I prefure to use a torch and then dress it with a grinder.

Make sure of a few things when using a torch:

angle the torch about 15* down so you have the tip pointing at where you are going:

cutting from right to the left angle like ----/.....
---= not cut yet
...= already cut

if you have slag build up torch may be to hot* but probable you are moving way to slow.

Practice on some scrap
to cut 1/8" you will have to move about 2 or 3 times as fast as you would 1/4"

have your atcetlyne knob tite snug and your oxygen knob open
you will use your oxygen knob on the torch head to control oxygen flow.
Fire up your torch and get a nuetral flame,when you hit the cut handle(oxygen) you should see the flame turn from a nuetral flame to something that looks like afterburners on a jet.two streaks of blue.

Practice makes perfect,so don't give up on cutting yet.

Also cut verticle from up to down,this will keep slag from puddling up and clogging your tip.

Bansil