Overview

This article explains how to adjust the air cushioning on SMC cylinders used in BestPack equipment. Air cushion adjustment affects how smoothly the cylinder decelerates at the end of its stroke. This guide covers what air cushioning does, where to locate the adjustment port, and how to tune it for optimal performance.

Step 1 — Understanding Air Cushioning

Air cushioning is a damping mechanism built into pneumatic cylinders that controls the final deceleration phase as the piston reaches the end of its stroke. It does not affect the main actuation speed during the cylinder's travel—only the last few millimeters before full extension or retraction. The cushion restricts air flow during this final portion, preventing sudden stops and impact shock.

What Air Cushion Does:

• Reduces shock and impact: Prevents sudden, jarring stops when the piston reaches the end of travel, protecting the cylinder rod and connected equipment from damage.
• Provides smooth deceleration: Creates a controlled, gradual slowdown rather than a hard stop, improving machine performance and longevity.
• Minimizes noise: Eliminates or reduces the loud "bang" sound that occurs when a cylinder fully extends or retracts without cushioning.
• Protects components: Reduces stress on mechanical linkages, clamps, and sensors connected to the cylinder.
• Improves product quality: Ensures gentle handling of products during machine cycles, reducing damage or misalignment.

Step 2 — Identify the Air Cushion Adjustment Port

SMC CM2 cylinders have cushion adjustment ports on one or both ends, depending on whether the cylinder is single-acting or double-acting with cushioning on both strokes.

Typical locations:

• Rod-end (front): Adjust deceleration when the piston retracts (returns)
• Cap-end (back): Adjust deceleration when the piston extends (moves forward)
• Both ends: Double-acting cylinders with cushioning on both strokes have adjustment ports on both sides

The adjustment port is a small hex socket (Allen key fitting) located on the end cap of the cylinder, typically marked with a label or visible as a small cavity. Refer to the cylinder nameplate or manual to confirm which end controls which stroke.

Step 3 — Gather Tools and Materials

You will need:

• Metric 1.5 mm Allen key (hex wrench) — standard tool for SMC CM2 cushion adjustment screws
• Clean cloth or rag — to wipe away any dust or debris from the adjustment port

Step 4 — Understand Adjustment Direction and Effect

The cushion adjustment screw follows this convention:

Step 5 — Perform the Adjustment

Follow these steps to adjust air cushioning:

1. Stop the machine and ensure it is depressurized. Cycle the cylinder a few times with the system off to bleed any residual pressure.
2. Locate the cushion adjustment port on the appropriate end (rod-end for retract cushion, cap-end for extend cushion).
   
3. Clean the area around the adjustment port with a clean cloth to remove dust or debris.
4. Insert the 1.5 mm Allen key into the hex socket. Ensure it is fully seated to avoid stripping the screw.
5. Turn the screw slightly — begin with a 1/4 turn in your desired direction (CW to increase, CCW to decrease).
6. Remove the Allen key and re-pressurize the system. Cycle the cylinder through one full stroke.
7. Observe the motion — listen for noise and watch for smoothness of deceleration at the end of stroke.
8. Repeat adjustments as needed, using small increments (1/4 to 1/2 turn) until the motion is smooth and there is no impact noise.

Step 6 — What to Expect: Increasing vs. Decreasing Cushion

Important reminder: Air cushioning only affects the final deceleration phase (the last few millimeters before end of stroke). It does NOT change the main actuation speed. The cylinder travels at normal speed, then cushioning only engages near the end.

When You Increase Cushioning (Turn CW):

• The cylinder's main travel speed remains unchanged.
• The final deceleration phase is longer and gentler — the piston slows more gradually in the last stage.
• The motion appears smooth and controlled as it approaches the end stop.
• Impact noise decreases or disappears at end of stroke.
• Mechanical shock on connected components is reduced significantly.
• Overall cycle time impact is negligible (only the final millimeters are affected).

When You Decrease Cushioning (Turn CCW):

• The cylinder's main travel speed remains unchanged.
• The final deceleration phase is shorter and faster — the piston slows less gradually or stops more abruptly.
• The motion may appear jerky or abrupt in the final stage just before the end stop.
• Impact noise may return or increase as the piston hits the end stop harder.
• Mechanical shock on connected components increases (risk of damage if over-adjusted).
• Overall cycle time impact is negligible (only the final millimeters are affected).

Step 7 — Fine-Tune for Optimal Performance

Once you have made an initial adjustment, continue to refine:

• Run multiple cycles (at least 10-20) to observe consistency. The behavior should be the same each time.
• Listen and observe: Note any changes in noise level, motion smoothness, or timing.
• Make micro-adjustments if needed — turn the screw in 1/4 increments between test runs.
• Record your settings — note the final adjustment position (e.g., "1.5 turns CCW from max cushion - closed all the way") for future reference.
• Monitor over time: Air cushioning can drift as seals wear. Check periodically (weekly or monthly depending on cycle rate) and re-adjust if needed.

Common Mistakes