Just because CNC machining is an automated process doesn’t mean you can just press a button and make a perfect part. There are a lot of inputs to a machining operation: the workpiece material, tool type, fixture, cutting fluids, toolpath, and speeds and feeds are all variables that affect the quality of the finished piece.
While experience is the best teacher, it doesn’t hurt to have a few CNC machining tips and tricks under your belt before you start. In this post, we’ll go over a few CNC machining tips and tricks to help both new and experienced machinists achieve the best results possible.
Use the Right Tool for the Material
No matter how nice your CNC machine is, it can only be as good as the tooling paired with it. Proper tool selection is essential for clean cuts and surface finishes. Plus, choosing the right tool for the job helps to maximize tool life and ROI.
You get what you pay for, so avoid cheap, low-quality tooling. That doesn’t mean you have to spring for expensive, professional-grade cutters—just look for well-known, reasonably priced brands like Kennametal or Sandvik. Starting with high-quality tools now will help you avoid problems later.
CNC tooling comes in a wide variety of materials, including:
- Cast iron.
- Low-carbon steel.
- Alloy steel.
- Tool steel.
- Stainless steel.
- Tungsten carbide.
- Nickel-based superalloys.
- High-temperature alloys.
Each of these materials behaves differently. For example, tungsten carbide cutters resist wear better than steel, but they’re more brittle. On the other hand, high-speed steel (HSS) cutters can hold a sharper edge than carbide, though they don’t last as long.
Use the Right Cutting Fluid—And Keep It Clean
When machining metal, the friction between the cutting tool and the workpiece generates heat. This can have several undesirable effects, including:
- Thermal expansion.
- Work hardening.
- Welding of surfaces (galling).
The cutting fluid cools and lubricates the tool and the workpiece, reducing friction and heat to prevent these effects. Lubrication also protects the tool from abrasion and lowers energy consumption.
There are different types of cutting fluids, but just like the oil in your car, the most important thing is to replace it when it gets dirty. Clean coolant increases tool life, reduces foaming and odors, and protects your skin from damage. Overusing dirty cutting fluid can stain parts, requiring additional cleaning. Residue can also build up on the tool and machine components, causing damage, or on the window, where it can obstruct your view.
Take Time for Fixturing and Workholding
Setup and fixturing are time-consuming. It can be tempting to rush through this step to get to the actual machining, but paying adequate attention to workholding up front will save you a lot of time and effort.
The more rigid your workholding, the more precise your parts will be. This is especially true in CNC milling, where the cutting tool exerts a significant sideload pressure on the workpiece.
That doesn’t mean you need to design a custom fixture for every part—although that might be worthwhile for a high-volume part. A quality vise, a clamping kit to mount it to the T-slots of your table, and a set of parallels to keep your workpiece evenly raised are enough to adequately keep parts in place for most jobs.
Know Your Speeds and Feeds
Before running any CNC machining program, it’s essential to understand tool cutting speeds and feed rates, or “speeds and feeds.” Speeds and feeds are variables used in every milling and turning operation, and how you set them will depend on several factors, including the workpiece material, tool material, and tool size.
What are speeds and feeds? Feed refers to the linear speed of the tool or the workpiece (whichever one is moving), expressed in units of surface feet per minute (SFM). Speed refers to the rotational speed of the tool (in milling operations) or the workpiece (in turning operations), expressed in rotations per minute (RPM).
The tool manufacturer’s recommended parameters are the best place to start when setting speeds and feeds. After that, it’s up to the machinist’s eyes, ears, and experience to adjust them.
Learning to adjust speeds and feeds on the fly takes practice. A feeds and speeds calculator can help you set optimal parameters based on materials, tooling, machine power, and other variables.
Start with Quality Material
It might sound obvious, but one of the best CNC tips and tricks we can give you is to start with high-quality, precision-cut metal. No matter how good your technique, you won’t get good results machining a block of low-quality, cheap steel. Furthermore, if you’re not precise with your raw material size, you’ll end up wasting a lot of material cutting it—not to mention the added time and tool wear.
Getting high-quality metal for CNC machining doesn’t have to be expensive. If you find a local metal supplier (or one that offers nationwide shipping) that resells metal remnants, you can get high-quality alloys at a heavy discount. Technologies like x-ray fluorescence (XRF) spectrometry can even be used to verify the exact composition of the alloy.
To minimize waste and costs, find a metal supplier that will precision-cut material to size. This will save you a lot of time and money that would otherwise be spent trimming down material or turning unnecessarily large workpieces into useless chips.
Practice these CNC Machining Tips and Tricks with Affordable, Precision-Cut Metal
While most metal suppliers process metal purchases in a three- to four-week period, Industrial Metal Service can cut your material to size within a few days. Our MetlSaw NF12-T12 can easily cut large, non-ferrous metals up to 12 feet long and 12 inches thick while holding tolerances up to ± 0.065″. Our Amada PCSAW 530 X band saw with pulse cutting technology also gives us the capability to cut specialty metals like titanium to precise tolerances.
We’ve been a trusted metal supplier to machine shops and fabricators in the San Francisco Bay Area and beyond for more than two decades. We supply both new metals sourced from U.S. mills and verified metal remnants at discounted prices. With our extensive inventory, we can help you find exactly what you need.