Tolerance, Wear, & Best Practices

Machining Best Practices

Precision machining requires more than just good equipment — it demands attention to the details that keep your parts accurate, your tools sharp, and your production running smoothly. Whether you're reaming precision holes, maintaining tolerance-critical features, or troubleshooting tool wear, this guide brings together best practices to help you reduce downtime, cut waste, and improve overall part quality.

This page covers three key areas:

• Tolerance in Manufacturing – what it means, why it matters, and how to control it
• Tool Wear and Failure – how to recognize, prevent, and design around it
• Reaming Precautions – techniques and tips to get clean, accurate holes every time

Use these insights to strengthen your processes, protect your tools, and consistently produce parts that meet spec — the first time.

Tolerance in Manufacturing

Tolerance in manufacturing refers to the permissible variation in a physical dimension—the allowable range within which a machined part can deviate from its specified size while still functioning correctly.

Tolerances define how close to “ideal” a dimension must be, ensuring consistency, interchangeability, and reliable performance across components.

Consider aerospace structural components, such as those used in aircraft fuselages. These parts require precisely reamed holes for fasteners that join critical sections of the airframe. If the hole diameters fall outside their specified tolerances—whether slightly oversized or undersized—fasteners may fit too tightly or too loosely. These deviations can compromise structural integrity, increase fatigue risk, and result in failed inspections or costly rework.

In aerospace applications, even minor tolerance violations can jeopardize part fitment, safety, and regulatory compliance.

An oversized hole may cause a fastener to loosen in service; an undersized one may prevent full insertion. Both scenarios threaten airworthiness.

Improper tolerance control can lead to:

• Poor component fit and alignment
• Increased mechanical wear and vibration
• Reduced product reliability and service life

At Gammons, we understand these challenges and engineer our reamers to extremely tight tolerances, ensuring your manufacturing processes consistently produce precise, reliable components and avoid these costly issues.

What Does a Tolerance Look Like?

Tolerances are commonly expressed as plus/minus values next to a nominal dimension. For example, using our aerospace example:

This tolerance ensures that fastener holes will reliably accommodate the specified hardware, even with minor machining variations.

Types of Tolerances

The type of tolerance you select should align with your application’s specific requirements:

Limit Tolerances

Clearly defines maximum and minimum allowable dimensions. Any measurement within these limits is acceptable, ensuring clear dimensional boundaries.

Unilateral Tolerances

Allows deviation in only one direction (positive or negative). For instance, a critical shaft diameter may be specified as +0.005 mm / -0.000 mm to prevent undersizing.

Bilateral Tolerances

Permits deviation above and below the nominal dimension:

• Bilateral Equal: Equal tolerance in both directions (e.g., ±0.002 mm).
• Bilateral Unequal: Different tolerances in each direction (e.g., +0.003 / -0.001 mm), useful in applications needing specific fitting characteristics.

Why Tolerance Matters

Precise tolerance control impacts all industries—from automotive to aerospace and medical devices. In aerospace applications, improper hole tolerances can lead to structural failures, increased maintenance cycles, and noncompliance with strict industry standards. Tight tolerance control ensures safe, reliable, and efficient performance—whether in flight-critical components, medical devices, or precision tooling.

Gammons is committed to manufacturing precision reamers, allowing your business to consistently meet quality standards, minimize production issues, and maintain excellent reliability and performance.

Tool Wear and Failure in Machining

Tool wear is a natural part of any machining operation — but how quickly a tool wears out, and how it performs along the way, depends on how well it’s designed for the job. Poor tool life, chipped edges, chatter marks, and inconsistent cuts often trace back to mismatched tooling or unstable setups.

At Gammons, we specialize in designing cutting tools that address these exact problems. Our team has decades of experience engineering tools that stay sharp longer, perform consistently, and help you get more from every run.

What Causes Tool Wear?

Most tool failures stem from five common issues. Here’s what to look for — and how we design around them:

1. Lack of Rigidity

If the tool or setup isn’t rigid enough, deflection and vibration can quickly damage both the tool and the part. Rigidity is essential for surface finish, accuracy, and tool life.

• We optimize tool geometry to reduce deflection and increase stability
• We recommend setups that minimize overhang and improve support

2. Excessive Cutting Forces

High forces from aggressive feeds, hard materials, or poor machine condition can overload tools. Even precision reamers can fail if they're pushed too hard without the right support.

