I measured that with snug fit, using precision calipers).

If the 30mm long screw is screwed in all the way, then it still sticks out about 15 mm from the part. 11mm IS NOT POSSIBLE if you follow the instructions.

Now, in order to get to 11mm, you need to use a 25mm screw, or use multiple washers. But then, the spring is extremely tense. I can hardly push in the black wheel when pushing the assembly down on the table!

So, how much tension is needed? If you use that creamy, soft PLA stuff (like the UM blue or PLA90) you will never have problems with grinding. But with the PLA I'm printing right now (as well as with ABS which "feels" pretty much the same) it just doesn't work that easily.

I'll try adding a few washers to increase tension a bit, but if it doesn't work I'll probably break something :mad:

/edit:

Just noticed that if you measure with filament inserted, then you can gain 3 mm. (if the black wheel is pushed all the way back instead of how it is in the picture). Then add the washer and you get to 11.5mm.

Okay, so I suppose that's what the 11 mm means?

*Maybe* it would be nice to correct that because at the point you measure these 11 mm, you don't have 11 mm because you're still holding the assembly in your hand and don't have the fully assembled printer with filament inserted yet o.O...

But anyways I still have the problem that it keeps grinding up my filament.

I print at 220°C with 50mm/s, that should definetly not be an overpressure issue.

I will add a second washer and see if that improves anything...

Also, on a side note:

I noticed there's some support from the injection molding, see pictures:

 

I've left this support as it is. Do you have to remove that thing? It doesn't say so... It might be grinding the little black wheel slightly when under pressure, but I'm not sure.

 

[aviphysics 9]

There is supposed to be a spring and washer around the screw that push on the bearing assembly.

n/m. I didn't even read that part of the assembly guide. I believe the answer as to how tight it needs to be is, just tight enough that the PLA doesn't slip. If you are making any kind of impression in the PLA, it is probably either tight enough or too tight.

BTW, being too tight can also cause grinding, as making the indentations damages and weakens the PLA.

 

[jonnybischof 60]

There knurled bolt actually leaves pretty deep tracks on the PLA. For now it printed well again (did a 26 hour print over the weekend which came out awesome as usual).

It seems there was a partial nozzle blockage that increased pressure and led to the grinding. My filament spool was empty just the next print, and when I tried to shove in the new filament I had to push really hard until it kinda blew out the blockage. Maybe not the best way to solve that - but now it works fine again

There was even some leakage through the brass thread which had never happened before. Guess I applied a "little bit" too much pressure...

I'll do a service on the printhead after I finished my second UM build (might take a while, I'm very busy atm) - I'll put in some upgrades anyways.

 

[ginobrancazio 0]

So should this have been a 30mm bolt or a 25mm bolt? I can't tell!

 

[aviphysics 9]

30 mm is correct, though depending on the hardness of your filament, you might need to add a few mm of washers.

[amedee 349]

I've left this support as it is. Do you have to remove that thing? It doesn't say so... It might be grinding the little black wheel slightly when under pressure, but I'm not sure.

 

Yes, you can remove that -- it is the attachment point for the mold...

Now... You remark about the length was puzzling me as I recently built my UMO+ and I can't remember I had any trouble.

I just looked at my UMO, it has a 30mm bolt, BUT I was missing the U part so I printed it and it might not have the exact same size...

I can't check the UMO+ as it is in use, but in the assembly instructions, they refer to a 25mm bolt!!! (I cannot find the manual online as they are re-building the site, but I have a local copy)

 

[ginobrancazio 0]

30 mm is correct, though depending on the hardness of your filament, you might need to add a few mm of washers.

 

Thanks, but could you clarify about the washers please? How would I tell when I need to use them?

[aviphysics 9]

Thanks, but could you clarify about the washers please? How would I tell when I need to use them?

 

The drive should dig in far enough to make indents into the filament, but not tight enough to significantly deform its shape.

In short, if your filament is slippling, try making the spring tighter. If the screw bottoms out, you could try adding some washers.