Cannot bridge

Hi,

I have issues bridging. PLA, printed at 205 degrees C, bed at 40 degrees C, speed 40mm/sec, 1.75mm filament.

I have attached two pictures (the same, one with flash, one without). The pictures show the first layer of bridging, over the big circle on the left.



I am using a fan, like this : [www.thingiverse.com]

Any idea as to what could cause this situation ? The filament doesn't seem "elastic" enough. But if I reduce the temperature, I cannot extrude properly, too much force is required. I believe my melting chamber in the extruder is a bit small.
Motor has more torque than the filament has grip : sometimes there is so much tension on the filament that it kicks-back, the motor can no longer hold that tension in. So the extruder is not extruding very easily at all, this is why I can't reduce the temperature. The extruder is not clogged, I measured it with a pin gage and it's 0.41mm (should be 0.4mm).

The printer is a Sunhokey Prusa i3 from China with the stock extruder, it looks like a E3D V5 clone but I'm not sure. I've seen people bridging successfully with this printer so I don't know what I'm doing wrong.

Please help ! Thank you

PS: This is a crosspost from [forums.reprap.org] - I initially posted there, but then I realized it was not the right forum, so now I'm posting here... normally I never do that, but as I can't move a thread I had to !

Hi uski,
I'll start it off...

We'll need more info, specifically:
- what slicer
- what printing speed for bridging
- what bridge flow ratio
- what speeds and extrusion widths for perimeters and infill
- you may possibly may need a link to the gcode file (contains more settings that were used)

So without specifics:
Usually the issue is related to printing too fast while not extruding enough.

When bridging a bead must be extruded that is the same diameter as the nozzle, at a feed rate that maintains that diameter. Too fast while not enough extruding and it is pulled thin and snaps, to slow while too much extruded and it droops.

Hope that helps.

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My printer: Raptosaur - Large Format Delta - [www.paulwanamaker.wordpress.com]
Can you answer questions about Calibration, Printing issues, Mechanics? Write it up and improve the Wiki!

Do a small testobject for bridging and test different sppeds, percentages for the extrusion during bridging and if still no luck try higher temps and speeds.
Sometimes a faster and stringy bridging works much better than a drooping bridging with thick lines

If the rest of the print looks ok and its only bridging then its a code issue not the hardware (not temperatures).
It actually looks like bridging is turned off and you are just using the residual filament in the hot end. Don't forget that some slicers allow parameters to be either absolute or percentages, Some 0 means default and some 0 means none. I don't think there are any firmware parameters specific to bridging so that should be OK.
I was going to ask if you were shore its PLA but the rest of the print looks ok so it has to be specific to bridging.
Do you believe the temperatures are correct?
When slicing do you do it from the host software or in the slicer?
You need the slicer parameters set up even if you use the host over ride as the override may only be to turn bridging on/off and if the slicer is set to 0 federate while bridging it wont bridge whether its on or off.

Hi

Thanks for your replies.
I am using Cura 15.04.4

I have attached the parameters I used. Let me know if you see anything wrong. I didn't see any special parameter about bridging.

I also used Slic3r but I switched to Cura because I had some issues and also because Cura is simple to use (not that I am afraid of Slic3r, I was using it with Repetier Host, but I like ease of use nonetheless).

Thanks !
uski

Cura had a setting for bridging in an old version (v13 I think), however the developers have decided that setting is not important. Perhaps it's not important for the printer type the developer used (typical problem).

So you have no settings for bridging at all... That's too bad as bridge flow ratio is crucial.

You can try changing the speed settings one at a time to see which one is used (probably one of the perimeter settings).
Of all the treads I've read abut bridging in Cura, they mostly try tweaking temp, add an external fan (for PLA) or make sure fan is on when needed, and try different speeds...

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My printer: Raptosaur - Large Format Delta - [www.paulwanamaker.wordpress.com]
Can you answer questions about Calibration, Printing issues, Mechanics? Write it up and improve the Wiki!

I'm going to do a few tests using Slic3r and I'll report back. Thanks guys !

I don't have experience in this area but does this mean you are bridging with a 0.15 layer thickness? Is that realistic given there is no support?

Hi guys

The issue seems to have been caused by poor filament. It's the filament that came with the Sunhokey printer.
I bought a reel of 1.75mm filament from MG Chemicals on Amazon and so far I recommend it, it definitely doesn't have the same texture than the chinese filament.
The MG filament is much more "elastic" when hot so now I can bridge !

I did the bridging test with Slic3r but I expect it should work as well with Cura considering the huge difference in filament quality.

Great! Please let us know how it goes with Cura if you have a chance.