Lapping grit on Granite surface plate

[Kevin Blunt]

Hello everyone,
I was wondering tonight if it would be ok to use a 90x lapping grit from LV on a granite surface plate for flattening waterstones while sharpening. I tried tonight for the first time and it made my waterstones dead flat using my staright edge as a reference. It was better than anything I have used in the past. My concern with this is whether or not it will eventually create a dished surface plate. My hope is that the lapping grit with not be hard enough to wear the surface plate.
Any thoughts or suggestions.
Thanks,
Kevin

[Roy Wall]

Kevin -

I use 120-220 grit sandpaper (wet) on the granite plate..... a la Lie-Nielson method. I know this won't dish the plate....so this is an option depending on what you hear forthcoming.
These are Norton Water Stones...... 1000 & 8000 grit

[Kevin Blunt]

I am dealing with Norton WS as well.

The reason I am thinking of the lapping grit is because it will be way cheaper in the long run based on my experience today.

Thanks for you thoughts.

[Chip Lindley]

Was always my understanding granite surface plates were for precision reference measuring only. The abrasive will certainly have its way with the granite, and ruin it as a reference tool.

Plate glass is flat, cheap, and easy to replace, for lapping of sharpening stones, with a grit slurry or silicone carbide paper stuck on with oil or water.

[jerry nazard]

Kevin,

I use 220 wet or dry on the surface plate. There is no reason that you could not set a piece of glass on the plate, and proceed to lap from there with your grit. The 220 paper for me works great and can be reused over and over.

-Jerry

[Van Huskey]

Wet dry sandpaper = good
Grit slurry = bad

[bob hertle]

Wet or dry (silicon carbide) paper, laid flat, and wet down. Lapping will ruin your surface plate if done directly on the plate with grit. Generally speaking you want to lap a harder material with softer lap. The softer (cast iron, copper lead, brass) material will "charge" with the lapping compound, and abrade away the harder material.

Bob

[Myk Rian]

Granite plates are not for lapping, grinding, surfacing, sanding, etc. anything.
There are cast iron plates better suited for that.
If you flattened stones on your surface plate, you now have a compromised plate, and it is useless for the purpose for which it was intended.

It takes a specialist with diamond dust, and a special steel plate to surface a granite plate. Congratulations. You have an expensive call to make.

[brian c miller]

Id by surface plate you mean a precision measuring tool than this is a no no. If however you mean left over sink cut out from the counter top guy than maybe. but unless the granite is harder than the paste you'll eventually dish it.

I'd go with PSA wet dry on a piece of glass.