A spiral guide on disk is a face cam with an Archimedean groove machined into one face of a rotating plate, paired with a roller follower that rides in the groove and is constrained to move only radially. As the disk turns, the constant pitch of the spiral pulls the follower inward or outward at a uniform rate per revolution, converting rotary input into precise linear feed. We use it on drilling heads to advance the quill at a controlled feed-per-rev — the same principle behind the auto-feed on classic Cincinnati and Archdale radial drills.
Spiral Guide On Disk Drilling Feed Interactive Calculator
Vary spiral pitch, drive reduction, disk size, and disk turns to see quill feed and the animated radial follower motion.
Equation Used
The calculator follows the worked example relationship for an Archimedean spiral guide: one disk revolution advances the radial follower by one pitch. With a drive reduction G, the spindle feed per revolution is p/G.
FIRGELLI Automations - Interactive Mechanism Calculators
- Spiral groove has constant Archimedean pitch.
- Follower is constrained to radial motion only.
- Drive reduction G means the disk turns at 1/G of spindle speed.
- Backlash, roller clearance, and elastic deflection are ignored.
How the Spiral Guide on Disk (drilling Feed) Actually Works
The geometry is simple but the behaviour matters. You cut a groove on the face of a disk that follows the equation r = r<sub>0</sub> + (p / 2π) × θ, where p is the pitch — the radial distance the groove advances per full revolution. A roller follower sits in that groove, attached to a slide or quill that's mechanically restrained from rotating. When the disk rotates, the spiral wall pushes the follower radially. The follower then drives the drill quill linearly through a rack, lever, or direct push-rod. One revolution of the disk equals one pitch-length of feed. That direct ratio is what makes the spiral guide on disk so useful for automatic drill feed mechanism design — the operator doesn't compute a feed rate, they pick a disk and a spindle gear ratio.
Why a spiral and not a straight rack? Because the spiral packs a long feed travel into a compact disk diameter, and you can engineer the pitch to be whatever you need without changing the gear ratio driving the disk. A 200 mm disk with 10 mm pitch gives 10 mm of quill travel per disk revolution. Drive that disk at 1/20 of spindle speed through a worm reduction and you get 0.5 mm/rev feed — exactly what you'd want for drilling 12 mm holes in mild steel.
Tolerances bite hard if you ignore them. The follower roller diameter must match the groove width within about 0.05 mm — too tight and it binds when the disk warms up, too loose and the follower clatters back and forth on each direction reversal, leaving chatter marks in the hole. The groove flanks need to be milled with a CNC plunge or profile cut, not hand-filed; any waviness in the flank shows up as feed-rate ripple, and on a drill press that ripple translates to uneven chip loading and broken small-diameter drills. If the disk runs out axially by more than 0.1 mm the follower lifts and drops once per revolution, which is the classic symptom of a worn or undersized thrust bearing on the disk shaft.
Key Components
- Spiral disk (face cam): A flat steel or cast-iron plate with an Archimedean groove machined into one face. Typical disk diameter runs 150 to 400 mm on small drills, with groove pitch of 5 to 25 mm depending on required feed-per-rev. Disk faces are usually ground flat to within 0.05 mm to keep the follower seated.
- Roller follower: A hardened roller, often 8 to 16 mm diameter, riding on a needle bearing inside the spiral groove. The roller-to-groove clearance must be 0.02 to 0.05 mm — tighter binds when the disk heats up under heavy duty, looser produces backlash on direction reversals.
- Radial slide or guide: Constrains the follower to pure radial motion. Usually a dovetail slide or linear bushing, sized so the side load from the spiral wall (which can hit 200 to 800 N at full feed) doesn't deflect the slide more than 0.02 mm. Deflection here shows up as tapered holes.
- Output linkage to quill: Couples follower motion to the drill quill. On a Cincinnati-style radial drill this is a rack-and-pinion off the follower carriage; on smaller benchtop conversions it's a direct push-rod. The linkage ratio sets final feed per disk revolution.
- Drive reduction (worm or gear train): Steps spindle speed down to disk speed. Typical ratios are 1:20 to 1:200. A worm drive is preferred because it's self-locking — the spiral can't back-drive the spindle when you hit a hard inclusion mid-hole.
- Disengagement clutch: Lets the operator break the feed mid-stroke for retract or rapid traverse. Usually a dog clutch on the disk shaft. Without it you'd have to wait through a full revolution to back the drill out, which is unacceptable on production work.
Real-World Applications of the Spiral Guide on Disk (drilling Feed)
The spiral guide on disk earned its reputation on drilling machines, but the mechanism shows up anywhere you need a slow, even, force-resistant linear feed driven from a rotating shaft. It handles axial loads well because the spiral wall presents a near-perpendicular face to the follower, and it gives positive feed in both directions, which a friction-driven feed cannot. You'll see it on older industrial drills, deep-hole boring rigs, certain tapping heads, and a handful of niche film-advance and recording mechanisms. Modern CNC has displaced it on new equipment, but it's still common on rebuilt manual machines and dedicated single-operation production drills where a servo would be overkill.
