What Are Cutting Fluids? & Exploring the Best Products for Metalworking Shops

High-precision metalworking tools and machinery encounter significant stress during machining processes. As cutting tools engage with metal, the intense friction involved generates heat and accelerates wear, sometimes damaging both tools and workpieces. 

To combat this, cutting fluids—often referred to as metalworking fluids—are essential components in the machining process. These fluids serve as lubricants, coolants, and corrosion inhibitors. In turn, they can improve tool life, part quality, and process efficiency.

From high-speed drilling to fine Swiss machining, choosing the right cutting fluid ensures your operation stays productive and cost-effective. In this article, our experts dive into the fundamentals of cutting fluids, their types, and the best products trusted by professionals.

What Are Cutting Fluids?

Cutting fluids are specially engineered liquids used during metalworking operations like milling, drilling, grinding, and turning. Their primary purpose is to manage the friction and heat generated during metal cutting processes. By acting as a lubricant and coolant, they help maintain the integrity of both the cutting tool and the workpiece.

Depending on your machine configuration and the task at hand, there are several application methods for metal cutting fluids:

• Flood Cooling: A continuous stream of fluid is delivered from multiple nozzles to the cutting area. This method is ideal for processes requiring aggressive cooling and chip removal, such as grinding or high-volume drilling.
• Mist Systems: These systems turn cutting fluid into a fine spray and direct it to the cutting area. Mist is best for high-speed, controlled machining operations that only need minimal fluid.
• Through-Tool Coolant Delivery: Advanced machinery may feature internal channels within tools that allow coolant to be delivered directly to the cutting edge—particularly useful for deep-hole drilling and tight-tolerance work.
• External Coolant Nozzles: Strategically placed nozzles offer a targeted fluid stream for cooling and lubrication, with the flexibility to adjust flow and positioning.
• Minimum Quantity Lubrication (MQL): MQL delivers mist or droplets of lubricant directly where needed, ideal for eco-conscious shops minimizing fluid use.
• High-Pressure Directed Coolant (HPDC): This method utilizes specific nozzles and pumps to deliver fluid at high pressures, perfect for hard materials, high-pressure systems, or chip-intense processes.

The Role of Cutting Fluids in Metalworking

Cutting fluids provide several benefits that contribute to high-performance metal machining.

#1. Cooling at High Cutting Speeds

When cutting at elevated speeds, cutting fluids absorb and dissipate the significant amount of heat generated, preventing overheating and thermal deformation of workpieces.

#2. Lubrication at Low Cutting Speeds

In slower operations, such as tapping or reaming, cutting fluids act as a barrier between tool and material. In turn, they minimize friction and reduce tool wear.

#3. Chip Removal

Fluids help flush away chips and debris from the cutting zone, maintaining cutting accuracy and preventing chip re-welding onto the workpiece.

#4. Corrosion Protection

Cutting fluids create a protective layer over both the tool and workpiece, shielding them from oxidation and rust.

#5. Surface Temperature Control

Hot parts are difficult to handle or measure. Cutting fluids cool surfaces post-cut, enabling quicker handling and inspection.

#6. Minimized Thermal Damage

By controlling heat buildup, cutting fluids help avoid surface burning, micro-cracking, and structural changes to the metal.

#7. Easier Swarf and Chip Handling

Cutting fluids make it easier to manage and remove swarf, the tiny metal chips, fragments, or curls produced during machining processes. This reduces the need for frequent manual cleaning and improves automation potential.

#8. Enhanced Surface Finish

By reducing tool chatter and material sticking, cutting fluids result in smoother, more consistent part surfaces.

#9. Extended Tool Life

Lower tool temperatures and reduced friction from cutting fluids directly translate into longer-lasting, more reliable tools.

#10. Improved Machinability

Metal cutting fluids enable smoother cutting of hard-to-machine materials like titanium, stainless steel, and aerospace alloys, ultimately improving productivity.

Exploring Cutting Fluid Types and Applications

There are multiple categories of cutting fluids, each tailored to specific applications.

Soluble Cutting Fluids

These oils mix with water to create a milky emulsion, providing good lubrication and cooling. Best suited for nonferrous materials, they’re widely used in general machining applications.

Synthetic Cutting Fluid

Synthetic fluids contain no oil and are composed of chemical solutions, polymers, and additives. With superior cooling and extended shelf life, they are well-suited for high-speed machines and ferrous materials. However, some synthetic cutting oils may stain nonferrous metals like copper or brass.

