Hi, Introduction to stone routing info.

[eco]

Hello

Apologies for diving straight in without introducing myself butI have never met a forum site with so many forum areas and I simply cannot find the introduction forum at all......

Anyways, I am a newcomer to cnc but for 20 years a sign maker and I want to add v-cut lettering and simple logos in stone (slate and marble) to my services.

Being on a budget I have been investigating building my own cnc but wonder if it would be better to buy an aluminium 'frame' and go from there.

I am looking at a work size of say 16-24" x 12 - 24".

Am I correct in thinking that a machine home built of some plastic material (EPDF?) would not be sturdy enough to handle engraving to a depth of 1/2" or so in stone slabs.

There, first of probably thousands of questions.

Thanks in anticipation

Ian (from the UK)

[skippy]

Hi Ian,
cutting or engraving stone requires diamond cutting tools manufactured specifically for stone work. These cutters need (1) very high RPM = high frequency spindle = cost in the thousands, (2) water cooling (flooding not mist). These cutters will last just seconds or even less if they see anything less than smooth movement which means (1) the machine must be built very heavily = generally cast iron = many tonnes in weight, (2) stepper motors are out and even servo motors need very expensive drives (none of this hobby stuff we talk about here) to achieve super smooth movement at very low speeds.
In short, cnc stone machines are so expensive (60,000 Sterling upwards) for a reason and the only alternative that I know of in the sign industry is sandblasting using machine cut stencil masks.

[eco]

Hi Skippy

Thanks for that input, I do have sandblasting in mind too, should have mentioned it but since this is a cnc forum I left it out.

I take on board your information, maybe certain kinds of stone are possibly suitable, close structured, less abrasive ones for example slate and marble, I have seen pantograph routing machines in monumental masons workshops with associated brass lettering templates in the past so presume it can be done.

Water, yes, lots of it, was thinking of building a water bath around the cnc base where cutting takes place.

I like the idea of a DIY cnc and so think I shall pursue this path for wood, metal and plastic work and set up also a small sandblasting unit for stone.

Eco

[Metal Maniac]

Ian,

I have produced a few signs out of granite and travertine.

The machine I ran was pathetic at normal operations on stone but excelled at signs. Thing would barely cut and polish yet lettering and routing came out much easier.

The depth of cut is the biggest factor in machine choice before price and complexity. If you only want to just etch the surface, sandblasting is better suited.

CNC is better for 3D relief. There are a few specialty bits available to make engraving and 3D profiling on stone. I have used a .75" dia. 1.5" long fingerbit, or what ever else they call that endmill type bit, to cut pocket routes and lettering in stone deeper than 1/2" @ 9 inches per minute. I have also used a special bit (not designed for this purpose) to make letters .5mm deep that went about 25" per minute. Good looking lettering needs a lot of control. Deep cutting (more than 3/32") requires thicker bits, more power and better workholding.

A DIY CNC could have less power and still produce engraving in a fair amount of time. Fit the machine to blast abrasive for one job and cut wood the next. I am using a waterjet right now that is supposed to do engraving (more like etching). If I had the space and money I'd make the sort machine you are talking about. I'd like a smaller machine that'll cut anything up to stainless steel and black granite.

By the way, grinding abrasive materials voids the warranties of many machines not intended for that use and can destroy critical machine components.

Nick

[Litografa]

Hi, may be hammer type engraver for stone will be interested for somebody. Working tool is needle. Cheapest is made from tungsteen steel, also there is needles made from synthetic and real diamond. Equipment can engrave up to 2 mm in depth (depends from material and number of passes).

[Cormac]

Ian,
Cutting slate. I make slate sundials. I engrave lines and lettering dry to depth of about .4mm. Spindle speed of 12,000 rpm. Feed and plunge of .4m/min. Machine is a 1.2kw Cadet CNC router from AXYZ / Pacer, Nottingham. Tool is 4mm dia with .2mm point, 60 degrees (30 degrees each side of tool axis). At the tip, 3/4 of shaft are cut away. This gives a clean engrave, with no chipping of fine slate engraving. To cut out my sundial disc (depth of 20mm), I use a 6mm dia carbide 4-tooth mill, with same speeds, feeds and plunge. .3mm per pass. Cutting under water. It works well, but considerable tool wear. Hope this is of some use; maybe you or others could advise me further. Best regards, Cormac (from Ireland)