Steel Milling Guide: How To Mill Steel

Watch this video introduction to steel milling basics. Tech expert Kurt Repsher walks you through how to choose the right end mill and lubricant for your steel milling application, the pros and cons of various tool materials, helix angles, coatings, and much more!
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STEEL BASICS:

Steel is machinable, and commonly found in pretty much any machine shop. The following steel milling basics will help you to hit the ground running, so you can land some good jobs and handle them like a pro.



SOME OF THE CHALLENGES:

If you’re making a part or two, it won’t really matter how hard you push the tool for maximum material removal. But if you’re making thousands of parts a week, you’ll need a more effective strategy. To effectively mill steel, you'll have to:

Prevent tool breakage: You'll have to learn how to achieve the maximum material removal rates without breaking a tool or causing downtime.
Keep your cool: If it gets too hot, some steels can work-harden, which will stop the tool in its tracks, potentially destroying both the tool and the workpiece. Maintaining a safe temperature is key.
Keep friction to a minimum: The main challenge with milling steel is keeping both friction and heat to a minimum, while maintaining good chip control and evacuation.

DIFFERENT GRADES OF STEEL:

To start with, all types of steel are machinable, unless it’s been surface, or through hardened. The harder you push the tool, the more you’ll notice the differences between them. As with all machining, you always need to be careful during fast, heavy cuts, especially when the tool exits the material, which is when the risk of tool chipping is at its highest.

CUTTING TOOLS FOR STEEL:

end mill for steel



Try to avoid using two or three flute end mills for steel. Technically they’ll work, but steel isn’t the easiest material to cut, so those 2 or 3 cutting edges will wear pretty fast. Here are a few tips on tool selection:



CUTTING TOOL MATERIAL:

High Speed Steel is the least expensive but offers the shortest life and the slowest operation.
Cobalt is a better choice than High Speed Steel, and only slightly more expensive.
Solid Carbide is the longest lasting end mill material, but it’s fragile, so treat it with care.
FLUTES:

More flutes result in less work per tooth, which extends tool life. Those additional flutes come at a price though.
An end mill with 4 flutes is a good choice most of the time. It’s the ideal balance of tool strength, chip clearance and reduced chatter. Larger end mills, 1-1/2” and up, might perform better with more flutes.
Center cutting end mills are better for ramping and plunging operations.
HELIX ANGLE:

A lesser helix angle will run cooler—since it’s spending less time in the steel.
A higher helix is smoother cutting, gives a great surface finish.
For roughing, a lower helix angle of about 30° works great. The tool stays cooler, and nobody cares about surface finish when roughing anyway.
A higher helix angle of 45° is an excellent choice for finishing. Light finishing cuts don’t generate much heat and it leaves a beautiful and more accurate surface finish.
For both roughing and finishing, use a 40° helix angle as a good compromise.
TOOL FINISH/COATING:

In general, uncoated end mills will work, but a coated cutter will work better. The most common coatings are: TiN, TiCN, TiAlN and AlTiN.
TiN (Titanium Nitride): an inexpensive, general-purpose coating.
TiCN (Titanium Carbon Nitride): the addition of carbon can improve the tool’s surface hardness over TiN coating.
TiAlN (Titanium Aluminum Nitride): bridges the gap between TiCN and AlTiN, and the use of coolant is optional.
AlTiN (Aluminum Titanium Nitride): is for the hardest of machinable materials and withstands the highest temperatures. The use of coolant is optional.
CORNER RADIUS:

Solid carbide is extremely hard, which makes it brittle.
While cutting steel, it’s easy to chip the corner of the cutting edge. If you can, use an end mill with a corner radius to reduce the risk of corner chipping.

WANT TO LEARN MORE ABOUT STEEL MACHINING?

We believe the right tool is everything! Download our Steel Turning & Machining Guide and ensure you have the information you need to select the right tool for your steel machining applications, every time!


By downloading the Steel Machining Guide you'll find information on:

How to select the best turning insert for the steel you're working on
Speed & feed recommendations for the steel you're working on
How scale & surface interruption should impact your insert choice
How to select the right turning insert for the finish you require
What chip breaker to use for your application
How to approach your steel turning applications
DOWNLOAD STEEL TURNING GUIDE

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