Short answer: do not treat YT28 feed force as a fixed pressure number. Use reduced air-leg thrust while collaring so the bit can seat without skating or bowing the H22 drill steel. Once the bit has a secure footing, increase feed gradually with the feed-control mechanism until penetration is strong and stable without visible rod bending, repeated jamming, abnormal vibration, or loss of rotation.
The key distinction is that rock-drill inlet air pressure and pusher-leg feed force are related but not the same setting. The current PerfoMax YT28 reference configuration lists performance at 0.50 and 0.63 MPa at the rock drill, while the YT28 operating manual describes a separate pressure-regulating control that changes feed force continuously. The exact air-leg suffix, control arrangement, and approved operating procedure must therefore be confirmed against the supplier manual supplied with the quoted machine.
This guide is for underground mines, tunneling crews, quarry teams, maintenance supervisors, and buyers using a YT28-type air-leg rock drill with H22 × 108 drill steel. It focuses on a practical question: how to apply enough axial thrust to keep the bit working efficiently without turning feed force into rod bending, hole deviation, or premature tool wear.
1. What Feed Force Does on a YT28 Air-Leg Drill
The air leg does more than support the weight of the drill. It pushes the rock drill and drill steel toward the face so the bit stays in contact with the rock while percussion and rotation do their work. Pusher-leg tube size and control design affect available thrust, so the exact drill–air-leg pairing and supplier manual must control the adjustment method. Treat the feed-control lever as a continuously tuned operating control, not as an interchangeable pressure setting across different leg variants.
Too little thrust can let the tool lose effective contact with the rock and reduce penetration. Too much thrust can compress and bow the drill steel, especially during collaring or when alignment is poor. Use only enough feed to maintain stable bit contact and penetration; added thrust that increases bowing, vibration or binding without improving penetration is evidence to back off and investigate the setup.
| Variable | What it controls | Why buyers/operators should separate it |
|---|---|---|
| Rock-drill inlet air pressure | Available pneumatic energy for percussion/rotation and overall tool performance | Pressure must be considered at the tool under load, not only at the compressor |
| Pusher-leg feed control | Axial thrust pushing the drill toward the face | Adjusted according to collaring, penetration, alignment, and ground response |
| Air-leg geometry | Direction and effective component of thrust | A poorly positioned leg can introduce off-axis loading even if the control setting seems reasonable |
| Drill steel and bit | Transfer impact/rotation into the rock | Length, straightness, bit condition, and hole size change how much feed can be used effectively |
2. Why a Compressor Gauge Is Not a YT28 Feed-Force Setting
The YT28 manual states that air requirements are defined at the rock-drill inlet and warns that pressure is lost between the compressor and the tool. PerfoMax's current YT28 page uses the same principle when it lists reference performance at specified tool pressures. These numbers describe the operating air supplied to the drill; they do not create a universal numeric pusher-leg feed setting.
The same manual identifies a pressure-regulating valve in the back head and states that turning it increases force continuously from zero toward maximum. That means feed is an adjustable operating variable. For procurement and setup, record both the tool-inlet air condition and the air-leg/feed-control configuration instead of writing a single number labeled “YT28 pressure.”
3. How to Collar a Hole Without Bending the H22 Drill Steel
Collaring is the most sensitive part of the cycle because the bit has not yet been guided by the hole. Model-specific pusher-leg instructions normally separate collaring from full drilling. Align the drill to the intended collar point, start in the supplier-approved partial-power condition and use reduced feed force until the bit has secure footing. Only then should the operator increase power and tune feed for stable penetration.
The same rule follows from drill-string geometry: while the bit is unsupported at the collar, uneven rock can make it skate, and excessive feed can bow the string and tilt the bit away from the intended axis.
Practical collaring sequence
- Position the air leg first. The leg should support the drill along the intended drilling line rather than push the drill sideways.
- Inspect the H22 rod. Do not start with visibly bent steel, a damaged shank, or an obviously worn/mismatched taper connection.
- Seat the bit at the intended collar point. Keep the drill axis aligned with the planned hole direction.
- Begin with reduced feed. Use only enough thrust to keep controlled contact while the bit establishes a seat.
- Watch for skating or bowing. If the bit walks or the rod bends, reduce feed and correct alignment rather than forcing the collar.
