Lathe machining involves a high-speed rotating workpiece that comes in contact with the cutting tool to remove the material from its surface.
This contact generates high frictional heat, making it important to use a coolant to prevent overheating of the workpiece and the cutting tool.
There are different coolants available on the market and selecting the best coolant for application will help increase tool like while improving the quality of machining.
This article discusses lathe coolant in detail by going through its types and delivery system.
In the end, the article also differentiates between dry machining and wet machining to help you select the appropriate technique for your application.
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What is Lathe Coolant? Why Use it
A lathe coolant is a substance, generally liquid, that is applied to the cutting area to minimize the heating effect, provide lubrication, and flush the chips away from the cutting tool. This enhances tool life and improves machining quality. Generally, lathe coolant is used when machining metal workpieces.
Lathe cutting tools are generally single-point cutting tools that provide enough clearance for chip evacuation.
However, using a single point for machining the entire workpiece can lead to heating of the tooltip, resulting in tool wear.
This effect is not prominent on wood lathes because wood is a soft material that is relatively easy to machine, without producing high frictional heat.
On the other hand, when using a metal lathe or a CNC lathe to perform heavy machining operations on tough metals like stainless steel, the frictional heat generated at the cutting area is significantly high.
This heat can result in the welding of the tooltip with the workpiece and cause severe damage to the workpiece and the cutting tool.
Therefore, a lathe coolant plays an important role in attaining a smooth surface finish with minimal heat generation even at high lathe speeds.
Depending upon the type of lathes, a coolant delivery system can be pre-installed in the lathe or has to be installed separately, which affects the overall cost of the lathe.
Types of Lathe Coolants
|Parameters||Synthetic||Soluble Oil||Pure Oil|
|Rust Protection||Depends upon its chemical composition||Moderate||High|
|Bacterial Growth||Needs bacteria inhibitor additives||Low||Only when contaminated with water|
|Applications||Available for almost all types of machining applications||Light to heavy machining operations||Low-speed machining of hard metals|
There are different types of cutting fluids or coolants available for lathe machining.
Generally, water has a high heat capacity and readily removes the heat from the cutting surface, regulating the temperature of the cutting area.
However, water is highly corrosive and can damage the workpiece and the components of the lathe.
On the other hand, oil has comparatively lower heat capacity but provides high lubricity and anti-corrosive properties.
Therefore, it is important to select the best coolant fluid for your application that ensures perfect output.
Synthetic coolants, such as Trim synthetic coolant, are chemical-based fluids that are mixed with water in desired proportion to get the required cooling and lubrication results.
The water present in these coolants provides high heat capacity, whereas the chemicals ensure high lubricity.
As a result, these types of coolants are ideal for applications that involve the turning of hard metals at high cutting speeds, leading to high heat generation.
These coolants are generally available in concentrated form, and you can mix them with water in desired proportions to get the required results.
However, these coolants are prone to unpleasant odors due to the presence of chemicals and the growth of bacteria in the water content over time.
Apart from that, these coolants can also consist of a small amount (5–35%) of oil, which further improves their lubricating properties and helps in reducing the heat generated during cutting.
This type of coolant, with oil content, is known as a semi-synthetic coolant.
Soluble Oil Coolants (Emulsions)
Soluble oil coolants, such as Trim MicroSol emulsion, consist of soluble oil mixed with water in the desired proportion.
Generally, a 40% oil base is maintained to achieve good cooling action along with high lubrication.
It provides the best of both properties. While water helps to regulate the temperature by taking away the generated heat, oil reduces friction and minimizes the generation of heat during the turning process.
This type of coolant is generally suitable when turning a moderately hard metal at high speed.
For example, machining mild steel using an HSS cutting tool will result in high heat generation and require a soluble oil coolant to regulate the temperature.
Pure Oil Coolants
Pure oil coolants, such as Evo Dyne cutting oil, consist of all oil content with no or minimal additives.
These coolants are not effective at dissipating the heat generated at the cutting area but can provide excellent lubrication to minimize friction, thereby reducing the amount of heat generated during the process.
As a result, pure oil coolants are generally preferable for slow-speed, high surface finish operations and machining of tough metals like stainless steel.
This type of coolant can consist of mineral oil or a mixture of multiple oils like vegetable, animal, mineral oil, etc. without any water or polymer content.
However, pure oil coolants can contain additives like chlorine or sulfur to further enhance their lubricating properties while making them toxic for the operator, in the long run.
Furthermore, the absence of water from these coolants eliminates the risk of bacterial growth and provides high corrosion resistance.
These coolants have a comparatively thick consistency and are generally used with Swiss lathes.
Coolant Delivery System in a Lathe
After selecting the type of coolant suitable for your application, it is also important to select the ideal coolant delivery system.
Conventional Coolant Delivery
A conventional coolant delivery system includes a coolant tank, a pump, and a hose that delivers the coolant to the cutting area.
This is the most commonly used delivery system that is suitable for most DIY and industrial applications.
Generally, conventional coolant delivery system is of two types: Flood type and Mist type.
Flood Delivery System
The flood delivery system delivers a continuous stream of coolant to the cutting area, thereby taking away the heat from the cutting tool and the workpiece.
