Anyone involved in machining knows this: if an end mill is sharpened properly, efficiency can double and scrap can be reduced; if it is sharpened badly, it wastes tools, material and labour. Many machinists still sharpen tools by hand and rely on feel alone, which often leads either to an uneven cutting edge or incorrect angles. The result is poor surface finish in machining, and the tool is also more likely to chip. This practical guide to end mill regrinding covers everything from wheel dressing, end-face edge grinding and opening a cross chip pocket, through to main cutting edge regrinding and angle correction, explaining each step clearly so that, once you have read it, you can follow the method yourself.
How can you sharpen an end mill properly?
Before sharpening, the grinding wheel should be inspected. If you find wheel runout, an irregular cylindrical surface or an excessively large corner radius, it needs to be dressed. In general, a wheel dresser, such as a diamond dresser or star-wheel dresser, can be used to dress the cylindrical surface of the grinding wheel. A worn grinding wheel with relatively higher abrasive hardness may also be used for dressing. If the side face of the wheel is already uneven, the wheel should be replaced.
End-face grinding technique for end mills
- 1.Technique for grinding the end face of an end mill flat
Regardless of how many flutes the end mill has, the first step is to grind the end face of the cutting edges flat and square to the tool axis. This is the key to ensuring that the highest point of each cutting edge lies in the same plane. The following methods may be used to check the squareness of the cutting-edge end face relative to the axis of the end mill.
① Visual inspection. With the help of a surface plate, place the end mill with the cutting edges facing down on the plate and observe the angle of tilt to the left and right. Then rotate the cutter by 180° and observe the left and right tilt again. If the tilt observed in the same direction differs between the two checks, regrinding is required until the tilt in the same direction appears identical in both observations. Then rotate the cutter by 90° and repeat the above process.
② Checking with a try square. Use a 90° engineer’s square on a surface plate for checking. Lay both the cutter and the square flat, then observe whether there is a gap between the cutter and the square, or whether the gap is even. Judge the squareness of the cutter from the gap and then regrind the cutter accordingly.
③ Self-checking. Clamp the end mill in the chuck of a drill press or milling machine, place a worn grinding wheel underneath, select a suitable speed and start the machine. Then lower the cutter onto the grinding wheel for grinding and regrind it according to the condition of the end-face grinding.
- 2.Technique for opening a cross chip pocket on the end face of an end mill
If there is no circular pocket at the front of the end face of a four-flute end mill, it is necessary to use the corner radius of the grinding wheel to reopen a cross pocket along the direction of the helical flute, to a depth of about 1–2 mm. If it is too deep, it is prone to chipping; if it is too shallow, it is difficult to grind the secondary clearance angle. When opening the pocket, take care that the side face of the wheel does not touch the lower cutting edge on the opposite side. (Note: this cross pocket serves for chip evacuation. If it is not opened, the inclination angle of the edge sinking towards the centre must be increased.)
- 3.Technique for grinding the end cutting edge of an end mill
① When grinding each cutting edge separately, the tip of each edge should be used as the reference point, and the principle should be to preserve the tip. Before grinding, the rake angle should be ground as required, unless there is no chipping and it does not need to be ground. The clearance angle, secondary clearance angle and cutting-edge inclination angle should also be ground. Where heavy cutting is involved and greater strength is required, it is recommended to increase the wedge angle of the cutting edge by grinding the tool face appropriately.
② As for the choice of angles, the clearance angle should be 6°–8°, the secondary clearance angle 30°–45°, and the cutting-edge inclination angle 1°–3°. The clearance angle should be selected according to the hardness of the workpiece. The harder the material, the smaller the angle should be. The principle for choosing the cutting-edge inclination angle is that all four edges should slope inwards towards the centre. The flatter the angle, the better the achievable surface finish and accuracy. At the same time, the greater the cutting depth, for example more than 2 mm but still within the permitted range, the better the resulting surface finish and accuracy may in fact become, because the full length of the cutting edge is taking part in the cut.
③ After grinding, stand the end mill upright on a flat surface. If the axis is vertical, all edge tips should be level and the edge offset angles should be evenly centred. In this case, the tool can be regarded as meeting the requirement.
At this stage, a 90° engineer’s square on a surface plate may again be used for checking. After laying the tool flat, observe whether there is any gap between the cutter and the square, or whether the gap is even. Usually, the first step is to observe the two comparatively higher lands, that is, the two lands that touch the base first. If they are not vertical, the higher pair should be reground until the two opposite lands are of equal height, which means the tool is vertical. At this point, a height difference will appear between these two lands and the other two opposite lands, and the cutter will rock. The two higher lands should then be ground down together. In the same way, rotate the cutter by 90° and observe the squareness of the other two opposite lands. Ultimately, all four lands should touch the base at the same time and the cutter should stand vertically. This indicates that grinding has been completed.
In manual grinding, it is not easy to control the height of the cutting edges or all the angles accurately. Practice varies from person to person, but as long as a small clearance angle is ground, attention is being paid to the right principle. If the top cutting edges are uneven, it is enough to ensure that the tip is the highest point. In addition, unless the cutter is intended for internal corner clearing, a chamfer greater than 0.2 mm may also be ground at the tip to increase tip strength.
- 4.Technique for grinding the main cutting edge of an end mill, that is, the side cutting edge
If the main cutting edge of the end mill is worn, it should be reground along the helical line on the grinding wheel, and a smaller wheel diameter is preferable. However, this is difficult for beginners to do well. After regrinding, there is usually some taper, and the smaller the taper, the higher the level of operating skill it shows.
Post time: Apr-22-2026
