Workshop presses: how to choose the tonnage

Pressing a 50 mm bearing onto a shaft with an H7/p6 fit requires around 0.65 tonnes of force. Not twenty. Tonnage is rarely the real constraint when choosing a workshop press: working clearance, ram stroke and whether the cylinder slides or stays fixed in the centre matter more. The tonnes are needed for the tough jobs, when a part has seized or a shaft needs straightening. Below you will find the calculation, specifications for our range from €140.30 to €2,537.69, and the criteria that come before tonnage. Official Bernardo distributor since 2007.

The formula used by bearing manufacturers relates four factors: friction between the two surfaces, the elastic modulus of steel, ring geometry and fit interference. In the form published by NSK in its technical manuals:

K = μ × E × π × B × (1 − k²) × Δd / 2

where μ is the friction coefficient (around 0.12 for assembly and 0.18 for removal), E is the elastic modulus of steel (208,000 MPa), B is the ring width, k is the ratio between the ring's internal and external diameters, and Δd is the interference in millimetres.

For a 6210 bearing, with a 50 mm bore, a width of 20 mm and 20 microns of interference, the calculation gives around 6.4 kN, or 0.65 tonnes. Removing it after several years of service, with higher friction, requires around 0.95 tonnes.

This figure surprises people who have found the rule of thumb of "1–3 kN per millimetre of diameter" online, which would give 50–150 kN for the same bearing. That rule applies to much tighter interference fits and press fits on solid components, not to a standard bearing on a ground shaft.

The practical consequence: if your work consists exclusively of fitting and removing bearings and bushes on shafts up to 60–70 mm, ten tonnes is enough, with a tenfold margin. Higher tonnage is bought for other jobs.

Because the operations that bring a press to its knees are not the clean, straightforward ones.

A bearing seized by corrosion after years of service can require five or ten times the assembly force, because oxide has formed between the ring and shaft and acts like a cold weld.

Straightening a bent shaft means taking the material beyond its elastic limit across the whole section. A solid 40 mm steel shaft already requires several tonnes, and the value cannot be calculated beforehand: you proceed by trial while reading the pressure gauge.

Cold-bending a flat bar or section on V-block supports is the most force-intensive application, and depends on thickness, width and the distance between the supports.

Removing silent blocks, plain bearings and taper pins from cast-iron housings where rust has taken hold is inherently unpredictable.

The rule we use when advising customers by phone is simple: calculate the force for the toughest job you expect, then double it. This is not excessive caution: it is the margin that prevents the press reaching its limit while the part still refuses to move, the situation in which things break and people get hurt.

This is where the most common purchasing mistake occurs. Two presses both claim twenty tonnes and appear interchangeable, but one accommodates your part and the other does not.

The three figures to look for on the specification sheet are:

The horizontal clearance (E), meaning the distance between the two uprights. This is the maximum width of a part that fits inside the press. It ranges from 330 mm on the WK 10 TH to 725 mm on the WK 50 FH Pro.

The distance between cylinder and table (F2), meaning the usable height with the table in its lowest position. It determines whether a wheel hub or housing fits underneath. This is 365 mm on the WK 10 TH and 1,100 mm on the WK 30 FH Pro.

The ram stroke, meaning how far the cylinder descends in one movement. It ranges from 150 to 210 mm across the range. If the part needs a longer push, the operation is carried out in two stages by repositioning the table.

One detail in Italian specification sheets causes confusion: when you read "diameter" in reference to the piston, it often means the rod diameter, not the cylinder bore. These are different measurements and only the second, multiplied by pressure, gives the force. If you are comparing two brands technically, check which measurement the figure refers to before drawing conclusions.

Specifications of the models in our catalogue; prices include VAT.

Two things stand out when reading across the table.

First: the WK 20 FH at €622.22 costs less than the WK 15 TH Pro at €671.02, despite offering five more tonnes and a cylinder that slides 400 mm rather than 170 mm. They differ in construction class, not in stated performance. If budget is the constraint, the FH provides more force per euro.

Second: the WK 20 FH Pro costs €427 more than the WK 20 FH for the same tonnage. You pay for self-regulating hydraulics, combined foot-pedal and hand-pump operation, the included V-block support and 18 kg of additional structure. It makes sense in a workshop where the press works every day, less so where it is used once a week.

Below ten tonnes there is another, often overlooked family: manual arbor presses. No oil, no pump, no seals: a gear wheel pushes a rack.

