IN-LINE Filament dryer, using the heated bed

This is a construction for a IN-LINE filament dryer, where the warmed and dried filament is pulled into the extruder for immediate printing.
Unlike the usual method of printing, where a full roll is placed in a dehydrator-oven and warmed for several hours at 50-65 degrees C, this system uses the heated bed, warmed to 75 C and slowly pulls the filament over the surface through a tunnel on the far right side of the heated bed.
This will reduce the useable surface for the print but it has been made as small and thin as possible so approximately 85% is still accessible.

Every length of filament is in the heated tunnel for 1,5-2 minutes with normal printing speeds. I tested this with 0.6mm nozzle and 0.3mm layer height . With smaller nozzles and thinner layers the drying time will be longer.

There is now a video on YouTube that shows a simple but effective test; moisture saturated TPU is printed and to show the difference between unheated and heated filament it was marked with a blue permanent marker: 2 strips to mark where the filament is untreated, 1 stripe to mark the 100% treated filament start.
The total video was 20minutes but it has been sped up for most parts to show the interesting changes in the surface and in the audio: it starts with popping bubbles , than after the first 2 stripes the popping becomes less and the layer more smooth, then the single strip comes and from that moment no popping any more and a shiny smooth surface appears.
This was with no-brand TPU, printed on 235 degrees on an Ender3V2 with aftermarket direct drive.

https://youtu.be/nTTVyFz-lQ4?feature=shared

To be printed in a more heat resistant filament, such as PETG.
Most parts are designed to have minimal s.
Some metal hardware (screws, rollers/pulleys) required.
The tunnel-cover is locked in its hinge with a piece of filament.
2 x 12mmx3mm Neodymium magnets are used to keep the tunnel flat on the metal build plate, while 2 screws are tightened on the underside to prevent the construction from sliding off the plate. I used M3 heat inserts to connect the 3 main parts, fan-body, filament heater and extend together. A small 30mm fan is used on a 12 volt power supply.
The pulleys have a 5mm axis/bearing and a long M5 screw is needed to keep them in place. I used a normal M5 tap to make a thread in the plastic.

A PTFE tube holder nut is used to lead the dried filament out of the dryer into a PTFE tube. That tube must be long enough to reach the extruder without a sharp bent, even when the bed is fully forward and the Z-axis raised to its maximum! The PTFE tube should also connect directly to the extruder, to avoid a sharp bend in the filament.

Adjust the bubble test STL in your slicer to fit the build plate. The other files are on the actual real-world dimensions.