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>>standard grinding disc, and a battery operated 750 watt 4.5 grinder.So,..what's the cord doing then,...get it, to look more dramatic.

I would experiment with differant steel, I'm thinking low carbon steel.
But now I'm thinking of something more dramatic effect and allot safer.

You would need some help,..getting a bunch of flints, perhaps from a welding supply, about a hundred or so, the type with a screw on end. Then a hundred or so little bolts what fits that thread.
Now, making a steel plate up, drill a hundred or so holes
through that plate and bolt the flints on. You have now a steel plate with sduded flints and now you need to test what wheel works best.
You don't need a grinding disk anymore,..thinking of just a plane flat, [perhaps knurled] steel wheel about 1/4inch wide. Somebody in a machineshop can make up.
Just hinking how to dublicate the spark effect, say 50 times more then you'll get on single hand flint, the one used to start a welding torch.

Before spending a bunch of money, do a test with one flint only first, I'm tinking to use a dremel wheel, try a wood cutting wheel, diamont etc. first and experiment.

Magnesium will put out a lot of high intensity sparks. It's also used in fire starting kits. That's why the low rider crowd puts in under there cars.