Thermal issues (overheating)

How to use the coolant calculator

Select ISO material, specify tool diameter, hole depth (L/D), coolant type and drilling mode. Then enter the available parameters for your machine - pressure and flow. The calculator will calculate the recommended pressure and flow rate, show the percentage of coverage of your capabilities relative to the norm and give recommendations for correction.

Why pressure and flow determine the result

When drilling, coolant performs two tasks: it cools the cutting zone and removes chips from the hole. If at least one of these functions does not work, the drill breaks. Moreover, in deep holes, coolant becomes the only mechanism for chip evacuation: gravity does not help, and centrifugal forces are insufficient.

Pressure and flow are two independent parameters and both must be sufficient at the same time. High pressure at low flow does not cool, but only pushes. High flow rate at low pressure does not penetrate to the cutting zone in a deep hole. The calculator evaluates both parameters and shows exactly where you are short.

What influences pressure and flow requirements

Hole depth (L/D). The main factor. At L/D = 3, 10–15 bar is sufficient. At L/D = 8 you need 25–35 bar. At L/D = 12 and deeper – from 45 bar, and at L/D = 20–30 – 75–100 bar and more. With each increase in depth, the coolant must travel a longer path and push out more chips.

Tool diameter. Consumption is directly proportional to the diameter: the cooling channels are wider, the volume of the grooves is larger, the area of ​​the cutting zone is larger. A Ø 20 mm drill requires approximately twice as many liters per minute as a Ø 10 mm drill at the same depth.

Workpiece material: Stainless steel (M) and heat-resistant alloys (S) generate more heat and produce tough chips - 20–30% more pressure is required. Aluminum (N) is the opposite: pressure can be reduced by 30%, but flow must be increased by 50% - aluminum requires flow volume to cool and prevent sticking.

Type of coolant supply. Internal (through-tool) - standard for deep drilling: coolant is supplied directly to the cutting edge through channels in the drill. The external one (nozzles) operates up to L/D ≈ 5, the jet does not penetrate deeper into the hole. MQL (micro lubrication) is even more limited - effective up to L/D ≈ 3.

Drilling mode. Peck cycle (G73/G83) partially compensates for the lack of coolant: the drill periodically leaves the hole and removes chips mechanically. This reduces pressure requirements by 10%. The “deep drilling” mode, on the contrary, increases the requirements - without interruptions, chips accumulate faster.

Frequently Asked Questions

What coolant pressure is needed for drilling L/D = 8? For standard materials (steel, group P) with through-tool supply - about 25–35 bar. For stainless steel (M) and heat-resistant (S) - 20–30% more, that is, 30–45 bar. For aluminum, the pressure can be reduced, but the flow rate must be higher.

Is it possible to drill deep holes with external coolant? Up to L/D = 5 - yes, if the nozzles are directed exactly into the hole. When L/D > 5, external coolant does not penetrate the cutting zone—the chips are packed together and the temperature rises. Solution: switch to through-tool, peck-loop, or a combination of both.

Is flow more important than pressure or vice versa? Depends on the task. To evacuate chips from a deep hole, pressure is critical—flow velocity is needed to “knock out” the chips. For cooling and preventing sticking (especially on aluminum), the more critical flow rate is the volume of liquid that takes away heat. Ideally, both parameters should be normal.

What to do if the machine does not provide the required pressure? Three options: 1) Switch to the Peck cycle - mechanical chip removal reduces pressure requirements. 2) Reduce the feed - less chips per unit of time = easier to wash out. 3) Install a coolant pressure booster (amplifier pump) - if the task is regular, it pays off.

At what L/D is HPC (high pressure) needed? At L/D ≥ 12, standard coolant (20–30 bar) usually fails: chips clog the grooves faster than the flow can carry them out. HPC (70–100+ bar) + through-tool is a required combination. For L/D ≥ 20, a gun drill or an STS system with a specialized chip channel is added to this.

Need help selecting a deep hole drill, setting coolant pressure, or choosing a strategy? Contact our specialists - we will select the tool and modes for your machine.

