Lapping the Tuniq Tower 120 HELP

[papasmurf211]

Ok well i looked up all the guides about lapping and i went out and bought some 1500 grit sandpaper from my local ace hardware store. I taped the sandpaper a piece of flat granite and i laided my tuniq tower down on my countertop. I wet the sandpaper as well as the actual bottom of the heatsink. Well i start lapping and it takes me about 30 minutes of lapping (constantly wetting) to achieve a somewhat mirror shine ALTHOUGH no matter how careful i am the sandpaper keeps making deep scratches into the bottom of the heatsink. I can feel it happen, i will be lapping and then all of a sudden ill feel the sandpaper sort of slip underneath my hand and it will make a scratch on the heatsink. I am applying even pressure, the sandpaper is always wet but the sandpaper keeps scratching the heatsink.. help?

 

[penation4000]

have you taped the sand paper down so it wont move?