If you like reel-to-reel compact cassette look and you don’t want to spend a fortune then you can create one – using 3D printed reels.
Just download attached zip file containing STL model files. Print it with the highest precision (0.1mm layer height, 0.3mm nozzle diameter, 100% infill). I use PLA filament.
White 
White/Red 
Pink/Oragne 
Kit
Then follow assembly video bellow.
Download
Model files: Cassette_reel_STL_v9A.zip
Note: It can be better to glue base part and top part together. Otherwise it might loose during the time and cause friction between reel and cassette body.
Note: you can use these model files for your own non-commercial usage!
If you don’t have access to a 3D printer then you can buy cassette upgrade kit in this e-shop or at eBay.
If you want to have text or logos on the reels then you can use “rub on decal” transfer sheets (available at eBay) for inkjet or laser printer.
improvement by Milan 
you can apply rub on decals for a better look.. 
customized reels by Alfi 
Amroh reels by Rob from Netherlands 
reels in Grundig MCF200 
reels in Grundig MCF200
Customized reels in action – by Alfi Groove from Australia:
http://www.youtube.com/watch?v=SONUmADGJgk&feature=youtu.be
Would it be possible to improve the design so that 90min tapes could be used without cutting them down?
Hello,
It is not possible because reel radius cannot be larger than half of the distance between reels.
Otherwise the reels will overlap. It is limitadion of any reel-to-reel casette.
What’s the highest time I could use then?
It depends on tape thickness. If you use 90min tape then max total time (side A + B) would be about 52 minutes. For 60min tape (thicker) is will be less.
what if i used a 126min tape?
kurt,
try, and let us know!
Rob
Hi, can you offer making the reels with my logo on them? I cannot print these off I do not have the tool.
Yes, it is possible to create reels with your own logo.