Semi-Synthetic Cutting Fluid

Blending synthetic materials with oil, semi-synthetic fluids offer the best of both worlds. They provide lubrication, coolant properties, and resistance to contamination across a broad spectrum of ferrous and nonferrous applications.

Straight Cutting Fluids

Also known as neat oils, straight cutting fluids are undiluted mineral oils, often enhanced with Extreme Pressure (EP) additives like chlorine, sulfur, or phosphorus. They offer exceptional lubrication for demanding machining processes but have limited cooling capacity.

What Are the Best Cutting Fluids?

Keller-Heartt offers a wide range of premium cutting fluids to meet versatile metalworking needs. Here are the top recommendations to help you make the best choice for your shop:

TRUEGARD SUPERCOOL #4086

Formulated with advanced polyesters, TRUEGARD SUPERCOOL #4086 delivers outstanding machining performance on both steel and aluminum. As part of the TRUEGARD SUPERCOOL #4000 series, this semi-synthetic coolant concentrate offers enhanced longevity and stability. It’s engineered without sulfur-containing emulsifiers, eliminating bacteria-feeding elements and extending coolant life. The product resists emulsification with hydraulic or way oil, maintaining emulsion integrity and allowing for easy tramp oil removal. TRUEGARD SUPERCOOL #4086 also boasts a high flash point and extremely low foaming, even under high-pressure conditions.

• Sizes Available: 55-gallon drum
• Applications: Machining operations involving steel and aluminum
• Features:
  • Polyesters for exceptional cutting performance
  • Bacteria-resistant formulation 
  • Excellent emulsion integrity
  • Ultra-low foaming under high-pressure machining
  • High flash point for added safety

TRUEGARD Tri-Purpose Cutting Oil

A multifunctional solution, TRUEGARD Tri-Purpose Cutting Oil serves as a cutting fluid, hydraulic oil, and machine lubricant. It helps reduce contamination between systems and is ideal for automatic screw machines. With a light, transparent color and chlorine-free composition, it’s a safe, versatile, and environmentally friendly option.

• Sizes Available: 275-gallon tote, 55-gallon drum
• Applications: Cutting, lubrication, and hydraulic systems in automatic machines
• Features:
  • Chlorine-free and easy to dispose of
  • Non-staining to yellow metals
  • Provides long tool life
  • Enables faster machine rates

TRUEGARD Cutting Oil D Plus

Designed for machining hard metals, this active cutting oil contains anti-mist and anti-weld agents, including active sulfur. It provides outstanding surface finishes and edge retention, making it ideal for operations where extreme pressure resistance is required.

• Sizes Available: 275-gallon tote, 55-gallon drum
• Applications: High-speed machining of difficult ferrous metals
• Features:
  • Active sulfur for extreme pressure protection
  • Excellent finish and tool life extension
  • Anti-mist additive for safer high-speed operations
  • Not recommended for nonferrous metals

TRUEGARD #1290 Cutting Oil

This medium-duty, 100% virgin mineral oil is specially formulated for challenging machining tasks. Enriched with active sulfur and fat, it excels in operations like broaching, threading, and drilling. TRUEGARD #1290 enhances tool life and finish quality, even on exotic alloys.

• Sizes Available: 55-gallon drum
• Applications: Drilling, tapping, threading, broaching, gear cutting, and forming of steel alloys and exotic metals
• Features:
  • High film strength for severe machining
  • Reduced misting and excellent surface quality
  • Versatile application via spray, roll, brush, or recirculating systems

TRUEGARD Swiss Cutting Oil #148

Built for Swiss-style machining, this oil delivers superior lubricity and exceptional heat dissipation. It helps prevent discoloration, maintains dimensional accuracy, and supports long machine cleanliness cycles thanks to its advanced thermal stability.

• Sizes Available: 55-gallon drum
• Applications: Swiss machining operations requiring precision and cleanliness
• Features:
  • EP additives and friction modifiers for enhanced lubricity
  • Fast heat dissipation and cool running
  • Improved tool and workpiece stability

TRUEGARD HD-258 Cutting Oil

An extremely heavy-duty option, HD-258 is built to handle stainless steel and nickel-based alloys. It can also be used as a performance booster when mixed with lighter oils. With superior load-carrying capability and wipe resistance, it’s ideal for slow, heavy-duty operations.