- Increase only after secure footing. Once the bit is guided by the new hole, move toward normal drilling and tune the feed to penetration.
4. After Collaring: Adjust Feed for Penetration, Not for Maximum Lever Position
After the tool has secure footing, adjust feed toward the most stable penetration response permitted by the exact supplier manual. That is different from simply applying the maximum available feed force.
In practice, increase feed gradually and observe how the complete system responds. The useful operating point is where the bit remains firmly engaged and penetration is strong while the drill steel stays reasonably straight, rotation remains stable, and the string does not repeatedly bind. If adding feed no longer improves penetration—or causes bowing, vibration, or jamming—the system is telling you that more thrust is not useful under those conditions.
5. Overfeed vs Underfeed: What the Symptoms Mean
| Observed symptom | Feed-related possibility | What to check before changing parts |
|---|---|---|
| Bit struggles to establish the collar; rod visibly bows | Feed may be too high for an unsupported bit or alignment may be poor | Reduce feed; re-check collar point, leg position, rod straightness, and drilling axis |
| Low penetration with weak contact at the face | Feed may be insufficient | Increase feed gradually; also verify tool-inlet air, bit condition, and air-leg seals/mechanism |
| Low penetration even as feed is increased | Problem may not be feed-limited | Check air pressure/volume at the tool, lubrication, bit condition, flushing, rotation, and rock condition |
| Repeated jamming or binding | Excessive thrust, poor alignment, difficult ground, or cuttings/flushing problem may be contributing | Stop percussion as required by the manual; relieve/retract the leg, then diagnose alignment and hole condition |
| Hole starts wandering from the collar | Excessive initial feed can amplify misalignment | Improve setup and use reduced collaring feed; inspect rod and bit condition |
| Feed force feels weak despite control adjustment | Pusher-leg fault or poor geometry may be limiting thrust | Check leg angle, seals, connections, trigger/change-over mechanism, and exact air-leg model |
Important: these symptoms are diagnostic clues, not proof of a single cause. A dull bit, low tool-inlet air pressure, poor lubrication, worn seals, fractured ground, a bent rod, or insufficient flushing can produce similar performance complaints. Change one variable at a time where practical and follow the applicable machine manual.
6. Five Variables That Change the Correct Feed Setting
Rock and face condition
A flat competent face supports the bit differently from broken, layered, or fractured ground. In difficult ground, forcing feed can make an initial alignment error worse. Reduce feed when the bit needs time to establish a stable path.
Drill-steel length and straightness
A longer or already bowed H22 rod has less tolerance for off-axis compressive loading than a short, straight starter. The current PerfoMax H22 rod page provides an 11° connection option for matched tapered drilling systems; exact rod length, bit, and taper must be confirmed for the job.
Bit condition and diameter
A worn bit may penetrate slowly even when feed is adequate. Do not compensate indefinitely by adding thrust. The current PerfoMax YT28 reference configuration is intended for 34–42 mm holes with H22 × 108 drill steel, but the ordered bit and taper still need to match the quoted tool system.
Tool-inlet air supply
If pressure or flow collapses at the drill under load, adding feed cannot recover the missing pneumatic power. Measure the operating condition at the tool or as close to it as the site procedure allows, not only at the compressor.
Air-leg model, angle, and condition
FT160 is a family name, not a universal configuration. PerfoMax's current FT160 page requires the exact suffix, manufacturer, dimensions, mounting interface, and approved drill pairing to be confirmed before quotation or substitution. Worn seals or poor leg geometry can reduce effective feed even when the feed control is advanced.
7. A Seven-Step YT28 Feed-Force Setup Workflow
- Confirm the system. Record YT28 manufacturer/revision, exact air-leg suffix, H22 rod, taper angle, bit diameter, and hose/oiler setup.
- Verify operating air at the drill. Use the supplier manual and quoted configuration. The PerfoMax reference page lists 0.50 and 0.63 MPa performance points, but the final supplier data sheet controls the supplied machine.
- Check rod and bit condition. Replace or evaluate damaged, bent, or mismatched tooling before tuning feed.
- Align the drill and air leg. Make the thrust line support the intended hole direction rather than pushing across it.
- Collar with reduced feed. Establish a stable seat before moving to normal drilling.
- Increase feed gradually. Tune for stable high penetration, not simply maximum feed-control position.
