So, you’ve mastered wood and and now you’re looking to add a touch of golden elegance to your CNC projects. Enter brass: a beautiful, and surprisingly machinable metal that can elevate your work from handmade to heirloom. But before you can create those stunning brass inlays, custom tags, or intricate clock faces, you need to understand that metal is a different beast entirely.
Fear not! While brass demands more respect than a piece of pine, it doesn't require a massive industrial machine. With the right knowledge and a cautious approach, most rigid hobbyist CNC routers can produce incredible results. This guide will give you the foundational knowledge to start cutting brass safely and effectively.
This guide is for cutting through brass, not for engraving. Maybe I'll do another follow up article about engraving, as that is a more fickle process.
The Golden Rules: Feeds and Speeds
The secret to machining any metal (or really any material) is balancing how fast the cutter spins (Spindle Speed) with how fast it moves through the material (Feed Rate). The goal is to create a clean chip, not fine dust or molten globs. Here are some reliable starting points for a 1/8" single-flute (O-flute) upcut carbide end mill, one of the best all-around bits for brass on a hobby machine. O-flute bits allow for keeping the bit cool and evacuating chips, so you are not melting metal. You can use any size, but brass is also not cheap, and I think 1/8th is a good size, as 1/16th and smaller has more of a chance of breaking.
Spindle Speed (RPM)
Unlike wood, where high RPMs are common, brass prefers a more relaxed pace. Too much speed generates excessive heat, which can cause the brass to get "gummy" and fuse to your bit.
- Starting Point: Set your spindle to its lower range, typically between 10,000 and 18,000 RPM. If your spindle can go lower, even better. Listen for a smooth cutting sound, not a high-pitched scream.
Depth of Cut (DOC)
This is the single most important parameter for success and bit survival. Forget the deep passes you take in wood; with brass, we're just shaving the surface. An aggressive depth of cut is the #1 cause of broken bits.
- Starting Point: Begin with a very shallow DOC of 0.005" to 0.01" (0.12mm to 0.25mm). It might feel painfully slow, but it ensures you aren't overloading the bit or the machine.
Feed Rate
This is how fast the machine moves sideways through the brass. You want to move fast enough to form a chip and prevent the bit from rubbing, but slow enough that you don't overwhelm the cutter.
- Starting Point: Aim for a feed rate of 5 to 15 inches per minute (IPM) or 127 to 381 mm/min. If you see dust instead of small chips, your feed rate is likely too slow for your spindle speed.
Plunge Rate
How fast the bit enters the material is just as critical as the DOC. Plunging is a high-stress move for any end mill.
- Starting Point: Be very conservative here. A plunge rate of 4 to 6 IPM (100 to 150 mm/min) is a safe bet.
| Parameter | Recommended Starting Range (for 1/8" Bit) |
|---|---|
| Spindle Speed | 10,000 - 18,000 RPM |
| Feed Rate | 5 - 15 IPM (127 - 381 mm/min) |
| Plunge Rate | 4 - 6 IPM (100 - 150 mm/min) |
| Depth of Cut | 0.005" - 0.01" (0.12mm - 0.25mm) |
Beyond the Numbers: Tips for a Flawless Finish
Getting the settings right is only half the battle. Follow these essential tips to ensure a smooth operation.
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Use the Right Tool: A sharp, high-quality single-flute carbide end mill is your best friend. The "O-flute" design is particularly effective as its large flute provides excellent chip evacuation. Don't even think about using a bit designed for wood.
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Keep it Cool (Lubricate!): Heat is the enemy. A small amount of lubricant will dramatically improve your cut quality and extend the life of your expensive bits. You don't need a fancy flood coolant system; a light mist or periodic drop of WD-40, 3-in-1 oil, or a specialized cutting fluid like Tap Magic for non-ferrous metals works wonders.
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Clear Those Chips: Chips are hot and sharp. If they get stuck in the cutting path, the bit has to recut them, generating even more heat. Use an air blast from a compressor or a vacuum dust shoe to constantly clear the area.
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Listen to Your Machine: Your CNC will tell you if it's happy. A smooth, consistent whirring sound is good. A high-pitched squeal means your RPM is too high or your feed rate is too slow. A deep, chattering rumble means you're pushing the machine too hard—back off your feed rate or depth of cut immediately.
- Always Make a Test Cut: Never run a full project with new settings. Clamp down a piece of scrap brass and run a small test pattern—a simple circle or square—to see and hear how the machine behaves. Adjust one setting at a time until you get the result you want.
Machining brass is a rewarding step into the world of metalwork. It requires patience and a willingness to start slow. But once you dial in the settings for your specific machine, you'll unlock a whole new level of creative potential.
Happy carving!