Press brake bed (lower beam) and lower die support: mid-length sag, wedge crowning tables and beam designs that keep the die parallel to the punch
Press brake lower beam · the bed that carries the lower tool holder and die, why it sags at mid-length, and the wedge crowning tables and beam designs that keep the die straight
On a press brake the lower beam, or bed, is the plate-steel member that the side frames hold at its ends and that carries the lower tool holder and the V-die along the bending line. When the ram presses a sheet into the die, the reaction pushes the bed down in the middle while the upper beam bows the other way, so the punch and die are no longer parallel and the bend angle at mid-length differs from the ends. Specifying the bed means specifying how that sag is countered: by a crowning table of wedges under the die, by hydraulic crowning, or by shaping the beam itself.
The lower beam (bed) of hydraulic and electric press brakes and the parts between it and the lower die: lower tool holders and die rails, wedge crowning tables, and lower beam designs that counter deflection, with checks of die straightness under load. Punches and V-dies themselves are covered on the V-die set page; upper tool holders under the ram on the Ram punch holder page; the ram and its Y1/Y2 cylinders on the Press brake ram page; crowning and tooling for thick high-strength plate on the Heavy plate bending press page; complete machines on the Hydraulic press brake page.
CNFX editorial research · Sources checked October 13, 2026 · 3 sources
Bed held at its ends: downward sag at mid-length and the open angle it leaves
Amada's die crowning patent sets out the cause. The upper and lower tables of a press brake are supported at their extreme ends by the two side frames, the drive acts at the sides, and the sheet resists bending in between, so the upper table deforms upward at mid-length and the lower table downward. The dies then do not engage accurately near the middle, and the bend angle there differs from the angle at the ends, its example being a larger angle in the middle. [1]
Rolleri, describing its crowning tables, states that press brake deflection is directly proportional to bending length and to the ratio between sheet thickness and the V opening of the die. [3] Editorial note: by that relation a long part bent in a V that is narrow for its thickness gives the largest deflection, so give the supplier the longest bend at the highest force you plan, not only the machine's rated tonnage.
Bystronic's patent US 12,097,550 B2 lists the two families of remedy: active crowning, where force is applied against the deformation during the bend, for example by hydraulic cylinders, which it says adds cost because sensors and drives are needed; and passive pre-shaping, where the lower beam is adapted in advance to the expected deformation by milling a curved surface or placing plates or wedges underneath. [2]
State the longest bend length, the thickest material and the narrowest V-die you will use together, and the angle tolerance you need along the full length.
02
Wedge-row crowning tables between the bed and the lower die
Rolleri's ROL TA/R1/MN is a motorised crowning table in C45 steel (560–710 N/mm²), hardened and ground, for R1-style dies, with a maximum load of 2500 kN/m. It consists of a bar of special steel opposite a row of wedges; each wedge can be set individually to compensate small working areas, and the bar is moved by hand or by a gear motor connected to the press brake CNC. Rolleri builds each table to the features of the press brake it goes on. [3]
Editorial calculation: at 2500 kN/m a table's rating over a 3 m bend is 2500 × 3 = 7,500 kN; for a shorter part concentrated at mid-length the load per metre, not the press tonnage, is the figure to compare with the table rating. [3]
Amada's patent describes a mechanism that sets all the wedges at once. Pairs of upper and lower wedges sit at intervals between the lower die and the lower table, each lower wedge engaging, through a groove in its underside, a long plate spring fixed to the table at its middle. A control motor driving sprockets and nut members bends the free ends of the spring symmetrically, which slides the lower wedges sideways together and raises the die into a convex shape set by the curvature of the spring; springs lift the lower die and its base so the wedges slide freely. [1] The same patent notes that wedges adjusted one at a time make setting complicated, which the single plate spring avoids. [1]
Ask for the table's load rating in kN/m, its material and hardness, its die interface (R1, R2 or other), manual or CNC-driven adjustment, and whether individual wedges can be trimmed.
03
Shaping the lower beam itself: recessed regions at the tool-holder ends
Bystronic's patent takes the opposite approach to adding a crowning mechanism: it changes the stiffness of the lower beam along its length. The beam is built from a plate-shaped central element with one or more side elements beside it in the thickness direction. Recessed regions, cut out or thinned, overlap each end of the tool holder to reduce the beam's bending stiffness at the edges, while in the central region the bending force is passed through the tool holder into both the central and side elements. [2]
In the patent the central portion of the tool holder occupies at least 50% of its length, and adjusting means between the elements leave a play of 0.05 to 5.0 mm, preferably 0.1 to 1 mm, so that the leg of the central element can flex. The combination of a stiffer centre and less stiff ends is intended to give more uniform bending along the workpiece. [2] Editorial note: a beam shaped this way is matched to the machine's force and length, so ask the builder what bend lengths and loads the shaping was designed for and whether a crowning table is still offered for off-centre or short bends.
04
Checking the lower die along its length
Amada's stated aim for crowning is that the upper and lower dies stay parallel over the whole length of the press brake during bending. [1] Editorial note: two checks follow from that. Unloaded, run a dial indicator along the die shoulders on the bed to see that the die and holder are straight and seated. Under load, bend a test strip of the full length at the planned force and measure the angle at both ends and the middle; the difference is what the crowning setting has to remove.
Rolleri's per-wedge setting is aimed at small working areas, which is where a single crowning curve set for the full length can leave an error. [3] Record the crowning value that gave an even angle for each tool, material and length, so it can be called up again by the CNC or set by hand.
Ask the supplier how the crowning value is set for each job (CNC table, manual scale or angle measurement) and what angle variation along the length the bed is rated to hold.
05
Bed and lower-die details for a press brake quotation
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Bending: [longest bend length; thickest material and grade; narrowest V]
Force: [maximum force; force per metre at short bends]
Tool interface: [lower holder or die rail; R1, R2 or other]
Crowning: [wedge table, hydraulic or shaped beam; manual or CNC]
Rating: [table load in kN/m; material; hardness]
Accuracy: [angle tolerance along the length; test strip result]
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
Why does the bend angle differ in the middle of a long part?
Amada explains that the lower table sags downward at mid-length while the upper table bows upward, so the dies do not engage accurately in the middle. [1]
What does press brake deflection depend on?
Rolleri states it is directly proportional to bending length and to the ratio of sheet thickness to die V opening. [3]
How much load can a crowning table take?
Rolleri rates its motorised C45 crowning table for R1 dies at a maximum of 2500 kN/m. [3]
Can the lower beam compensate without a crowning device?
Bystronic's patent reduces the beam's stiffness at the tool-holder ends with recessed regions, while the central region carries force into all its plate elements. [2]
Sources and what still needs a direct check
Sources checked 2026-10-13. Amada's die crowning patent US 4,732,032 A, Bystronic's bending machine patent US 12,097,550 B2, and Rolleri's ROL TA/R1/MN crowning table product page.