• Our designs balance cutting efficiency with manageable force loads
• We account for horsepower limits, feed rates, and expected material behavior

3. Poor Chip Evacuation

Chips that get trapped or recut cause overheating, edge breakdown, and tool breakage. This is especially common in blind holes or materials that curl tightly.

• Gammons tools feature flutes and rake angles that maximize chip flow
• We design for coolant-assisted evacuation and correct chip space

4. Vibration and Chatter

Chatter causes noise, visible marks, and wear. It often stems from unstable setups, tool overhang, or machine backlash.

• We use relief angles and tooth geometry that resist vibration
• We help you select tools suited for long-reach or delicate applications

5. Misalignment or Inconsistent Feed

Improper alignment or uneven feed rates can introduce shock loads, causing chipped cutting edges and shortened tool life.

• We offer guidance on floating holders, spindle alignment, and smooth feed control
• Gammons tools are designed to perform reliably even under less-than-perfect conditions

If your tools are wearing out faster than expected, the cause is often a combination of small setup issues and tool mismatch. That’s why we design tools to work with real-world machines, materials, and shop-floor challenges.

Understanding these causes isn’t just about solving problems — it’s about preventing them before they start. Our design process anticipates wear, manages forces, and delivers cutting solutions that last longer and perform better.

Reaming Precautions and Best Practices

Reaming is one of the most precise operations in machining — but achieving accurate, clean holes requires careful attention to setup, feed, alignment, and tool condition. Below are speed and feed rates, key precautions and tips to avoid reamer failure, poor finish, or dimensional inaccuracies.

Feeds and Speeds for High-Speed Steel Reamers in Straight Holes

Reaming should generally be done at about two-thirds the speed used for drilling the same material. However, feed rates for reaming are often much higher — 200% to 300% of drill feeds.

Too low a feed rate can cause the reamer to rub or burnish instead of cutting, accelerating wear and leading to undersized or poor-quality holes.

Stock Allowance

As a general rule, stock removal during reaming should be approximately 3% of the hole diameter. To cut cleanly, reamers need enough material left from the prior operation. Too little stock can cause the tool to burnish rather than cut, while too much can overload and deflect the tool.

• Machine reaming: 0.010" for 1/4" holes, 0.015" for 1/2", up to 0.025" for 1.5" holes
• Hand reaming: 0.001" to 0.003" stock allowance is typical

Alignment Matters

Ideal reaming conditions require that the spindle, tool, bushing, and hole be perfectly aligned. Misalignment causes tapered, oversized, or bell-mouthed holes, and accelerates tool wear.

Solutions include:

• Using floating or adjustable tool holders
• Ensuring rigid and concentric setups
• Grinding a slight back taper on the reamer

Chatter Control

Chatter during reaming reduces tool life and leaves poor surface finish. It can stem from excessive speed, insufficient feed, poor machine rigidity, or tool overhang.

Common causes:

• Too much clearance on the reamer
• Weak fixturing or holding of the workpiece
• Overhang of the spindle or tool
• Looseness in floating holders
• Use of straight flute reamers

Correcting these issues — even small ones — can dramatically improve hole quality and tool longevity.

Coolant Selection

In reaming, the primary function of coolant is to improve surface finish, not necessarily to reduce heat. Choose lubricants that aid cutting action and flushing of chips from the hole. Below are our reccomendations for cutting fluids for each common material.

Reamer Regrinding

To get the best life from a reamer, don’t wait until it stops cutting. Regrind the chamfer before major dulling occurs. Only the chamfer (taper) should typically be resharpened.

Use a cutter grinder to ensure uniformity across flutes. Avoid hand sharpening — uneven flutes can cause oversize holes or poor finishes.

Summary

Precision machining is a combination of science, experience, and attention to detail. By maintaining proper tolerances, monitoring tool wear, and applying thoughtful reaming techniques, you can avoid costly mistakes, extend tool life, and ensure that every part meets spec.

Whether you're working with tight production schedules or fine-tuning high-tolerance components, applying these best practices will help you produce more reliable results — consistently and confidently.

Have questions about tooling or reaming for your application? Contact the Gammons team — we're here to help.