Great post - I rarely edit a post but I did yours - hope you don't mind. Let me know if you want me to revert to original. I did some bridging tests also recently but your zoom-in-photo is fascinating! It makes me think Cura should output a little extra flow for the first 2 millimeters maybe?
Currently post #17 (but that will likely change within a month):
http://umforum.ultimaker.com/index.php?/topic/1872-some-calibration-photographs/?p=25304
1. For well spaced threads, those that fail to survive do so because their thickness drops to zero just after leaving the starting wall (not the destination wall). This seems to be reduced if the overlap on the wall is reduced.
2. For closely spaced threads (ie. where the hot nozzle may contact the previous thread) failure rate is very high at high print speeds but at low print speeds 2 or 3 adjacent threads tend to amalgamate to form one.
Wow. First of all, your photos don't show #2. Did you do many more tests? Can you upload more pictures to the same album - put notes with each picture that describes what it is showing (if you have these pictures already).
For example is there some way to have Cura place comments in the g-code at the beginning and end of bridging?
Oh! Daid please! Please add comments to show each individual bridge line! That way this guy can write a plugin to do some experiments to improve bridging string strength!
Great research, Rich! I've been meaning to do something like this for a while, and just never managed to fit it in.
Your post gives me all kinds of ideas. It's common to have under-extrusion during acceleration (start of a string) and over extrusion at the end. This is caused by the delay between when you ask for more filament and when it comes out (delay mostly caused by bowden tube and other stretchy/springy physical elements).
This "error" is reduced if you print at slower speeds but should also be reduced if you greatly lower acceleration parameters. So I'm thinking that simply lowering the speed when you get near a bridge would help. Also lowering the XY acceleration for the section of print that involves a bridge might help. You want to lower it a LOT. I would lower it to about 1/10 of the current value for a test.
I have many experiments on my list right now so I might never get to this one, but this is very intriguing!
Jonny - thanks for your comments re using the gallery.
gr5 - mind? Thank you. I do have more images and there are a few more experiments to come. I haven't looked at acceleration settings - excellent thought. My comment #2 is illustrated in #2 image. Counting from the right, threads 7 & 8, 9 & 10 then 11 & 12 are amalgamated (see bottom near wall).
threads 7 & 8, 9 & 10 then 11 & 12 are amalgamated
I see that now. I thought maybe you printed closer together in another experiment (.4mm apart) to be more realistic with what Cura does. Didn't realize they would cling together like that even though so far apart.
@rich and gr5:
When you did your bridging tests, did you ever have the problem that the first few lines of the bridge layer did not stick to the bridge head but curled along the nozzle?
I'm just on the way to get really nice results with bridging and this is (hopefully) the last obstacle... it occurs after I cleaned the nozzle from old PLA...
Never. The first bridge line was *always* perfect. But then the second line sometimes destroys the first line.
I would look at your nozzle tip under a powerful magnifier (or just reading glasses). You may have somewhat damaged your tip.
edit: they cost < 5 euros including shipping so don't get too upset if you did.
edit: they cost < 5 euros including shipping so don't get too upset if you did.
You're certainly not talking about the Ultimaker store, are you? If you know such a source, I would really be interested...
They are on ebay here in USA but I would try UM first and if they don't help you, contact "Illuminarti" - send him a personal message. Post #5 above.
Never. The first bridge line was *always* perfect. But then the second line sometimes destroys the first line.
I an idea I had last week from another post about bridging. To keep subsequent bridge lines from destroying the prior lines, how about lowering the print bed slightly after starting the bridge, then dropping back down at the other side to make the connection. This would help keep the nozzle away from the prior laid lines.
Also, why doesn't the first bridging layer always pick the shortest possible unsupported span?
Also, why doesn't the first bridging layer always pick the shortest possible unsupported span?
I think it does. Cura detects bridging and usually seems to do the shortest span - I'm not sure if that's always true but it was for my part. The part above was printed with excel, not Cura. Re-read that post.
To keep subsequent bridge lines from destroying the prior lines, how about lowering the print bed slightly after starting the bridge, then dropping back down at the other side to make the connection.
I was thinking the same thing. This might help the shape a bit also. Kind of like pre-stressed beams.
OK, you know how it is... if something doesn't work as you think it should, you have to stick with it until you got the case solved...
For me, this was the case today with bridging. After I found out that the nozzle was still ok (I will anyway organize some spares, you never know what's happening next...)
and the curling of the extruded filament was due to insufficient adhesion of the bridge layer on the previous one, I found a way to produce nice bridging - even with the standard Ultimaker fan!
The model is the well known one from Thingiverse (no. 12925) with 5mm instead of 10mm height (as I wanted to see my Ultimaker doing brigdes not struts... :wink:).
Your post gives me all kinds of ideas. It's common to have under-extrusion during acceleration (start of a string) and over extrusion at the end. This is caused by the delay between when you ask for more filament and when it comes out (delay mostly caused by bowden tube and other stretchy/springy physical elements).
