Bridge Torture Test

by triffid_hunter, published

Bridge Torture Test by triffid_hunter Oct 26, 2011

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See if the circle on the bridge comes out ok!

Struts are hollow to speed printing.

My test with this show me that I must print bridges slowly!


1) print
2) observe bridge
3) adjust bridge settings
4) goto 1 unless great
5) observe quality of circle
6) fine-adjust bridge settings
7) goto 1 unless excellent
8) ???
9) profit!

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I am not able to get a single string across the two towers. The filament just sticks to the nozzle and forms a blob. Does anyone have any suggestions to how I can get a bridge ? I'm printing at 0.1 mm layer height.

The trick is to slow the bridging speed to 28mm/sec, use a flow ratio of 0.85 and to tweak the temperature very carefully.
2 degrees celsius makes a difference.
Good results: http://www.thingiverse.com/make:80768http://www.thingiverse.com/mak...

thanks for the tip, got me closer to achieving it but still getting a sag with 1.75 ABS, not sure if its my bed temp that is too high. first layer is 120, then dropping to 100. extrude temp at 242, flow rate as per your recommendation. have tried multiple at different temp still not there:(.

you succeeded in between?

yea I did..I found the trick is to have a fan blowing on the print when it starts bridging. I'm printing on Kapton tape and my settings were 245 extruder temp, 100 bed temp, abs 1.75: .2 layer height and 0.85 flow ratio and speed 28 mm/s.
Are you managing?

simplify3d you use?
if yes? you can send me your setting to better configure mine
thank you

I find it hard to configure bridging :(

Jul 16, 2015 - Modified Jul 16, 2015
MiksPrusa - in reply to boolat

I use Slic3r through repetier host.

Hmmm, what are are your bridge settings? and do you have a fan?

Jul 16, 2015 - Modified Jul 16, 2015
boolat - in reply to MiksPrusa

unsupported area threshold 50,0 sq mm //
extra inflation distance 0 //
bridging extrusion multliplier 100% //
bridging speed multiplier 30% //
fan yes davinci no off ! //

try with your bridging extrusion multiplier at 85% and make sure your fan is on for bridging

yea I did..I found the trick is to have a fan blowing on the print when it starts bridging. I'm printing on Kapton tape and my settings were 245 extruder temp, 100 bed temp, abs 1.75: .2 layer height and 0.85 flow ratio and speed 28 mm/s.
Are you managing?

Sag is when the temperature is too high and the plastic is drooping because it is too liquid. Lower the temperature at 2 degree increments. You'll know the temperature is too low if the plastic is not sticking on the ends.

You can also try increasing your bridge acceleration and speed. I get better results with ABS when I increase bridge speed and better with PLA when I lower it and use a fan. YMMV

Hi Bruce... Did you try giving it a 10mm Brim? I haven't tried printing this item, but from experiance of Slic3r (which is good BTW) it does try to print a circular hole with no support normaly. On items similar to this I have (if there is good access to the hole area) made some sort of support for the hole, like having a thin square hole, or have the hole not go quite all the way through...

For some reason slic3r would remove the pads under the columns which would end up with the piece coming loose during print. Had to switch on rafts. Not sure why it did that. I was slicing at .2mm layer height. Anyway, it worked with the rafts and printed out fairly nice.

Do you know that this doesn't want to print correctly on Cura? I think I'm going back to Slic3r. I've had a lot of good prints with Cura, but in the end Slic3r still seems to outprint it...

All the small details simply are ignored by Cura, the ring on top? It doesn't even generate gcode for it! Printing with a 0.5mm nozzle.

Also, it messes up infill and it has very illogical ways of preheating (first hotend and after the bed, while it should be the other way around, I hate to let my filament cook).

Tomorrow I will try it again with Slic3r. Cura also wants to print this too fast and too hot. Let's see what Slic3r does :)

I'm having the same problem as related by Panda762. The bridge perimeter is being treated as perimeter and not bridge, so it prints slowly and doesn't follow bridge settings (I tried to use a bridge flow of 0.3 and it is still printed with a perimeter's flow). The inner strings are just fine, a perfect bridge.
Again, if I have "perimeters (minimum)" set to 2, I´ll have 2 sagging strings on each side and 4 or 5 perfectly bridging strings in the center.

and how did u fix it?

Updating Slic3r!

printed brilliantly, will post picture later. No change in the setting what so ever with my MakeGear Mosaic printer.

90% of the printtime on this is those long struts.
Is it really that important to discern sag of 2mm and sag of 10mm?
3mm tall struts would be plenty I think.

I couldn't print this one since the bridge flow ratio settings seems to be ignored at least since v0.8.4 to 0.9.9, Any clue?

Thanks for posting this Triffid. I thought I was going mad or there was something weird about my extruder when I realised that going faster was not better for bridging.

