Buyer guide

Stone CNC Buyer Guide: 7 Checks Before You Place an Order

This stone CNC buyer guide is written for engineers and sourcing teams who need machined stone parts, not slabs. We cover what drives cost, which tolerances the process can actually hold, and the questions that separate a capable shop from a reseller.

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The ultimate guide to stone CNC processing - stone CNC buyer guide

On this page

1
Key takeaways
2
What to compare across stone CNC suppliers
3
Why a stone CNC buyer guide starts with the stone, not the machine
4
Tolerances you can realistically hold on stone
5
Tooling, feeds and the cost of a chipped edge
6
Finishing, edge profiles and what the quote leaves out
7
Lead time, MOQ and how to read a stone CNC quote
8
Red flags to check before you commit
9
Step by step: how to run a stone CNC order

Quick answers

Key takeaways

Match the machine to the partA 3-axis router handles flat profiles and sink cutouts. Curved moldings and undercut edges need 5-axis.

Tolerance depends on the stoneGranite and engineered quartz hold tighter than veined marble, which can chip along the edge.

Ask how they hold the blockVacuum tables and fixture design decide whether your ±0.1 mm callout is realistic.

Finishing is a separate quote lineHoning, polishing and edge profiling often cost more than the cutting itself.

Check the stone sourceIf the shop buys your slab, the batch can differ in color and grain from the sample.

Selection criteria

What to compare across stone CNC suppliers

Use the same part drawing for every quote so the answers line up.

Criterion	What to ask	Why it matters
Machine setup	3-axis, 4-axis or simultaneous 5-axis?	Decides whether curved profiles and undercuts are possible
Work envelope	Maximum part size they can hold	Large architectural pieces need long-bed routers
Tolerance	What they hold on your stone type	Marble and granite behave differently at the same callout
Tooling	Diamond tools, feed and spindle speed	Wrong feed rate causes chipping on the exit edge
Finishing	Honing, polishing, edge profile in-house?	Outsourced finishing adds days and handoff risk
MOQ	One-off or batch only?	Prototypes and replacement pieces are often single units
Quote basis	Per part, per linear meter or per hour?	Per-hour quoting makes budget comparison hard
Inspection	Reports and measurement method	CMM or profile gauge on stone needs agreement upfront

Fix the stone, the tolerance and the finish before you ask for a price

A stone CNC buyer guide is only useful if it changes what you put on the drawing. Name the stone, set tolerance per feature, list the finishing steps, and ask for an itemized quote. Those four moves remove most of the surprises.

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Section 1

Why a stone CNC buyer guide starts with the stone, not the machine

Most buyers shortlist machines first. That order is backwards. The stone decides the tool, the feed and the achievable tolerance, so start there. Granite is hard and abrasive but consistent. Engineered quartz is uniform and machines predictably. Marble and travertine are softer and often veined, which means the edge can chip even when the cut itself is clean.

Ask your supplier what they have actually run before. A shop that cuts quartz countertops daily may never have held a 0.1 mm profile on a curved granite molding. The machine is the same class. The experience is not.

One more point on thickness. A 20 mm slab and a 100 mm block are different problems. Thin slabs flex under clamping pressure and need support underneath. Thick blocks need a machine with enough Z travel and a fixture that will not let the piece walk during a long roughing pass.

1
Hard and abrasiveGranite and quartz wear diamond tools; expect tool changes mid-run on long profiles.
2
Soft and veinedMarble and travertine chip at the exit edge; lower feed rates help.
3
Thin sectionsUnder 30 mm, support the full underside or the part will flex.

Section 2

Tolerances you can realistically hold on stone

Every shop quotes a headline tolerance. On stone, that number means less than it does on aluminum. A realistic working range for sawn and milled granite faces is ±0.1 mm on flat surfaces, tighter on features cut into a stable block. Veined marble pushes that out to ±0.2 mm or worse at the edge.

The reason is grain pull-out. When the diamond tool exits the cut, individual crystals or binder particles detach. The cutter path is accurate; the material surface is not. No controller setting fixes that.

This is where the metal fixture matters. If your stone panel sits in a machined aluminum frame with a ±0.005 mm locating face, the assembly tolerance is dominated by the stone, not the frame. Buyers who need the whole assembly to a tight number should plan for a metal carrier and treat the stone as the insert.