This "error" is reduced if you print at slower speeds but should also be reduced if you greatly lower acceleration parameters. So I'm thinking that simply lowering the speed when you get near a bridge would help. Also lowering the XY acceleration for the section of print that involves a bridge might help. You want to lower it a LOT. I would lower it to about 1/10 of the current value for a test.
gr5, you mentioned two ideas in your post. You were perfectly right with both of them (thxs). I reduced the x/y-acceleration by a factor of nearly two magnitudes for the bridge layer. And I gave the extruder an extra kick at the beginning of the bridge layer by adding a small amount of extruded material. I did it with Cura 13.11 by using an experimental TweakAtZ plugin as very special conditions are needed for the bridge layer.
However, the sticking together of the various strings is indeed a problem and for my cooling fan setup unavoidable as the standard fan has to blow in lateral direction in order to cool the strings in both directions. It would require a different cooling setup (two fans and/or special fan duct). Thus, I lowered the print temperature to the pain level, i.e. 185°C, but only for the bridge layer as I got underextrusion for the rest when printing everything with that temperature.
@rich: what cooling fan setup did you use for your tests?
Could you tell us exactly what acceleration you went to? I think the default might be 9000.
I used 100. But it was just a very rough setting as 1000 turned out to be not effective... I did'nt try any other numbers yet.
For the previous and the following layers I used the default value...
I don't think you can change the acceleration that precisely. Marlin plans out many segments in advance. That's why when you change the speed setting on the UC it takes a little while before anything happens. The same is true with acceleration settings. So you have to adjust accel something like 30 line segments ahead of time.
What do you mean by precisely? Precisely in time or precisely in value?
I just had another look at a video I made during the print and I do not see a huge difference in the different movements of the bridge lines which means the acceleration changes more or less instantanously. The same thing when changing back to 'normal' acceleration: the printer runs racily again at once...
Marlin plans out many segments in advance.
I'll never play chess against my Ultimaker... :wink:
>Precisely in time
Precisely in time. In other words if you send a gcode to change the acceleration (or do it from the front panel) it seems to happen about 10 line segments *after* that gcode because Marlin has already planned 10 line segments in advance.
I don't know if it's exactly 10 or if it's 20 or what. But I would guess between 10 and 30 from my experience with how long it takes to speed up or slow down when you mess with the feed rate. It's the same amount of delay.
Edit: changed "cura" to "Marlin". I meant Marlin.
Now, you confused me... :wacko:
Who is the big planner: Cura or Marlin?
I had some further looks into the GCODE generated by Cura. The first bridge line is the second segment of the bridge layer; there is just a very short segment before on the bridge head.
This is the video I made during one of the various test print runs (don't worry about the fan noise; there are other devices than the Ultimaker running in the same room):
You may see or rather hear that the acceleration is indeed not excactly constant for all the bridge lines. However, the differences are quite small as the acceleration change from 9000 to 100 and back is a huge leap.
I meant "Marlin". I fixed the post. Thanks for pointing that out. Yes, you are right - you definitely were successful in changing the acceleration.
Very impressive video Dim3nsioneer.
I've not been able to get the g-code M201 to have any effect on my printing. I haven't used plugins - for my test setup I add them to the g-code in a spreadsheet. You are clearly modifying Amax X and Y. I tried lowering acceleration to 800 but the printing is unaltered. Neither have I had any success with M203 - I would like to try to increase the maximum extrude rate because the bridge threads at 150 mm/s are thinner (0.1mm) than those at 20 mm/s (0.3mm) and a bit of arithmatic says the default value of Vmax e of 25 mm/min will not supply the material required at the higher speed. I'd be interested in pushing as much plastic as possible through the nozzle.
Any suggestions on why these g-code are not being executed? What version of Marlin are you using?
Re the fan .. I use the standard fan. I also use a 50W quartz halogen desk lamp just above and to the side of the printing. I've not succeeded getting it on film but with the naked eye I'm convinced it keeps the bridge threads straight and in the nozzle plane. When the model is cooling the threads buckle out of that plane and move significantly with even minor air currents.
I use a Marlin version downloaded from http://marlinbuilder.robotfuzz.com/
I made the download on the 14th of October 2013 so it must be the Marlin version from the 7th of August 2013 as it is still this version there.
The plugin does nothing else than just to add 'M201 X100 Y100', as if you would insert it manually... as Cura plugins do not change the world but make it more comfortable... :cool: So the difference has to be somewhere inside Marlin... which is absolutely not my area of expertise...
If you have an Ulticontroller you could try to alter the Amax X and Y there...to see if your Ultimaker just ignores you or not.
Thanks. I have an Ulticontroller I'll give that a go.
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jonnybischof 60
I'm very interested in this research, and the pics
Why not create a gallery for them in the forum? Then you can put them into your post..
I've had problems with much shorter bridging parts, which is why for now I always construct my designs without any bridging, or with as little as possible...
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