An arbor press delivers just over a tonne, so it covers precisely the 50 mm bearing example at the start of this article. In return, the downward movement is immediate and provides feedback through your hand: you can feel when the part gives way, something a hydraulic pump requiring thirty lever strokes does not convey in the same way. For marking, pressing in pins, fitting small bearings and repetitive work on small parts, a DP2 at €225.71 does the job of a ten-tonne hydraulic press in half the time.

The limitation is working clearance: 135 mm on the DP1 and 190 mm on the DP2. These are bench machines, not floor-standing models.

The way the ram moves down affects productivity more than you might think.

With a hand pump alone, one hand is occupied by the lever. This is fine for a part that stands securely by itself on V-block supports. This is the configuration of the WK 10 TH and WK 15 TH Pro.

With a hydraulic foot pedal, both hands remain free to hold the part as the ram advances. In the Bernardo range, the pedal is standard from the WK 12 FH upwards, and is the main reason why this model costs €135 more than the WK 10 TH despite offering only two more tonnes. Anyone working alone recovers that difference on the first day.

Pneumatic operation at 6–8 bar moves the ram down at a constant speed and force, regardless of who operates the pump. It is useful when the same operation is repeated dozens of times a day, and requires an existing compressed-air supply in the workshop.

On budget presses, the cylinder is fixed in the centre of the frame: every part must be positioned directly beneath it. Across the WK range, the cylinder slides sideways, from 170 mm on the WK 15 TH Pro to 245 mm on the WK 50 FH Pro.

It may seem a minor detail, but it determines how much time you spend repositioning. When you need to press a bearing near the edge of a housing, or straighten a long shaft resting on two widely spaced V-blocks, moving the cylinder twenty centimetres is the only way to reach it without dismantling and rearranging everything on the table.

With its 400 mm sliding travel, the WK 20 FH covers the widest section of the table in the entire standard series.

No standard defines the boundary. In commercial practice, it is recognised by four signs.

The tooling. A workshop press uses universal pins and V-blocks suitable for any part. An industrial press uses dedicated tooling made for a single component.

The controls. In the workshop, the ram descends while you hold the control and stops when you release it. In production, the cycle is automatic and starts through a two-hand control or a light curtain.

The price. A workshop press has a price list. An industrial press is configured and quoted individually because the stroke, table and hydraulic power unit vary with the application.

The duty cycle. Occasional versus continuous use, which ultimately determines the sizing of the hydraulic power unit and oil cooling.

For us, the boundary lies at around fifty tonnes: beyond this, with the 30–150 tonne HCP series and the twin-column AT and AP models, you enter the world of industrial hydraulic presses, which we supply by quotation because every configuration is different.

We often hear this on the phone: "I need a thirty-tonne press to bend sheet metal." These are two different machines.

A workshop press has a single ram and a narrow table, from 140 to 260 mm. It can bend a flat bar supported on two V-blocks, but only over short lengths and without angle control.

A press brake has a beam one to three metres long, a punch and a V-die, and its required tonnage is calculated from the bending length and thickness. To bend a metre of 2 mm sheet, thirty tonnes concentrated at one point is not enough: that force must be distributed along the whole bend line. This is the domain of press brakes, a different category.

Three points to know before buying.

Presses are not included in Annex VII of Italian Legislative Decree 81/2008, so they are not subject to mandatory periodic inspection in the same way as vehicle lifts and lifting equipment. They remain work equipment under Title III: the employer must ensure maintenance, operator training and risk assessment.

Presses for cold-working metals have a harmonised technical reference standard, EN ISO 16092, divided into several parts according to the type of drive.

From 20 January 2027, EU Regulation 2023/1230 replaces Machinery Directive 2006/42/EC. Machines placed on the market before that date remain compliant: there is no obligation to retrofit equipment already in your workshop.

In practice, the two measures that prevent the most common injuries are a protective screen in front of the working area, because a bearing that suddenly fails can fly off like a projectile, and floor anchoring. WK models do not require special foundations: a standard industrial floor with 15–20 cm of concrete and four M12 bolts is enough up to the 50-tonne version.

When customers call us, this is the process we follow, in this order.

First, measure the largest part you will place under the press, both its width and height. These measurements establish the minimum clearance and immediately rule out half the range.

Second, list the operations you will actually perform. Only bearings and bushes on medium-sized shafts: ten or twelve tonnes. Also straightening shafts and removing rusty parts: twenty. Working on heavy-vehicle or agricultural components: thirty or fifty.

Third, decide whether you work alone. If so, the pedal is not an optional extra.

Fourth, consider frequency. Daily use justifies the Pro version; occasional use does not.

If you are still unsure between two models, call us on 0825-1494022 with the part dimensions to hand: in two minutes we can establish which one accommodates it. The full catalogue range is available online with all specifications.