The CNC vs waterjet decision comes up most often with thick plate, heat-sensitive alloys and flat parts with a few precise features. Waterjet cutting uses a high-pressure stream of water and abrasive to cut 2D profiles in almost any material with no heat affected zone. CNC machining uses rotating cutters to produce precise holes, pockets, threads and finished faces. The two are frequently combined, with waterjet removing bulk material and machining finishing the critical features.
CNC vs Waterjet: Comparison Table
Figures are typical for a thick plate part with a profile and holes. Cost is a relative per-part index, where one machined part at quantity 1 equals 100.
| Factor | CNC machining | Abrasive waterjet |
|---|---|---|
| Relative cost, qty 1 | 100 | 25 to 40 |
| Relative cost, qty 10 | 45 | 12 to 18 |
| Relative cost, qty 100 | 25 | 8 to 12 |
| Relative cost, qty 1,000 | 18 | 6 to 10 |
| Typical tolerance | ±0.001 to ±0.005 in | ±0.005 to ±0.010 in, plus edge taper unless compensated |
| Edge and surface finish | Ra 32 to 125 µin | Sandblasted texture, roughly Ra 125 to 250 µin; striations at speed |
| Materials | Metals and plastics | Nearly anything: metals, plastics, composites, glass, stone |
| Thickness | Any, including 3D features | Up to about 6 in or more, slower as thickness grows |
| Lead time | Days to a few weeks | Often a few days |
| Material effects | No heat affected zone | No heat affected zone; abrasive may embed at the edge |
| Typical use case | Precision features, bores, threads, 3D shapes | Thick profiles, heat-sensitive alloys, mixed materials, blanks |
When Waterjet Wins
- Thick plate profiles. Waterjet cuts titanium, stainless and tool steel plate several inches thick where laser cannot.
- Heat-sensitive materials. No heat affected zone means hardened or heat-treated plate keeps its properties at the edge.
- Unusual materials. Composites, rubber, glass and stone cut cleanly.
- Rough blanks from expensive plate. Nesting profiles saves material compared with sawing rectangles and milling away the waste.
When CNC Machining Wins
- Precise holes and fits. Waterjet holes have taper and are not suitable for reamed, bearing or dowel fits.
- Partial-depth features. Pockets, counterbores, chamfers and threads need a cutting tool.
- Controlled surface finish and flatness. Machined faces and edges meet Ra and flatness callouts that waterjet edges cannot.
- Round and turned parts. Shafts, bushings and fittings are lathe work and do not start as waterjet profiles.
Common Mistakes
- Assuming waterjet edges are square. Without taper compensation, the bottom of the cut can be wider or narrower than the top by several thousandths.
- Tapping or reaming waterjet holes directly. Pierce points and taper make it better to cut undersize and machine to size.
- Leaving no stock for finish machining. Allow about 0.030 to 0.060 in on edges that must be precise.
- Using waterjet for small, simple parts in high volume where laser or stamping would be faster and cheaper.
Waterjet Blank, Then Machine
For thick plate parts, cutting a near net blank on a waterjet and then machining the precise holes, pockets and datum faces often gives the lowest total cost. Define datums on the drawing so the machine shop knows which surfaces to locate from, and confirm how much stock remains on each machined surface.
How This Applies at Wexmar
Wexmar does not operate a waterjet. We machine parts from bar and plate, sawing stock on our KASTO saws, and we can machine customer-supplied waterjet blanks when the precise features justify it. Our six horizontal machining centers handle heavy plate and multi-face work, and CMM inspection verifies the finished features. We machine stainless, titanium, nickel alloys and tool steels. See CNC milling, machine list, and the related guide on CNC vs laser cutting.
Getting a Quote
Send the drawing and tell us whether you will supply blanks or want parts machined from solid. You can upload a drawing for an instant estimate, reviewed by a human estimator, or call (315) 400-2654.