Like the topic says, could the pulleys and idlers for the Lowrider v3 be 3d printed? Or do they need to be metal?
For the idlers, you need something that will be as smooth and consistent, which basically means bearings, which more or less need to be metal. Printed plastic might work for a while, but will wear quickly.
I have a bunch of the bearings that are about the same as the 20T idlers that we use with a 5mm bore, but 2 of them cost about the same as an idler, so why would I put up with even a slight irregularity in the belt surface?
For the motor pulleys, maybe you could do it of you have a super precise printer. It would be weaker than the metal part, sure, but should have no friction surfaces. You will be limited in the strength of a grub screw, but maybe you could make the opening a D shape like the motor shaft.
Any wobble though will introduce inaccuracies in the machine. This would be a very picky part to print.
The most I’ve ever tried is a 5mm motor shaft to 8mm lead.screw coupler, which was a stop-gap piece until I could get a real coupler shipped to me. I think it worked well, and was in place for about 4 days.
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I bet you could get pretty far with 3DP idlers and pulleys.
The idlers are in compression. They move slowly and the motors are pretty strong.
The pulley teeth and the connection to the motor shaft are what worry me the most. If there is any slop, you will have backlash. Backlash is a pain to diagnose.
But, I am sure it would work for a plotter, and if you had a good reason to do it, then go for it.
My question to you is, why would you want to do that? Are you having trouble sourcing them? Are you hoping to save money (one bad job because of backlash is going to blow that savings away).
I’ve seen printed motor pulleys with a nut trap for the grub screw(s). Used them on a printed extruder on an early rep-rap style printer. That printer had a lot of issues, but the motor pulley didn’t slip.
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Printing low-tooth-count GT2 pulleys is no fun and requires a lot of trial and error (either in the models themselves or with your slicer) to get a tooth profile that fits. I printed a large 120T toothed pulley as part of a gear reduction just fine but my attempts at a complementary 30T gear did not go well. I could probably have made it work with enough trial/error but I just went with a 30t metal pulley instead.
Even if you can get a good tooth form there are questions of strength, accuracy, and so forth. I agree with Jeffeb3 that the question is “why?”. If there is a good reason to want to try it you can probably achieve some level of success if you put in the time. And remember “because I want to” is a 100% valid reason to try almost any harebrained scheme.
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I’m having trouble sourcing them from amazon and/or ebay and the freight/shipping seems expensive or maybe I’m just cheap 
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I didn’t mean “why” in a derogatory sense. I figured it was something like that. Maybe we can help you source them (are they in the v1 shop?) or solve the problem if it was something else.
If it is close to holding up your build, I would suggest ordering some on the slow boat and print some anyway. They are easy to get to to replace them later. You have a lot to learn while waiting for the final parts.