1. you need a hot end set up for Bowden.

2. You will need to buy some PTFE tubing for 1.75 filament. http://www.filastruder.com/collections/ … tfe-tubing

3. Two maybe Three Bowden couplings http://www.filastruder.com/collections/ … ded-1-75mm

4. Hobbed Goblin http://www.filastruder.com/collections/ … drive-gear

The rest you can print yourself using the files attached.  The MK-5 body is modified to accept the coupling for a guide tube but is not required.  Hence the ("two maybe three') statement.
The Guide is also modified to accept the coupling and this makes for a clean tubing flow with your motor mounted on the frame.
This allows for feeding from the top or the bottom depending on your placement of the motor.
The tension arm is modified to work better with the Hobbed Goblin.

Here's a couple pictures to answer your earlier question.

So after you get your Bowden couplings the first thing you will do is take them apart like this.

And then place the insert into the guide like this.  I didn't push it all the way in as they can be difficult to remove.

Then you can do the same to the MK-5 Body like this.

When you are all done you should end up with something that looks like this.

Thanks for all the info (though I still have no idea exactly how the pneumatic push fit connectors actually work :-). Good to know that direct drive works well - I can avoid worrying about gears (at least at first), and direct drive is much simpler.

The connectors simply hold the tube in place. The first quarter inch of the Y ube is all that can be inserted and is locked in by retractable blades. This tube effectivly makes a very long direct drive so the filament can actually be pushed into the hot end.

I'm keen on bowden on printer #2. Can't stop watching videos of the ultimaker drive system either!

I have since changed them to feed from the bottom and out the top to reduce the tubing length.
I also purchased from Filastruder the E3d Hobbed Goblin drive gear and installed them.  They are smaller in diameter and have much more aggressive teeth.  I have been very happy with the setup and have had no problems.  Just increase retraction distance and speed until there's no blobbing or stringing.

I've never seen a bowden extruder close up, and I'm mystified by the pneumatic connectors that seem to be used in a lot of them. How the heck do they work? Can you push the tube all the way through them to get the end down right next to the hobbed gear or bolt?

And speaking of bowden extruders, does anyone have a favorite 3D printable one that seems reliable?

What sort of adjustments do you normally need to make for retraction?

I see a bunch of geared versions on thingiverse. Are 3D printed gears really reliable? I'd think there would be backlash problems with retraction.

Bowden setups rely on the stiffness of the filament. They don't work well with flexible filaments. The tube simply goes into the fitting about a quarter inch at the most. It works just like a direct feed that has been stretched very far.

Printed gears work very well and most home brew printers use only printed gears. to be honest I have not seen a printer that uses a Bowdeb or Wade setup that did not have printed gears. The only one a saw that was not printed was a guy that had them casted in aluminum. Retraction is not a problem as all you do is modify the settings to compensate for the very slight delay. Bowden setups have been around for years and are very comon. Most just prefer direct feed for compactness and simpicity.

The main advantage of Bowden is a much lower head weight that will increase speed and accuracy.

And speaking of bowden extruders, does anyone have a favorite 3D printable one that seems reliable?

What sort of adjustments do you normally need to make for retraction?

I see a bunch of geared versions on thingiverse. Are 3D printed gears really reliable? I'd think there would be backlash problems with retraction.