Replaceable-Insert Spade Drill Basics, Advantages

Replaceable-insert spade drills are used in a range of industries, from automotive to heavy equipment to firearms. These drills work well in medium-sized job shops as well as high-production facilities. Specifically, the long-term, repeatable process of high-production runs benefit from the investment in replaceable-insert spade drills because the overall cost per hole is reduced. Compared to the cost of new solid carbide tools, the initial investment of the insert holder or drill body is justified through reduced cycle time and cost by simply replacing inserts, and the tool body can remain in the milling machine or turning center.

Designed to enable machinists to quickly change out worn inserts, replaceable-insert spade drills are made up of drill bodies and inserts available in a wide range of tool diameters and body lengths. Additionally, through a combination of new carbide insert geometries and coatings, shops can create application-specific solutions.

When using a spade drill, it’s important to have a flat, milled surface or in some cases a pilot hole for the drill to enter because it enables the insert’s point to start on an even surface to begin the drilling process. This enables the tool to drill an accurately sized, straight hole. Otherwise, there’s a risk of the tool walking or leading off from where the hole needs to be located.

Replaceable insert spade drills are particularly advantageous for challenging deep hole drilling jobs because they are pointed, which helps with straightness. They also have longer margins, which helps improve stability. Shops performing these types of operations should reference deep-hole drilling guidelines to establish a centered, straight and round pilot hole, and prepare for the full to depth drill in addition to ensure user safety when drilling.

ISO-specific geometries available for replaceable-insert spade drills make this tooling concept applicable for a variety of metals. For example, a P-geometry insert is well suited for low- to medium-carbon steels, alloy steels and tool steels, while a K-geometry insert can be used for both nodular and ductile cast irons. N-geometry inserts can drill cast and wrought aluminums as well as copper and brass. M-geometry inserts are designed for ferritic and austenitic stainless steels in addition to high-strength super alloys such as Inconel and titanium.

In addition to various ISO-specific geometries, shops can select carbide inserts for longer-run jobs or high-speed steel inserts for standard work. Other geometrical attributes such as hook angle or rake angle can also be selected based on application needs. Plus, a selection of insert coatings are available to provide thermal barriers to enable faster drilling operations while increasing the surface hardness of the tool.

The price of a replaceable-insert spade drill will be applied to the cost to drill the requisite amount of holes and then calculated to obtain a cost-per-hole (CPH) figure. For these drills, it will be just the one insert that will be run until it must be taken out of service. All costs associated with that insert and how many inches it has drilled will be used in the CPH calculation. 

The number of steps in the holemaking process also contributes to overall cost. While applications that use a solid drill might need a finishing operation to meet the job’s requirements, replaceable-insert spade drills can often complete the holemaking process to specification in a single operation. Similarly, when changing the cutting edge on a replaceable insert spade drill, the diameter and length are not impacted, unlike a solid carbide drill that should be touched off after replacement because it needs to be reground once worn. Ultimately, this difference results in time that parts are not being machined, impacting overall manufacturing costs.

Replaceable-insert spade drills are a cost-effective cutting tool solution that also extend the useful life of the cutting edge; drilling operations can continue with minimal interruption by quickly replacing inserts. This can lead to a lower cost of ownership over the life of the insert. There is no need to order an entire new tool; rather, costs are kept lower because only the insert is being replaced once it is worn or damaged. Additional cost savings can be found in the amount of machine time saved when changing out the drill’s inserts instead of an entire tool.

Allied Machine and Engineering continues to produce spade inserts while holding true to its namesake: T-A, the throw-away spade. The T-A insert, in all its forms, is said to offer high cost-per-hole performance while eliminating the need for regrinds.