I apologize if this has been covered to death – I couldn’t find much on engraving stone on the forums after a quick search … I worked out a good process and wanted to share it with the community.
I wanted to engrave some custom stone coasters for sale at our local farmers market. Slate, soapstone, and travertine (limestone) are all fairly soft materials. A reasonable source for these materials are standard 4x4" tiles used for counter backsplashes. Some tiles have a rugged surface like they were hewn from the mountain by hand. I needed a flat (ish) surface for engraving. Eventually I found a source of suitable slate tiles on Amazon (of course).
I imported my images into VCarve, sized them, and used the Quick Engrave feature. After experimenting I found that a 0.005" depth of cut at 25 in/min worked fine for slate. I probably could go faster / deeper per pass but this worked and I’m a firm believer in “Don’t let perfection be the enemy of good enough”. I selected a total depth of cut of 0.020" – the front and back of the tile aren’t perfectly parallel so I found that a deeper cut is needed.
Initially I started with a carbide 90 deg v-bit but with the deep cut, the line width varied too much from place to place on the tile. I switched to a tapered, solid carbide bit. I was worried that being more delicate that it would break but it worked fine.
I also tried a travertine tile. This was an earlier attempt with only a 0.009" total DOC – you can see how the tile varies in thickness: the antlers are very deep and the rear hoof barely is carved in the surface. Increasing the DOC would hide this difference better.
I have tried to use a DDE bit on slate like that, and the uneven (and soft) surface really beats up the diamond tip. And by beats up, I mean, the bit sinks in pretty far (farther than it should because the slate is so soft) and puts a lot of side load on the diamond insert. I made it through about half of a 4 hour run and the diamond was removed, I assume from he side loading, because I have used them on granite and marble with no issues.
Those look really nice! You can use some thin shims to level the uneven coasters before cutting to help reduce the difference in thickness.
You can buy an inexpensive polycrystalline diamond (PCD) bit as well (and wait, and wait, and wait. . .) and then do marble if you want! You could probably do granite, but I haven’t done it yet, so I am hesitant to mention it with these bits. They have performed just fine though so far.
What are you doing for the bottom of the coasters? I put this adhesive backed cork on the bottom of the ones I make.
The only experience I’ve had were a drag cutter is the kind used for vinyl engraving. It had a very small carbide ‘knife’ on a swivel. I don’t think it would work well for this purpose.
The slate coasters I got from Amazon had four little soft foam dots in the corners already. The travertine tiles had nothing so the cork you mentioned would be great.
