Welding magnets

When assembling a frame, gate, shelving unit or another steel structure, it is often necessary to hold several profiles at the correct angle while operating the welding torch at the same time. Without an assistant, jig or clamps, accurate tack welding can be difficult.

A magnetic square attaches to both parts being welded and temporarily holds them in the required position. This leaves the welder's hands free to check dimensions, measure diagonals and create the first tack welds.

What is a welding magnet?

A welding magnet, also referred to as a magnetic square, is a workshop positioning tool with a permanent magnet enclosed in a rigid protective body.

Its edges create several fixed angles, or in the case of an adjustable model, the individual arms can be moved relative to one another. When placed against ferromagnetic material, the magnet attracts both parts and helps hold them in the selected position.

A magnetic square can be used for:

• welding steel profiles,
• assembling frame structures,
• tack welding square hollow sections and tubes,
• assembling steel components,
• drilling and marking holes,
• light grinding and machining,
• bonding or sealing ferromagnetic components,
• temporarily holding material during measurement.

How does a welding magnet work?

The permanent magnet inside the square creates a magnetic field. When its working edges are placed against a steel profile or sheet, part of the magnetic circuit closes through the material being held.

If two parts are placed against the square, the magnetic force holds them against the respective working edges and helps maintain their relative position.

1. Clean the working surfaces of the magnetic square and the material.
2. Place the magnet against the first part.
3. Carefully move the second part towards the next working edge.
4. Check the angle using a measuring square.
5. Check the dimensions of the entire assembly.
6. Create light tack welds at the joints.
7. Remove the magnetic square.
8. Check the assembly again and complete the welding.

Why does a magnetic square not guarantee a perfectly accurate angle?

The magnetic tool holds the parts according to the geometry of its working edges, but the final accuracy can be affected by contamination, gaps, uneven surfaces or deformation of the material.

Deviations can be caused by:

• a metal shaving caught on the magnet,
• a thick layer of paint or rust,
• an uneven or twisted profile,
• a rounded edge on a square hollow section,
• burrs left after cutting,
• insufficient contact area,
• movement of the structure during tack welding,
• thermal contraction caused by the first welds.

Before making the tack welds, always check the angle with a separate precision square. For frames, also measure the side lengths and both diagonals.

Which materials are welding magnets suitable for?

Magnetic squares only hold materials with a sufficiently strong ferromagnetic response.

They most commonly work on:

• standard carbon steel,
• structural steel,
• steel square hollow sections,
• steel tubes,
• steel sheet,
• steel flat bar,
• cast iron,
• ferritic and martensitic grades of stainless steel.

Which materials will the magnet not hold?

• aluminium,
• copper,
• brass,
• bronze,
• titanium,
• zinc,
• plastic and wood,
• most austenitic stainless steels.

Will a welding magnet hold stainless steel?

It depends on the specific stainless-steel grade. The term “stainless steel” alone does not indicate whether the material will be magnetic.

Ferritic stainless steels

These are usually ferromagnetic and a magnetic square generally holds them well.

Martensitic stainless steels

These also usually show a strong magnetic response.

Austenitic stainless steels

These may be non-magnetic or only weakly magnetic. A magnetic square may therefore not provide sufficient holding force for safe positioning.

The easiest solution is to test the material at several points with an ordinary magnet before starting work.

Which angles can be set using a welding magnet?

A fixed magnetic square has several working edges. The available angles depend on the shape of the specific product.

Common options include:

• 45° for diagonal braces and angled joints,
• 90° for frame corners, gates and shelving,
• 135° on selected magnetic square designs,
• 180° for holding two parts in the same plane.

Not every model offers all of these angles. Always follow the shape, markings and product description of the specific magnetic square.

Fixed magnetic square

A fixed magnetic square consists of one compact body with several working edges. It is simple, quick to position and requires no adjustment.

Advantages of a fixed version

• quick handling,
• simple and durable construction,
• repeatable fixed angles,
• lower purchase price,
• available in several sizes,
• suitable for common workshop tasks.

Disadvantages of a fixed version

• arbitrary angles cannot be set,
• accuracy depends on the cleanliness of the working surfaces,
• a large model may not fit inside a small frame,
• a small model may not hold a heavy or long profile,
• the magnetic force is permanently active.

Adjustable magnetic square

An adjustable magnetic square consists of two magnetic arms connected by a joint. Their relative position can be adjusted according to the required joint.

