Product Detail
Corner Radius / Bull Nose End Mill
Corner radius (bull nose) carbide end mills for steel pockets and shoulders, with the tool radius matched to the fillet on your drawing.
In a steel pocket, the sharp corner of a square end mill is the first part of the tool to chip. And the drawing usually shows a fillet where the floor meets the wall anyway.
A corner radius end mill, also called a bull nose end mill, keeps the flat bottom of a square tool but replaces each sharp corner with a ground radius. The corner gets stronger and the fillet is cut in the same pass, as long as the tool radius fits what the drawing allows.
End mills are a supporting line for HENTRY, beside the drills and reamers that are our main line.
What the corner radius changes
The load spreads along an arc. A sharp corner meets the work at a single point, and in interrupted or hard cuts that point takes every impact. A radius carries the same load along a curved edge, so the corner is less likely to chip.
The floor stays flat. Across the middle the end of the tool is still flat, so a pocket floor comes out flat, without the ridges a ball nose leaves between passes.
The radius is copied into the part. Whatever radius is ground on the tool corner becomes the fillet between floor and wall.
Light depths run on the curve. At a shallow axial depth most of the cut happens on the radius, which thins the chip at the corner.
Match the tool radius to the drawing
Start from the fillet callout where the floor meets the wall.
- One pass forms the fillet: order a tool radius equal to the drawn fillet.
- The toolpath finishes the corner: a smaller tool radius works, and the program blends the rest.
- Never larger than the drawing allows: an oversized tool radius leaves a fillet that is too big, and the corner then needs a second tool or the part is rejected.
- No fillet allowed at all: a corner radius tool is the wrong choice; that corner needs a square tool.
A larger radius makes a stronger corner but leaves more material in it, so the upper limit comes from the drawing. The tolerance on the radius also comes from the drawing: put it in the RFQ and we grind the radius to that value. We do not work from a fixed list of stock sizes.
The corner radius sets only the fillet between floor and wall. The corner where two walls meet, seen from above, takes its size from the tool diameter; that is covered on the square end mill page.
Corner radius, square or ball nose
| Job or print cue | Tool | Why |
|---|---|---|
| Flat floor with a specified floor-to-wall fillet | Corner radius | Flat bottom and the fillet in one pass |
| Sharp internal floor corner, no blend allowed | Square end mill | Only a sharp tool corner leaves no fillet |
| Freeform 3D surface, or a fillet that needs full sphere contact | Ball nose end mill | The rounded end meets the surface at any angle |
| Roughing or semi-finishing mold or pre-hardened steel where sharp corners chip | Corner radius | The radiused corner takes the impact |
| Gently sloping 3D surfaces | Corner radius | The flat part of the end covers a wider band per pass than a ball would |
| Abrasive aluminum walls and corners | PCD square end mill | PCD holds its edge where aluminum wears carbide |
Where a corner radius won't help
If the corner chips because of runout, long stick-out or chips packing in the pocket, a radius only delays the same failure; the setup or the toolpath needs fixing first. A drawing that calls for a sharp floor corner rules the tool out, however strong its corner. In aluminum the usual trouble is material sticking to the edge rather than corner breakage, which is why the PCD route above fits better.
Corner-radius quote: the details we check
The fillet callout matters most; the rest helps us size the tool.
- Steel, stainless or cast-iron grade, and its hardness
- Tool diameter, flute length and any reach or neck
- The corner radius and its tolerance, or the fillet callout from the part drawing
- Where the tool works: pocket floor, shoulder or 3D surface, and whether it roughs, semi-finishes or finishes
- Coolant on the job
- Machine and toolholder
- The tool you run now, and how its corner fails: chipping, wear or poor finish
- Order quantity
Flute count is a separate choice, set out on the 4-flute carbide end mill page. Coating follows your tool and part, applied by Oerlikon Balzers; see the AlTiN coated end mill page. Worn corner radius tools can be reground at HENTRY, and re-coated if you require it.
The standard end mill types are listed on our carbide end mills page. For a radius, neck or length that no standard tool offers, see our custom end mill manufacturer page. Send the fillet callout and the material through the custom cutting tool RFQ, and we propose a tool radius and diameter for your approval.
Corner radius FAQ
What is the difference between a bull nose and a ball nose end mill?
A bull nose has a flat end with a radius only at the corners, so it cuts flat floors with a fillet at the wall. A ball nose has a fully rounded end for 3D surfaces, and on a flat floor it leaves small ridges between passes.
What corner radius should I order?
Take it from the fillet and its tolerance on your drawing. Order the same radius if one pass must form the fillet, a smaller one if the toolpath finishes the corner, and never a larger one than the drawing allows. We grind the radius to the drawn value instead of offering a stock list.
Can I use a carbide corner radius end mill on aluminum?
For light work it will cut, but aluminum tends to stick to carbide edges, and high-silicon grades wear them quickly. For abrasive aluminum walls and corners, a PCD square end mill is the better choice.
Is a corner radius end mill stronger than a square end mill?
At the corner, yes. The radius spreads the cutting load along an arc instead of a sharp point, so it chips less. The trade-off is that it cannot cut a sharp internal corner.