Thread milling has a lot of advantages over cutting threads with a tap and die set. It is faster, more efficient, and produces results of far higher quality.
To that end, thread milling with solid carbide cutting tools has even more advantages over alternatives, like HSS.
But even with the advantages of solid carbide thread mills, there is still always room for operator error.
Improve the quality of your thread milling jobs with these tips and observations.
Choose a Tool of Appropriate Diameter; Smaller May Be Better
When thread milling with solid carbide tools, choose a tool that is as large as needed and not larger. In fact, using a smaller thread mill may actually be more suitable, as smaller thread mills produce a finer finish and higher quality threads.
This is because as the cutting diameter increases, small profile errors can occur at the root of the thread. These small profile errors are magnified by tools with larger cutting diameters. In general, it is advisable to use a thread mill that is not greater than 70% of the thread diameter.
Elect a Suitable Tool Path
Thread milling requires machines that are capable of making simultaneous, coordinated movements across the X, Y, and Z axes, and there are two basic options for thread-milling: up-milling and down-milling.
Down-milling, in which the tool is fed in the direction of tool rotation, is generally the preferred method, as chip thickness decreases from the start of the cut. While up-milling is sometimes necessary, it produces more heat and friction since the cutting edge of the mill must be forced into the cut. This can result in decreased tool life.
On the entrance to the cut (if possible) “roll in” to the first cut, by performing an extra circle, which eases the mill into the workpiece. This produces a smoother entrance and results in less vibration and wear on the tool.
If Possible, Make More Passes
Making several radial passes when thread milling with solid carbide, especially when working with difficult materials, produces finer thread quality and helps protect against tool breakage. Making several passes also minimizes the chance of tool deflection which adversely affects the quality of finished threads, so if the application will allow it, make more passes.
Be Confident with Your Chip Evacuation Strategy
Chip evacuation is a crucial component of thread milling; where necessary, coolant may improve lubricity and help prevent complications associated with overheating.
However, dry machining is often recommended when thread milling with solid carbide because the introduction of cutting fluid can result in thermal stresses that result in cracks. In some applications, the use of compressed air to facilitate chip evacuation is superior.
Work Only with High-Quality Solid Carbide Tools from a Reputable Manufacturer
It is also important to work with a well-respected manufacturer if you are going to be thread milling with solid carbide mills. Consider a supplier such as Online Carbide, that sells high-quality, American-made solid-carbide thread mills. They offer competitive prices and orders over $250 may be eligible for free shipping; see their website for details.