A needle-bar slot cam converts shaft rotation into guided reciprocating motion. Hiscox item 1038 describes a pause while the shuttle passes. Explore an illustrative groove with an adjustable bottom dwell and calculate how long that pause lasts at the entered shaft speed.
Declared Needle-Bar Dwell Profile
Enter a declared stroke, bottom-dwell angle and shaft speed. The viewer synthesizes a rotating groove whose current point remains coincident with the guided follower throughout the cycle. It illustrates Hiscox's topology without claiming original cam dimensions or timing.
Equation Used
- The needle bar is constrained to ideal vertical translation and the follower pin stays on the synthesized groove centreline.
- The declared dwell is symmetric about 180 degrees and limited to 0-120 degrees.
- Motion outside the dwell uses two raised-cosine half-strokes solely as a transparent illustrative profile.
- Stroke, dwell and speed are declared inputs, not dimensions or ratings from Hiscox.
- Follower diameter, clearance, contact force, elasticity, friction, lubrication, shuttle timing, stitch formation, materials, wear, manufacturing and safety are excluded.
The entered dwell angle sets the pause in the follower profile. Shaft speed determines the calculated dwell time; playback uses a fixed illustrative cycle and the drawing uses a normalized stroke.
A rotating pin groove drives a guided needle bar and includes a stop
Hiscox item 1038 shows a needle bar constrained vertically beside a rotating slot cam. Its caption states that a depression in the pin slot gives the needle a stop motion while the shuttle passes.
The viewer prescribes a declared bottom dwell, synthesizes the corresponding rotating groove and keeps the follower pin coincident with that groove throughout the cycle.
A historical sewing-machine cam arrangement
Hiscox describes a sewing-machine needle-bar slot cam whose groove provides a pause for the shuttle. The profile shown here illustrates that principle rather than the geometry or timing of a particular sewing machine.
An illustrative bottom-dwell profile
From top position, a raised-cosine half-stroke reaches y=S at 180°-δ/2. The needle remains at y=S through 180°+δ/2, then a second raised-cosine half-stroke returns it to y=0 at 360°.
The profile is an illustrative motion law; its numeric dwell angle is an input rather than a historical measurement.
Declared profile example
For a 30 mm stroke, 40° bottom dwell and 1,200 rpm, half-stroke is 15 mm, active-travel angle is 320°, dwell occupies 11.1% of a revolution and lasts 5.56 ms per revolution.
How a dwell changes the motion
A sinusoidal stroke reverses at the bottom without a finite pause. Adding a dwell holds the follower at its lowest position for part of the shaft turn, leaving less angle for downward and upward travel. Choosing a working cam also requires contact geometry, loads and coordination with the shuttle, which this illustrative profile does not determine.
Needle-bar slot-cam questions
Does the historical mechanism have a dwell?
Yes. Hiscox states that the pin-slot depression gives stop motion while the shuttle passes.
Is the displayed 40° dwell historical?
No. It is a declared default for the illustrative profile.
Does this calculator size a real sewing machine?
No.
Needle-bar slot-cam references
- Hiscox, Mechanical Movements, page 260, item 1038: primary public-domain plate and caption documenting the needle-bar slot cam and its depression-produced stop motion.
- Pictorial Handbook of Technical Devices, cam mechanisms: later technical handbook reproducing the identification and stop-motion description.
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