Corner Round vs Flat End Mill: Which Should You Buy?

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Corner round vs flat: the short answer

A corner rounding end mill has its cutting edge ground to a fixed radius, so one pass leaves a rounded edge of that exact size. The Accusize mill in the gear section below cuts a 1/8 inch radius. A flat end mill, also called a square end mill, has a square cutting edge that leaves 90 degree shoulders and flat floors, which is what the SpeTool and WEN sets below provide. Pick the tool that matches the edge on your drawing: radiused edge, corner rounding mill; square shoulder, flat end mill.

When to pick a corner rounding end mill

Pick a corner rounding end mill when the project needs a finished, radiused edge in one pass: deburring a sharp machined edge, adding a consistent round-over to a part, or matching a drawing that specifies a radius. The Accusize 1011-0018 is built for this job, with a 1/8 inch radius, a 1/2 inch shank and a 5/8 inch cutter diameter on a 3 inch overall length. Its form-relieved design lets it be sharpened repeatedly without altering its form, per the listing. M2 high-speed steel suits both ferrous and non-ferrous materials, per the listing.

When to pick a flat end mill

Pick a flat end mill for square shoulders, flat-bottomed pockets, facing and general milling where the edge must stay sharp. The SpeTool 5-piece set gives solid carbide 2-flute square nose mills with a 1/4 inch shank, 1/4 inch cutting diameter and 3/4 inch cutting length on a 2.5 inch total length, with a TiAlN coating the listing rates for HRC 55 materials including steel, stainless steel, titanium alloy and Inconel. The WEN DB003E set goes bigger: 3/8, 1/2 and 5/8 inch indexable end mills with APKT1003 carbide inserts that reverse to double cutting life, in an aluminum storage case. Flat mills also handle side milling, end milling and finish machining, per the SpeTool listing.

Corner round vs flat end mill: the gear

Three end mills from the listings, ranked by versatility and stated specs.

End mill	Type	Sizes	Material	Notes
WEN DB003E 3-Piece Set	Flat, indexable	3/8, 1/2 and 5/8 inch	Carbide inserts	Reversible APKT1003 inserts, aluminum case
SpeTool 5-Piece Square Nose Set	Flat, solid	1/4 inch cutting diameter	Solid carbide, TiAlN	5 pieces, 2 flutes, for HRC 55
Accusize 1011-0018	Corner rounding	1/8 inch radius	M2 high-speed steel	1/2 inch shank, form-relieved

1. WEN DB003E 3-Piece 90 Degree Square Shoulder Indexable Carbide End Mill Set

The most versatile pick of the three. The listing includes 3/8, 1/2 and 5/8 inch end mills with indexable APKT1003 carbide inserts, and the inserts reverse to double the cutting lifespan of each bit. It ships in an aluminum storage case, fits the WEN 33013 metal milling machine and the WEN 33182A R8 collet set, and the universal design fits any collet set on the market, though a collet set is required for operation. Best for a mill owner who wants three square-shoulder sizes with long insert life.

2. SpeTool 5-Piece 2-Flute Square Nose End Mill Set

The router-friendly pick. Five solid carbide square nose mills with a 1/4 inch shank, 1/4 inch cutting diameter, 3/4 inch cutting length and 2.5 inch total length, TiAlN coated for HRC 55. The listing states they suit CNC routers and plunge routers with a 1/4 inch collet, naming Makita and Bosch, for side milling, end milling and finish machining in steel, stainless steel, titanium alloy and Inconel. Best for CNC router work with the 1/4 inch collet the listing names.

3. Accusize 1011-0018 Corner Rounding End Mill

The specialist pick and the only corner rounding mill here. It cuts a 1/8 inch radius with a 1/2 inch shank, 5/8 inch cutter diameter and 3 inch overall length, in M2 high-speed steel for ferrous and non-ferrous materials. The listing gives exact dimensions: 0.2625 inch small end diameter, 5/8 inch large end diameter, 0.8437 inch shoulder length, 0.1822 inch flute length and 2.1563 inch shank length. Best for finishing radiused edges to a drawing.

Common mistakes to avoid

• Buying a corner rounding mill when the part needs square shoulders.
• Using a flat end mill where the drawing calls for a radiused edge.
• Ignoring shank size: the Accusize uses a 1/2 inch shank and the SpeTool a 1/4 inch shank, so match the collet.
• Skipping the collet set for the WEN mills: the listing says one is required for operation.
• Assuming one mill does both jobs: radius and square shoulder are different cutting edges.

FAQ: lasers and CNC

Can a flat end mill round a corner?

Not for a radiused edge. A flat end mill cuts square shoulders and flat bottoms, so for a radiused edge you need a corner rounding mill, like the Accusize with its 1/8 inch radius.

What does indexable mean on the WEN set?

The WEN DB003E uses APKT1003 carbide inserts that reverse to double the cutting life of each bit, per the listing. It fits the WEN 33013 metal milling machine and the WEN 33182A R8 collet set.

What materials can the SpeTool set cut?

The listing states solid carbide with a TiAlN coating for HRC 55, suitable for steel, metal, Inconel, stainless steel and titanium alloy. It suits CNC routers and plunge routers with a 1/4 inch collet.

Which of these suits a router and which a mill?

The SpeTool set suits CNC routers and plunge routers with a 1/4 inch collet, naming Makita and Bosch. The WEN set fits the WEN 33013 metal milling machine and R8 collet sets. The Accusize has a 1/2 inch shank for milling machines.

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