Do you urgently need prototypes, but don't have the dedicated tool yet?
ottobre 07, 2026
Could gear prototyping with electrical discharge machining be the solution when you need to quickly validate a component, but the dedicated tool needed to produce the internal teeth is not yet available?
It is a concrete situation that can occur during the development of a new project.
The drawing is ready.
The geometry has been defined.
The component must be built quickly to perform the initial assembly tests and functional checks.
But something is missing : the tool needed to produce the internal teeth. At this point, the question seems inevitable: should we wait for the broach or the final tool to be built before we can produce even a few prototypes? Not necessarily.
And it is precisely in situations like this that it becomes important to distinguish the ideal production process for the series from the one most suitable for the prototyping phase.
Gear prototyping with electrical discharge machining: the best process depends on the objective
When developing a process for continuous production, we typically think in terms of repeatability , productivity , cycle time, and unit cost. If we need to produce thousands of identical components, investing in a dedicated tool can be perfectly rational. The initial cost is distributed across the volume, but the situation changes when we need to produce a small number of components to verify a design.
At that point, our goal isn't yet to produce thousands of parts as efficiently as possible. We need to quickly obtain a few representative components, inspect them, assemble them, and determine if the design works. For some complex internal geometries made from electrically conductive materials, electrical discharge machining ( EDM ) can offer precisely this flexibility . EDM is used industrially for machining operations that are difficult to achieve with conventional mechanical processes and is also used in the production of cavities and complex internal geometries.
There are also documented industrial applications of EDM in the production of samples and prototypes with internal grooves, precisely to increase flexibility during development. The point, however , is not to say that EDM is always better.
The point is to ask: what is the process most consistent with the phase the project is in today?
The real cost may be the time it takes to build the tool .
When we compare two production processes we naturally tend to compare their cost.
How much does it cost to produce the component with EDM?
How much would it cost using a dedicated tool?
But during prototyping, a fundamental variable is missing: when can I have the component?
Let's assume that the final solution involves a dedicated broach: the broach must be designed, built, verified, and possibly corrected.
Only then can the production of the components begin. If we are already working on the series, this investment can make perfect sense.
But if the R&D department is waiting for five prototypes to perform a functional test, the tool's lead time can become the real constraint on the project. The advantage of EDM , in this case, is not just avoiding or postponing an investment. It is above all preventing the time required to build the final tool from determining the validation schedule .
How much is a prototype really worth?
The cost of a prototype shouldn't be evaluated with the same logic used for a series component. If a part produced using EDM costs more than the same component made with a high-volume process, we might conclude that it's less cost-effective.
But the context is missing:
Does that component need to be produced ten thousand times?
Or does it need to be available next week for a technical team to check out an assembly?
In the second case, the value of the prototype also depends on the information it allows to obtain.
Can verify a pairing.
It can highlight interference .
Can you confirm a geometry?
It can allow a functional test.
It can reveal a change before the final tool is built .
This completely changes the way we should evaluate cost. Spending a little more on a single prototype can be perfectly rational if it allows us to avoid weeks of waiting or to discover a design change before committing capital to the final tooling.
A concrete case: an internal tooth in a blind hole
In the case we faced, the situation presented an additional difficulty . The teeth had to be made inside a blind hole . This detail is important.
Before EDM , the component had to be prepared by turning. It was therefore necessary to correctly obtain the internal geometry and, above all, the required terminal relief to allow for subsequent production of the gear teeth. Once the component was completed, that area would have been difficult to access for a simple visual inspection.
We therefore had a very concrete problem: how can we be sure that the geometry obtained from turning is correct before proceeding with the subsequent machining? It might be tempting to simply rely on the process, but we preferred to verify it.
Before the teeth, we destroyed a piece
The chosen solution was very simple: an initial sample was turned, then sectioned. We deliberately sacrificed the component to be able to directly observe what would have been difficult to see on the intact piece. This allowed us to check the internal geometry obtained by turning and verify the terminal relief before proceeding with the components intended for testing.
Of course, this is a destructive test, but destroying a sample early in the process can be much less costly than later discovering that all the components started from an incorrect geometry.
The principle is simple: before adding a complex and expensive process, we reduce the uncertainty about the previous process.
Only after this verification did we move on to the creation of the internal teeth on the complete components.
It's useful to make a technical clarification here: when we talk generically about " electrical discharge machining, " we risk lumping together different processes. Wire EDM is particularly suited to profiles that the wire can pass through. Blind cavities and non-passing geometries, however, require a different strategy, typically involving die-sinking EDM with a specially designed electrode .
