For a long time, I haven’t used any springs on my extruder, and it also worked just fine with the ABS I was using, which was nice and round.
Then I bought this orange filament, which is a bit oval. The extruder is still working fine, and I haven’t had any problems with it slipping, but I still wanted to get some springs on the idler, just in case.
After a bit searching for springs, I found absolutely nothing I liked, and I started to look for alternatives instead.
What I found, was rubber O-rings! They are compressible, easy to get, and also very cheap (~£1.5 for a 200 piece set on eBay)
A week has passed and I had around 15 hours of printing, and I have had no problems at all with this system. So I would say, O-rings is a usable alternative for springs! 🙂