Flowing of coolant over the cutting area provides an excellent cooling effect and minimizes the heat-affected area, producing a clean cut with enhanced tool life.
This type of delivery system does not require any special equipment, but the constant delivery of coolant creates a mess and requires a drainage system to drain the excess coolant from the lathe bed.
Mist Delivery System
The mist delivery system requires similar equipment to the flood delivery system, with the only difference being the delivery nozzle which sprays the coolant instant of pouring it.
This system sprays a fine mist of coolant that covers the workpiece and the cutting tool, thereby providing the desired cooling effect.
It uses comparatively less coolant fluid and does not require a drainage system.
However, the mist gets diffused in the air and can be harmful if inhaled by the operator.
Therefore, it is advised to use this delivery system in a well-ventilated workshop with proper safety gear.
Precision Coolant Delivery
Apart from the conventional delivery system, you can also implement a precision coolant delivery system during lathe machining.
This type of delivery system uses a special cutting tool that consists of an internal coolant flow and delivers the coolant precisely at the point of contact between the cutting tool and the workpiece.
Depending upon the positioning of the delivery outlet on the cutting tool, precision coolant delivery systems can be of two types: Under coolant and Over coolant.
However, for a greater surface finish and excellent cooling effect, both systems are often used in combination for high-performance industrial applications.
Under coolant is the technique where a pressurized jet of coolant is released from the flank side of the cutting tool and precisely delivered to the cutting area.
This precise jet of coolant reduces the cutting edge temperature and reduces flank wear on the tool, increasing tool life.
The reduced temperature at the cutting area eliminates the risk of welding between the cutting tool and the workpiece, making it feasible to use softer cutting inserts.
Apart from that, it also facilitates easy evacuation of the chips by forcing them away from the cutting tool.
Over coolant is the technique where the coolant is delivered from the rake side of the lathe cutting tool.
In this system, a high-pressure jet of coolant is delivered from the leading edge (rake) of the tool which facilitates easy chip break-off.
Generally, it is preferable for machining ductile materials, that produce long and stringy chips.
These stringy chips can lodge onto the cutting tool, causing frequent stoppage of the cutting process or even damaging the cutting tool.
Apart from that, over coolant also reduces the risk of build-up edges on the cut, thereby enhancing tool life and improving the quality of the cut.
Dry Machining vs Wet Machining- Is Lathe Coolant Actually Needed?
|Parameters||Dry Machining||Wet Machining|
|Cutting Fluid||Not Used||Used|
|Corrosion Resistance||Good, as no fluid is used||Depends upon the coolant used|
|Tool Life||Short||Enhanced tool life|
|Machining Capability||Light machining operations||Light to heavy machining operations|
|Surface Quality||Burns or oxidation marks on the machined surface||High surface finish|
|Applications||Machining wood, plastics, and soft metals||Machining of hard metals|
Conventional machining operations involve contact between the cutting tool and the workpiece at high speed, which results in material removal from the surface.
This contact can often result in frictional heat that can damage the workpiece and the cutting tool.
Machining of soft materials like wood, plastics, etc., requires comparatively less cutting force, resulting in less heat generation.
This type of machining operation does not require any cooling fluid to absorb heat and is thus known as a dry machining operation.
It is suitable for machining soft materials at low to moderate cutting parameters.
Apart from that, dry machining is also performed on metal workpieces by using specialized cutting tools like a ceramic cutting tool that provides lubrication to minimize frictional heat without the use of coolant.
On the other hand, metals like high-strength and temperature-resistant alloys require an extremely strong cutting force that can generate immense heat leading to tool wear and fire hazards.
Making it important to use a coolant fluid to regulate the cutting temperature. This type of process is known as the wet-machining process.
This type of machining is suitable for heavy machining operations, and the minimization of heat eliminates the risk of burns or marks on the surface of the workpiece.
Lathe machining generally uses single-point cutting tools, that generally do not require coolants for regular machining of non-metals and some soft metals.
However, It is strongly recommended to use a coolant if your application involves heavy machining of metal workpieces regularly.
Although flood and mist coolant systems are very effective, if machining of high-strength and temperature-resistant metals is your primary requirement, it is advised to use a precision coolant system to maximize tool life and produce clean cuts.
On the other hand, for light metalworking on the lathe, you can also use a WD-40 spray or a squeezer bottle for intermittent sprays of coolant to regulate the temperature and maximize tool life.
Frequently Asked Questions (FAQ)
Is it safe to use water-based coolants?
Yes, it is safe to use water-based coolants, provided that they contain anti-corrosive additives. Most modern lathes are optimized for water-based coolants that contain chemical additives to induce anti-rust properties in the material and protect the equipment and the workpiece from corrosion.
How to reduce frictional heat on wood lathes without coolant?
The frictional heat on wood lathes can be reduced by using a sharp cutting tool. A sharp cutting edge glides through the material effortlessly, producing minimal heat during the operation.
Do CNC lathes require any specific type of coolant?
No, regular coolants can be used with CNC lathes. However, CNC lathes often use a special delivery system that is automatically controlled during the operation. Apart from that, certain CNC lathes such as Swiss lathes, are only compatible with pure oil coolants.