In this design the Front and Rear poles are separate pieces and are attached by bolts to the Core piece.

Although in principle, it would be possible to machine a U-type magnet body from a single piece of steel, it would then not be possible to install the coil and thus the coil would have to be wound in situ (on the machined magnet body).

In a production situation it is highly desirable to be able to wind the coils separately (on a special former). Thus a U-type design effectively dictates a fabricated construction.

On the other hand the E-type design lends itself well to a magnet body machined from a single piece of steel because a pre-made coil can easily be installed after the magnet body has been machined. A single-piece magnet body also performs better magnetically as it does not have any construction gaps which would otherwise reduce the magnetic flux (and hence the clamping force) a little.

(Most Magnabends made after 1990 employed the E-type design).

Selection of Material for Magnet Construction

The magnet body and the clampbar must be made from ferromagnetic (magnetisable) material. Steel is by far the cheapest ferromagnetic material and is the obvious choice. However there are various special steels available which might be considered.

1) Silicon Steel : High resistivity steel which is usually available in thin laminations and is used in AC transformers, AC magnets, relays etc. Its properties are not required for the Magnabend which is a DC magnet.

2) Soft Iron : This material would exhibit lower residual magnetism which would be good for a Magnabend machine but it is physically soft which would mean that it would be easily dented and damaged; it is better to solve the residual magnetism problem some other way.

3) Cast Iron : Not as easily magnetised as rolled steel but could be considered.

4) Stainless Steel Type 416 : Cannot be magnetised as strongly as steel and is much more expensive (but may be useful for a thin protective capping surface on the magnet body).

5) Stainless Steel Type 316 : This is a non-magnetic alloy of steel and is therefore not suitable at all (except as in 4 above).

6) Medium Carbon Steel, type K1045 : This material is eminently suitable for the construction of the magnet, (and other parts of the machine). It is reasonably hard in the as-supplied condition and it also machines well.

7) Medium Carbon Steel type CS1020 : This steel is not quite as hard as K1045 but it is more readily available and thus may be the most practical choice for the construction of the Magnabend machine.

Note that the important properties that are required are:

High saturation magnetisation. (Most steel alloys saturate at around 2 Tesla),
Availability of useful section sizes,
Resistance to incidental damage,
Machinability, and
Reasonable cost.
Medium carbon steel fits all these requirements well. Low carbon steel could also be used but it is less resistant to incidental damage. There also exist other special alloys, such as supermendur, which have higher saturation magnetisation but they are not to be considered because of their very high cost compared to steel.
Medium carbon steel does however exhibit some residual magnetism which is enough to be a nuisance. (See section on Residual Magnetism).