# Thread: How flat is a granite worktop?

1. I've been shopping for kitchens (yes SWMBO has finally persuaded me that our 20y old kitchen is in need of some refurbishment) and got chatting to the designer guy in the shop about stuff such as CAD (as you do :)) and the use of granite worktops as a base for aligning things (he's a model RC builder). He reckoned they're pretty flat (at least by by his standards) and promptly offered me two 12" square offcuts of 1.5" thick granite worktop which I couldn't refuse, much to the annoyance of SWMBO ("I can't believe you did that!") :D

A quick test with the edge of an engineers square (about the only thing I have close to a true straight edge) suggests they are pretty good although I can see daylight in places between the edge and the top face, but how could I measure the flatness?

2. If I had one :)

Well put a 1.5thou (.02mm) feeler gauge under it and I can push it through in places, so I suppose the answer is 'not very flat'

I have 2 pieces roughly the same size. I was wondering about lapping them together to get it flatter. Thoughts anyone?

A 12" sq 3" thick granite surface plate is about £35-£40 new. So it might be worth the effort.

3. You need three surfaces to scrape/grind/lap something perfectly flat.

By only using two, you can end up with one perfect concave surface, and one perfect convex surface.

4. I remember seeing a mate checking his surface plate, not sure why he had a surface plate as he painted cars;-) he had plotted the surface out into squares and was checking between squares by resting a spirit level across a pair of cylinders placed in two squares.

I gather gravestones, surface plates and worktops are all finished on the same machinery. I asked in a stomnemason and they said they often had a skip full of bit's, I keep meaning to call back and get some bit's.

I would look into suface tension, if you could get a bit of plate glass and seperate the plate glass and surface plate at one end with a feeler gauge the surface tension of a thin liquid would show as a straight line, if the surface was flat.
Last edited by graffian; 06-01-2009 at 11:40 PM. Reason: none

5. with a section of plate glass you can do the old machinist trick of printers ink and paper. You just have to figure a way of lowering the glass completely evenly (spirit levels, even of the torpedo version, can help here) anything that touches first needs to be ground down slightly and go from there. There is also taking the pieces to a stonemason and having them level and polish. My question is how much dampener are you going to put between any Mill/Router that you plan on mounting on it and the tool. Reason being that stress will build up in the stone and it WILL split along any inherit fault lines within the stone (ask me sometime about a number 1 diamond wheel and Obsidian). Great idea if you can control the vibration reaching the stone or give it an ability to transfer it.

6. Originally Posted by irving2008

Well put a 1.5thou (.02mm) feeler gauge under it and I can push it through in places, so I suppose the answer is 'not very flat'

I have 2 pieces roughly the same size. I was wondering about lapping them together to get it flatter. Thoughts anyone?

A 12" sq 3" thick granite surface plate is about £35-£40 new. So it might be worth the effort.
You certainly shouldn't be able to put a .02 feeler under it even at 30mm means you got Chinese or indian granite.
as for granite a 30mm sheet 3 metres long will bend 30mm or more.
lapping will bring a higher polish but will wear the softer parts of the granite.

If you are near Marlborough Wiltshire Give me a call I,ll give you a couple of pieces for free at 30mm or 40mm.
Google: ramsbury stone for contact details

7. Did you not see the date on this post.? . . . . 2008.!! .. . Lol

8. No just aw latest activity 4 hours ago, RAFLAO thanks for letting me Know.

9. I think it is not easy.

______________________
SHIVA GRANITE AND STONE
Last edited by miguelgarbutt; 27-03-2017 at 12:55 PM.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•