• Sizes Available: 5-gallon pail, 55-gallon drum, 275-gallon tote
• Applications: Drilling, tapping, threading, broaching, gear cutting, stamping, punching, and drawing of tough ferrous metals
• Features:
  • Additive-rich formula for maximum lubricity
  • Sustains high loads across varied temperatures
  • Suitable as a base or additive oil

TRUEGARD Cutting Oil 1230-15

This dual-purpose oil is both a cutting fluid and machine lubricant. It contains a moderate level of chlorine, is sulfur-free, and is perfect for light to medium-duty tasks. Its clean, low-odor formula supports a healthy working environment.

• Sizes Available: 55-gallon drum
• Applications: Drilling, turning, and threading of steel, copper, and aluminum alloys
• Features:
  • Dual-use formula enhances convenience
  • Excellent heat transfer and surface wetting
  • Safe, light, and low-volatility composition

TRUEGARD #1011A Cutting Oil

Formulated for screw machines and lathes, this oil balances sulfur and fat content to offer great lubricity in moderately demanding tasks. Its mild detergency reduces swarf buildup, and its high flash point ensures safe, stable operation.

• Sizes Available: 55-gallon drum
• Applications: Drilling, tapping, threading, reaming, and boring on steel and steel alloys
• Features:
  • Excellent film strength for reliable tool protection
  • Low misting and clean-running properties
  • Ideal for less severe machining

Check Out the Metalworking Product List →

How to Select the Right Metal Cutting Fluids

Not all fluids are created equal—and the ideal fluid for one application might be a poor fit for another. Here’s a deeper look at the key factors you should consider when selecting metal cutting fluids for your shop:

• Machining Process: The specific operation—whether it’s drilling, milling, grinding, turning, or broaching—plays a major role in fluid selection. High-speed operations, such as CNC milling or surface grinding, generate substantial heat and would benefit from synthetic or semi-synthetic fluids with superior cooling capabilities. Low-speed or high-pressure operations, like deep-hole drilling, could benefit from straight oils or heavy-duty oil-based fluids to help minimize friction and wear on the tool.
• Material Type: Different metals have distinct chemical and mechanical properties that influence how they react with cutting fluids. 
  • Stainless steel and titanium alloys are hard to machine and generate significant heat. Look for fluids with active sulfur or extreme pressure (EP) additives that can prevent tool welding and ensure smooth chip evacuation.
  • Aluminum and copper alloys are prone to staining and corrosion when exposed to fluids with reactive additives. Use sulfur-free or non-staining fluids like synthetic or specific soluble oils.
  • Cast iron often requires high-flushing capacity to remove abrasive chips. Water-based fluids with excellent wetting properties are typically ideal.
• Cutting Speed: Cutting speed directly affects the amount of heat generated at the tool-workpiece interface. High-speed applications demand fluids with superior cooling properties to reduce thermal stress and preserve dimensional accuracy. Low-speed machining places more emphasis on reducing friction, making high-lubricity oils more appropriate. For multi-speed operations, consider a versatile fluid that performs well across a broad range of speeds and materials.
• Tool Type and Application: The type of tooling and how coolant is delivered also influence fluid choice. For example, through-tool coolant systems require fluids with appropriate viscosity and particle-free formulations to avoid clogging internal channels.
• Environmental Considerations: Shops are increasingly prioritizing safety, sustainability, and ease of fluid disposal. Look for low-odor, chlorine-free, and biodegradable fluids to maintain a healthier work environment. Plus, fluids designed for low misting reduce airborne contaminants and improve air quality. Some cutting fluids are also non-hazardous under OSHA and EPA standards, making them easier to store, handle, and dispose of.
• Operational Longevity: Operational efficiency isn’t just about cutting performance; downtime and maintenance matter, too. Fluids with extended sump life and biostability reduce the frequency of change-outs and microbial growth. Plus, low-odor products that stay clean-running even under heavy workloads can minimize downtime.

Only the Best Cutting Fluids for Your Operation

Whether you're running a high-speed CNC machine or precision Swiss lathe, the right cutting fluid makes all the difference. At Keller-Heartt, we’re more than suppliers—we’re partners in your operation’s success. 

We recommend starting with trusted solutions from our extensive TRUEGARD lineup to keep your tools sharp, your parts pristine, and your production moving forward. Simply place your order online or contact our team today to inquire about bulk pricing or personalized recommendations.