- Metalworking machine tools: Quill feed on Archdale and Cincinnati radial arm drills — the spiral disk drives a rack that advances the spindle quill at a selectable feed-per-rev between 0.05 and 0.5 mm.
- Deep-hole drilling: Feed control on gun-drilling rigs similar to a UNISIG B-series, where consistent low feed rates of 0.02 to 0.08 mm/rev are needed over hole depths exceeding 1 m.
- Tapping and threading: Lead control on dedicated tapping heads where the spiral pitch matches the thread pitch being cut, giving synchronous feed without a leadscrew.
- Cinema and recording equipment: Film-advance and lens-focus mechanisms on archive cameras like older Mitchell BNC variants, where the spiral cam delivered repeatable focus pulls.
- Powder metallurgy and tablet presses: Punch-feed advance on small-batch tablet presses, where a spiral disk indexes the upper punch downstroke rate without needing servo control.
- Educational and demonstration mechanisms: Teaching rigs showing rotary-to-linear conversion — Reuleaux model collections at Cornell include spiral cam demonstrators dating from the 1880s.
The Formula Behind the Spiral Guide on Disk (drilling Feed)
The feed rate of a spiral guide on disk is the product of disk angular velocity and groove pitch. What changes across the operating range is what the cut feels like. At low disk speeds the feed is so slow you'll see rubbing rather than chip formation in soft materials; at high disk speeds the feed outruns the spindle's ability to clear chips and you stall the drill. The sweet spot is the band where chip thickness matches the drill manufacturer's recommended feed-per-rev for the spindle speed you're running.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| vfeed | Linear feed rate of the follower (and quill) | mm/s | in/s |
| p | Spiral groove pitch (radial advance per disk revolution) | mm/rev | in/rev |
| Ndisk | Disk rotational speed | RPM | RPM |
| frev | Feed per spindle revolution (= p × N<sub>disk</sub> / N<sub>spindle</sub>) | mm/rev | in/rev |
Worked Example: Spiral Guide on Disk (drilling Feed) in a rebuilt 1950s pillar drill
You're rebuilding the auto-feed on a 1950s Pollard 15AY pillar drill for a small toolroom. The spindle runs at 600 RPM for drilling 10 mm holes in mild steel. The original spiral disk has a 12 mm groove pitch and is driven through a 1:60 worm reduction off the spindle. You want to verify the feed rate matches the drill manufacturer's recommended 0.15 mm/rev for a HSS twist drill in EN3B steel, and figure out what happens if you swap to a 300 RPM spindle setting for tougher 4140.
Given
- p = 12 mm/rev
- Nspindle = 600 RPM
- Reduction ratio = 1:60 —
- Target frev = 0.15 mm/rev
Solution
Step 1 — at the nominal 600 RPM spindle, the disk speed after the 1:60 worm reduction is:
Step 2 — feed-per-spindle-revolution is the disk pitch divided by the reduction ratio:
That's 33% above the 0.15 mm/rev target. Linear feed rate is:
Step 3 — at the low end of the practical range, drop the spindle to 300 RPM for 4140 steel. Disk speed halves to 5 RPM, giving vfeed = 1.0 mm/s and frev still equal to 0.20 mm/rev (the ratio doesn't care about absolute speed). At that feed rate in 4140 you'll cook the drill — chip loading is too aggressive for the harder material. You need a different disk with smaller pitch.
Step 4 — at the high end, running the same machine at 1200 RPM for aluminium gives vfeed = 4.0 mm/s, still 0.20 mm/rev. In aluminium that's actually fine and chip evacuation keeps up. The real limit is the worm gear — at 1200 RPM input the worm hits 20 RPM output, and continuous duty on a sleeve-bushed worm above that point chews through the bronze wheel inside a few hundred hours.
Step 5 — to hit the 0.15 mm/rev target, swap to a disk with 9 mm pitch:
Result
At nominal 600 RPM spindle with the original 12 mm pitch disk, the drill feeds at 2. 0 mm/s and 0.20 mm/rev. That feels heavy on the handwheel and you'll see thick blue chips coming off mild steel — workable but the drill will dull faster than it should. Swapping to a 9 mm pitch disk drops you to 0.15 mm/rev exactly. Across the operating range, the feed-per-rev stays constant regardless of spindle speed (1.0 mm/s at 300 RPM, 4.0 mm/s at 1200 RPM), which is the whole point of this mechanism — but the worm reduction and chip-clearance physics impose hard limits the formula doesn't show. If you measure feed slower than predicted, the usual suspects are: (1) a worn dog clutch slipping under load and intermittently disengaging the disk drive, (2) follower roller wear opening up groove clearance beyond 0.1 mm so the follower lags on each disk reversal, or (3) a glazed worm wheel where the bronze has work-hardened and the worm is skipping teeth under peak cutting load.