Advantages of an adjustable model

• different angles can be set,
• suitable for non-standard structures,
• can hold wider profiles and sheet metal,
• useful when making inclined frames,
• greater flexibility than a fixed magnetic square.

Disadvantages of an adjustable model

• higher purchase price,
• the angle must be measured accurately,
• larger dimensions and weight,
• more moving parts,
• the setting must be carefully tightened or secured.

Where can a magnetic square be used?

Frame production

Magnetic squares help when assembling frames for tables, shelving, gates, doors, stands and other rectangular structures.

Metalworking

They can be used when making brackets, supports, braces, protective frames and steel assemblies.

Automotive and service workshops

They can help position smaller steel brackets, reinforcements or structural components during repairs.

Home workshop

They are suitable for making shelves, stands, workbenches, barbecues and simple garden structures.

Assembly and drilling

A magnet can temporarily hold a profile during marking, drilling or assembly before a rigid clamp is applied.

Painting and coating

Under certain conditions, it can hold a small steel part in a convenient position. It must not be used as the only load-bearing element above people or sensitive equipment.

How should a welding magnet be used correctly?

1. Clean the material

Remove the following from the contact areas:

• loose rust,
• scale,
• thick layers of paint,
• oil and grease,
• metal shavings,
• burrs left after cutting.

A cleaner and flatter surface provides a larger contact area and higher holding force.

2. Prepare the parts

Remove burrs, align the cut edges and check that the profiles are not twisted.

3. Position the magnetic square

Place it against one part first and carefully move the second profile towards it. Do not allow the magnet to snap suddenly into place and pinch your fingers.

4. Check the angle

The magnetic tool makes positioning easier, but verify the exact angle using a separate measuring tool.

5. Measure the entire structure

For a frame, check the side lengths and both diagonals. Equal diagonals are an important indication that the frame has been assembled squarely.

6. Make the tack welds

Create several small tack welds in a sensible sequence so that the assembly does not move or begin to deform due to heat.

7. Remove the magnet

Once the parts have been sufficiently tack welded, remove the magnetic square from the immediate vicinity of the weld.

8. Measure the structure again

The first tack welds may cause slight contraction of the material. Check the angle and dimensions again before completing the welds.

9. Complete the welding

Work alternately and take thermal deformation of the structure into account.

Why should the parts only be tack welded first?

Tack welds stabilise the structure while introducing less heat into the material than a long continuous weld.

This allows you to:

• remove the magnet in time,
• check the final geometry,
• correct a small deviation,
• reduce overheating of the magnetic square,
• reduce the risk of the magnetic field affecting the welding arc,
• reduce weld spatter sticking to the magnet.

Can a welding magnet affect the welding arc?

Yes. The magnetic field of the square can interact with the magnetic field generated by the welding current and cause the arc to deflect.

This phenomenon is known as magnetic arc blow or simply arc blow.

How can it appear?

• the arc bends away from the joint,
• the weld pool moves irregularly,
• the weld forms more strongly on one side,
• arc ignition becomes more difficult,
• weld spatter increases,
• an irregular weld profile develops.

How can the risk be reduced?

• remove the magnet after tack welding,
• position it farther away from the weld area,
• change the position of the work clamp,
• use a shorter arc,
• reduce the current if permitted by the welding procedure,
• change the welding direction,
• use a mechanical clamp instead of a magnet,
• consider alternating current where appropriate for the welding process.

If the arc becomes unstable only when the magnetic square is attached, remove the magnet and secure the structure mechanically.

Does the magnetic square replace the work clamp of the welding machine?

No. A magnetic square is used to position material. It is not designed to act as a work clamp, return conductor or replacement for the welding circuit cable.

Connect the work clamp, sometimes informally referred to as the “earth clamp”, directly to a clean conductive surface of the welded part according to the instructions provided by the welding machine manufacturer.

Incorrectly passing welding current through the magnetic square can cause:

• overheating of the magnet,
• damage to the protective casing,
• sparking at contact points,
• an unstable welding arc,
• damage to the magnetic system,
• risk of injury or fire.

How can you protect a welding magnet from heat?

A permanent magnet may partially or permanently lose its magnetic strength if its permitted temperature is exceeded. The paint, adhesive or internal construction of the square may also be damaged.

You can reduce the risk of overheating by:

• using the magnet only during assembly and tack welding,
• not making a long weld directly next to its edge,
• moving it away from the heat-affected zone after tack welding,
• not placing it on a freshly welded hot part,
• not cooling it suddenly with water,
• allowing it to cool naturally before using it again.

