After mounting the turret on my CNC lathe, I started thinking about how to outfit it with the required tools. Factors influencing tool selection include prior experience, expert advice, and research. I’d like to share nine important considerations to help you in setting up tools on your CNC lathe. It’s important to remember that these are just suggestions, and the tools may need to be adjusted based on the specific tasks at hand.
#1 OD Roughing Tools
Rarely can a task be finished without OD roughing tools. Some commonly used OD roughing inserts, such as the renowned CNMG and WNMG inserts, are utilized.
There are many users of both inserts, and the best argument is that the WNMG can also be used for boring bars and has better accuracy, while many consider the CNMG to be a more robust insert.
When discussing roughing, we should also consider facing tools. Since there are a limited number of flutes available in a lathe turret, some people use an OD roughing tool for facing. This works well as long as you maintain a depth of cut that is less than the nose radius of the insert. However, if your work involves a lot of facing, you might want to think about using a dedicated facing tool. If you’re facing competition, CCGT/CCMT inserts are a popular choice.
#2 Left vs. Right-Sided Tools for Roughing
CNMG Left Hook Knife (LH)
CNMG Right Side Knife (RH)
There is always a lot to discuss about LH vs. RH tooling, as both types of tooling have advantages and disadvantages.
RH tooling offers the advantage of spindle direction consistency, eliminating the need to reverse the spindle direction for drilling. This reduces wear on the machine, speeds up the process, and avoids running the spindle in the wrong direction for the tool.
On the other hand, LH tooling provides more horsepower and is better suited for heavier roughing. It directs force downward into the lathe, reducing chatter, improving surface finish, and facilitating coolant application.
It’s important to note that we are discussing an inverted right-side holder versus a right-side up left-side holder. This difference in orientation influences the spindle direction and force application. Additionally, LH tooling makes it easier to change blades due to its right-side-up holder configuration.
If that wasn’t complicated enough, you can turn the tool upside down and use it to cut in the opposite direction. Just make sure the spindle is running in the correct direction.
#3 OD Finishing Tools
Some people use the same tool for both roughing and finishing, but there are better options for achieving the best finish. Others prefer using different inserts on each tool – one for roughing and another for finishing, which is a better approach. New inserts can be initially installed on the finishing machine and then moved to the roughing machine once they are no longer as sharp. However, opting for different inserts for roughing and finishing provides the greatest performance and flexibility.The most common insert choices for finishing tools I find are DNMG (above) and VNMG (below):
The VNMG and CNMG inserts are quite similar, but the VNMG is better suited for tighter cuts. It’s crucial for a finishing tool to be able to reach into such tight places. Just like on a milling machine where you start with a larger cutter to rough out a pocket but then switch to a smaller cutter to access tight corners, the same principle applies to turning. Additionally, these thin inserts, such as the VNMG, facilitate better chip evacuation compared to roughing inserts like CNMG. Small chips often get trapped between the sides of an 80° insert and the workpiece, leading to imperfections in the finishing. Therefore, the efficient removal of chips is essential to avoid damaging the cnc machining metal parts.
#4 Cut-off Tools
The vast majority of jobs that involve cutting multiple parts from a single bar stock will require a cut-off tool. In this case, you should load your turret with a cut-off tool. Most people seem to prefer the type of cutter with replaceable inserts, such as the one I use with a GTN-style insert:
Smaller insert styles are preferred, and some may even be ones that are hand-ground to improve their performance.
A cut-off insert can also serve other useful purposes. For example, certain chisel edges may be angled to minimize the slug on one side. Additionally, some inserts feature a nose radius, enabling them to be used for turning work as well. It’s worth noting that the small radius on the tip may be smaller than a larger outer diameter (OD) finishing nose radius.
Do you know what is the effect of face milling cutter speed and feed rate on the CNC machining part processing process?
The speed of the face milling cutter and the feed rate are critical parameters in the CNC machining process that significantly influence the quality, efficiency, and cost-effectiveness of the machined parts. Here’s how these factors impact the process:
Face Milling Cutter Speed (Spindle Speed)
Surface Finish:
Higher speeds typically lead to improved surface finish because of the increased cutting velocity, which can reduce surface roughness. However, extremely high speeds can occasionally cause thermal damage or excessive wear on the tool, which can negatively impact the surface finish.
Tool Wear:
Higher speeds increase the temperature at the cutting edge, which can accelerate tool wear.
