Flying Extruder Suspender

Using a flying extruder like this one can shorten your retracts from 5-7mm down to about 2mm, because it will shorten your Bowden tube's length from ~450mm (for a 750mm tall printer) down to ~150mm. If you have a taller printer, this is an even bigger win.

This can work with a variety of extruders, but I'm using it with Shane's: https://www.thingiverse.com/thing:245677
I've used the Shane's extruder on about 15 printers, and it has been very reliable. I like that it is easy to load, compact and that it doesn't use any unusual parts.
I use the variant which uses an M4 nut to secure the Teflon tubing and a Mk8 drive gear.

To build this, you'll need:
* 2x M3x16 SHCS
* 2x M3 nuts
* 1x M3x10 SHCS
* 4x M3 nylock nut
* 3x 190mm long pieces of 3/8" OD, 1/4" ID rubber tubing. (These three pieces need to be slightly longer than half the length of the horizontal extrusions in a Delta printer.)
* 1x KeyBak (heavy duty): https://www.amazon.com/KEY-BAK-Retractable-Stainless-Polycarbonate-Oversized/dp/B0088MQ9JS
* 10x small zip ties

I am using this Flying Extruder in my Kumu-3D printer design: http://www.kumu-3d.com

Here are the steps to assemble the flying extruder suspender:

• Use an M3x10 SHCS and an M3 nylock nut to attach the "wye" to the top of the motor suspender.
• Slip one end of each of the three pieces of rubber tubing onto the three arms of the "wye", and use a small zip tie to secure each one.
• Have an M3x35 SHCS (or something similar) go through each carriage, and extend toward the center of the printer. Slide each of the small printed tubes (which I call tubing adaptors) onto the ends of the M3x35's, and then use an M3 nylock nut to keep them from sliding off.
• Slide the remaining free ends of the rubber tubing onto the tubing adaptors and use a small zip tie to secure each one.
• Measure and shorten your Bowden tube. On my printers it is about 150mm, down from about 450mm. This reduced the retraction settings by a factor of 3x! Also, you can probably set your retraction acceleration to a large value -- I'm using 3000mm/s^2, and the retraction speed is 200mm/s.
• On my printers I suspend the spool at the top, and I also have a piece of aluminum L-channel near the front, going between the top X-Z and Y-Z horizontal extrusions. I used two zip ties to attach the Key-Bak to this piece of aluminum L-channel, and an additional zip tie to act as a loose filament guide.
• On the Key-Bak, I removed the split ring, and replaced it with a small zip tie. I used a little bit of fishing string looped around the three arms of the "wye", and have the zip tie running through these loops. This is how the Key-Bak pulls up on the "wye" to counter the extruder's weight.

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