A screw bench clamp uses an anchored post, a supported arm and a threaded spindle to press a pad onto a workpiece. This calculator models the axial force of a direct screw, with a generic bench-mounted arrangement that makes the load path visible.
Screw force and powered workholding
This clamp develops axial force through a rotating screw. A powered clamp with a different drive needs its own force, travel and load-holding design; the screw-force result alone does not establish the capacity of an actuator, frame or workpiece.
For a separate positioning linkage, the FIRGELLI actuator force calculator covers supported mounting arrangements. Compare the required load, stroke and installed length with the FIRGELLI linear actuator range, or use the linear actuator replacement finder for an existing actuator. Confirm workholding requirements against the selected clamp and machine documentation.
Bench Clamp Interactive Calculator
Adjust input torque, threads per inch and overall screw efficiency. The animation shows approach, contact and release; calculated force is a static screw estimate, not a hardware rating.
Equation Used
- Single-start thread: lead equals 1/TPI.
- Direct axial screw load; no additional lever amplification.
- Entered efficiency is an assumed overall value, not derived from thread geometry.
- The 0.30-inch approach and frame dimensions in the animation are illustrative. Contact is rigid; tightening deflection is not modeled.
The construction reference and the torque–lead work balance are described below. The drawing is generic and does not assign a product load rating.
How the screw bench clamp works
The bench supports the workpiece and anchors the clamp post. A sliding arm is positioned above the work, then held by its clamping action on the post. Turning the spindle through the threaded end of the arm advances a swivel pad toward the workpiece. Once contact is made, further tightening develops force through elastic deformation in the real assembly.
The illustration shows a generic direct-spindle bench clamp with a separate post, arm, screw, pad and bench adapter. The post and arm stay fixed during the tightening cycle. The pad remains aligned with the workpiece while the spindle turns. It is a schematic arrangement based on the construction visible in BESSEY’s bench-clamping documentation, not a dimensioned replica or a capacity claim for that product.
The animation includes approach, a stationary contact interval and release. The workpiece is treated as rigid, so tightening deflection is not shown. A force arrow appears during contact only. The inputs determine screw lead and calculated static force; they do not determine the frame size.
Bench workholding
A bench-mounted screw clamp can hold a workpiece against a supporting surface during assembly or machining. Actual suitability depends on the clamp rating, anchorage, workpiece, load direction and operation. Axial force alone does not establish resistance to sideways cutting loads or vibration.
Holdfasts, cam clamps and rocker-arm clamps use different force paths. Their wedge angles, cam profiles or lever ratios are not included in this direct-screw calculator.
Torque, lead and axial force
One full revolution supplies input work 2πT. A single-start screw advances L = 1/TPI inches in that revolution. Equating output work FL to η times input work gives F = 2πTη/L. With entered torque in ft·lbf, multiply it by 12 before using an inch lead.
The ideal force uses η = 1. The calculated force uses the entered efficiency. Work loss fraction is 100 minus the efficiency percentage. Efficiency represents losses once; a separate friction denominator is not added to this model.
Threads per inch does not identify screw diameter, thread form, strength or number of starts. This calculator assumes one start. Multi-start screws advance farther per turn and require their actual lead.
Worked screw-force example
At 10 ft·lbf input torque, 10 threads per inch and 20 percent overall efficiency, the lead is 0.1 in/rev. Ideal force is 2π × 120 / 0.1 = 7539.8 lbf; applying the assumed efficiency gives 1508.0 lbf. The work loss fraction is 80 percent.
This is an energy-based estimate for the entered assumptions. It is not a recommended operating torque or a rated capacity for the illustrated clamp. The real clamp, bench attachment and workpiece must be assessed separately.
What the comparison can tell you
At equal torque and efficiency, finer single-start threads produce greater calculated force and less advance per turn. Increasing torque or efficiency increases the estimate in direct proportion. A practical design also depends on thread geometry, lubrication, pad friction, stiffness and strength.
The animation preserves this travel-per-turn relationship. Its contact dwell merely identifies the loaded state; it does not calculate the extra rotation or deflection needed to build preload.
Bench-clamp questions
Does the calculated force mean my clamp can carry it?
No. The calculation converts torque through lead and assumed efficiency. It does not check the spindle, threads, arm, post, bench or workpiece against a load limit.
Why does the pressure pad stop turning?
The illustrated swivel connection allows the spindle to rotate while the pad stays aligned with the workpiece. Its frictional losses are included only through the assumed overall efficiency.
Why is there no force arrow during approach?
The pad is not touching the workpiece then. The displayed calculated force describes the loaded screw state rather than a force applied across the visible gap.
Can this calculate a rocker-arm clamp?
Not directly. A rocker-arm clamp needs its lever geometry and force directions as well as screw force. This page shows a direct spindle acting on the pressure pad.
Construction reference
BESSEY bench-clamping elements and TW16AW adapter brochure illustrates the post, sliding arm, spindle, pressure plate and bench attachment used as the construction reference. The generic drawing does not reproduce that product’s dimensions or specify its load capacity.
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