Spiral Guide on Disk (drilling Feed) vs Alternatives
The spiral guide on disk competes with leadscrew feed, rack-and-pinion feed, and modern servo-driven ball-screw systems. Each option trades cost, precision, force capacity, and serviceability differently. The spiral cam wins on simplicity and self-contained feed-rate selection but loses on flexibility — you change feed rate by swapping disks, not by turning a dial.
| Property | Spiral guide on disk | Leadscrew feed | Servo ball-screw feed |
|---|---|---|---|
| Feed rate accuracy | ±2-3% per rev (groove pitch tolerance) | ±0.5% (precision leadscrew grade C5) | ±0.01% (encoder closed loop) |
| Maximum feed force | 500-2000 N typical | 1000-5000 N | 5000+ N depending on screw |
| Max disk/screw RPM | 20-50 RPM disk speed | 200-1000 RPM leadscrew | 3000+ RPM ball-screw |
| Feed rate change | Swap disk (5-10 min downtime) | Change gear or dial | Software parameter, instant |
| Cost (small drill class) | $200-500 fabricated | $400-900 with gearing | $3000+ with servo and drive |
| Service life before rebuild | 10-20 years typical | 5-15 years (screw wear) | 10+ years (ball-screw) |
| Backlash on reversal | 0.05-0.15 mm groove clearance | 0.02-0.10 mm (anti-backlash nut) | <0.005 mm preloaded |
| Best application fit | Repetitive single-feed-rate drilling | Variable-feed manual machine work | CNC machining centres |
Frequently Asked Questions About Spiral Guide on Disk (drilling Feed)
The spiral guide locks feed-per-rev to the gear ratio between spindle and disk — that's a geometric ratio, not a function of speed. So if your reduction is 1:60 and pitch is 12 mm, you always get 0.20 mm/rev whether you spin at 200 or 2000 RPM.
What changes is surface speed at the drill cutting edge and chip evacuation rate. Doubling spindle RPM doubles the heat into the chip but only doubles chip evacuation if flute geometry can keep up. In small-diameter drills below 6 mm, chips pack in the flute at high RPM, which jams the drill and forces the spiral cam to push harder — sometimes hard enough to shear the dog clutch pin. The fix is matching spindle RPM to material so chip thickness and evacuation balance; the cam doesn't help you there.
You can, but watch the disk RPM floor. Below about 2 RPM disk speed the follower roller stops rolling cleanly and starts skidding in the groove, which scores the groove flank and accelerates wear. Most spiral feed mechanisms have a practical lower limit around 1.5-2 RPM disk speed.
If you need feed rates that would push disk speed below that, the better answer is a finer-pitch disk with a moderate reduction. A 4 mm pitch disk at 5 RPM disk speed will outlast a 12 mm pitch disk at 1.5 RPM by a factor of 5 or more, even though the feed-per-rev is identical.
Decide on three things: how often the feed rate changes, how much axial force the drill produces, and whether the operator is going to set up the machine or a fixed setup runs all day.
If you're drilling the same hole all day in the same material, the spiral cam is faster to operate — engage clutch, drill cycles, retract, repeat. No dialling-in. If feed rate changes between parts, a leadscrew with a feed-rate gearbox wins because disk swaps take five minutes and you only carry a finite set of disks. Above roughly 3 kN of thrust force the spiral groove starts to wear measurably within months unless you go to a hardened and ground groove with a carbide-rollered follower, which gets expensive — at that point a leadscrew with a thrust bearing is cheaper.
Side load from the spiral wall is deflecting your radial slide. The spiral pushes the follower radially with significant force — easily 200-500 N on a moderate drill — and that force has a tangential component that tries to twist the follower carriage. If the carriage slide has more than about 0.02 mm of clearance, the quill axis tilts a fraction of a degree under load and the drill walks sideways as it descends.
Check slide preload first. On dovetail slides this means tightening the gib screws until you can just feel drag with the disk disengaged. On linear bushings, check for radial play on the bushing — replace any bushing that shows more than 0.03 mm of rock when you wobble the carriage by hand.
One-sided flank wear means the follower is loading only one wall of the groove during the cut, which is normal — the cutting thrust always pushes the follower toward the same flank. So wear concentrates on the load-bearing side. That part is fine.
What's not fine is if the wear depth exceeds about 0.15 mm, because that's when the follower starts dropping into the worn track and feed-per-rev becomes inconsistent across the disk's travel. The diagnostic check: measure groove width at the start, middle, and end of the spiral with a pin gauge. If the spread exceeds 0.1 mm, the disk needs regrinding or replacement. A common rebuild trick is to flip the disk and run the unused face — most original disks are machined on both sides for exactly this reason.
Mechanically yes, but it's slow and stresses the worm. The disk speed during retract is the same as during feed — 5-20 RPM in most setups — so retracting a 50 mm hole takes 25-50 seconds versus under 2 seconds with a clutched return spring. Operators get impatient and start cycling the spindle direction switch, which slams the worm gear teeth into reverse contact and chips the bronze.
The proper architecture is a one-way drive with a clutch and return spring on the quill. Engage the clutch to feed, disengage to let the spring pull the quill back. Every production drill from the 1900s onward used this pattern for a reason.
References & Further Reading
- Wikipedia contributors. Cam. Wikipedia
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