- Re-check when conditions change. A new rod length, different bit, fractured band, changed hole angle, or changed air supply can require a different feed setting.
8. Controlled Feed-Window Trial: Release the YT28–Air-Leg Setup
A correct feed setting is not a copied pressure number. It is a repeatable operating window in which the exact drill, air leg, rod and bit collar cleanly, remain aligned and maintain stable penetration without visible bowing, binding or loss of control. Use the following trial after a new installation, air-leg replacement, meaningful rod-length change or recurring feed complaint.
Scope boundary: this is a controlled commissioning and comparison method, not permission to exceed the supplier manual. Isolate the air supply before inspection or adjustment. Do not place hands near the steel, chuck, controls or exhaust during a live test, and stop if the leg, drill or work area cannot be kept stable.
Freeze the inputs before comparing feed
- Record the drill model/revision and complete air-leg suffix.
- Use one serviceable H22 rod and bit configuration for the comparison.
- Hold the hole angle, collar condition, operator, hose, lubricator and flushing setup constant.
- Record tool-inlet air under load where the site procedure and supplier instructions permit measurement.
- Use the same observation interval for each trial state; do not compare one short collaring burst with a long production run.
| Trial state | Hold constant | Evidence to record | Decision signal |
|---|---|---|---|
| 1. Static identity check | Isolated system | Nameplates, air-leg suffix, rod straightness, bit condition, hose and control identity | Do not test if identity, damage or compatibility is unresolved |
| 2. Controlled extension | No drilling load | Smoothness, leakage, control response and whether the leg holds position | Jerky motion, creep or leakage sends the leg to the troubleshooting Owner |
| 3. Reduced-feed collar | Same face point and alignment method | Bit skating, rod bow, collar stability and operator correction | Proceed only after the bit has secure footing without unstable bowing |
| 4. Incremental feed increase | Same rod, bit, air and flushing state | Penetration response, sound, vibration, rotation continuity and rod line | Keep the lowest stable setting that reaches the best repeatable response |
| 5. Repeatability check | Same approved setup on a comparable collar | Whether the chosen window repeats without added bowing, binding or leg slip | A one-off good result is not enough for release |
Choose one setup disposition
| Status | Use when | Required action |
|---|---|---|
| READY | Identity is controlled and the feed window repeats with stable collaring, alignment and penetration | Release the recorded configuration and operator method |
| CONDITIONAL | The setup is stable only within a documented rod length, hole angle, ground condition or restricted feed range | Limit use to that condition and schedule re-verification after a change |
| HOLD FOR DIAGNOSIS | Low penetration, leg slip, pressure loss or unstable response prevents a repeatable comparison | Use the air-leg, air-supply or low-power troubleshooting Owner before retesting |
| STOP / RESELECT | Compatibility is unresolved, damage is present, or more feed increases bowing, binding or loss of control | Isolate the system and correct the drill–leg–steel–bit configuration |
Copy-ready feed-window record
Drill model and revision: ________ Air-leg model and suffix: ________
Rod / taper / length: ________ Bit type / diameter: ________
Hole angle / ground condition: ________ Air, hose, oiler and flushing setup: ________
Collaring evidence: ________ Selected repeatable feed window: ________
Observed penetration / bow / vibration / slip: ________
Disposition: READY / CONDITIONAL / HOLD FOR DIAGNOSIS / STOP—RESELECT
Limits and next check: ________ Approved by: ________
9. Troubleshooting Low Penetration Before You Blame Feed Force
Model-specific pusher-leg troubleshooting treats insufficient feed as only one possible cause of low penetration. Leg angle, worn seals, loose connections, restricted controls, tool-inlet air volume and pressure, and lubrication can create similar symptoms.
Use this sequence to avoid chasing the wrong variable:
- Confirm the bit is sharp, correctly connected, and appropriate for the hole.
- Confirm the H22 rod is straight and the shank is in serviceable condition.
- Measure or verify tool-inlet air under drilling load.
- Confirm lubrication and flushing are functioning.
- Increase feed moderately and see whether penetration responds.
- If feed remains weak, inspect air-leg geometry, seals, connection points, and controls.
- If more feed causes bowing or binding without higher penetration, reduce feed and investigate alignment, ground, bit, or air-supply limitations.