Ask for a first article before the full run. Measure it on the features you care about, not on the overall length. Edge quality and hole position usually matter more than the outside profile.

1
Flat faces±0.1 mm is a reasonable target on granite and quartz.
2
Edges and veined stone±0.2 mm or looser; chipping sets the limit.
3
Mixed assembliesMachine the metal carrier to ±0.005 mm and let it control location.

Section 3

Tooling, feeds and the cost of a chipped edge

Diamond tooling is the only practical option for stone. Electroplated tools cut fast and cheap but wear quickly, so a long profile run may need two or three tools. Sintered or brazed diamond tools cost more and last longer, which matters on production runs above a few dozen pieces.

Feed and speed depend on hardness and on how much material you are removing. A light finishing pass at a low feed rate produces a cleaner edge than one heavy pass, even though it takes longer. If a quote looks unusually cheap, ask how many passes are planned.

Water cooling is not optional. It controls dust, keeps the tool cool and extends diamond life. A shop running stone dry is either using a very specific tool or cutting corners.

For holes and pockets, drill with a peck cycle and clear the slurry. Stone dust packs into the hole and the tool rubs instead of cutting. That is the most common cause of a broken drill on a job that looked simple on paper.

1
Electroplated diamondLow cost, short life; fine for one-offs.
2
Sintered diamondHigher cost, longer life; better for repeat runs.
3
Always flood coolantDry cutting shortens tool life and raises dust.

Section 4

Finishing, edge profiles and what the quote leaves out

Cutting is only part of the job. A stone part usually needs the edge profiled, the face honed or polished, and sometimes a sealer applied. These steps are often hand work, and hand work is where lead time slips.

A polished face at Ra 0.2–0.8 μm is achievable on granite but not on a soft, porous limestone. On softer stone, expect a honed finish around Ra 0.8–1.6 μm and accept that the surface will not be mirror-bright. Promising otherwise is a warning sign.

Ask whether finishing happens in the same building. If the shop sends parts out for polishing, you inherit a second schedule and a second set of handling risks. Each move is a chance to chip an edge that was already accepted at inspection.

One last item: engraving and lettering. Minimum character height around 1.5 mm is a practical floor on stone. Below that, the tool cannot clear the slurry and the letters fill in.

1
Profile edgesBullnose, chamfer and ogee need a shaped tool, not a straight cutter.
2
Polished vs honedPolish suits granite and quartz; honed suits limestone and slate.
3
Engraving depthKeep characters at 1.5 mm height or larger for legible results.

Section 5

Lead time, MOQ and how to read a stone CNC quote

Quoting on stone is harder than quoting on metal because the material may not be in the shop yet. If you supply the slab, the schedule starts when it arrives and is inspected. If the supplier sources it, add time for the quarry or distributor to ship.

A workable sequence looks like this. Drawing and DFM feedback within 12 hours. Production start within 24 hours of approval, assuming material is on hand. Parts ship in 3–5 days for typical jobs. Anything with a large profile run or hand polishing will take longer, and a supplier who says otherwise has not read your drawing.

MOQ is usually not the constraint. A single replacement baluster or one prototype panel is normal work. What drives cost on a one-off is setup and tooling, not volume. Getting a second identical piece later is cheaper because the setup already exists.

Read the quote line by line. Material, cutting, edge profile, surface finish, inspection and packaging should each appear. A single lump sum hides which step is expensive, and that is the step you will want to negotiate or simplify.

1
DFM firstSend the drawing before committing to a stone type.
2
Setup dominates one-offsTooling and fixturing, not material, set the floor price.
3
Itemized quotesSeparate cutting from finishing so you can compare shops.

Section 6

Red flags to check before you commit

A supplier who cannot describe their fixture for your part has probably not cut anything like it. Ask for the holding method, the tool sequence and the inspection plan. Vague answers on all three are a pattern, not a coincidence.

A quote far below the others usually means one of three things: fewer finishing passes, outsourced polishing, or stone of a different grade than you specified. Any of those can be fine if it is stated. It is a problem when it is discovered at delivery.

Confirm who owns the risk on material defects. Natural stone has fissures and color variation. Decide in advance whether a hairline fissure on a visible face is a reject, a repair or an accepted feature. Written acceptance criteria save an argument later.

Finally, check confidentiality terms if your drawings are proprietary. Uploads should be handled as confidential, and an NDA should be available on request before you send CAD files.

