A gig saw uses a rotating crank to reciprocate a saw blade. In the spring-tensioned form described in Henry T. Brown’s Five Hundred and Seven Mechanical Movements, the crank drives the lower end while a spring tensions the upper end. Explore the crank-and-rod motion here, and calculate average work feed from advance per feed stroke and strokes per minute.
Gig Saw Feed Rate Interactive Calculator
Vary feed per stroke and strokes per minute to see the carriage feed rate and animated crank-to-sash motion.
Equation Used
The feed rate is the carriage advance per stroke multiplied by the saw stroke rate. Dividing by 1000 converts millimetres per minute to metres per minute.
- Carriage advances once per saw stroke.
- Feed per stroke is constant through the cut.
- SPM counts the feed strokes used to define the advance per stroke.
How the gig saw moves
The crank pin moves in a circle. A connecting rod, also called a pitman, transfers that motion to the guided blade attachment. The guides restrict lateral movement while allowing reciprocation; the upper spring maintains tension as the attachment moves.
The work must also advance relative to the teeth. Feed can be intermittent or continuous, depending on the machine. The calculator treats each counted feed stroke as advancing the work by the entered distance. It does not determine how much feed a blade or material can accept.
Parts shown
- Crank: supplies cyclic motion from a rotating shaft.
- Connecting rod: joins the crank pin to the guided attachment.
- Guides: locate the reciprocating member.
- Spring: represents the blade-tensioning element.
- Work support: locates the material relative to the cutting path.
Understanding reciprocating sawing
This historical mechanism illustrates rotary-to-reciprocating motion and spring tensioning. It can be compared with a framed reciprocating saw, whose blade is tensioned in a moving frame, and with band and circular saws, whose cutting edges follow continuous paths.
For an actual saw, use its specified blade, speed, tension and feed arrangements. This feed calculation does not select equipment, cutting settings or an allowable production rate.
Feed-rate calculation
Let f be work advance in millimetres per counted feed stroke and N the number of those strokes per minute. Use the same definition of a stroke for both inputs.
Average feed V = f × N / 1000 m/min
Feed speed in mm/s is f × N / 60. Strokes per metre are 1000 / f, and minutes per metre are 1 / V. If the work advances once per complete crank revolution, N equals crank rpm. If it advances twice, N is twice crank rpm.
No cutting-duty factor is required for this distance-per-event calculation. Feed advance and its event rate already determine average work travel. Cutting force, blade speed and power are separate quantities.
Example: average work feed
Suppose the work advances 2.5 mm per feed stroke and there are 300 such strokes per minute. These are example inputs, not recommended cutting settings.
- Work travel per minute: 2.5 × 300 = 750 mm/min = 0.75 m/min.
- Feed speed: 750 / 60 = 12.5 mm/s.
- Strokes for one metre: 1000 / 2.5 = 400.
- Time for one metre: 1 / 0.75 = 1.333 minutes, or 80 seconds.
This is travel time during steady feeding. Loading, return travel, positioning and interruptions are not included, so it is not a parts-per-hour estimate.
Comparing cutting motions
| Mechanism | Motion | Design consideration |
|---|---|---|
| Spring-tensioned gig saw | Blade reciprocates; spring maintains tension | Guidance and tension must suit the blade and cutting load |
| Framed reciprocating saw | Blade travels with a tensioning frame | The moving frame adds reciprocating mass |
| Band saw | Endless blade travels around wheels | Wheel alignment, blade tracking and tension matter |
| Circular saw | Teeth rotate around a spindle | Blade diameter, spindle speed and work support matter |
Kerf, finish, capacity and feed depend on the particular machine and blade. They cannot be ranked reliably from motion type alone.
Frequently asked questions
What does Stroke Rate mean here?
It is the number of feed strokes per minute. Define a stroke consistently with Feed / Stroke. If feed occurs once per crank revolution, enter crank rpm; if it occurs twice, enter twice that value.
Does stroke rate change the playback speed?
No. Playback is slowed to show the linkage motion. Stroke rate changes the feed-rate and time results; it does not set real-time animation speed.
Does a cutting stroke require a factor of one-half?
Not in this calculation. Enter the actual advance per feed event and the number of those events per minute. Whether cutting occurs on one or both directions does not independently halve that travel.
Can these inputs establish blade tension or motor power?
No. Blade dimensions, tooth geometry, material, cutting force and dynamic loads are not inputs.
Why could measured travel differ?
The calculation assumes constant advance for every counted event. Missed feed events, slip, pauses or a different definition of stroke change actual travel. Measure advance and event rate before comparing.
Further reading
Henry T. Brown, Mechanical Movement 392: spring-tensioned gig saw. The historical description identifies a crank-driven lower blade end and a spring-tensioned upper end.
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