PLA Bridges welling upwards?

can i get some advise on PLA bridges that are playing me up rotten.

I was getting dropping down of bridges. So i added some fans etc.

Now it seems its as if the fans are too much even though iv tried them as low as 80%.

When i print the pla seems to go down okay
Next line then pulls upwards then the same happens on the next line.
Untill the bridge is pulled upwards around 1 mm then it bands the hotend.

Im using a MGS extruder on an I3
Using 2 40mm fans pointed 45deggres down using prusai3 fan bracket

J-Head 5 0.5mm

PLA running at 195C heated bed at 62 (i have the same effect when running at 185C i like to run a little hotter to get a nice shine on the PLA)

im using slicer and i have even tried settings the bridge flow ratio at 0.6 and still have the problem

You will get better bridges if you print cooler.

The lifting upwards happens because the PLA contracts as it cools. Now that you have added fans it cools before gravity can do its work on it, so instead of drooping you get lifting.

You can try progressively dialing down the fan speed until you find a balance, this is probably the first thing I would try.

Looks like i might of found my problem (see attached pic)

designed a little stl to test the problem and created gcode in slicer for fan speeds at 50% 40% 30%

looking at it while its printing the bridges are not touching the one side of the bridge so that side wells up and then passes it on across the bridges next line.

does any one know if this is a known slicer bug?

I had alot of problems bridging with slicer. The problem depends on which version you are running. One version works ok then the next has a bug, then they fix that on the next version and end up with another bug. It never ends and you can spend alot of time trying to determine if your problems are the printer or slicer software. My advice, use a different slicer.

Can some one try printing the STL i attached above and keep and eye on the 1st bridging layer.

just incase its its the file as i have no idea why this is happening now

Ignore the last request

File does not have enough room for the bridge to cross over so does not touch.

I forgot when briding happens it gives around a 1 - 2 mm over hand of the hole so it has something to stick too.

slow down the bridge speed. this will lower flow rate what i think is happening is the pla is being laid down unevenly, perhaps micro slips in extruder feedstock. slow down speed bridges are done by at least 30%. see if that helps. you want bridge feed rate to be as slow as possible without oozing effects. somewhere between 30-40mm/s max.

tried everything i can think of now.

tried slower speed and fan no difference.

Any one else using the MGS with PLA and a fan?

any chance someone can print the attached file im using and take a pic as its printing the bridge layer?
prove its not my file