Method for drilling precision hole through common drilling machine

Abstract

The invention discloses a method for drilling a precise hole by using a common drilling machine, which is simple and practical, is extremely easy to master, and greatly reduces the cost and the labor hour. A method for drilling a precise hole through a common drilling machine comprises the following machining steps that the scribing error of a scribing ruler is found out, two lines are precisely scribed on the machining face of a workpiece, a cross curve is formed, and the cross point of the cross curve is determined as the hole center position of a hole to be drilled in the workpiece; the method comprises the following steps: clamping a workpiece by using a clamp on a workbench of a drilling machine, taking a mandrel with a conical tip, clamping the mandrel on a main shaft, rotating the conical tip of the mandrel to approach a cross point on the workpiece, respectively observing whether the conical tip corresponds to the middle position of the width direction of two lines from the directions of the two lines, if so, judging that the main shaft has no deviation, and if not, judging that the main shaft has no deviation. If yes, the position of the clamp is adjusted according to the offset of the conical tip until the conical tip corresponds to the middle position of the two lines in the width direction; and S3, a twist drill is ground, a reamer is manually used, and then drilling and reaming are conducted.

Description

Technical Field

[0001] This invention relates to the field of machining technology, and in particular to a method for drilling precision holes using a conventional drilling machine. Background Technology

[0002] When drilling precision holes on a conventional drilling machine, common techniques include alignment and tool setting methods, such as using center punches, mandrels, gauge blocks, and spindles, as well as template alignment and tool setting. The mandrel, gauge block, and spindle alignment method can generally guarantee a hole position accuracy of ±0.02mm, but it is labor-intensive, requires high operational skills, and increases the time and cost of machining threaded holes and manufacturing precision centering sleeves. The template alignment method can generally achieve a hole position accuracy of ±0.03mm, but it increases the manufacturing cost of the template. In short, the cost and time consumed by the commonly used techniques are directly proportional to the hole accuracy; that is, the higher the accuracy requirement of the hole, the higher the cost and time required. This high cost and long processing time severely restrict the widespread application of these techniques in production. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for drilling precision holes with a common drilling machine. This method is simple, practical, and easy to master. No special tooling or auxiliary devices are required during the processing, which greatly reduces costs and labor hours.

[0004] The objective of this invention is achieved as follows: A method for drilling precision holes using a conventional drilling machine, comprising the following steps: Step 1: Draw precise lines Find the scribing error of the scribing ruler, accurately scribing two lines on the machined surface of the workpiece to form a cross. The intersection of the cross is determined as the center position of the hole to be drilled on the workpiece. Step 2: Aligning the center of the hole In the case of spindle wear, to eliminate the adverse effects of spindle misalignment, a mandrel tip rotating at high speed is used for alignment. The spindle speed is above 800 rpm. When the spindle is rotating at high speed, the trajectory of the tip is a circle. The center point of this circle is the correct axis of the spindle. Specifically, the workpiece is clamped in a jig on the worktable of the drilling machine. A mandrel with a tip is taken and clamped onto the spindle. The tip of the rotating mandrel is brought close to the intersection of the crosshairs on the workpiece. The tip is observed from the direction of the two lines to see if it corresponds to the middle position of the width direction of the two lines. If it corresponds, the spindle has no deviation. If it does not correspond, the jig position is adjusted according to the offset of the tip until the tip corresponds to the middle position of the width direction of the two lines. Step 3: Grind the twist drill and hand reamer, then drill and ream the hole.

[0005] Furthermore, the method for identifying line drawing errors in step one is explained: (a) Take a standard pad block with a thickness of H, coat it with colored paint, adjust the scribing ruler to H / 2, and draw a line segment a on the pad block. Then flip the pad block over and draw another line segment b on the same scribing plane. Line segments a and b should at least partially overlap. Then observe whether the width of the overlapping part of the line segment is equal to the width of the non-overlapping part of the line segment a / b. If they are equal, it means that line segments a and b are at the same height and the scribing ruler meets the accuracy requirements for use. (ii) If line segment a and line segment b are at different heights, adjust the scribing ruler and repeat step (i) until line segment a and line segment b are at the same height. At this time, the height position of line segment a and line segment b is H / 2, and the vernier of the scribing ruler is not at the H / 2 scale position, indicating that the scribing ruler has an error. This error is the scribing error of the scribing ruler.

