A double toggle-joint screw press uses a screw to move two toggle knees toward or away from one another. Straightening the links moves a guided platen. The animation shows two mirrored, equal-link toggles driven by opposed screw threads. The calculator relates their dimensions to ideal force and travel.
Double-screw Toggle Press Interactive Calculator
Adjust the two endpoint angles, four equal links and opposed screw lead. Watch both toggle knees move with the floating screw while comparing ideal platen force and travel.
Equation Used
- Four equal-length rigid links in two mirrored toggles.
- Opposed threads of equal lead and anti-rotating knee nuts.
- Guided level platen; screw follows the knees vertically.
- Total input torque shared by two nut loads; friction omitted.
Ideal frictionless symmetric model. No part strength, buckling, workpiece, thermal or safe load rating.
A floating opposed-thread screw straightens two toggles
The top pivots are fixed to the press frame. Four equal-length links connect them through two moving knees to the guided platen. Right- and left-hand threads move the knee nuts symmetrically as the screw rotates. The screw follows the knees vertically while its two axial nut loads balance each other.
The handwheels at either end represent access to the same screw. The entered tangential rim force is the total equivalent input, not a force applied separately at both wheels. The visible wheel radius follows the input. Thread bands identify opposite handedness; their drawing is schematic, while screw rotation and nut translation follow the entered lead.
Hiscox shows a double toggle-joint screw press with heated platens. This model explains its screw-and-toggle principle using a stated symmetric geometry; it is not a dimensional replica or a thermal model of the historical press.
Compare geometry, travel and ideal force
Adjust the start and end link angles, equal-link length, screw lead, handwheel radius and equivalent hand force. The animation moves between the two entered configurations and returns. The output cards compare endpoint force and show platen travel, screw turns and total torque.
The platen is shown with clearance above the lower bed. The model does not compress a workpiece or predict stiffness, material forming pressure, friction, buckling or structural capacity.
Force from the defined motion and virtual work
With link length L and angle θ from vertical, each knee lies h=L sinθ outside its top and bottom pivot line. The top-to-platen distance is y=2L cosθ. Each nut moves one lead l per screw revolution, so the number of turns between endpoints is |L(sinθA−sinθB)|/l. Platen travel is |2L(cosθB−cosθA)|.
For total screw torque T, both nuts share the input work. One revolution supplies 2πT and moves two nuts through l, giving horizontal force per nut Fh=πT/l. Each toggle contributes Fh/(2 tanθ) to the platen; together they produce Fplaten=πT/(l tanθ). For tangential hand force F at radius r, T=Fr.
Forces are ideal frictionless values. The angle controls stop above dead center; the mathematical force rise near alignment is not a usable machine load rating. Both nut loads and both toggles contribute to the virtual-work balance.
Example: 250 mm links and a 4 mm lead
With start 10° and end 2°, 250 mm links move the platen about 7.29 mm while each knee moves about 34.69 mm inward. The opposed screw turns about 8.67 revolutions.
A total equivalent 100 N tangential force at 150 mm radius supplies 15 Nm torque. The ideal platen force is about 66.81 kN at 10° and 337.36 kN at 2°. These large near-alignment values demonstrate geometric amplification only; no part strength or friction limit is included.
Large ideal force comes with small platen motion
As the links approach vertical, further screw rotation produces less platen travel and greater ideal force multiplication. Real deflection, friction, pin bearing stress and link buckling become decisive, none of which are calculated here.
The equal mirrored geometry keeps the platen level. The two knee nuts are anti-rotated by their links, and the screw is free to follow their vertical motion. The guide columns are depicted behind the toggle and screw plane.
Double-toggle press questions
Does the force input apply to each handwheel?
No. It is the total equivalent tangential input at the selected radius, shared across however the screw is operated.
Why does the screw move vertically?
The screw passes through the toggle knees, which move vertically as well as horizontally. Fixing it at a constant height would contradict this symmetric linkage.
Can the ending angle be larger than the starting angle?
Yes. The demonstration then starts by retracting the platen. Travel and turns are reported as magnitudes, with endpoint forces evaluated at their own angles.
Does the force result specify a safe press capacity?
No. It is an ideal virtual-work calculation, without structural or friction limits.
Historical mechanism reference
Hiscox, Mechanical Movements, Powers and Devices, printed page 343, figure 1432 (PDF page 353), shows the double toggle-joint screw press with heated platens. This calculator’s explicit symmetric-link model and force equations are derived from its stated geometry and virtual work.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