How can you protect the square from weld spatter?

Hot droplets of metal can stick to the steel surface of the magnetic square. Metal shavings and weld spatter are also attracted by its magnetic field.

To reduce contamination:

• position the square as far away from the weld joint as possible,
• remove it immediately after tack welding,
• use a suitable anti-spatter product if permitted by the manufacturer,
• clean the working edges regularly,
• do not remove welded-on spatter by aggressively grinding the working surfaces.

Damage or unevenness of the working edges may reduce accuracy during subsequent use.

How do you choose the right size of magnetic square?

A larger model is not automatically better. Its dimensions must correspond to the size, weight and shape of the profiles being welded.

Smaller magnetic square

Suitable for:

• smaller square hollow sections,
• thinner sheet metal,
• small frames,
• confined working areas,
• light assembly work.

Larger magnetic square

Suitable for:

• larger steel profiles,
• longer parts,
• heavier frame structures,
• applications requiring a larger contact area,
• more robust workshop work.

Adjustable magnetic square

Choose an adjustable model if you regularly make structures with different or non-standard angles.

What affects holding force?

Holding or pull-off force is usually specified under ideal conditions. In practice, a profile may be held with significantly less force.

Holding force is reduced by:

• thin sheet metal,
• a small contact area,
• a rounded profile,
• a layer of paint,
• rust and scale,
• a gap between the magnet and material,
• contamination on the working edge,
• weakly magnetic stainless steel,
• sideways pulling force,
• vibration and impact.

Can several welding magnets be used at the same time?

Yes. When assembling a frame, several magnetic squares can be used at different corners to hold multiple profiles at the same time.

When using several magnets:

• first assemble the entire frame without welding,
• check the lengths and diagonals,
• do not position the magnets too close together,
• check that they are not attracting one another,
• tack weld the structure gradually and alternately,
• remove all magnets after tack welding,
• measure the frame again before completing the welds.

Can a magnetic square be used on tubes?

Yes, but the contact area of a cylindrical tube is smaller than that of a flat square hollow section. The actual holding force may therefore be lower.

When working with tubes:

• use a model with suitably shaped edges or an opening,
• secure the tube against rolling,
• check the alignment of both parts,
• add a mechanical clamp for heavier components,
• do not rely solely on a small point of magnetic contact.

Can a welding magnet be used on thin sheet metal?

Yes, but thin sheet may not close the magnetic circuit as effectively as a thicker profile. The holding force may be lower and the sheet can move or deform more easily due to heat.

For thin material, use smaller tack welds, monitor deformation and add mechanical holding where necessary.

How do you clean a magnetic square?

The magnet attracts metal grinding dust, shavings and small amounts of weld spatter. Contaminants must be removed from the working edges regularly.

1. Allow the magnetic square to cool completely.
2. Wear work gloves.
3. Move larger contaminants towards the edge using a non-magnetic scraper.
4. Remove fine metal dust with a brush or cloth.
5. Check that the working edges remain straight.
6. Remove oil and grease using a suitable cleaning agent.
7. Dry the square thoroughly.
8. Store it away from loose metal shavings and tools.

What should you avoid during cleaning?

• rapidly cooling a hot magnet with water,
• aggressively grinding the working edges,
• striking it with a hammer,
• prying into the casing with a screwdriver,
• drilling or disassembling the body,
• long-term storage in damp conditions.

How should a welding magnet be stored?

• In a dry place away from high temperatures.
• Away from sensitive electronics and measuring equipment.
• Separately from loose steel tools.
• In a position where it cannot fall or suddenly snap towards another tool.
• With clean working edges.
• With adjustable models secured in position.

Safety when using welding magnets

Recommended magnetic squares

The selected products represent a larger fixed magnetic square for more robust profiles, an adjustable tool for different angles and a compact model for smaller workshop structures.

Frequently asked questions about welding magnets

Summary

Welding magnets and magnetic squares help quickly hold steel profiles, tubes and sheet metal while assembling a structure. They free up the hands and make it easier to create the first tack welds.

Fixed models provide common working angles such as 45°, 90° or same-plane positioning. An adjustable magnetic square is suitable for non-standard structures and different inclinations.

The magnet only works on ferromagnetic materials. It will not hold aluminium, copper, brass or most austenitic stainless steels.

A magnetic square does not replace precise measurement, a mechanical clamp or the welding machine work clamp. First tack weld the parts, remove the magnet, check the geometry and only then complete the welds.