Fixing Slamming Hydraulic Tool Presetter on FEMCO Durga 25-E

Problem Details

Symptom: on a FEMCO Durga 25-E CNC turning center (1998 vintage), the hydraulic tool presetter (touch-setter) arm swings violently to both end stops after the presetter assembly was removed and reinstalled to repair a broken wire. Before the repair the arm cycled at a controlled rate. Nothing in the CNC program or the M-code logic changed — only the mechanical/hydraulic joint was broken and remade.

Two failure mechanisms produce this exact symptom, and they are not mutually exclusive:

• Loss of metered flow control. The presetter swing speed on this machine is set by a dedicated valve in the main valve stack. If that valve was disturbed, backed out, or its adjustment lost during the repair, the actuator sees full pump flow and reaches the hard stop at maximum velocity.
• Air trapped in the presetter branch. Breaking a hydraulic joint admits air. A compressible air column downstream of a meter-out restriction lets pressure build, then release suddenly — the arm stalls, accelerates, and slams. This also explains erratic or inconsistent cycle behavior between shots.

Root Cause: Where the Presetter Speed Is Set

The presetter swing speed is not a servo or drive parameter on this machine — it is a hydraulic flow adjustment. The controlling valve is the middle valve in the valve stack, located between the chuck pressure valve and the tailstock pressure valve. The stack sits at the bottom left of the front of the machine.

Why the arm slams in both directions

If the arm is uncontrolled in both extend and retract, the fault is upstream of the direction valve — a single speed adjustment feeding both legs, or air in the common supply/return line. If it slams in only one direction, look at that leg specifically: a meter-out cushion, a check valve installed backward after reassembly, or a crushed/kinked hose from the wire repair.

Confirm the repair did not create a new fault

Before touching the valve stack, verify the mechanical work:

1. Confirm the replaced presetter is seated on its mounting face with all fasteners torqued evenly — a cocked mount binds the arm and produces stick-slip that mimics slamming.
2. Inspect the hydraulic lines that were disconnected. Check for reversed fittings, missing or damaged O-rings/copper washers, and pinched hose routed against the new wiring.
3. Verify any inline flow-control or cushion fitting at the actuator port was reinstalled in the correct port and correct orientation. Arrow-marked check/throttle fittings reversed 180° give exactly this symptom.
4. Confirm the repaired wire — the arm-position proximity or limit switch feedback — is landed correctly and terminated with correct polarity for a PNP/NPN sensor. A missing in-position signal will not cause slamming by itself, but it will cause the control to alarm or hang after the mechanical fix.
5. Check reservoir level and fluid condition. Low level aerates the pump and causes exactly the spongy/slam behavior across every hydraulic function, not just the presetter.

Solution: Purge Air, Then Re-Tune Speed

Work in this order. Bleeding first, then adjusting, prevents you from tuning the valve against a compressible air column and ending up with the wrong setting once the air is gone.

Step 1 — Purge the presetter branch

1. Bring the hydraulic system up to normal operating pressure and let the fluid warm to normal running temperature. Cold, high-viscosity oil masks flow-control behavior.
2. Clear the arm's full sweep path of tooling, workpieces, and the tailstock.
3. Cycle the presetter in and out repeatedly — 10 to 20 cycles — using the machine's manual/MDI presetter command. Repeated stroking drives entrained air back to the reservoir through the return line. On many machines this alone resolves post-service slamming.
4. If cycling does not settle it, crack the highest fitting on the presetter branch approximately one quarter to one half turn with a rag wrapped around it and a catch pan below. Command the arm toward that side until clear, foam-free oil issues from the joint, then retighten. Repeat for the opposite leg.
5. Recheck reservoir level after bleeding — purging removes fluid and the level will drop.

Step 2 — Re-establish the speed setting

1. Locate the middle valve in the stack (bottom left front). Remove the lower-left sheet metal cover if the adjuster is not accessible.
2. Loosen the lock nut on the adjuster if one is fitted. Note the starting position — count and record turns so you can always return to the as-found state.
3. Close the adjuster (typically clockwise, reducing flow) until the arm barely creeps, then open it in small increments — roughly a quarter turn at a time — cycling the arm after each change.
4. Target a swing that completes in a smooth, controlled motion and seats against its stop without a metallic bang. The arm should decelerate visibly rather than arrive at full speed.
5. Retighten the lock nut and re-verify — locking an adjuster often shifts the setting slightly.
6. Reinstall the sheet metal.

Step 3 — Restore the pressure valves you did not intend to change

If the chuck or tailstock adjuster was moved by mistake, do not guess. Restore clamping pressure using the machine's pressure gauge and the values on the machine data plate or in the OEM documentation. Verify chuck grip on a test bar before running production — an under-set chuck at speed is a projectile hazard.

Verification

1. Dry cycle, 20 repetitions. Command the presetter in and out 20 times. Every cycle must be visually identical in speed and end-of-travel behavior. Inconsistency between cycles means residual air or a sticking spool.
2. Audible check. No metallic impact at either end stop. A soft seat is the pass criterion.
3. Feedback check. Confirm the arm-position sensors make and break reliably each cycle. Monitor the input bits at the control's I/O diagnostic screen if available; the in-position bit must be stable, not chattering, with the arm at rest.
4. Leak check. After 20 cycles, inspect every joint that was broken during the repair and every bleed point for weeping. Wipe dry and re-inspect after a 30-minute run.
5. Repeatability check. Touch off a known tool against the presetter three times and compare the recorded offsets. Values must repeat within your normal tolerance. A slamming arm that has been running for a while may have knocked the touch probe or its mount out of position — if offsets do not repeat, re-qualify the presetter against a master tool or gauge bar before cutting.
6. Chuck and tailstock check. Verify clamping pressure on the gauge matches the machine plate value and that the chuck holds a test bar without slip.

Preventive Notes for Future Presetter Service

• Before disconnecting any hydraulic line, mark the fittings and record the adjuster position on the presetter speed valve in turns from fully closed. This turns a tuning exercise into a repeat setting.
• Cap open lines and ports immediately. Contamination that enters an open port ends up in the valve stack and causes spool sticking — a much harder fault to chase than trapped air.
• Route the repaired sensor wire clear of the arm sweep and clear of hydraulic hose flex. Use strain relief at the arm end; a wire that fails once at a flex point will fail again.
• Plan on purging after every hydraulic disconnection. Budget the cycle time rather than treating slamming as a new fault.
• On a machine of this age, log the as-found and as-left settings for all three valves in the stack. That record is worth more than any manual when the next fault appears.

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