Circles

​This month I’ll give you a few tips on marking out circles on rock.
 
Firstly, you’ll need a compass with an attachment to hold pens.  They are inexpensive and available from most stationers.
 
Take the dry, grease-free, smooth-faced slab of stone you want to mark the circle on.  Stick a piece of masking or electrical tape on the rock in the approximate centre so you can place the compass point on it and it won’t slip.  Then jiggle the tip around until you get the best fit for the circle.

Figure 1 shows the simple arrangement for marking circles on a slab of stone.

​Mark the circle with a permanent spirit marker.  Test the marker first and see if it washes off easily – some “permanent” markers work on clothing and paper but will wash off as you work the stone.  So make sure you use one that is fit for purpose.
 
If you are removing the centre of the circle, this can easily be achieved with a core bit or grinding it out with burrs.
 
Now, having done this, the hole is quite likely to not be perfectly central in the circle any more, so sand down the face and having temporarily plugged the hole with a small piece of dowelling, remark it.

Figure 2 shows the wooden bung in place, having re-centred the circle.

And off you go!  You can remove the excess stone with your trim saw, by grinding it off using a coarse lap, or coarse belt for your expandable drum sander.  Easy!
 
Enjoy!!