Reddit reviews 2 Meters PTFE Teflon Bowden Tube 1.75 Filament 3D printer RepRap Rostock Kossel

This is so true! If you can summarize your issue succinctly without ranting, people will be more than willing to help you. (Parts of) the internet are nicer than you might imagine!

I think you're also reading a bit too much into the issues. The inner tube in the Maker Select v2 is supposed to be plastic - it's made of PTFE. This is a very common design in cheaper printers. There is absolutely no problem with this! PTFE has a reported melting/charring point ~240 C, though I've heard it may begin degrading as low as ~230 C. You should be okay to print in PLA temperature ranges and even ABS if you're careful.

I'd say that on the grand scale of things, the MonoPrice printers are some of the lowest maintenance printers you can get at that price range. Unless you're willing to go up above the thousand-dollar range, they're probably the most reliable you can get. They WILL print very well with a little tuning and basically no hardware modifications. The v2/Plus are both excellent choices for a beginner.

Not really, no. The point of the PTFE tubing is to be an ultra low friction material, not just to be flexible. Luckily, PTFE tubing isn't expensive at all, though, two meters of it is like $5.

However, I'm honestly curious as to why you think a Bowden system would be an "upgrade" for your printer. A Prusa clone isn't going to run very fast, and removing mass from the X carriage isn't going to change that very much, but at least with a direct drive you can work with flexible filament a bit better, among other perks.

It's hard to tell what printer you mean (the names in your list that I know refer to multiple different printer models) but the Duplicator i3/Maker Select (and some Flashforges) use a Mk. 10 style extruder and hot end, and googling the others just gave me similar looking setups, so I assume that.

My understanding is that both heads on a dual head setup need to be correctly leveled to the build plate, whether they are both in use or not. If the second head crashes into the print while the first doesn't, either the second one is more than your layer height lower (which implies that this is more likely to be an issue whenever you print at a smaller layer height) or your print is shifting enough to cause part of it to stick up. That's assuming that you are not printing parts sequentially, which needs accurate clearance defined in the slicer to account for both print heads.

If by "bushing" you mean the PTFE liner inside the hot end, then running without it is, I would think, a bad idea. The hot end is designed to have that liner. Otherwise nobody would bother buying the all-metal hot end from Micro Swiss; they'd just take their liners out.

I suspect that without a liner, melted plastic is neither building up the correct pressure to fully depart the nozzle, nor constrained to do so, so it just sits there where the liner would normally be and burns. It may also be creeping back upward toward the cold end and solidifying.

(I'm also not clear how taking it out would help with Ninjaflex, since the extra wiggle room would give the filament more excuses to bunch up.)

You can buy lengths of PTFE liner from Amazon. Just make sure it's the same inner and outer diameter as the original (the mk.10 uses 2 mm and 4 mm, I believe).

The price you're seeing is quite high. It should be more like $15 for 2 meters, or about 6 ft. Here's some on Amazon for even less.

2 Meters PTFE Teflon Bowden Tube 1.75 Filament 3D printer RepRap Rostock Kossel https://www.amazon.com/dp/B00THZKC8Y/ref=cm_sw_r_cp_awd_owqywb1RNPAHK

edit: 1.75mm tubing - http://www.amazon.com/Meters-Filament-3D-printer-Rostock/dp/B00THZKC8Y/ref=sr_1_fkmr2_1?ie=UTF8&qid=1452791517&sr=8-1-fkmr2&keywords=mk10+ptfe+tubing

That would work, you'll just have to be careful that you've still got enough length on the tube that you don't choke up the filament path when the X axis is all the way out.

Here's a link for replacement fittings.
https://www.amazon.com/gp/product/B00WE1A3D2

This is for extra PFTE tubing
https://www.amazon.com/Meters-Filament-3D-printer-Rostock/dp/B00THZKC8Y