The tool is quite easy to make. There are just a few things to consider.
You can find all .stl files here: https://www.thingiverse.com/thing:3732756
1x cover Deckel_cover-7.stl
1x guide 1 Fuehrung_1_guide_1-7.stl
1x guide 2 Fuehrung_2_guide_2-7.stl
1x grip 1 Griff_unten_lower_grip-7.stl
1x grip 2 Griff_oben_upper_grip-7.stl
1x bolt schraube_bolt-7.stl
1x nut Stellmutter_nut-7.stl
you can order the set here
4x bearing 15x10x4mm 61700
8x bolt M3x8mm DIN 7985 A
2x ptfe tubes
The parts in detail
Guides 1 & 2
There is nothing special about them. Print it with standard settings and you are good. Maybe use 3 perimeters for them to last longer.
It is the grip with the spring. Use support everywere. There is not much to say about the printing. Again, I'ld use more (4) perimeters so the spring lasts long. The removal of the supports of this part is actually the only tricky part but it is not too bad eighter.
Use supports on built plate only, 4 perimeters
Bolt & nut
Standard settings are good enough
It's straight forward really. Have a look at the expolosion drawing to see how it all fits together.
The bearings might fit pretty tight. Please understand that it depends on your setup. So if you have trouble getting them on try to sand the fit first.
When you use the straightener you will find not all filaments react the same when noddle them through those bearings. PLA thends to brake, nylon does not care at all.
That's why I added this bolt and nut to adjust the stopper. But it is not good yet. I will add updates just do not know when. You can always contact me and I'll help with any issue.