This is 3rd version of this remix I've tried out and I think I have worked out most of the kinks. The first version didn't use a Bowden tube causing to much drag on extrusion and retraction. Version 2 I decided to reuse the stock Bowden tube I had left over from upgrading to line the guide and with it being a mostly clear tube could just measure from the entrance 100mm to get a good reference but, the stock Bowden tube wasn't as see-through as I had hoped and finding an exact 100mm on a curved tube proved more difficult then anticipated. Which brings me to version 3 this guide works perfectly for guiding the filament into the extruder without the need of any other guides up top closer to the spool. There is a bit of a bend as it comes out the tube into the extruder but I haven't noticed any ill effects. Depending on how tuned your machine is the first gap should be 100mm followed by a 2mm marker than an 18mm gap. The idea behind this was at first just a quicker and easier way to calculate E-steps without fiddling with calipers or other tools But, in the end, I almost feel like this is such a great tool I needed to post it up here.
P.S. Props to original designer DrStreet