Brown’s first portable cramp drill has a C-shaped frame, a drill spindle in its upper arm and a feed screw in its lower arm. Turning the lower screw brings the supported work toward the drill. A separate upper crank rotates the spindle.
Cramp Drill Form 1 Interactive Calculator
Explore the separate screw feed of Brown’s first portable cramp drill. The screw beneath the work raises it toward an independently rotated drill. Enter feed-screw pitch, feed-screw speed, required axial travel and feed-handle radius.
Equation Used
- Single-start screw: pitch equals axial lead per revolution.
- Specified constant forward feed-screw speed; animation timing is illustrative.
- Feed handle rotates at the screw speed with a fixed radius.
- Drill rotation is independent and is not an input to the feed calculation.
- No cutting force, material, bit geometry, chip clearing, work restraint or elastic-deflection model.
The lower feed control and upper drill crank are independent. The animation follows the original C-frame arrangement and compresses the feed motion into a repeating demonstration.
Separate rotation and feed
The frame keeps the drill and opposing feed screw on a common axis. The upper crank turns the spindle. Beneath the work, a second handle turns a screw through the frame nut and advances its support pad.
The cutaway makes these connections visible. The work and screw move together toward the fixed-height bit, and the lower handle rises with the screw. The illustrated return is included to repeat the motion; it is not a drilling procedure.
The original drawing does not couple the two handles. Consequently the calculator’s speed input refers to the feed screw, while the spindle’s animated rotation is only a visual cue.
Portable screw-feed arrangement
The cramp frame provides an opposing support where access permits the work to fit inside its opening. The drawing illustrates the mechanical arrangement, not a specified tool capacity or a recommendation for a particular work material.
Feed-screw calculation
For screw lead p in mm/revolution, screw speed n in rpm and travel d in mm, required turns N = d/p and axial feed f = pn in mm/min. Ideal feed time is 60d/f seconds.
A handle of radius r mm travels 2π(r/1000)N metres over those turns. This path length is not a force or energy calculation. The model assumes a single-start screw, so the pitch input is also its lead.
Example: 25 mm of feed travel
A 2.5 mm/revolution feed screw takes 10 turns to advance 25 mm. At a selected screw speed of 40 rpm, the theoretical feed rate is 100 mm/min and the forward-feed time is 15 seconds. A 125 mm radius feed handle travels about 7.85 metres around its axis.
Those figures describe the chosen screw motion. They do not establish how quickly a bit can cut a particular material. The drill’s upper crank remains a separate control.
What the model leaves open
Useful feed depends on the drill, work material and applied effort. A smaller screw lead reduces advance per turn; it does not by itself determine a permissible cutting force. Frame stiffness, screw friction, thrust support, clearance and work restraint are not calculated.
The frame and bit dimensions are schematic. Work thickness is drawn with extra material below the selected feed, and the section removes the central material graphically to keep the bit visible.
Cramp-drill feed questions
Does the upper crank also turn the feed screw?
No. Brown’s form 1 shows separate drill and feed controls.
What speed does the calculator use?
The rpm input is the feed-screw speed. It determines axial feed from screw lead.
Is the displayed time an actual drilling time?
No. It is the theoretical time for the selected axial travel at the selected constant screw speed.
Why does the lower handle move upward?
It is attached to the translating feed screw, which raises its support pad and the work.
What does handle radius change?
It changes the distance travelled by the hand. No cutting force is inferred from it.
Historical reference
Henry T. Brown, Five Hundred and Seven Mechanical Movements, drawings 379 and 380, printed pages 92–93. The diagram illustrates movement 379. Movement 379 description.
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