What is non-rotating drilling?
Non-rotating drilling is when the workpiece rotates instead of the drill. When using this method, it is extremely important to ensure that the drill is aligned with the centre line of the machine.
Alignment recommendations for non-rotating drilling
Minimize tool run-out or TIR (Total Indicator Runout) for best performance.
Note: An indexable insert drill forms a small centre core which can be seen at the bottom of the hole or the disc. The size of the core should be within 0.05-0.15 mm (0.002-0.006 inch), otherwise it can cause edge fracture, vibrations, oversized holes and wear on the drill body. When turning the drill, the core dimension will vary due to the different positions.
Solid carbide drills
Indexable insert drills
Exchangeable tip drills
Aligning the non-rotating drill
Drill alignment must be parallel with the spindle axis, otherwise the hole can be over or undersized, or funnel-shaped. Measurement can be carried out with a dial-indicator together with a test-bar.
Drill with four flats (indexable insert drills)
Use a drill with four flats equally positioned around the drill shank. Make holes with the drill mounted in each of the four flat positions (0°, 90°, 180°, 270°). Hole measurement will indicate the position of the peripheral insert in relation to the work piece centre line, which in turn will indicate the state of machine alignment
Misalignment due to turret deflection
Deflection of the turret on a CNC lathe can be a problem, especially when using larger drills and high feeds,
fn, which can cause a high force.
To test stability, drill one hole with low feed rate and one hole with high feed rate and measure the hole sizes. If there is a large difference in hole size, the turret may have a tendency to deflect.
To minimize turret deflection
First, check if the leverage can be minimized by mounting the tool differently. Always mount the tool as close to the centre of the turret as possible. Position B is preferable to position A.
If this is not possible, a reduction in feed/revolution (fn), will decrease the feed force. To maintain the same productivity, the speed,
vc, can be increased as it doesn’t affect the feed force.
For indexable drills, if turret deflection/misalignment can’t be avoided, the drill should be mounted with the peripheral insert set as shown in the picture to the left, in order to avoid wear on the drill body.