Fan doesnt't work at low speeds

[Muko 0]

Hello, 

when printing ABS with my UM 2 +, I allways have the problem, that the layer fan doesn't start after printing the first layer. This just happens when the speed isn't 100% like I use for PLA. I just Updated to the latest firmware, that cames with cura 3.1 and there isn't any difference. 

Someone an idea? 

[gr5 2,172]

Play with the fan speed in the TUNE menu.  I find 30% is a safe speed for me where the fan always comes on and it's not too fast for ABS.  Your machine may be a bit different.  Also note that on the UM2 there is this strange interaction where you can set a material "fan speed" and also a fan speed in cura and the two speeds are multiplied together.

 

So if you have it at 50% in cura and 50% in materials menu you end up with 25% fan speed (which usually gets things spinning for me).

 

ALSO be aware that cura defaults to zero fan on the bottom layer (which is advised for both PLA and ABS) and then the fan comes on gradually over several layers.  So maybe you just didn't wait long enough.  You can make the fan come on sooner in cura in the fan related settings.  The reason it comes on gradually is so the nozzle doesn't get too cold too fast but for ABS where the top speed is probably 30% this is completely unnecessary.

 

[Muko 0]

Thanks for your answer. I just tried with 35 and 40 percent and nothing happens. Afte the fitst layer the fans starts turning for half of an second and the they switchbof and stay off for the hole rest of the print. I can try higher speeds, but this would be to much for abs. 

[gr5 2,172]

Did you play around with the fans in TUNE menu during the print?  Maybe you didn't experiment enough?  How do they do at 100%?  What is the minimum speed if you start at 100% and go downwards?  What is the minimum speed if you start at 0% and go upwards?

[Muko 0]

When I switch them on in the menu during the print everything works fine even at 20%. This makes me think its an firmware issue

Edited January 19, 2018 by Muko

[gr5 2,172]

It's not a firmware issue.  Does it work at 20% if you start slowly at 0% and move towards 20%?  where EXACTLY does it turn on.  You want to pick a value above that because what happens is the first layer will be at 0% and then gradually increase as per cura settings until it gets to full power which may indeed be 20%.

 

BUT ALSO it's multiplying these values with the Material Fan setting in your material menu on the printer itself.  You want these 2 values to multiply out to a value well above where the fans come on if they are increased very slowly.

 

Note there is a feature in the firmware if you go from 0% to 10% it gives the fan 100% for some portion of a second to get them kick started.  But if the final value is 10% and the fans then stop, and then later the fans are increased to 15% it doesn't do that kick start feature the second time.  It only does the feature when starting from 0%.  So Cura makes this feature useless because cura increases very slowly each layer for the first few layers.

 

Is all this clear?  Please experiment more.  I want to know where your fans come exactly on WHEN YOU INCREASE SLOWLY - NOT WHEN YOU DECREASE AND NOT WHEN YOU INCREASE QUICKLY FROM 0%.  If the answer is 19% then you need a higher value than 20% to be safe (maybe 25%) but in cura you probably should set it to 100% and in your material settings you can set it to 25% for ABS.

 

But when in the TUNE menu it doesn't do these multiplications.  It just goes directly to what you request.

 

Also when you enter TUNE menu it shows the % fan it was told to do (cura gcode multiplied by material fan %).

[Muko 0]

Ok, I tried it and the fans starting at 19%

So I cura that the minimum speed is 100%. The material settings in the printer was at 25% "and it worked. But I still dont get why it doesn't work when I start with 20%. It should start turning  after a while. But it doesn't, even if the print takes 10h...