Woodruff keyseat cutters are circular cutting tools made of high-speed steel, used by machinists for cutting seating in shafts for woodruff keys and, in some cases, keyways in fitting parts. Some machining operations are not only impractical but also impossible without woodruff keyseat cutters.

It’s beneficial to know when and how to pick the right woodruff keyseat cutter and how to use it correctly if you're ever in need of one. In this article, we'll discuss woodruff keyseat cutters, what exactly they are, and what the important parts are.

Correlation Between Geometry and Strength

Calculating the ideal cutting diameters and adjusting the speeds and feeds on your milling machine is usually a lot easier than selecting and using the right milling cutters. The first thing that should be carefully evaluated is the strength of the keyseat, especially in challenging applications and materials that are difficult to mill, like hardened steel or titanium.

However, when it comes to tool and cutter selection, it's important to note that t-slot cutters with greater reach are usually more susceptible to deflection and fracture, which is why it's important to pick the strongest tool with the shortest permitted reach.

The performance — as in resistance to deflections and breaks — of woodruff cutters is heavily influenced by its shank diameter, also called "neck diameter." A tool with a narrower neck has a greater radial depth of cut and better clearance, but it's also weaker.

The cutter's radial depth of cut is decreased if the tool has a thicker neck diameter, but the cutter as a whose is substantially strengthened. In general, keyseat cutters with thicker necks and larger cutter diameters should be prioritized over those with narrower necks and smaller cutter diameters for as long as clearances allow.

The strength of the tool is also affected by the cutter width, and the wider cutters are usually more prone to deflection and breakage due to the sheer amount of pressure acting on the tool. The best approach when milling with a keyseat cutter that has a thick cutting width is to use the strongest possible tool, with a light radial cut of depth.

What Is the Radial Depth of Cut (RDOC)?

In order to select the best tool and achieve the best results, it is essential to comprehend how a keyseat cutter's radial depth of cut impacts your tool path. While it may be tempting to use a keyseat cutter's maximum RDOC, doing so will put more strain on the tool, produce a subpar finish, and raise the risk of catastrophic tool failure.

In nearly all applications, it's always preferable to use as light a depth of cut as possible, paired with as many passes as possible, to significantly mitigate any stress on the cutting tool. It's always the best approach to refer to the speeds and feeds recommended by the tool's manufacturer in case you have any doubts about the appropriate RDOC.

What Are the Main Benefits of Staggered Tooth Keyseats?

Unlink standard keyseat cutters, which are right-hand cuts and have all straight teeth, staggered tooth keyseat cutters teeth alternate between right- and left-hand shear flutes. This type of cutter has its own set of benefits due to its distinctive geometry, including indexing, enhancing feed rates, and better overall component finish.

Indexable Tooling

The alternating flutes on the cutter allow both end mills and back cutting, which adds a layer of versatility to the keyseat cutter, granting it an axial movement for the purpose of expanding the keyseat slot to an uncommon dimension.

Increased Feed Rate

The distinct design of the staggered tooth keyseat cutter allows chips to escape more efficiently and quickly, thanks to the combination of right- and left-hand flutes, which result in an alternating upcut and downcut. This results in the ability to accommodate chip loads that are roughly 10% larger than on average, leading to increased feed rates and reduced cycle times across the board.

Better Part Finish

The shear flute geometry lowers chip dragging, as well as the amount of force required to cut through the material. Additionally, shear flutes lessen vibrations that might cause chatter and a subpar finish, offering a better part finish as a result.

What Factors Affect the Speed of Keyseat Cutters?

There are several factors that can affect the speed and performance of keyseat cutters, and they mostly come down to the cutting machine, cutting machine's horsepower, and lubricants in use. These factors are non-specific to keyseat cutters and are more cutting-machine-specific.

They're best used in conjunction with your tool's manufacturer guide, from which you should be able to derive the depth of cut and grooving speed and factor them into the aforementioned variables.

Why Is Carbide Preferred for Keyseat Cutters?

In recent years, carbide has largely replaced steel in tooling since steel can't really compare to the strength and heat resistance of solid carbide. Admittedly, carbide-tipped tools, like the American standard straight-tooth or dovetail cutters, as well as HSS staggered-tooth tools, cost more than those made of steel and are thus more cost-effective, as they last longer.

You can observe that carbide is a thick, polished cutting surface that has been brazed to a steel straight shank body when comparing carbide tools to steel. There's also a significant difference in quality between different brands of carbide-tipped tools.

For instance, Amana uses a fine micro-grain carbide; saw blades are dynamically balanced and tensioned, and router bit shanks are carefully cut to size for a snug fit in the router collet. Casual observation can't actually reveal these variances, but the quality and smoothness of the cut make the distinction clear.

How Accurate Is a Woodruff Keyseater?

Keyseating accuracy is comparable to that obtained by broaching or other conventional machining techniques when a part is somewhat tiny in size and relatively soft in composition. However, it will require more lenient tolerances for pieces that are exceptionally lengthy, or made of particularly hard material, due to the cutting tool deflection. Keyseating exhibits substantially less deflection throughout the cut when compared to vertical shaping.

Is the Woodruff Keyseat Cutter the Only Option?

For most applications, you can also use parallel keys. Cutting a straightforward keyway groove along the entire axial diameter of the workpiece is the first step in the parallel keyway milling process. This is followed by cutting a keyway into the shaft and inserting the parallel key between two aligned keyways, interlocking them together.

These cuts could be made using an endmill, but a key cutter is much simpler. There are numerous cutter widths and cutting sizes available for key cutters, and a pre-cut key stock is offered in both metric and standard inch sizes.

Summary

A woodruff keyseat cutter is a versatile tool used to cut grooves that can help you mate a part on a shaft. They're an essential component of every machinist's toolbox, and some applications are nearly impossible without them. If you're interested, you can learn more about keyseat cutters here.