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A guide to Ferrite Lapping

Updated: Nov 16, 2023

Ferrite is a ceramic compound with magnetic properties (Ferrimagnetic) which is useful for a number of different applications due to the lack of electrical conductivity. Predominantly, Ferrite is used for power applications, home appliances and EMI suppression – uses include antennas, magnetic cores for transformers, and ferrite beads for cables. The Ferrite Gateway Machine Shop offers a range of machining capabilities to help you achieve bespoke solutions for your project, with one of the most recent additions being Ferrite Lapping. To help you understand how Ferrite Lapping could work for your next project, we are going to be taking a look at what the process is, why it is used, and what it can be used for.

What Is Ferrite Lapping?

Ferrite Lapping is a process used to remove material from the surface of a workpiece, which is beneficial for creating a smooth finish after machining (removing any grooves or indentations). By creating a flat surface finish, Ferrite Cores can attain a tighter mating which increases AL value. This is done through using abrasives in a rotational motion to ensure that an even amount of material is being removed – this is essential for creating a perfectly flat finish. Lapping is typically used on cores with a permeability of 5000 or more, which helps to achieve maximum AL value. In addition to Lapping, the Gateway Machine Shop can offer a Mirror Finish – this is achieved by an additional process after Lapping where finer abrasives are used to further reduce imperfections (meaning that an even greater AL value can be accomplished).

Why Is Ferrite Lapping Used?

Lapping is a process used on ungapped cores – helping to remove imperfections on the surface of the core, as well as reducing the effects of an air gap on mated cores (also referred to as parasitic air gaps). The benefit of Ferrite Lapping is that it can produce a surface finish of 0.1-0.2 microns (compared to 0.5-1.0 microns for a normally flat-ground surface). Achieving this level of finish creates a datum face, improving the mating surface of the workpiece which increases the resultant AL value. Polishing, which helps to achieve a Mirror Finish, also has the ability to improve the flatness of the core by reducing minute deformations or scratches that can occur when Lapping.

LCR Meter measuring the inductance of unlapped cores
LCR Meter measuring the inductance of unlapped cores

To demonstrate the effect that Lapping has on Ferrite cores, we have put together a comparison of two pairs of POT cores – one pair is the standard off-the-shelf version (unlapped) and the other pair has had the surface lapped. Both pairs were tested using a bobbin wound with 100 turns of wire which sits on the centre limb. Using the LCR meter in our Machine Shop, we were able to measure the Inductance of each pair of cores. The unlapped cores (see image above) came to 66.349mH, giving them an AL value of 6634.9 – in comparison to this the lapped cores (see image below) came to 74.032mH which equates to an AL value of 7403.2. From this is it clear to see that by simply Lapping the surface of the cores it is possible to significantly increase the AL value – in this case by just shy of 770.

LCR meter measuring the inductance of lapped cores
LCR meter measuring the inductance of lapped cores

What Can Ferrite Lapping Be Used For?

There are many applications where Ferrite Lapping would provide a suitable finish to workpieces, including EMI Suppression, Power Applications, Sensors and Antennas, and Absorption of High Frequencies (shielding). These applications are used across a range of industries, such as Electronic Manufacturing, Medical, and Aerospace. Lapping is a finishing process, so if you require a core for your project Ferrite Lapping may help you to achieve increased precision.


As you can see, Ferrite Lapping provides a range of advantages which can benefit a variety of solutions, and our team in the Machine Shop have worked extremely hard to refine the process to ensure that our customers receive the highest quality finish.

Have a project in mind that would benefit from Ferrite Lapping? Our team would love to work with you – fill out an enquiry form here.

For more information, please feel free to get in touch with our team of technical experts –

Phone: +44 (0) 1270 615 999


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