Ball Nose End Mill
Total found: 65
A ball nose end mill has a full radius tip, which is what lets it follow a curved surface without leaving a step. It is the tool for 3D contouring, mould and die work, fillets and finishing passes on anything that is not flat.
It is also the tool that gets run at the wrong speed more often than any other, because two numbers that matter are not the ones printed on the box. Both are worth understanding before the first pass.
The range below covers ball nose cutters in 2, 3 and 4 flutes across the diameters we stock, coated and uncoated. Details are on each product page.
Surface speed is rotational speed multiplied by diameter. At the exact centre of a ball nose the diameter is zero, so the surface speed there is zero as well. The tool is spinning and the centre is not cutting - it is pressing.
Machine a flat surface with a ball nose held straight down and the dead centre drags across the material, generating heat, smearing rather than shearing, and wearing a flat onto the very tip. That is why a ball nose used as a general-purpose flat-bottom cutter dies quickly and leaves a poor finish.
The fix depends on the machine. On five axis, tilt the tool axis ten to fifteen degrees so contact moves off the centre. On three axis, keep the contact point on the flank of the ball by working the slopes rather than plunging the tip in, and use a square or corner radius tool for genuinely flat areas.
The second number is the one that ruins finishing passes.
On a shallow pass the ball is only engaged near its tip, so the diameter actually doing the cutting is far smaller than the tool diameter. For a depth of cut ap on a tool of diameter D, the effective diameter is 2 × the square root of ap × (D − ap).
Work it through on a 1/4" ball taking a 0.010" finishing pass: the effective diameter is 0.098", not 0.250". Program the rpm for a 1/4" tool at 300 SFM and you get about 4,600 - but at 0.098" effective diameter that is barely 120 SFM of actual cutting speed. To reach 300 SFM where the tool is really cutting you need closer to 11,700 rpm.
Run the shallow pass at the nominal rpm and the tool rubs, the finish goes grey and streaky and the ball wears flat. This single calculation explains most ball nose complaints.
A ball nose cannot leave a flat surface. Between adjacent passes it leaves a ridge - the scallop or cusp - and its height is what you are really choosing when you set the step-over.
For a ball of radius R and a step-over ae, scallop height is approximately ae² divided by 8R. Two consequences follow.
Scallop grows with the square of step-over. On a 1/4" ball, a 0.020" step-over leaves about 0.0004"; double it to 0.040" and the scallop does not double, it quadruples to about 0.0016". Halving your step-over is expensive in cycle time and buys four times the improvement - which is why it is worth calculating rather than guessing.
Scallop shrinks as the ball gets bigger. Use the largest ball nose the geometry allows for finishing, and reserve small ones for the tight radii that force them.
Diameter is set by the smallest concave radius on the part - the tool has to fit into it - and then by finish, since a larger ball leaves a smaller scallop at the same step-over. Stocked sizes: 1/8", 3/16", 1/4", 3/8" and 1/2".
Flute count follows material as usual - 2 or 3 for aluminum and non-ferrous, 4 for steel and stainless - but note that finishing passes are light, so chip room matters less here than on a roughing tool.
Coating follows heat: coated for steel and hardened material, uncoated for aluminum.
For a floor that must be flat, or a wall that must meet it at 90 degrees, this is the wrong tool - see square end mills.
Prices and stock are on every product page and you can order online without waiting for a quote. Delivery is free across Alberta and we ship anywhere in Canada.
We run our own machine shop in Calgary and cut with these tools ourselves. Send us the surface, the finish you need and the machine, and we will work out ball size, step-over and the rpm that matches the effective diameter rather than the nominal one.
