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The Brunsfield Center/Manufacturing Technologies/Coolant

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Most CNC systems, as well as some manual machines have built-in recirculating coolant systems.

Coolant plays a vital role in milling operations—even in a shop that uses manual application methods like hand squeeze bottles. Though it’s easy to overlook, proper coolant use can significantly improve tool life, surface finish, and machining performance.

This page outlines what coolant does, when and why to use it, and how to apply it effectively in a manual shop setting.

Using coolant while milling isn’t just about keeping things from getting hot—it improves surface finish, extends tool life, and helps with chip control.

Why Use Coolant?

  1. Heat Control - Milling generates heat—especially in harder materials like steel. Coolant reduces tool and workpiece temperatures, helping maintain tolerances and prevent thermal expansion.
  2. Tool Life - Excessive heat and friction dull or chip tools prematurely. Applying coolant lubricates the cutting edges and reduces wear, especially on HSS tools.
  3. Surface Finish - A lubricated cut typically produces a smoother surface and fewer burrs, especially on aluminum and softer metals.
  4. Chip Evacuation - Coolant helps clear chips from the cutting zone. This is critical during slotting or deep cuts, where chips tend to pack in.

When to use Coolant

Brunsfield coolant bottles used for the mills, lathes, drill presses, etc.

Coolant is not always required, but here are the most common scenarios where it makes a noticeable difference:

  • Drilling: Especially for holes deeper than 2× diameter or in steel.
  • Slot milling and pocketing: Helps clear packed chips and reduce heat.
  • Steel or stainless machining: These materials build up heat fast.
  • Using HSS tools: High-speed steel dulls quickly if it gets too hot.
  • Reaming or tapping: Requires lubrication for good finish and thread quality.
  • Finishing passes: Helps improve surface finish and avoid burrs.

Often Not Necessary

  • Shallow milling in aluminum: Especially with carbide tools, dry cuts are often fine.
  • Roughing passes with large tools: Coolant might not reach the cutting edge or can fling off.
  • When chips clear easily: If there’s no heat or chip buildup, coolant adds little benefit.

How to Apply It:

  1. Aim the nozzle just ahead of the cutting edge—not directly on top, so chips are cleared effectively.
  2. Apply a steady stream, not just a few drops—especially in steel or when drilling deep.
  3. Pause between passes to reapply as needed.
  4. Watch the chips: if they’re starting to discolor, cling, or weld to the tool—apply more coolant.
Blue coolant drum in Brunsfield

Tip:

Use compressed air or a chip brush to clear chips before reapplying coolant. Reapplying coolant on top of packed chips can make things worse.

Lathe coolant reservoir.

Refilling Coolant

Transfer Bucket

When coolant bottles are empty, they can be refilled from the main drum beside the sink. This drum contains a coolant solutions that is used for all machines ASIDE FROM THE VERTICAL BANDSAW.

Lathes

The lathes have their own built-in coolant pumps that are controlled with a toggle switch on the control panel. The coolant is ejected from a flexible hose and can be easily positioned depending on the operation.

To refill the coolant, fill the transfer bucket with roughly 1L of coolant from the blue drum, then fill the reservoir at the back of the lathe once it's getting low.

Types of Coolant

Your shop likely uses a water-soluble coolant or cutting oil in squeeze bottles. Here’s a quick guide to types:

  • Water-soluble coolant (emulsion)
    • Mixes with water, offers good cooling, safe for most materials.
    • Needs cleanup to avoid corrosion on steel parts.
    • This is the blue liquid that you see around the shop in hand-squeeze bottles or pumps.
  • Cutting oil
    • Straight oil, better for tapping, reaming, and threading in steel.
    • More lubricating, less cooling.
  • WD-40 (sometimes used for aluminum)
    • Helps reduce sticking and improves finish, but offers minimal cooling.
    • Can become gummy over time.

Never mix coolant types in the same bottle or apply flammable oils near high-speed cuts.

Coolant Use: Best Practices

  • Don’t just “spray and pray.” Use coolant when it adds value: cooling, lubricating, or clearing chips.
  • Don’t rely on it to fix a bad setup. If your cutter is chattering, coolant won’t solve the real issue.
  • Learn the signs: blue chips, squealing, and welding chips all mean coolant might help.
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