How to use the nozzle calculator

The calculator operates in two modes. In the “Q by P and Ø” mode, specify the pressure at the nozzle, the flow coefficient (Cd), the diameter of the nozzle opening and the type of liquid - get the calculated flow (l/min) and jet speed. In the “Ø by P and Q” mode, specify the pressure and desired flow - the calculator will calculate the minimum nozzle diameter. A visual indicator shows the jet speed and assesses whether the flow is sufficient for flushing.

Why nozzle characteristics are important

Between the coolant pump and the cutting zone are hoses, filters, valves and the nozzle itself. Every element creates waste. But it is the nozzle that determines what flow and at what speed will reach the tool. A nozzle that is too narrow at high pressure will produce a fast but thin stream - it will not cool the entire area. Too wide at low pressure will produce high volume but a lazy flow that will not flush chips out of a deep hole.

The correct selection of nozzle diameter is a balance between jet speed (needed to hit the chips and penetrate the cutting zone) and flow volume (needed to remove heat). The calculator helps you find this balance without trial and error.

What affects the flow through the nozzle

Pressure (P). The main parameter that determines both the speed and volume of flow. The flow is proportional to the square root of the pressure: to double the flow at the same diameter, the pressure must be quadrupled. Standard machines give 20–30 bar, HPC systems — 70–100+ bar.

Nozzle diameter (Ø). Flow is proportional to the square of the diameter: increasing Ø from 1.5 mm to 2.0 mm almost doubles the flow. Typical nozzle diameters range from 1.0 to 3.0 mm. For internal feeding through the tool, the diameter of the channels is fixed by the manufacturer.

Flow coefficient (Cd). Shows what fraction of the ideal flow the nozzle passes in reality. Sharp hole edge - Cd ≈ 0.62, standard nozzle - 0.70, rounded or profiled - up to 0.80. The difference between 0.62 and 0.80 is 30% of the flow at the same pressure.

Liquid density (ρ). Water-based emulsion (≈1000 kg/m³) and oil (≈850 kg/m³) behave differently. The oil is lighter - at the same pressure the flow is slightly higher, but the viscosity of the oil creates additional losses in the hoses and channels, which the model does not take into account. For an accurate calculation, use the measurement at the nozzle exit.

Jet speed. Determines the “impact force” of the flow. A jet with a speed of > 50 m/s effectively knocks chips out of the drill flutes and washes the cutting zone. Below 20 m/s - washing is weak, chips remain. The calculator shows the estimated speed at the nozzle exit.

What nozzle diameter is needed for a pressure of 20 bar and a flow of 15 l/min? For Cd = 0.70 and an aqueous emulsion - approximately 2.2–2.4 mm. The calculator will calculate the exact value. If the available nozzle diameter is standard (for example, 2.0 or 2.5 mm), choose the nearest larger one - there are always losses in a real system.

Calculation formula - where does it come from? This is the classic flow equation: Q = Cd × A × √(2 ΔP / ρ), where A is the cross-sectional area of ​​the nozzle, ΔP is the pressure drop, ρ is the density of the liquid. It gives an upper estimate of the flow under ideal conditions. Actual flow is 10–30% lower due to system losses.

What is the difference between an external nozzle and a through-tool? An external nozzle (nozzle) directs the jet from the outside - it works well with open access to the cutting zone (turning, milling). When drilling deeper than L/D = 5, the external jet does not penetrate the hole - feed through the tool is needed (through-tool), where the coolant exits directly from the cutting edge.

Why doesn’t the flow double when the pressure doubles? Because the relationship is square-root: Q ∝ √P. To double the flow, the pressure must be increased by 4 times. This is a fundamental law of hydraulics. If you need to significantly increase the flow, it is more effective to increase the nozzle diameter than the pressure.

How to check the actual flow on a machine? A simple method: direct the coolant into a measuring container (bucket) and note the time. 10 liters in 1 minute = 10 l/min. Compare with the calculated value - the difference will show the losses in the system. If actual flow is <60 % a clogged design, faulty filters, for hoses, look of or p pinched pump.<>

Need help setting up your coolant system, selecting nozzles, or switching to HPC? Contact our specialists - we will select a solution for your machine and operation.