Cutting and defraying metal railing cable
You are using the wrong tool. You need a cable cutters. These cutters are constructed so they &quot;hold&quot; the strands together while they cut through the cable. See picture below.

In a pinch, you can put a small hose clamp around the wire, tighten the heck out of it and then use  tool with a cutoff wheel or your grinder. Think about getting the proper tool though. It will make your job easier since you've got a lot of cutting to do.