I have a 25th anniversary cube that is as loose as my DIY's. It took about 2hr to make it extremely loose. Heres what you do.
1. Take some really fine grain sand and pop a pice out of your cube and poor some sand in.
2. Work the sand around really well- or solve it about 6 times.
3. Clean the cube out by taking the pieces out and putting them in a strainer and run hot water and soap on them. (DO NOT PUT THE CORE IN THE WATER WITH THEM)
4. Take all the pieces out and have them start drying.
5. While they are starting to dry, take a hairdryer and blow all the sand away from the core. (Be sure to get the spot between the center peice and the core, where you can see the spring)
6. Speed up the drying process by blowdrying all the pieces.
7. Make sure there is no more water on any pieces.
WARNING: THIS NEXT STEP CAN BE MESSY!
8. Take some steel wool and sand the ridges off the cubies with that. (When you are done with this step all the pieces including the core should be very smooth)
9. Re-assemble your cube.
10. Re-lube your cube.
11. Enjoy your new lose cube!

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3x3 single: 18.69
3x3 average: 26.05