Cura bridging

[rich 0]

Hello,

I'm having trouble bridging the flat top of a small box-like structure. The rectangle is 70mmx32mm - so the distance to be bridged is 32mm. Cura chooses to do it at an angle which makes it just over 45mm. The lower part of the model prints very well including quite a bit of fine detail and overhang, but the bridging makes the model not useful.

The first bridge filament adheres at both ends and looks great -- then the extrusion head moves back across the gap putting the second filament close and parallel to the first. This melts the fist thread in the middle and leaves an impressive looking second thread standing alone with two short pieces of number 1 hanging from the walls. This continues to happen with only an occassional drooping thread surviving in one piece.

I'm using a UM1, ABS, V2 0.4mm extruder at 245C, Print speed 100mm/s, SD card with Ulticontroller, recent Marlin, Cura 13.10, Heated bed with Kapton on Basalt and Bed Temperature 110C.

Can anyone suggest a way to overcome the difficulty please?

I've turned the fan on (during the preceeding layer) and that has a small effect but not enough. I assume that the heat radiated from the nozzle is able to melt the single strands in the middle but not near the walls where the cooling has been greater. Lowering the nozzle temperature would reduce the radiated heat but would probably lower the quality of the rest of the model.

If Cura were to enable the initial bridging threads to be much further apart, I think the isolated bridging strands would not get the heat from the nozzle and would survive unscathed. The gaps could be progressively filled - one strand per gap at a time, so the earlier strands would be revisited by the hot nozzle when they were significantly cooler. I guess its easy to say but may be hard to implement.

Any suggestions/comments would be greatly appreciated please.

 

[owen 19]

Hi rich

You could turn your model 45 degrees in Cura so the strands get put straight accross

Print much slower 50mm/second max

Only guessing but I think thicker layers may help

btw what is the Basalt bed like. Does ABS stick well to it?

 

[illuminarti 18]

Hi Owen! QU-BD is one of the main people I've seen selling Basalt beds, and my QU-BD Revolution XL printer has one. It's a little slow to heat up - takes about 11 mins to reach 95ºC with their standard silicon pad heater, but it's resilient, flat, doesn't warp, and both PLA and ABS seem to stick pretty well.

 

[rich 0]

Hi Owen & Illuminarti.

Thank you.

I'm not sure that the shorter distance would help because the melting occurs as the nozzle is going past the middle. The slower speed would be good to try but I can only do that by manually changing the g-code or changing the print speed for the complete model. I'll give both a try.

How can we change just bridging speed in Cura?

Your correct Illuminarti, the Basalt is the 200mm bed from QU-BD and it behaves as you say. Its very flat and great for PLA and ABS. My main complaint is that it takes ages to cool (? an hour - I'll measure it) before I can get the printed model off with a spatula. I use their silicone heater as well.

 

[maxtex 0]

We just need the so often requested bridge setting from cura 13.04 in the actual version! There are so many parts with bridges where I can´t use the new and awesome version of cura -.-

But it seems that the developer doesn't see the importance of this feature...

 

[owen 19]

Thanks illuminarti

I just ordered the 225mm X 225mm Silicon Pad from QU-BD

I wasn't sure about getting the Basalt bed.

I would have needed to get the 300mm X 300mm bed and I wasn't sure about cutting it either.

It does sound a bit slow for my tastes. It would be good to have 2 of them for swapping though.

btw Rich I found and old thread http://umforum.ultimaker.com/index.php?/topic/2241-nozzle-diameter-correction/

where Daid is talking about bridging and suggests a fast speed so not sure on what would be the best speed now.

Maybe you could find a bridging test model and experiment.

 

[rich 0]

Thanks for the link Owen.

It looks like a few tests are in order - I've cut much of the bottom off my existing model so its quicker but still totally relevant. But Daid's bridging sounds ideal, I would definitely be happy with a 120mm bridge capability.

 

[mastory 44]

Just an idea here. May be foolish, but might also might inspire something else. If bridging subsequent lines, maybe the bed could drop a mm for the bulk of the travel, and then go back to the normal Z height to connect the bridge at the other end??

 

[gr5 2,265]

If you are only worried about bowing (center of bridge sagging) then just tilt your UM onto it's side. The UM will print upside down or in any orientation.

But this problem where the head remelts the previous string won't be helped by printing on one's side.

 

[mastory 44]

Ive been wondering for a while why printing with the platform standing vertical isn't done to improve overhangs.

 

[gr5 2,265]

I've tried it and it doesn't help as far as I can tell. You just can't print an overhang in thin air regardless of gravity. For example if you are printing someone's head and are having trouble under their chin, tilting the UM onto it's back doesn't help much. But tilting the print *before* slicing does help of course.

 

[Daid 306]

You can put an Ultimaker upside down, prints look the same, which shows that gravity has little to no effect on the prints. Maybe bridges will act differently a bit. But I think with bridges it's the same as most other effects, it's all down to cooling.

 

[gr5 2,265]

which shows that gravity has little to no effect on the prints.

 

That is mostly true but with the below bridges (150mm!) there is clearly some gravity interaction that would be fixed if the printer was on it's side:

http://www.3dgeni.us/a-bridge-too-far/

 

[duesentrieb 0]

I think Daid is right. Cooling is the most important factor to take into consideration. Don´t have much experience with the UM, but I printed out a hollow dodechaedron on which the last part to be printed is a pentagon, means five briges to be printed at the same time.

Printing bridge one, the fibre looks like a rope bridge, but while printing bridge two it tightens, because of the cooling fan, when printing bridge three bridge one is completely tightened, bridge two tightens, and bridge three hangs at the beginning... So when the printhead was back at bridge one it was perfectly flat and so on... The print looked great. I had some problems with stringing, but that´s another topic.

I did not use the original fan mount. I used this fan duct: http://www.thingiverse.com/thing:17768

I like it. It has to be printed in good quality and mounted right, otherwise it might touch the hotend and melt away.

Maybe there are better fan mounts, but this one works for me...

Good luck.