Even in this case, it is not enough to say: “ let's do it with EDM ” . The geometry must be analyzed, the electrode access must be verified and the discharge conditions and evacuation of processing residues must be considered .
In deep or blind cavities , in fact, debris removal can become an important element for the stability and efficiency of the EDM process. This aspect is also documented in the technical literature dedicated to the machining of complex cavities and blind holes.
So EDM expands production possibilities , it does not eliminate the need to correctly design the process.
Why not build the ultimate tool right away?
We could ask ourselves the opposite question: if we know that the component will be mass-produced in the future, why not build the final tool immediately?
Because during prototyping , we're still acquiring something very important: information. The prototype may completely confirm the design, but it could also indicate that a modification is needed.
A diameter might change.
A drain could be revised.
The geometry of the teeth may require adjustment.
Problems may arise during assembly.
Functional tests could lead to a new revision.
If we've already built a specific tool based on the previous geometry, a design change can result in a modification to the equipment or, in the worst case, the need to rebuild it again. Postponing investment in the final tool doesn't necessarily mean postponing a decision. It can mean making that decision when we have more information .
Is EDM always the best solution for prototypes ?
Each component must be evaluated based on geometry, material, tolerances, required finish, number of pieces, time, and available machining options.
Is EDM always the best solution for prototypes? No, and it would be wrong to portray it that way. EDM also has its own constraints. It requires electrically conductive materials. The process can be relatively slow, and, with certain geometries, debris evacuation and electrode wear must be carefully managed. Research on EDM of complex cavities clearly shows how flushing conditions can affect process efficiency .
And above all, as volumes increase, the economic logic changes. An industrial case study involving the production of internal groove samples describes EDM as a flexible solution for sample production, while specifying that the process is not suited to the high outputs of mass production.
That's exactly the point: there's no single best process. There's a process that's best suited to a given goal.
Prototype and series are optimizing two different things
This distinction is probably the most important part of the whole case. In series production, we want a stable, repeatable, and cost-effective process. We want to reduce cycle times, distribute tooling costs across as many parts as possible, automate, and increase productivity .
In prototyping, the goal is different : we want to quickly transform a digital design into something we can measure, assemble, and test.
Unit cost remains important, but it is not the only variable, we must also consider lead time, flexibility , the cost of the equipment, the risk of project modification, the quantity needed and above all the value of the time we can gain in validation.
For this reason, using the same economic criterion for prototype and series can lead us to make the wrong choice.
The final tool should arrive when the project is sufficiently definitive
Of course, there comes a time when continuing to use a flexible process no longer makes sense.
The project is stabilized.
The tests are complete.
The geometries are confirmed.
The quantities are increasing.
Revisions become less likely.
At that point, we can invest in the final production process. A broach, a special tool, or another dedicated solution can drastically reduce cycle times and make continuous production economically sustainable. The initial investment begins to be distributed across hundreds or thousands of components.
It is therefore wrong to contrast the two technologies. The question should not be: “Is EDM or broaching better ? ”
The question should be: “ Which process is best suited to the stage this project is in today? ”
And the answer may change over time.
The producer's work begins before the machine
This case also highlights another aspect I consider important in the production of special mechanical components. Receiving a drawing shouldn't automatically mean associated machining.
Internal teeth equal broaching.
Complex profile equals EDM.
Large quantity equals dedicated process.
Small quantity equals flexible process.
The reality is more complex, you need to understand what the customer wants to achieve.
How many components are needed today?
How many might be needed tomorrow?
Is the drawing final?
Should the component be used for testing?
How much does it cost to wait?
the tool already exist ?
Is it reasonable to build it now?
Which characteristics need to be validated?
What checks are necessary before moving on to the next step?
Only after answering these questions can we choose the process, because a manufacturer's job isn't to automatically propose the technology it uses most often. It's to identify the combination of technology, timescales, costs, and controls that best fits the actual project phase.
Do you urgently need a few prototypes with internal teeth, but the final tool is not yet available?
Waiting is not necessarily the only solution.
Under certain conditions, gear prototyping with electrical discharge machining can allow for the production of complex internal geometries without tying the first tests to the availability of the tooling planned for future production.
And only afterwards, when the project is sufficiently stable, decide whether and how to invest in the definitive tool.
Because accelerating a project doesn't mean skipping controls. It means choosing the controls and processes that reduce uncertainty without introducing unnecessary waiting . Sometimes the most technically convenient solution isn't the one with the lowest unit cost. It's the one that allows you to get to the answer the project really needs first.
For more information on internal gear prototyping and solutions for gears and mechanical transmissions, contact GSI Ingranaggi.
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