How to Use a Reamer: Expert Techniques for Precision Hole Finishing

Knowing how to use a reamer is essential for achieving the precision hole tolerances that modern engineering demands. A reamer removes only a small amount of material to refine a pre-drilled hole, and how you prepare, feed, and cool the tool determines whether you hit an H7 tolerance or scrap the part. The following techniques, refined through years of production reaming, will help you get consistent, accurate results on every hole.

Step-by-Step Reaming Procedure

1. Drill the pre-ream hole 0.1-0.4 mm undersize. Leaving the correct stock is critical — too little material gives the reamer nothing to cut, while too much overloads it and degrades accuracy.
2. Select the right reamer for the material and hole type. For hardened steel, the H7 tolerance CNC reamer delivers exceptional wear resistance, while the through-hole finishing reamer is ideal for through-hole applications.
3. Set the cutting speed to roughly one-third of drilling speed — approximately 15-25 m/min for carbon steel.
4. Apply generous flood coolant to flush chips and control thermal expansion.
5. Feed smoothly and steadily, entering and exiting without dwell, and never reverse rotation while the tool is in contact with the bore.

Selecting the Right Reamer

Reamer choice is driven by the hole geometry and the workpiece material. Straight flute reamers suit most general-purpose through-hole work, while spiral flute designs provide better chip evacuation in blind holes. For hardened and difficult materials, carbide construction is essential to hold tolerance over long production runs. In specialized forming applications, a carbide forming knife complements the reaming process by creating complex hole profiles that standard reamers cannot achieve.

Optimizing Speeds and Feeds

Speed and feed directly govern hole quality and tool life. As a rule, reaming speed should be approximately one-third of the drilling speed used for the same material, while the feed rate is typically two to three times higher than drilling feed to keep the tool cutting rather than rubbing. For carbon steel, use 15-25 m/min with feeds of 0.2-0.4 mm/rev; for stainless steel, reduce speed to 8-15 m/min; and for aluminum, speeds can reach 50-80 m/min. Always consult the manufacturer’s recommendations for specific geometries and coatings.

Common Mistakes to Avoid

• Undersized pre-drill holes — leaving too much stock overloads the reamer and produces oversized or bell-mouthed bores.
• Excessive speed — generates heat that causes thermal expansion and premature edge wear.
• Dwelling at the hole bottom — rubbing without cutting dulls the edge and scratches the finished surface.
• Insufficient coolant — chips pack in the flutes and score the bore wall.

Mastering these fundamentals turns reaming from a source of scrap into a reliable, repeatable finishing process. With the right tool, the right stock allowance, and disciplined technique, consistently hitting H7 tolerance holes becomes a routine achievement rather than a recurring headache.