A HSD ES915A spindle was hand-delivered to Atlanta Precision Spindles after a tool holder reportedly became stuck in the taper.

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At first glance, this might seem like a simple service call.

It wasn’t.

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What We Found During Disassembly

Our inspection revealed several critical issues:

1️⃣ Severe Mechanical Impact Damage

• The front bearing locknut had clear ball peen hammer impact marks.
• The shaft end had been struck directly.
• The bearing preload system was compromised.

Impacting a precision spindle shaft — even lightly — can:

Why Hammering a Spindle Shaft Destroys Bearing Preload

In this case, the hammering destroyed the front and rear bearing assemblies.

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2️⃣ Contamination at the Rear Housing

When we opened the back of the spindle, we discovered water intrusion inside the housing.

Moisture inside a high-speed spindle leads to:

• Corrosion on races and journals
• Lubrication breakdown
• Premature bearing failure
• Electrical component degradation

The customer had been previously made aware of contamination concerns during the last repair.

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Why the Damage Escalated

What began as:

“A stuck tool holder”

Turned into:

Complete bearing failure
Journal rework
Full spindle rebuild

This is a textbook example of why field hammering is one of the most expensive “quick fixes” in CNC shops.

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The Repair Process

Because of the damage, the spindle required a complete rebuild, not just bearing replacement.

Precision Restoration Steps:

✔ Shaft centers re-qualified
✔ Front bearing journal ground and re-qualified
✔ Damaged locknut machined to remove impact deformation
✔ All rotating components dynamically balanced (pre & post assembly)
✔ Assembly performed in our Class 10,000 clean room
✔ New sealed ceramic hybrid bearings installed (front & rear)
✔ Full run-in, break-in, and certification testing

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Final Verification & Certification

Before release, we completed:

• Drawbar retention force measurement & documentation
• Proximity sensor testing and preset using ISO/DIN certified master
• Tool eject dimension preset and recorded
• Final clean room inspection
• Controlled packaging for pickup

The spindle left fully certified and documented.

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What This Case Teaches

🚫 Never strike a spindle shaft or locknut with a hammer

🚫 Never attempt to force a stuck tool holder out manually

🚫 Never ignore moisture intrusion

Common Causes of Stuck Tool Holders in HSD Spindles

If a tool holder is stuck, the problem is usually:

• Drawbar malfunction
• Retention knob deformation
• Belleville washer failure
• Taper contamination

All of which can be diagnosed without destructive impact.

Before you try a fix:

• Check tool holder retention force
• Inspect taper for contamination
• Verify drawbar function
• Contact our technicians for stuck taper diagnosis 678-225-7855

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