5mm CNC Router Bit: A Useful Metric Size for Specific Applications
Five millimeters is close enough to 3/16-inch that some users mistake the two, but they’re not identical (5mm = 4.97mm, 3/16-inch = 4.76mm). In CNC routing, metric and imperial sizes aren’t interchangeable in collets and tool holders. A 5mm bit in a 1/4-inch (6.35mm) collet won’t cut accurately and may slip. This is one of those details that matters before the bit goes in the spindle.
A 5mm CNC router bit is an end mill with a 5mm diameter and typically a 5mm shank. This metric size appears more frequently in European CNC workflows where metric tooling is standard, and in specific applications where a 5mm radius is the right inside corner specification.
The direct answer: 5mm end mills are appropriate when your project requires inside corner radii of 2.5mm, when 6mm leaves too much material and 3mm is too fragile for the cut depth required, or when your machine uses metric collets (ER11 or ER16 with 5mm inserts). Verify your collet accepts 5mm before purchasing.
When 5mm Is the Right Size
Inside corner radius: A 5mm bit produces a 2.5mm inside corner radius. This matters when fitting parts together: a piece cut with a 6mm bit leaves a 3mm radius corner that a square-cornered mating piece won’t fit into without filing the corners or adding a radius to the part.
European hardware fitting: Some European hardware standards specify 5mm hole dimensions.
Between 3mm and 6mm: When 3mm is too fragile for a deep pocket and 6mm leaves too large a radius.
Feed Rates at 5mm
5mm bits are more fragile than 6mm. Reduce feed rate and DOC proportionally:
- Softwood/MDF: 1200 to 2000mm/min, 1.5mm DOC
- Hardwood: 800 to 1500mm/min, 0.8 to 1.2mm DOC
- Spindle RPM: 18,000 to 22,000
Collet Compatibility
5mm shank bits require a 5mm collet insert in ER11 or ER16 collet systems. A standard 1/4-inch (6.35mm) collet will not securely hold a 5mm shank. Verify your collet set includes a 5mm insert.
Verdict
A 5mm end mill is a problem-specific tool: the right choice when 2.5mm inside corner radius is specified, when European hardware dimensions require it, or when 3mm is too fragile and 6mm leaves too much material. Verify collet compatibility before ordering.
FAQ
Is a 5mm CNC router bit the same as 3/16-inch? No. 5mm = 4.97mm; 3/16 inch = 4.76mm. Not interchangeable in collets or for close-tolerance fitting.
What collet holds a 5mm router bit? A 5mm collet insert for an ER11 or ER16 collet system. Not the standard 1/4-inch (6.35mm) collet.
What feed rate for a 5mm end mill in wood? 1200 to 2000mm/min in softwood and MDF. 800 to 1500mm/min in hardwood.