CNC Knowledge: Summary of methods to improve drilling accuracy

Drilling is an important basic operational skill for riggers, but improving drilling accuracy is a difficult area. The main problems are: insufficient plotting accuracy, leading to excessive hole spacing; poor sharpening quality of the drill bit, resulting in enlarged hole diameter and rough hole surface; lack of alignment or inaccurate alignment during drilling, blind drilling, resulting in drill bit failure; . The center line does not coincide with the center line of the hole; forced alignment when adjusting the tool causes the drill bit (especially the small drill bit) to bend and tilt the axis of the hole when tilted, which causes the axis of the hole to tilt hole ; drill bit to break. How can we avoid the above problems and drill accurate holes?

1. Basic Drilling Concepts

Drilling refers to the machining process of using a drill to create holes in solid materials. Generally speaking, when drilling materials on a drill, the drill bit should make two movements at the same time:

① Main movement, that is, the rotational movement of the drill bit around the axis (cutting movement);

② Auxiliary movement, that is, the linear movement of the drill bit along the direction of the axis towards the workpiece (feed movement).

When drilling, due to the defects in the structure of the drill bit, the processing quality of the workpiece will be affected to a certain extent. The processing precision is generally less than IT10 level, and the surface roughness is about Ra12.5μm, which corresponds to coarse processing. .

2. Stages of drilling operation

1. Marking: Before drilling, you must first familiarize yourself with the drawing requirements according to the drilling location and size requirements, use a height ruler to mark the cross center line of the hole position. precise, and the finer the better, steel calipers or rulers will be used for inspection in the future.

2. Draw an inspection square or inspection circle: After drawing the line and passing the inspection, an inspection square or inspection circle with the center line of the hole as the center of symmetry should also be drawn drawn as inspection line during test drilling for easier drilling. Check and correct the drilling position.

3. Proofing and punching: After drawing the corresponding inspection square or inspection circle, proofing and punching should be carried out carefully. First, make a small dot and carefully observe in different directions of the transverse center line to see whether the sample punch hole is touched at the intersection of the transverse center line. Finally, force the sample punch hole to be straightened, rounded and enlarged. , so as to precisely center the drill.

4. Clamping: Wipe the machine table, fixture surface and workpiece reference surface, then clamp the workpiece. The tightening should be smooth and firm, making it easier to observe and measure. Pay attention to the method of clamping the workpiece to avoid the workpiece being deformed due to clamping.

5. Trial drilling: Trial drilling should be carried out before drilling, so that the chisel edge of the drill bit is aligned with the center of the hole to drill a shallow pit, and then visually check whether the position of the Shallow pit is okay. and continuous corrections must be made to make the shallow pit and the inspection circle coaxial. If the gap is small, you can push the workpiece in the opposite direction of the gap while drilling to achieve gradual correction.

6. Drilling: Closer drilling is usually carried out by a manual feed operation. When the test drilling reaches the precision requirement of the drilling position, drilling can be carried out. When feeding manually, the feeding force should not bend the drill bit to avoid tilting the hole axis.

3. Methods to improve drilling accuracy

1. Drill sharpening is a prerequisite

The corresponding drill bit should be selected for sharpening before drilling. In addition to ensuring that the vertex angle, clearance angle and chisel edge bevel angle of the sharpened drill bit are accurate, the length of the two main cutting edges is equal and symmetrical with the centerline of the drill bit. , and the two main flank surfaces are smooth, in order to facilitate centering and reduce the roughness of the hole wall, the chisel edge and the main cutting edge should also be properly ground (it is better to first grind coarsely on the grinder, then grind finely on the oil stone).

2. Precise tracing is the basis

When using a height ruler to mark lines precisely, you must first make sure the dimensions are accurate. When marking, ensure that the angle between the needle angle and the workpiece marking plane is between 40° and 60° (in the marking direction). ), so that the drawn lines are clear and regular. Pay attention to the choice of the tracing reference plane. The reference plane must be processed precisely and its flatness and perpendicularity to adjacent surfaces must be ensured. After the hole position cross lines are drawn, to ensure easy alignment when drilling, use a center punch to punch the center point on the cross lines (the punching point should be small and the position should be accurate) .

3. Correct tightening is key

Under normal circumstances, for holes with a diameter of less than 6mm, if the precision is not high, the workpiece can be clamped with hand pliers to drill holes with a diameter of 6-10mm, if the piece is regular and flat; , flat-nose pliers can be used, but the workpiece surface must be perpendicular to the drill spindle. When drilling a hole with a larger diameter, the flat nose pliers should be fixed with a bolt pressure plate; For larger workpieces with a drilling diameter greater than 10mm, the pressure plate clamping method should be used for drilling.

4. Find key points accurately

After the workpiece is clamped, do not rush to drill, but first carry out alignment. Alignment includes static alignment and dynamic alignment. So-called static alignment refers to the alignment before starting the drill to align the centerline of the drill spindle with the intersection of the workpiece cross. This method is safe and convenient for beginners and easier to master. Do not take into account the swing of the drill spindle, for example, or other uncertain factors, the drilling accuracy is low. Dynamic alignment is performed after starting the drill. During alignment, some uncertain factors are taken into account and the accuracy is relatively high.

5. Careful testing is essential

The inspection can accurately and quickly discover the correctness of the holes so that necessary measures can be taken to remedy them. For holes with high drilling precision, we generally adopt the processing technology of drilling, reaming and reaming. After drilling the small hole in the first step, use a caliper to detect the offset error between the center of the bottom hole and the reference. After the actual measurement, the position of the bottom hole and the ideal center can be calculated if the error. is not more than 0.10mm, you can widen the hole. Appropriately increase the angle of the drill tip, weaken the self-centering effect, properly push the workpiece in the positive direction, and gradually increase the diameter of the drill tip to remedy the problem. If the error is greater than 0.10mm, you can use a matching round file to cut the side walls of the bottom hole. The cut part should be smoothly connected to the arc of the lower hole.