Minimal Layer Time Question

[entomophile 9]

I am trying to print something tall and thin and it is coming out looking kind of melted. I increased my minimal layer time to make sure each layer had time to cool, but it doesn't look like it changed the print any. I set the minimal layer time to 30 seconds but each layer does not take that long to print. Even in Cura, when I double my layer time setting to 60 sec, the total print time doesn't even change. What am I missing?

 

[tinkergnome 927]

I assume that Cura ignores these settings during the calculation of the estimated print time - so don't worry about this.

Do you have pictures of the failed attempts?

First you should try to print with a nozzle temperature as low as possible and with the fans on 100%.

And you can try to fiddle about the "Cool" section in the "Expert config" Dialog - especially read the hints for "Minimum speed" and "Cool head lift".

Additionally the possible results for those tiny parts are often depending on the print material...

Good luck and keep us informed!

 

[jweaver 2]

There s also an option for minimum print speed, which over-rides this option. (Look under advanced options)

If you want to let small layers cool, there is also,an option to do "cool head lift" which will stop printing between the layers until the time you set is reached, but this can lead to "oozing" whilst it waits.

You just need to find the sweet spot by playing with these 3 options.

[gr5 2,270]

it is coming out looking kind of melted

 

For PLA usually 3 seconds is enough. 10 seconds should be enough even on a very hot day.

Anyway please post a picture. What you call "looking kind of melted" we probably call something totally different. Like "pillowing" or overextruded or underextruded or "too much overhang" or who knows what.

All I know is every time I guess what people mean, once they post a picture everyone is like "oh - wow - that's not what I thought you meant".

 

[entomophile 9]

OK, here's a pic. Material is PLA. Cura is version 14.09.

The print on the left was done at 205C with the high quality defaults. The middle print was done at 200C with the high quality defaults. I lowered the object in Cura to just print the bad part over. The print on the right was done at 200C with a 30 sec minimal layer time, 0.06 mm layers and 20 mm/s print speed. As it was printing, it was just printing one layer after another, in much less than 30 seconds.

 

[tinkergnome 927]

OK, here's a pic. Material is PLA. Cura is version 14.09.

 

Looks ugly... :-)

Ok, some additional suggestions -

- consider updating the Cura version

- what is the shell width? Have you tried thicker walls and/or more infill?

- try to print more than one piece at a time (it doesn't have to be the same model)

There are ever possibilities for the real tinkerer...:-)

[peggyb 171]

for these small tops you can use the 'cool head lift'. this will leave some stringing, but that can easily be removed afterwards.

Another option is to print two of them next to each other with the 'print all at once' option (under tools). That will give each layer enough time to cool before the printhead returns.

 

[entomophile 9]

- consider updating the Cura version

- what is the shell width? Have you tried thicker walls and/or more infill?

- try to print more than one piece at a time (it doesn't have to be the same model)

 

Funny, I thought I had the latest version of Cura! I check the update software option in Cura often, and it always tells me I have the latest version? I had to go to the Ultimaker downloads page to get the latest version.

Shell is 0.8 mm with 20% infill.

I updated Cura and the firmware on my UM2 and tried again. Same result. The minimal layer time function just isn't working. Every layer prints one after the other, about 1 sec per layer. I know there are other ways to get a better print, but that doesn't explain why the minimal layer time setting isn't working.

I ended up printing 3 at once and spacing them out on the build plate to force a little more cooling time. That gave me a pretty good print.

 

That's OK for a small print like this, but that won't work on a larger print. I'd really like to get the minimal layer time function working.

 

[gr5 2,270]

I'd really like to get the minimal layer time function working.

 

For something this small, printing slower won't help because the head will be touching the part and transferring all the heat into keeping the PLA melted kind of like a soldering iron.

Anyway I think someone answered your question and you missed it. Under "expert config" in the "cool" section there is a setting called "minimum speed (mm/s)". You need to set this to zero or it overrides "minimum layer time".

 

[gr5 2,270]

Also I would put the 3 parts much closer together to minimize stringing. You probably wanted to increase the layer time by making the head move farther but that's not necessary as you really only need about 2-3 seconds cooling time per layer.

Also if you are really clever you can have the fans on the side cooling one part while printing the next.

 

[entomophile 9]

There s also an option for minimum print speed, which over-rides this option. (Look under advanced options)

 

Ooooooh! I mis-read this to mean the print speed under the expanded settings. I set the minimum print speed to zero and now the minimal layer time function works. Thank you all.

However... As you already know, the print looked like crap. I thought minimal layer time would print a layer at the set print speed, then pause and wait the remaining minimal time until it started the next layer.

For those who don't get it like me, minimal layer time slows down the print speed so the entire layer takes at least as long as the minimal time to print. So, my printer was trying to print a 3 mm cylinder over 5 seconds, and it ended up a big plastic blob.

So, is there a way, when printing small or thin objects, to get the printer to wait a second or two before going to the next layer?

[gr5 2,270]

lol. Yeah that was also mentioned above by peggy I think. "cool head lift". But like she said - you end up with lots of strings. Putting a tower slightly taller than your print, next to your print is a much better option. Or just print 2. Or 3 like you did.

 

[peggyb 171]

the stringing is easy to remove,

in the picture: one tower without cool head lift, the other with.

These were printed separate, height is about 4 cm.

 

[Daid 306]

the stringing is easy to remove,

 

And on low temperature, the stringing shouldn't be that bad at all.