how to cut flat base on stone

Quoted text begins.RE: "How can I cut a perfect base on the rock so it lies flat, perfectly
flat?"
End of quote.

Hi Dulce,

Assuming you have hand tools only?
1. REQUIRED:
a. nice flat surface you can put the boulder on with a few inches empty flat space around all sides

b. crayon
c. tape
d. small scrap (wood/stone/metal/books) in various thicknesses of two-parallel-sided small objects
e. whatever stone tools you have

2. POSITIONING: With little scraps of stone or wood wedge the boulder in the position you want it to end-up, with the flat 'bottom-to-be' parallel to the flat tabletop. The wedges should not protrude beyond the edge of the stone above where the cutting or demarcation-line is ? that space needs to be free for the marking operation.

3. MARKING: You need a crayon or pencil taped (masking-tape, duct-tape or whatever)to the top of a two sided flat object (scrap of wood, paperbackbook(s), chunk of marble, etc.) that puts the pencil-lead at the level of the line you want to mark. Go all the way around the boulder with the marking-jig you have made. This will be the cutting line that sets the stone in the orientation you choose for the flat bottm.

4. INITIAL CUT: (with hand tools) first use a flat chisel to carve a precise edge directly on the waste-side of the cutting line all around the stone. (with a diamond or abrasive-blade saw cut instead of chisel the line)

5. WASTE CUTS: with a point or toothed chisels remove all the waste inside that original line -- if using hand chisels only then a slight concavity is OK and easier to achieve than perfectly flat, but a convex surface is no good and will allow the base to wobble.

6: SMOOTHING: if you have a concrete driveway or sidewalk outside (with a bit of surface texture rather than smooth like interior concrete floors) place the base on the concrete bottom-side down and push it across or back-and-forth. After you have done it a couple of times, turn it over and you will see the abrasions where the high points protrude from your flat surface. If you carved the bottom slightly concave you are trying to achieve a rim of evenly abraded stone around the bottom 'footprint' of the bolder. If you really want it perfectly flat then you need to keep abrading until that is achieved.
If you don't want the hassle of picking the stone up and setting it down on the concrete and then having to shove it around, you can take a good stout PERFECTLY FLAT and UNWARPED piece of plywood (or steel, plate glass, marble slab, etc.) and scribble one surface with a crayon. Place and rub this over the upturned 'bottom' side of the boulder ? this will show the high points that need to carved/ground/sanded away. Repeat as often as needed. (I have had the necessity to do this on a couple of one-ton carvings and can tell you patience is required!)
Good Carving to You
Don