10. Common Procurement and Operating Mistakes
| Mistake | Why it creates risk | Better requirement |
|---|---|---|
| Ordering “YT28 + FT160” without suffix/revision | FT160 variants and supplier pairings differ | Confirm exact air-leg model, interface, dimensions, and approved drill pairing |
| Using compressor pressure as the feed-force specification | Main air supply and adjustable pusher-leg thrust are not the same control variable | Specify tool-inlet air requirement separately from feed-control/air-leg configuration |
| Maximizing feed during collaring | Unsupported steel can bend and the bit can skate off line | Use reduced collaring feed until the bit has secure footing |
| Increasing feed to compensate for a dull bit or low air supply | Additional thrust may add bending/load without solving the actual power or cutting problem | Inspect bit, air, lubrication, and flushing before increasing feed further |
| Ignoring air-leg angle and condition | Effective thrust depends on geometry and mechanical condition | Inspect leg placement, seals, connections, and controls |
| Changing rod length without re-checking feed | Longer steel can respond differently to compressive and lateral loading | Re-collar and re-tune feed after a meaningful drill-string change |
11. RFQ and Field-Diagnosis Checklist
For a YT28 system quotation or feed-force problem, send the information that determines the complete operating setup:
- rock drill manufacturer, exact YT28 model/revision, and nameplate photo;
- exact air-leg suffix/model and manufacturer;
- air pressure measured at or near the drill under load, plus compressor capacity;
- air hose internal diameter, approximate length, and manifold arrangement;
- H22 × 108 rod length and taper connection;
- bit type and diameter;
- hole angle, planned depth, and collaring orientation;
- rock condition, especially fractures, seams, and uneven faces;
- symptom: low penetration, rod bowing, hole deviation, repeated jamming, or weak leg thrust;
- photos/video of the drill, air-leg position, rod, bit, and collaring setup.
For the current product boundary, review the PerfoMax YT28 Air-Leg Pneumatic Rock Drill, the FT160-Series Air-Leg Matching page, and the H22 × 108 mm tapered drill rod. For a broader machine-selection check, see How to Choose an Air-Leg Rock Drill for Underground Mining.
Frequently Asked Questions
What is the correct feed pressure for a YT28 rock drill?
There is no single universal pusher-leg feed-pressure number that should be copied across every YT28/air-leg combination. The YT28 manual describes continuously adjustable feed force, while the exact air-leg model and supplier configuration determine the actual setup. Use the supplied machine/air-leg manual and tune feed according to collaring and penetration response.
Should I use maximum feed force when starting a hole?
No. Use reduced feed force during collaring and move toward the normal drilling setting only after the bit has secure footing. Excessive feed at the collar can bend the drill steel and worsen initial misalignment.
Can too much feed force bend an H22 drill rod?
Yes. Excessive axial feed can make a slender drill string bow, particularly when the bit is unsupported, the alignment is poor, or the rod is long or already damaged. Treat visible bowing, unstable contact or added deviation as a stop-and-correct signal rather than a reason to add more feed.
Can too little air-leg feed cause slow drilling?
Yes. Insufficient pusher-leg feed can reduce penetration. But low air pressure/volume, bit wear, lubrication, flushing, seals, and ground conditions can produce similar symptoms, so diagnose the system rather than assuming feed is the only cause.
Is 0.63 MPa the correct air-leg feed setting for YT28?
Do not use 0.63 MPa as a universal pusher-leg feed setting. On the current PerfoMax YT28 page it is a reference operating-pressure point for the rock drill's performance. The pusher-leg/feed control is a separate adjustable function, and the final supplier manual controls the approved configuration.
Technical and Safety References
- ISO 11148-5:2011 — Safety requirements for hand-held rotary percussive drills
- UK HSE HSG39 — Compressed air safety
- OSHA 1926.302 — Power-operated hand tools
These references set the safety boundary; they do not provide a universal YT28 feed setting. The exact drill and air-leg manuals, approved configuration and controlled field trial remain the sources for model-specific operating limits.
Next Step: Match the Drill, Air Leg, Steel, and Operating Conditions Together
If feed-force problems are consuming drill steels or slowing development work, do not specify a replacement by model family alone. Send the YT28 nameplate, exact air-leg suffix, H22 rod/bit details, operating air condition, hole orientation, and symptom to PerfoMax. Use the technical recommendation / RFQ form so the replacement and operating notes can be checked against the quoted configuration.