It makes some kind of sense if you think about the extruded bridge filament needing enough time to freeze behind the nozzle so that it doesn't sag as much under its own weight.

This thing gives me Headaches, did about 20 of them going back and forth with the quality.......guess i have to keep tryin. Some of the "i made em" pictures are just so amazing precise and clean....wow. Using a Beta Prusa Deluxe with Printrund and Slicer 9.9. But even with the secret Weapon Cura it didnt work out :( The first strokes of the Bridging are done with very slow nozzle movement, seems like they are treated as Perimeter not Bridging??? Then after a few lines it starts to switches to bridging speed, but than i already have drooping and slacking lines. The bridging works fine but the nozzle often destroys the fine lines when it goes over them a few times.......ARGHHHGHGH

Panda762, I´m having the exact same problem, have you been able to print it correctly?

Replicator 2 did it perfectly right out of the box

Pics/vid or it didn't happen.

One thing I have found when calibrating is that not only do the speed and flow rate need to be changed, but also the temperature. My original settings were not hot enough, so the plastic would be so viscous it stuck to the nozzle. Good luck printing!

I dialed my TOM in and bridging is far better then it was before I calibrated. My issue now is the initial strings are good and straight but when subsequent material is put down on top of those initial strings there is some sag. Do I continue to dial the speed down (at .5 for bridge flow rate multiplier) or is there another setting?

you need a fan to cool and solidify the bridge before the next layer goes on top. It sounds like it's still molten and gooey when the next layer is done at the moment

yeah, that is what looks like is happening. will try a fan.

I didn't found the perfect settings for the Huxley (not much improvements either by lowering or increasing speed), but will try again later :p

Do you have a fan blowing on the print? That helped a lot for me.

unfortunately not yet, I hoped to make a nice bridge without but I'm considering to had one since I've some more pins for that on the sanguinololu

I'm currently printing a 6th one now. Is there a guide to help with this?

if your strings droop, lower the flow rate. if they snap, increase flow rate.

if they don't stick to the towers, reduce speed.

please write a more elaborate guide if you work something out!

I have the settings making perfect bridges but the fill comes along too fast and the weight seems to overload the strings. Any tips?

hm, dial down infill speed perhaps?

Adding fans can help immensely, one of the reasons the bridge droops is that it's still soft when the next layer comes along

+1 on the fan.

I didn't find it necessary to slow down to get this bridge printed. In fact, I didn't change anything! I printed with my usual settings of 52 mm/sec perimeters, 130 mm/sec infill, and active cooling.

Very nice bridge on the last... what were your settings (only tweaking bridge feed/flow?) before and after ? :)

the last one was printed with LH=0.2, feed=80mm/s, bridge feed=0.2, bridge flow=0.15 but of course it'll be machine-specific!

LH=Laier Height, feed is in speed, bridge flow in advanced, but where is bridge feed in slic3r?

of course, but good to know that you were slowing.

In fact I was thinking the exact opposite, making bridges faster, will try...

I had to slow otherwise the bridged strings wouldn't stick at either end! might work better with a larger layer height at higher speeds

Do you know you nozzle size? And perhaps width over thickness setting? I'll give this a go on my next run.

slic3r will automagically work out suitable settings given your nozzle diameter and chosen layer height. This is probably just as much a test of your cooling as anything, bridges need to be cooled quickly :)

Am I right that you actually did that bridging in the picture with PLA?

yes, that's PLA.

I wasn't aware that there was a difference in bridging between PLA and ABS, care to elaborate?

I know that this is a stale thread, but this is still a really popular model for people calibrating printers, so I thought that I'd respond.

ABS is generally printed without a fan. ABS expands and contracts more than PLA and the prints will tend to separate if you use aggressive cooling. Using a heated bed helps reduce the temperature gradient between layers and allows the print to slowly contract as a unit. Some people take this even further and create a heat box around the entire print area to keep the ambient temperature up until the entire print is complete. Others print a full height wall around the print to channel the heat from the bed up into the higher layers.

You can still get the bridging to work, but it's a real balancing act between temperature and speed. Slow bridging doesn't seem to work well for me. I've had better results dropping the temperature until the threads start snapping, then add 2 degrees and increase bridge speed until they snap or sag. Repeat until you get the right balance. I actually find your model to be one of the best ways to dial in filament temperature.

On a Printrbot Simple Metal with an E3D, my bridge acceleration is 700mm/sec^2, Bridges at 125mm/s and between 206-227 depending on the color of the ABS. 2 degrees below optimal and it will be a mess of gaps. 2 degrees higher and I have a mess of loose threads underneath (though those can actually be fixed with a quick brush of acetone). My room temperature also tends to make a big difference. Unfortunately, it's really hard to crank my heated bed above 90C, so I'm always printing cooler than I probably should.

It seems that there will be much torture before I even start printing my first non printer related part. I hope my repstrap will have a high pain tolerance when it's complete...