How do I polisha metal yoyo? specifically the cut
Heres a “little” guide I found just for you, See if it helps at all! 
You will need:
3M Blue Masking tape
Razor Blade
3M Scotch brite pads (red) for metal
600 grit sand paper (grey) also called “wet sand” sandpaper
Steel Wool #0000 (final finish)
Blue Magic Metal Polish
Paper towels
Step 1: Prep
All I did here was take masking tape (I used the blue 3M stuff since I had some laying around from painting the house). Wrap the plastic areas good and secure. It is ok to cover some of the metal area at first. What I did was take a razor blade and gently cut along the grove where the plastic and metal mate and used that as a guide. Don’t press too hard or you will cut into the plastic. GO SLOW and be careful! The sole purpose of this is to protect any plastic areas from being scratched from sanding. The Sirius was very easy to mask since the plastic area is very minimal. Its more tricky with yoyos with smaller rings.
Step 2: Rough Sanding
If you look carefully in the metal ring you will see that there are small grooves in the metal. These grooves are machining marks. (Basically they take a chunk of metal and cut into it while it spins until they create the round shape of the ring) this leaves behind machine marks. Your goal is to remove these marks and make the surface smooth.
Cut out a small square of the scotchbrite pad (whatever you feel comfortable with in your hands).
Take it and start scrubbing the metal. I suggest scrubbing against the grain of the machine marks. That way you start the process scrubbing down the ridges. Scrub until you have a hard time seeing the original machine marks. This may be scary to a lot of you as it will look worse before it gets better. It will be very rough and you will see scratches all over. This is ok as long as you are eliminating the deeper machine marks. Trust me.
Step 3: Medium Sanding
Now that you have the rough scratches on your yo yo you need to start refining it a bit. Take the 600 grit sand paper and repeat the previous step by using the sand paper instead.
At this step I would use more of a circular motion while pressing firmly with the sand paper. This will create a more smooth finish. Obviously if you move in a straight sided to side motion you tend to gouge into the material. Going in circles creates a more even sanding. After that it will look like this:
*Note to get even better results, you can get a slightly rougher grit of sand paper (say 450-500 grit) and add another step of sanding before going down to the 600 grit as I am showing you here. That will help to create an even smoother sanding transition and mae finish even more flawless. Basically the more steps you take by moving down the level of roughness the better it will turn out. I was lazy and only did 3 sanding steps.
Step 4: Pre-polishing
Ok we’re getting closer. This is the part where you begin to make the finish to start looking smooth. Grab your bag of steel wool and pull out a small piece to work with. (Maybe a wad big enough to stick in your mouth as if you are pulling a piece of coton candy to eat. BUT DO NOT EAT IT! ;D )
You will need to take a small wad of steel wool and start rubbing the surface. At this step, you can rub along the original grain of the machine marks. You will not gouge the metal as the steel wool is very very fine. Keep rubbing until you get a semi smooth surface like this:
Step 5: Time for Da BLING! Polishing.
(I used “Blue Magic” but there are many other brands you can use. I have also used a product called “Brasso” with similar results and its more common. I am sure products like “Flitz” and other metal polishing compounds will do the same)
This is where it gets interesting. Take your polishing compound and squirt a small dab on a paper towel. As they say, “shake well before using.” A little goes a long way especially on something as small as a yoyo. You don’t want to use too much. It’s not that its bad for the yo yo as much as it will make more of a mess. You can always apply more if the compound starts drying out.
With a little dab on a paper towel start rubbing again. You will notice that the area will start getting black and tarnishy looking. If you see your paper towel turning black, you know its working . Keep rubbing the surface adding more dabs of polish as you need.
Then take the clean side of the paper towel and rub of all the excess. You will see it shine. Keep repeating these steps until you reach a desired shine. Voila! You can see your reflection on the ring!
Thanks Connor! exactly what I was looking for
No problem!