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dezorian

Blob at the end of a print

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Hi,

I have the following problem:

when printing this file head.jpg I always get a blob at the end like this: blob.jpg

I tired the same file on a makerbot (orange one) and it printed correctly. that leads me to the fact that the file is ok. Taking a closer look in cura i noticed some larger paths at the end of the object in the layers view cura.jpg.

No matter how i position the object, cura always make an extra extrusion of filament at the end. The print is perfect till the last 1 or 2%.

Has someone a solution to this problem?

I have used these settings: settings.jpg

 

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There could still be a problem with the file. Different slicers deal with file errors differently. A file that works fine in cura might not work well in MakerWare and vice versa.

Regardless of that I'm guessing there's also a cooling issue. On small tips like that the right fan of the UM2 tends to miss the target (as the nozzle is off center). Consider printing two copies of your object at once and also make sure that your fans are going full blast when the printer reaches the tip of the print. You could also try decreasing the print temperature if you can do that without causing under extrusion.

 

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I think this is a problem with the newer Cura versions. I get this smeared top (albeit not that bad) on all objects with a round top. However, I have other objects here that were sliced with Cura 14.02 or .03 and they are fine.

One way to circumvent this issue is to either use the "Cool head lift" feature (but then you'd have a seam of surplus filament on one side).

 

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What is happening here, is that the nozzle is moving so slow, that it's melting the layers below it. The material is also flowing out faster then intended, causing it to blob more.

A work-around is to use the tweak-at-z plugin to lower the temparture around the height where the chin is. This should help a bit.

In the future, I would like the temperature to be speed related. But figuring out the correct parameters for this is quite complex.

The cool-head-lift feature could help. Or printing multiple at the same time. As this gives each one time to cool down, and then the head does not have to move as slow as it does now.

(The paths you see in the layer view are because of a viewer optimization, only the top X layers are drawn full, the others are drawn with thin lines)

 

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Thanks Guys.

I think that the Temperature ist not the problem, else the nose would have warped down. But I agree that the fan position are not optimal due to the asymmetrical arrangement. Maybe there is a printable upgrade to optimize air flow like the ones on the UM1.

I also think that it has to do with cura, especially with the gcode flavor: UltiGcode.

I printed the head on a UM1 with gcode flavor: RepRap (Marlin/Sprinter) and I worked much better as u can see

um1.jpg

There is still a dot of filament but i could easily remove it with a knife.

Also in the preview of cura the amount added at the end was less but still visible. I have tried these 3, you can see the differences:

cura1.jpg

I dont know if unchecking the horrible fix a/b changes something but in the preview there is no difference. I have to try a print.

In the past I encounter this problem with the UM1 but this was because the nozel didnt got out of the way at the end of the print fas enough. Wich I could altered in the end gcode. Problem is with the UltiGcode that you cant see or write the code. It only is visible when you select RepRap marlin.

Therefore this must be to 99% a sofware/code problem.

I own a UM1, UM2 and a Replicator 2. I also had few moths ago the new makerbot replicator fifth gen wich i send back because it was a piece of shit.

In comparison I must say that Makerware is much better in handling Prints. I almost never got a fail print. With the UM / cura its always a guess work why things dont print out as planned. But the print quality is by far the best I have seen. Especially with 0.060 layer height. It´s like a resin printer.

Well I will keep trying to solve the problem, I appreciate any suggestion If you get a solution for this problem.

 

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In the future, I would like the temperature to be speed related. But figuring out the correct parameters for this is quite complex.

 

There is a plugin which tries this already (Flowthermostat). However, I needed quite some time to find the right parameter as you indicated. One of my long-term plans is to dive into the physics behind that plugin in details.

Don't get me wrong, I fully support your idea. But I think a clever temperature regulation is more complex than 'just' match temperature and speed. For instance when you have a lot of small surfaces to print (lets call it struts), the total area might be reasonably large for a higher temperature. However, print quality would improve if they were printed more slowly and at a lower temperature while you can speed up for large scale structures.

And you will always have the issue of the heat capacity of the hotend. It is significantly larger for the UM2 but with the UM Original hotend it is definitively an issue you cannot neglect.

 

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Thanks Daid,

indeed this sounds logic.With the UM2 I had and have temperature problems when printing. I always have to identify the perfect temperature for each filament that I have. Especially with colorfabb filaments, wich melt like butter (print some of them at 178C°). I print slow and with high quality cause thats the only way I get resin like prints.

However I also suspected that the hot air flow caused by the heated build plate and the nozzle itself put some extra temperature on the print. The layers dont cool fast enough and the temperature form the layers above spread to the lower layers causing them to store heat. At about 2 mm heigth the print starts to behave like chewgum. Which end always in a fail print. This happen to me on the UM1 and UM2.

Does cura calculate the heat from the nozzel at low speed + the 50-60c° hot airflow when setting up the gcode?

How do I set up the cool-head-lift, cant find it in cura?

And how about the cool minimal layer time, do the layers have extra time to cool if i increase the sec. to lets say 10?

 

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AFAIK the plugin looks for a temperature command in the gcode. Thus, I wouldn't expect it to work with UltiGCode.

But if you switch the flavour to 'RepRap', then it works as on an UM Original. Of course you will habe to use the Cura settings for temperature, filament diameter etc. then.

 

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