Those of you with a Prusa MK2/3, do you use a glue-stick or something when printing with flexible filaments? I’ve been trying to print a test with this 3D Prima flexible filament, but it always comes loose from the printbed. All the instructions I’ve seen claim that flexible filaments stick so hard to the printbed that you’ll damage the PEI-sheet unless you use glue-stick or similar on it, but since the prints come loose, I don’t really see what option I have other than trying without.
Not prusa, but: I’ve been printing with wax and had a horrible time getting it to stick. Glue sticks didn’t do it. Blue masking tape and spray adhesive, specifically 3M Super 70, did, hard enough that the tape came off the bed and I had to razor scrape it off the print.
I almost entirely use Ninjatek brand for flexibles, and mostly Cheetah filament. In my experience it sticks too well to the PEI so I apply a thin coat of glue with Elmer’s Disappearing Purple glue stick. I’ve found normal Elmer’s or UHU don’t work as well.
@Adam_Steinmark Well, I suppose I’ll have to try that unless I find some other solution. Too bad it takes months to order anything from the U.S. 
I use blue tape from 3M the adhesion is good and I don’t risk to damage the PEI.
Since it was mentioned twice I’ll give my 2 cents on 3M tape. I used it a lot starting out and it works really well but only lasts a few prints at most. It gets to be an expensive consumable if you use it for every print, not to mention a hassle to apply every time.
Instead of glue stick you can also use normal white or wood glue diluted in water that you brush on the surface. Wood glue is normally made up of PVA, which is also what they use in the “working” glue-stick brands.
I decided to give the glue-stick one more try before I go and buy anything else and this time it seems to be working, at least so far – it’s still printing. The trick seems to have been in applying the stick very, VERY liberally, like almost half a stick!
I’ll try to find some wood glue to try with, maybe it’ll work better.
Oh, and if anyone else should happen to be using the 3D Prima PrimaFlex, I took the flexible filament - profile that Prusa’s tools come with and modified it to use 250C nozzle-temp and 90C printbed, otherwise keeping the other settings the same. It’s probably not optimal, but seems to print well enough.
Odd – I print in Ninjaflex and Rigid Ink TPU and in both cases I need to coat the MK2 and the MK3’s bed in PVA. I know I need to as occasionally when I restart a print I forget to re-coat the front of the bed where the filament is purged, and it’s then really difficult to get that off afterwards.
And this is with no bed heat – heated bed switched off, and there’s zero chance the print will come off mid-print – it sticks almost too well even with the PVA.
@Nita_Vesa It doesn’t have to be Elmer’s. I think most locally bought glue sticks can work, it probably has the same chemistry. For example, I’ve seen people say Pritt sticks work.
If you have to apply a very thick layer it sounds like your Z offset might be too high. Does it look like the nozzle is displacing the the glue or printing right on top of it?