Here is a ten step process to size down a platinum ring and the tools needed to do the job.

Tools needed:
Jewelers Saw
3/0 Sawblades
Chain nose pliers
Shank pliers
Chasing hammer
Bench block
Three square needle file
Half round file
Torch with either Natural gas/Oxy or Propane/Oxy
Eye protection (#5 Lens)
Ring Mandrel
Sanding stick
Flex Shaft with assorted abrasive and polishing wheels
Tungsten Burnisher
Polishing buff and felts
Platinum Polishing compounds

Step 1:
To size this platinum ring down, begin with determining how much metal needs to be removed. Size s represented by 2.55mm or 1/10th of an inch. Using a divider, mark the area and then cut the shank twice to remove this piece. It is recommended not to cut all the way through on the second cut. Instead, use pliers to break it off. This prevents the piece from flying off and eliminates the need to search for it on the floor.

Step 2:
Bend the two shank ends together with a pair of inside shank pliers. Using a three square needle file, create a chamfer (groove) along the seam. This will help create a strong weld as the metal will fill the groove when melted.