Can 1.75 mm filament be used in a printer that takes 3 mm filament?
As an extension from this question, is there any reason that you would not be able to use 1.75 mm filament in a printer that takes 3mm filament? I know you would have to change the filament size in the slicing of prints but would there be any other problems?
Also, would using 1.75 mm filament be possible if the nozzle diameter was greater than 1.75 mm but less than 3 mm?
Perhaps you should restrict the question to a specific printer, and the part about the 1.75mm nozzle should probably be a question in its own right (though it is right on the edge of what I'd consider a good-quality question, considering the answer will just be "no").
I was mainly asking this as a hypothetical question based off the previous question I mentioned. For the 1.75mm nozzle, I added that part to clarify what I assume the answer to the first part will be. I assume that 1.75mm could be used, but only if it was smaller than the nozzle. if you normally were using 3mm with a 2.5mm nozzle, 1.75 should not work.
Typically an extruder and hot end are designed for one or the other, and cannot support the other without mechanical changes.
The extruder may not be able to grip a smaller diameter filament with enough force to assure even feeding and retraction.
The hot end, however, is much more complex. The filament has to be pushed with force into the melting zone, which means the filament has to slide along an area inside the hot end where the filament is plastic but still put pressure on the filament ahead of it.
When you put filament into a hot end, the filament softens before the melt zone, but since the walls of the hot end are just barely larger than the filament it has no choice but to continue pressing down on the liquid filament below.
With a narrower diameter filament, though, the filament can heat, soften, then travel backwards along the sides of the hot end and cool in place, jamming the hot end, or at least preventing an even continuous flow of plastic.
Some hot ends will accept a small Teflon tube that takes this space up and allows you to do this with fewer issues, and if you like to tinker you can experiment with this, but be prepared to learn a lot and fail a lot as you find out the hard lessons of hot end design.
Generally you should upgrade your entire extruder and hot end setup to the size you want to use.