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IndustryArena Forum > Material Technology > Glass, Plastic and Stone > Engraving (stone) with 3018 pro for prototype project
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  1. #1

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    Oct 2019
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    Engraving (stone) with 3018 pro for prototype project

    I know its not recomended for stone work, but, if i have as many time that it takes, will it do the small job that i need? (I heard that drops of water can make a hole in a stone.)

    Im planning to cut mostly soft limeston.
    Im planning to use a diamond bit like the dremel 7134 or 7144 or 7103.
    Im planning to creat a circle of about 20mm diameter, and 3mm deep in the stone.
    Im planning to go very very slow.

    Will it do the job?

    I thought to make the first 3mm hole by hand and let the bit engrave only sideways in a few layers

    What are the x,y speeds i need to go to be more than safe?

  2. #2
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    Re: Engraving (stone) with 3018 pro for prototype project

    Those plated diamond tools will work great for the first minute or so, less well in 5 minutes, and not at all after ten minutes of routing (if it doesn't break first). The trouble is that all the diamonds are on the outside, and once they've fallen off, there's no cutting action.

    Soft limestone can be cut effectively with tungsten carbide tooling, which will keep cutting a lot longer before it gets dull. Keeping the cut wet and flushing away the stone slurry will help keep things from overheating and hurting the stone. The limestone slurry will get all over the place, and it's not good for the moving parts of your router, so protect them with plastic as best you can. Your circle probably won't be perfectly round, but otherwise the machine will most likely work okay.

    Without knowing the size of the tool you plan to use, or the depth of cut or RPM range of the spindle, it's hard to give you specific feeds and speeds, but stone, unlike wood, isn't harmed by going too slowly, so get a few tools and start slow, building up to higher feedrates as you gain confidence. If the tool breaks from trying to go too fast, dial back the speed.
    Andrew Werby
    Website

  3. #3

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    Re: Engraving (stone) with 3018 pro for prototype project

    Thank you very much for your reply.

    Its common to find flint or other hard yet small rocks inside the limestone, the tungsten carbide can handle it?

    Will you recomand tungsten carbide for hard limestone or basalt?

    Still i dont understand why the coated diamond bits will get so warm and fall if i plan to go at speeds of 10mm per minute.. even if it takes 10 hours to create the small circle (20mm diameter, 3mm deep in the stone)

  4. #4
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    Re: Engraving (stone) with 3018 pro for prototype project

    A couple of things come to mind -

    Diamond is hard, but brittle. As the grains of diamond hit the material being ground (and in this case it is a grinding process, not a conventional chip-making process that you'd get with an endmill) they can shatter. Eventually all the diamond grains have broken down, and the part that's projecting out the farthest is actually the bonding material that holds the diamond grains to the tool shank. When that happens, you no longer have a cutting action; just a rubbing one - and all the energy being put out by the spindle is now going into heat.

    The other thing that can happen is that the diamond grains just get ripped right out of the bonding material.

    Another concern might be the minimum feed rate of your control - does the machine you have use Grbl as it's firmware? If so, Grbl has a minimum step rate (it's got a hardware timer in the microcontroller that's only 16 bits wide - and I'm over-simplifying this - but eventually that timer maxes out it's possible delay between steps).

  5. #5

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    Re: Engraving (stone) with 3018 pro for prototype project

    I will check the control limits for this machine (3018 pro by sainsmart). It is a Grbl. I thought about that possibility..

    I work a lot with stone, but never with a cnc machine, i saw that for cutting or grinding stone in larger cnc machines they use diamond bits.

    I use a dremel 3000 with some diamond bits and it works fine with most stones even on 8,000 rpm like this machine has.
    What is the difference between a rotary tool to a cnc in a matter of grinding a stone?

  6. #6
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    Re: Engraving (stone) with 3018 pro for prototype project

    [QUOTE=Itamarg;2329284]Thank you very much for your reply.

    Its common to find flint or other hard yet small rocks inside the limestone, the tungsten carbide can handle it?

    [Maybe, maybe not. If they are sand-size grains, it will probably dig them out, but larger pebbles of flint would damage the tool.]

    Will you recomand tungsten carbide for hard limestone or basalt?


    [Hard limestone (2.5 on the Mohs scales) would probably be okay, but basalt (6 on the Mohs scale and tough) is a whole other matter. ]

    Still i dont understand why the coated diamond bits will get so warm and fall if i plan to go at speeds of 10mm per minute.. even if it takes 10 hours to create the small circle (20mm diameter, 3mm deep in the stone)

    [The feedrate isn't that significant as far as the tool bit is concerned; the RPMs are what's causing the heat, and it will heat up just as much if not more from rubbing as from actually cutting. Even if you cool the cut with water, though, the diamonds will still come off or shatter - Britt describes the breakdown process pretty well.]

    I work a lot with stone, but never with a cnc machine, i saw that for cutting or grinding stone in larger cnc machines they use diamond bits.

    I use a dremel 3000 with some diamond bits and it works fine with most stones even on 8,000 rpm like this machine has.
    What is the difference between a rotary tool to a cnc in a matter of grinding a stone?

    [There's a lot of variation in diamond tooling. The bits used in large CNC machines for stone processing are made differently. The diamond is distributed throughout the metal matrix of the cutting parts of these tools, so that as they wear down, more diamond edges are exposed and the cutting action continues. These are a lot harder to make and considerably more expensive than the cheap diamond-plated tools you were talking about.
    If you're doing light intermittent cutting on stone for a short period of time and keeping things cool, they can last a while, but CNC puts a lot of load on a tool and it's constant until the diamonds wear off and it breaks.]
    Andrew Werby
    Website

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