1.   Machined Workpieces

Many characteristics of machined workpieces have to be considered when choosing a magnetic chuck:

Workpiece Material

Magnetic force isn’t universal; some materials enhance it, some make it weaker. To be compatible with a magnetic chuck a workpiece needs to be made from a ferromagnetic material. The magnetic field is strongest for low-carbon steel workpieces (with 0.04-0.3% carbon content). High-carbon and alloy steels need to be clamped more forcefully as they contain multiple non-magnetic elements.

Workpiece Thickness

Standard magnetic chucks will securely clamp a 12 mm thick workpiece. To safely clamp thinner workpieces a magnet with denser poles is required. Alternatively, one can use an additional pole plate atop the chuck — into which is milled an imprint of the workpiece, creating a template of sorts. When machined, the template holds the workpiece in place as it fits snugly into the form.

Using a strong magnetic chuck is not a solution for clamping thin workpieces as they let the magnetic field pass through them. The densest flux lines, which indicate the strongest area of the magnetic field will be outside of the thin workpiece parameters, which results in a weaker magnetic clamping force meaning this type of workpiece will not be held securely and/or potentially suffer deformity. 

Surface of the Workpiece

The ideal workpiece for clamping with a magnetic chuck is flat, clean, and even. Dirt, dust, impurities, and additional layers (coats of paint or polish) always decrease a magnet’s holding force. Similarly, perforated workpieces and workpieces with openings will always be held less strongly by a magnet.

With these specific pieces, it’s best to calculate the magnetic force of a magnet individually, or borrow a magnetic chuck to try it out. Please ask us if we have something available for a trial — we completely understand that some of our clients need to test the magnets before they take the plunge and buy them. 

Shape of the Workpiece

For machining circular workpieces, we recommend getting a round magnetic chuck — a popular solution for machining saw blades, ring bearings, cylinders, and other round parts. A circular magnetic chuck allows one to perform multiple machining operations at once, without having to re-clamp the workpiece. Clamp round workpieces just once and machine their inner, outer and face surfaces.

Regularity of the Workpiece

To safely clamp a workpiece on a magnetic chuck, one needs to clamp it evenly in multiple places. This is difficult to do with uneven workpieces — they need to be supported before they’re clamped.

Our most popular Mastermill magnetic chuck deals with uneven workpieces by using firm and flexible pole extensions. Firm extensions are used to make a reference level, and flexible pole extensions are added to reflect the shape and support the workpiece. Once the magnetic chuck is turned on, flexible pole extensions fix the workpiece on the reference level, making it perfectly even and repeatable.

2.   Machining Operations

To select the best magnetic chuck, one must make a list of all the machining operations that are going to be performed on it. 

The most common machining operations are:

Milling

Need an all-purpose magnetic chuck for milling but also for other types of machining operations? Get the Neomill Compact magnetic chuck which can be used for planing, drilling, and withstands even heavy-duty grinding.

To clamp smaller and medium workpieces, get the Mastermill magnetic chuck. For larger workpieces, consider the Neopower chuck or Mastermill 70.

Drilling

The key here is prevention against drilling the workpiece through all the way to the magnetic chuck underneath and damaging the chuck. Use extensions which enable the workpiece to be placed higher on the magnetic chuck.

Grinding

Heavy-duty grinding requires a strong magnet with high magnetic force and a robust construction. For precision grinding, one needs to prevent the magnet from warming up as heat is capable of deforming the workpiece. Electro permanent magnets are the perfect choice for precision grinding as they don’t get heated up (contrary to electromagnets) — such as our Grindmaster.

Lathe Turning

Round magnetic chucks are most popular for lathe turning operations as they guarantee free access to the workpiece from five sides without having to re-clamp the piece.

Precision Machining

Similarly to grinding, the key point here is to prevent the magnet from heating up. Electro permanent magnetic chucks are the best choice.

3.   Other Specifics of Your Production Facility

Consider all the factors at play in your production facility. Is a cooling agent used during machining operations? A waterproof magnet might be a good idea — ideally made of the monoblock style. A monoblock magnet lacks grooves through which liquid could get in to the core of the magnet. The same logic applies to facilities with a high concentration of dust.

4.   Control Unit

In the case of some magnetic chucks, their control unit can be integrated into the control unit of the machine tool, allowing the operator to control clamping and machining on one display.

When getting a large system of magnetic chucks, decide whether the control unit should control the entire magnetic setup or whether individual magnets in the set need to be independently activated. The latter is a common requirement for large machines which enable the operators to perform machining operations on one side, while still getting workpieces ready for machining on the other.

We’ll happily design and manufacture a bespoke magnetic clamping system for you. In such cases, we prepare a blueprint for the magnetic set, based on your machine’s precise measurements. On the blueprint, we mark placements of magnets for various machining operations.