In Brown’s second portable cramp drill, the spindle runs through the center of a hollow feed screw. The upper crank turns the spindle directly. A separate feed handle turns the threaded sleeve through the frame and moves the spindle toward work supported by the lower arm.
Cramp Drill Form 2 Interactive Calculator
Adjust the independent drill and feed controls of Brown’s second cramp-drill form. The spindle passes through a hollow feed screw and rotates directly from the upper crank. See how screw lead and screw speed determine feed per minute and feed per bit revolution.
Equation Used
- Direct crank-to-spindle drive as shown in Brown figure 380.
- Feed-screw lead is axial travel per screw revolution.
- Rigid frame and schematic thrust collars; no friction or load model.
- Feed motion and spindle rotation are independently controlled.
- Constant selected screw speed for the time calculation; animation is time-compressed and rotation cues are independently slowed.
This form has a direct spindle crank and a separate feed handle. Choose spindle speed, screw lead, screw speed and required travel to compare axial feed, feed per bit revolution and ideal feed time.
Spindle inside the feed screw
The cutaway shows the blue spindle running inside a gold threaded sleeve. The fixed upper frame acts as the sleeve’s nut. Turning the feed handle translates the sleeve, while thrust support transfers that axial movement to the spindle without locking their rotation together.
The upper crank is attached directly to the spindle, which turns inside the hollow feed screw. The work rests on the lower frame arm.
During the demonstration the crank, sleeve and spindle descend together, then return. Rotation cues are slowed independently to keep the two controls visible. The drawing is a kinematic section, not a manufacturing design for the thrust support or bit.
Portable drill feed
This arrangement places the feed adjustment on the same side of the work as the drill spindle. It illustrates how axial feed can be controlled separately from tool rotation inside a compact frame. Work holding and cutting suitability require details beyond this diagram.
Independent speed and feed
The direct crank makes spindle speed n equal to crank speed. A screw lead p and screw speed n_f give axial feed f = pn_f in mm/min. Feed per bit revolution is f/n.
For axial travel d, ideal constant-feed time is 60d/f seconds. At zero feed-screw speed, the spindle can still rotate, but it cannot complete a nonzero axial travel. The time tile therefore shows No feed.
Example: separate controls
With a 60 rpm spindle crank, 2 mm/revolution lead and 1 rpm feed screw, the axial feed is 2 mm/min. This is about 0.033 mm per bit revolution. Advancing 10 mm takes 300 seconds at that constant screw speed.
Changing the spindle speed changes feed per bit revolution but not the screw’s axial feed rate. Changing the lead or feed-screw speed changes both axial feed and feed per bit revolution. Travel changes the time required.
What these results mean
The model describes chosen motions. It does not select cutting speed, cutting force, allowable feed or a material-removal rate. Those depend on the bit, material and actual tool construction. Choose actual cutting conditions for the bit, material and tool; the input range is not an operating-speed rating.
The crank drives the spindle directly. Required travel determines ideal feed time, while screw lead and screw speed determine axial feed.
Hollow-feed-screw questions
Does the feed handle turn the drill at the same speed?
No. The spindle rotates inside the sleeve, and its crank is independent of the feed control.
How does the crank drive the spindle?
The upper crank is fixed directly to the spindle, so each crank revolution produces one spindle revolution.
What happens when screw speed is zero?
The spindle can rotate, but the axial feed remains zero and the required travel has no finite completion time.
Does a larger lead change spindle speed?
No. It changes axial advance per feed-screw turn and therefore feed per bit revolution.
Is the calculated time a cutting-time prediction?
No. It is the time for the selected feed motion, without a material-removal model.
Historical reference
Henry T. Brown, Five Hundred and Seven Mechanical Movements, figure 380 on printed page 92 and description on page 93. Movement 380 description.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