1
Vague fixture answersAsk for the holding method in writing.
2
Unexplained low priceAsk which step was removed to get there.
3
Undefined defect rulesAgree on visible-face acceptance criteria upfront.

Workflow

Step by step: how to run a stone CNC order

Each step lists the action and the detail that most often goes wrong.

1
Define the function of every surfaceMark which faces are visible, which are locating faces and which are hidden. Visible faces drive the finish spec; locating faces drive the tolerance spec. Sending one tolerance for the whole part is the most common cause of an expensive quote and a rejected delivery.
2
Pick the stone and confirm the gradeName the exact stone, not just the color. Granite, engineered quartz, marble and limestone each need a different tool and finish plan. If the stone comes from the supplier, ask for a sample piece before the run starts so both sides agree on grain and tone.
3
Send the drawing for DFM reviewInclude the overall size, the maximum section, hole diameters, edge profile and finish callout. A useful review comes back within 12 hours with notes on tool access, minimum inside radius and where a 5-axis setup is required instead of 3-axis.
4
Agree on tolerance per featureSet ±0.1 mm on machined flat faces for granite and quartz, and loosen edge and hole position to ±0.2 mm on veined or soft stone. Write the numbers on the drawing. Verbal tolerance agreements do not survive a shipping inspection.
5
Confirm the holding and tooling planAsk how the block is clamped and which diamond tool runs the profile. On thin panels under 30 mm, the full underside should be supported. On long profiles, ask how many tools the run will consume so the tooling line in the quote makes sense.
6
Fix the finishing scope in writingList each edge profile, the face finish (polished, honed or as-machined) and whether sealing is included. Polished granite can reach Ra 0.2–0.8 μm; honed limestone sits around Ra 0.8–1.6 μm. Anything outside those ranges needs a sample first.
7
Set acceptance criteria before the runDefine what counts as a chip, a fissure and a color mismatch. State the inspection method and whether a report is required. A first article on one piece is cheaper than a debate over twenty.
8
Plan packaging and handlingStone parts are heavy and brittle. Specify edge protection, individual wrapping and pallet loading. Damage in transit looks like a manufacturing defect when it arrives, and sorting it out costs more than the packaging would have.

FAQs

Frequently asked questions

Can a stone CNC shop hold ±0.05 mm?

On the metal fixture, yes. On the stone itself, rarely. The tool path can be that accurate, but grain pull-out at the exit edge puts the real limit closer to ±0.1 mm on granite and ±0.2 mm on veined marble.

If your assembly needs ±0.05 mm, machine a metal carrier to ±0.005 mm, seat the stone in it, and treat the stone as the insert rather than the datum.

Is 3-axis enough, or do I need 5-axis?

Flat panels, sink cutouts, straight edge profiles and simple through-holes run fine on 3-axis. The part sits flat and the tool comes down from one direction.

Curved moldings, undercut edges, tapered columns and any feature that wraps around a corner need 4-axis or simultaneous 5-axis. Ask the supplier which machine they plan to use before you compare prices, because the two quotes are not for the same operation.

What is a normal lead time for stone CNC parts?

For a typical job with material on hand, production can start within 24 hours of drawing approval and parts ship in 3–5 days. Hand polishing and long profile runs extend that.

If the supplier is sourcing the stone, add the distributor or quarry transit time on top. Ask for the schedule to be split into material, machining and finishing so you can see where the days are.

Is there a minimum order quantity?

No. Single prototypes and replacement pieces are normal, and production runs from one part to 10,000+ pieces are handled on the same equipment.

The cost curve is driven by setup and tooling, not by volume. A second identical piece ordered later is cheaper than the first because the fixture and program already exist.

How do I compare quotes from different stone CNC suppliers?

Give every supplier the same drawing, the same stone and the same finish callout, then ask for an itemized quote covering material, cutting, edge profile, surface finish, inspection and packaging.

A lump sum tells you nothing about which step is expensive. Once the lines are visible, you can simplify a profile or accept a honed instead of polished finish and see the effect on price immediately.

Do you sign an NDA for stone parts with proprietary geometry?

Yes, an NDA is available on request and uploads are handled as confidential. Send the NDA before the CAD files if the geometry is sensitive.

For parts where only the function matters and the shape is generic, a written note confirming that drawings will not be shared outside the project is usually enough.