Cut point (also called cut size or separation point) is the target particle size at which a vibratory screener divides material into oversize and undersize fractions, technically defined as the particle diameter that has a 50% probability of reporting to either fraction. It is the fundamental performance specification for any screening operation, determining what material passes through the screen and what discharges over the top.
While the mesh size of the screen cloth sets the nominal cut point (a 100 mesh screen has a nominal opening of 149 microns), the actual effective cut point in operation is influenced by many variables. Particle shape, moisture content, static charge, feed rate, G-force, and residence time all shift the effective cut point above or below the nominal mesh opening. Understanding these influences is what separates a well-optimized screening operation from one that produces off-spec product.
Factors That Shift the Cut Point
| Factor | Effect on Cut Point | Explanation |
|---|---|---|
| Feed rate (too high) | Shifts cut point coarser | Thick material bed prevents fines from reaching screen surface |
| Feed rate (too low) | Minimal shift | Low feed allows maximum passage but underutilizes capacity |
| Moisture (>5–8%) | Shifts cut point coarser | Wet particles agglomerate and blind the screen |
| High G-force | Shifts cut point finer | More aggressive action forces near-size particles through |
| Elongated particle shape | Shifts cut point finer | Elongated particles pass through openings by orienting lengthwise |
| Longer residence time | Shifts cut point finer | More opportunities for near-size particles to find openings |
| Screen wear | Shifts cut point coarser | Worn wire creates larger openings over time |
Why This Matters
Cut point is the specification that connects your screening operation to your product quality requirements:
- Product specification compliance — Every product has a maximum or minimum particle size specification. The cut point must be set correctly to ensure 100% of the product meets spec. In pharmaceuticals, food, and chemicals, out-of-spec product due to an incorrect cut point means rejected batches and lost revenue.
- Multi-deck optimization — In multi-deck screeners, each deck has its own cut point. The cut points must be selected together to produce the desired number of size fractions. For example, a three-deck separator might use cut points at 500, 200, and 75 microns to produce four distinct product grades.
- Mesh selection — Knowing the desired cut point is the starting point for selecting the correct mesh size. Because the effective cut point can shift from the nominal aperture, experienced operators sometimes select a mesh size slightly finer or coarser than the target to compensate for operating conditions.
- Process troubleshooting — When product fails particle size specifications, the cut point has drifted. Identifying whether the drift is caused by screen wear, overfeeding, moisture, or incorrect G-force is the key to corrective action.
Related Glossary Terms
- Separation Curve — The probability curve showing how particles of each size report relative to the cut point
- Mesh Size — The screen specification that sets the nominal cut point
- Aperture — The actual opening size that defines the nominal cut point
- Screening Efficiency — How well the screener separates material at the target cut point
- Oversize / Overs / Tails — Material larger than the cut point
- Undersize / Fines — Material smaller than the cut point
Cut Point FAQs
What is cut point in vibratory screening?
Cut point is the particle size at which a vibratory screener divides material into oversize and undersize fractions. It is the particle diameter with a 50% probability of passing through the screen. The cut point is primarily determined by the screen's mesh size but is also influenced by G-force, feed rate, moisture content, and particle shape.
Is cut point the same as mesh size?
Not exactly. Mesh size defines the nominal opening size of the screen cloth, while cut point describes the actual particle size where separation occurs in practice. Due to factors like particle shape, moisture, and near-size particle behavior, the effective cut point is often slightly different from the nominal mesh opening. A 100 mesh screen (149 micron opening) may have an effective cut point of 130–160 microns depending on conditions.
Get the Right Cut Point with the Right Screen
ScreenerKing's screening experts can help you select the optimal mesh size to achieve your target cut point. We manufacture replacement screens from 4 to 500 mesh for Sweco, Kason, Midwestern, Cleveland Vibratory, Russell Finex, and Rotex vibratory separators. Over 30 years of application expertise from Houston, TX.
