I thought the hacksaw was the "crude" part, but sure you could use sanding paper. But it is very hard nylon, so you'll be at it for a while. The Dremel bit I used was also just sandpaper on a roll, but it went a lot quicker than manually grinding sand paper over the ring:

Hi, I just assembled everything, so I'll try and explain better. The Deda compression ring is higher than the original provided C-ring. So you need to shave a couple of mm's of the top of the ring. So you grind down the ring to the required height. The smaller bottom part of the Deda ring fits in the bearing perfectly, but if you leave the wider upper part at the original height you will be left with circa 4mm of space between the frame and the headset cover.

I tried to do my best to illustrate in paint . You need to grind the ring down to the red lines. So remove the purple material in smalls steps at a time to check if it is still high enough to compress the headset.

OK, so I fixed the situation pretty easily. I bought the Deda compression ring 45 degrees:



First I sawed the largest part of the top (circa 2mm I guess) with a hacksaw and then I ground the top down a smal bit at a time with a Dremel tool till it was at the correct height to compress correctly but also not leave a gap between the frame and the headset cover (there is still a very minimal gap say 0,5mm). I also used a Deda 70mm expander plug to get a bit more grip while tightening the top cap. No play anymore and a very cheap solution.

That C-ring will cause you trouble. It too open and too stiff. You will have a bad time, guaranteed. It'll never feel tight, and it will start to creek.

Please offer a better solution SP Cycle.

OK, so this is true. I have the Velobuild GF-003 (very similar I guess) and it is impossible to tighten the headset because there is too much room between the C-ring and the fork steerer tube... Could also be that the C-ring is too open. There is also significant amount of space between the c-ring and the headset cover:



What's the solution to this problem? There remains a very small amount of play while using the front brake.  There are some very thin spacers left over, but I can't see how they would solve this problem.

UPDATE: I bought the DEDA Nylon 270 degree compression ring. Hope this can solve the issue. Should I make this ring thinner?