Optimal speed must be chosen to balance efficient cutting with minimal tool wear.
Machining Time:
Increased speeds can reduce machining time, improving productivity.
Excessive speeds lead to reduced tool life, increasing downtime for tool changes.
Feed Rate
Material Removal Rate (MRR):
Higher feed rates increase the material removal rate, thus reducing the overall machining time.
Excessively high feed rates can lead to poor surface finish and potential damage to the tool and workpiece.
Surface Finish:
Lower feed rates produce a finer surface finish as the tool makes smaller cuts.
Higher feed rates can create rougher surfaces due to larger chip loads.
Tool Load and Life:
Higher feed rates increase the load on the tool, leading to higher wear rates and potentially shorter tool life. Optimal feed rates should be determined to balance efficient material removal with acceptable tool life. Combined Effect of Speed and Feed Rate
Cutting Forces:
Both higher speeds and feed rates increase the cutting forces involved in the process. It is crucial to balance these parameters to maintain manageable forces and avoid tool deflection or workpiece deformation.
Heat Generation:
Increased speeds and feed rates both contribute to higher heat generation. Proper management of these parameters, along with adequate cooling, is necessary to prevent thermal damage to the workpiece and tool.
Face Milling Basics
What is face milling?
When using the side of an end mill, it’s called “peripheral milling.” If we cut from the bottom, it’s called face milling, which is usually done with precision cnc milling cutters called “face mills” or “shell mills.” These two types of milling cutters are essentially the same thing.
You might also hear “face milling,” referred to as “surface milling.” When selecting a face mill, consider the cutter diameter- they come in both large and small sizes. Choose the tool diameter so that the cutting speed, feed rate, spindle speed, and horsepower requirements of the cut are within the capabilities of your machine. It’s best to use a tool with a cutting diameter larger than the area you are working on, although larger mills need a more powerful spindle and may not fit into tighter spaces.
Number of Inserts:
The more inserts, the more cutting edges, and the faster the feed rate of a face mill. Higher cutting speeds mean the job can be done faster. Face mills with just one insert are called fly cutters. But faster is sometimes better. You need to adjust the individual heights of all the inserts to ensure your multi-cutting-edge face mill achieves a smooth finish like a single-insert fly cutter. Generally speaking, the larger the diameter of the cutter, the more inserts you’ll need.
Geometry: This depends on the shape of the inserts and how they’re secured in the face mill.
Let’s look at this geometry question more closely.
Choosing the best face mill: 45-degree or 90-degree?
When we refer to 45 degrees or 90 degrees, we are talking about the angle of the cutting edge on the milling cutter insert. For example, the left cutter has a cutting edge angle of 45 degrees and the right cutter has a cutting edge angle of 90 degrees. This angle is also known as the lead angle of the cutter.
Here are the optimal operating ranges for different shell milling cutter geometries:
Advantages and Disadvantages of 45-degree Face Milling
Advantages:
According to both Sandvik and Kennametal, 45-degree cutters are recommended for general face milling. The rationale is that using 45-degree cutters balances cutting forces, resulting in more even axial and radial forces. This balance not only enhances surface finish but also benefits spindle bearings by reducing and equalizing radial forces.
-Better performance in entry and exit – less impact, less tendency to break out.
-45-degree cutting edges are better for demanding cuts.
-Better surface finish – 45 has a significantly better finish. Lower vibration, balanced forces, and -better entry geometry are three reasons.
-The chip thinning effect kicks in and leads to higher feed rates. Higher cutting speeds mean higher material removal, and the work is done faster.
-45-degree face mills also have some disadvantages:
-Reduced maximum depth of cut due to the lead angle.
-Larger diameters can cause clearance issues.
-No 90-degree angle milling or shoulder milling
-May cause chipping or burrs on the exit side of the tool rotation.
-90 degrees applies less lateral (axial) force, about half as much. This feature is beneficial in thin walls, where excessive force can cause material chatter and other issues. It’s also helpful when holding the part firmly in the fixture is difficult or even impossible.
Let’s not forget about face mills. They combine some of the advantages of each type of face mill and are also the strongest. If you have to work with difficult materials, milling may be your best choice. If you are looking for perfect results, then you may need a fly cutter. In most cases, a fly cutter provides the best surface results. By the way, you can easily convert any face mill into a fine fly cutter with just one cutting edge.
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Post time: Jun-18-2024