Hiscox movement 912 uses a three-part worm screw to rotate three screw gears in a chuck so the three jaws close in the same direction. This explanatory calculator applies ideal worm-ratio and screw-lead kinematics to that three-branch arrangement.
Three-part Worm Screw Interactive Calculator
Set illustrative worm turns, jaw-screw lead, screw-gear tooth count and worm starts. The calculator reports ideal synchronized travel and ratio only; it does not calculate backlash, force, strength or chuck capacity.
Equation Used
- The three screw gears are identical and are driven without slip by the three-part worm.
- The worm has z_worm starts and each screw gear has N_gear teeth.
- Each screw-gear revolution advances its jaw by the entered screw lead.
- Backlash, handedness details, tooth geometry, friction, load, deformation, strength, tolerances, interference and safe chuck capacity are omitted.
Hiscox Movement 912
Gardner D. Hiscox identifies movement 912 as a three-part worm screw operating three screw gears for a chuck. The arrangement makes the jaws close in the same direction.
The drawing shows one central three-part worm driver distributed to three equally spaced screw gears and radial jaws. Its dimensions are illustrative and do not specify a manufactured chuck.
What This Calculator Does
The tool applies the ideal worm relation to identical displayed screw gears, then converts gear revolutions to equal linear jaw travel using the entered jaw-screw lead.
The model assumes synchronized ideal motion. It does not calculate backlash, preload, actual gripping force or chuck accuracy.
Ideal Synchronized Kinematics
jaw travel = gear revolutions times screw lead
gear angle = 360 degrees times gear revolutions
ideal ratio = gear teeth / worm starts
The same ideal result is applied to each of three identical branches.
Worked Illustrative Example
With 3 worm revolutions, a one-start worm, 30-tooth screw gears and 4 mm/rev jaw screws, each screw gear turns 0.1 revolution or 36 degrees. Each jaw travels an ideal 0.40 mm in the common closing direction.
The 30:1 ratio is kinematic only; it is not a torque, efficiency or strength rating.
Model Boundary
- Historical arrangement: a three-part worm screw operating three screw gears so three chuck jaws close in the same direction.
- Calculated: ideal screw-gear revolutions, equal jaw travel, displayed gear angle and reduction ratio.
- Not calculated: backlash, preload, worm section construction, handedness details, tooth contact, friction, torque, force, stiffness, strength, wear, tolerances, accuracy, work holding or safe capacity.
Frequently Asked Questions
Is this an anti-backlash split worm?
No. Hiscox movement 912 distributes worm-driven motion to three screw gears for a chuck; this calculator does not model an anti-backlash preload arrangement.
Why are there three screw gears?
Hiscox states that the three-part worm operates three screw gears for a chuck.
Why do all jaw outputs match?
The explanatory model assigns identical gear tooth counts and screw leads to all three branches.
Does ratio predict force?
No. Efficiency, friction and geometry needed for a force model are omitted.
Are the input values historical specifications?
No. They are illustrative.
Can this set a safe gripping load?
No. Use the chuck manufacturer's limits and instructions.
References
- Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, movement 912, printed page 234: three-part worm screw operating three screw gears for a chuck so the jaws close in the same direction.
- MIT OpenCourseWare, 2.72 Elements of Mechanical Design, Lecture 12: worm-gear geometry and transmission-ratio context.
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