[0006] Furthermore, the method for grinding the twist drill in step three is explained as follows: First, grind the two main cutting edges at the front of the drill bit to create a first apex angle of 120 degrees (the included angle between the two main cutting edges) and a second apex angle of 100 degrees. Let the total length of each main cutting edge be L, and the length of the opposite cutting section of the two main cutting edges be 1 / 4L. Grind a 0.5mm radius arc at the intersection of the main cutting edge and the helical side edge to create a slight squeezing effect during cutting and a good finishing effect. Finally, grind the front and rear faces of the two main cutting edges with a fine grinding stone to remove burrs from the cutting edges. When drilling, control the feed rate within 0.03mm-0.15mm / revolution. If the feed rate is >0.15mm / revolution, the Ra value increases; if the feed rate is <0.03mm / revolution, the cutting edge cannot cut smoothly and may cause vibration.

[0007] Furthermore, the reaming allowance after drilling is one percent of the hole diameter.

[0008] Furthermore, in step three, when grinding twist drills and hand reamers, ensure that the back angle of the cutting edge of the hand reamer is 0° to -5° so that the cutting edge is removed from the hole wall, preventing scratches on the hole wall and reducing the likelihood of chatter marks.

[0009] Due to the adoption of the above technical solution, the present invention has the following beneficial effects: Precision holes are machined using ordinary drilling equipment, aided by technological processes and auxiliary devices, to ensure the required hole accuracy. This is achieved through precise scribing, hole center alignment, and grinding of the drill bit and reamer to guarantee positional accuracy, hole diameter, and surface roughness. This method is simple, practical, and easy to master. No special tooling or auxiliary devices are required during the machining process, significantly reducing costs and labor time. Positional accuracy can generally reach ±0.025mm, and hole diameter accuracy can reach ±0.015mm. This method has significant potential for widespread application. Attached Figure Description

[0010] Figure 1 For precise line drawing diagram; Figure 2 A schematic diagram of a mandrel with a tapered tip; Figure 3 Diagram showing the alignment of the center of the hole; Figure 4 This is a schematic diagram of a twist drill. Figure 5 This is a schematic diagram for reading the vernier scale of a scribing ruler; Figure 6 for Figure 5 A magnified view of a portion of the image; Figure 7 This is a schematic diagram for grinding a twist drill. Detailed Implementation

[0011] A method for drilling precision holes using a conventional drilling machine, with the following specific processing steps: (a) Precise line marking First, precise scribing is necessary to determine the exact position of the hole center on the workpiece. To achieve precise scribing, it is essential to identify the scribing error of the scribing ruler. The steps to identify the scribing error are as follows: 1. Find a standard pad with a thickness of H (commonly used in factories for high-precision clamping and machining), coat it with cinnabar solution or copper sulfate solution, and let it dry. The coating should be thin and not affect the width observation. Adjust the scribing ruler to H / 2 and scribing a line segment a of about 10mm in length on the pad (e.g., ...). Figure 1 Then flip the pad 180 degrees and draw another line segment b, about 10mm long, on the same scribing plane. Line segments a and b should overlap by at least 5mm. Figure 1 (The text indicates two lines are not overlapping.) In this case, a magnifying glass can be used to observe whether the width of the overlapping 5mm line segment is equal to the width of the non-overlapping line segment. If they are equal, it means the two line segments completely overlap. Marking is done using a fixture with a fixed marking width; factories usually use a marking ruler directly.

[0012] 2. If the overlapping portion of the two line segments is only partially overlapping, repeat step one by adjusting the scribing ruler until the width of the overlapping line segment is equal to or completely overlaps with the width of the non-overlapping line segment. Complete overlap indicates that the tip of the scribing ruler is at H / 2. If the vernier scale is not at the H / 2 mark, it indicates an error in the scribing ruler. This error is the scribing error of the ruler. The scribing error found using this method can be accurate to within 0.01mm. The theoretical basis is that a difference of 0.02mm between the vernier scale and the main scale on a vernier caliper is easily distinguishable to the naked eye. With a magnifying glass, an error of 0.01mm between the scale lines can also be easily distinguished (see instructions for reading 0.01mm). Figure 5 , 6After eliminating the error of the scribing ruler, the scribing accuracy can reach 0.01mm.

[0013] (II) Finding the center of the hole Use a mandrel to align the tool on the drilling machine. Note that the mandrel used here is a mandrel with a tapered tip (e.g., ...). Figure 2 ).

[0014] Normally, tool setting and alignment are achieved using the outer diameter of the mandrel, its taper tip, or a punch. However, if the spindle's axis at rest deviates from its axis during rotation after wear, using only the mandrel's outer diameter or taper tip for tool setting doesn't adequately account for this deviation, as well as the offset between the drill bit's axis and the spindle's axis. This offset can typically be 0.02mm-0.05mm or more. To eliminate the adverse effects of spindle misalignment, we can use the mandrel's taper tip at high speed (spindle speed above 800 rpm) for alignment. At high spindle speed, the taper tip traces a very small circle close to a single point; the center of this circle is the correct spindle axis. High-speed spindle rotation eliminates the misalignment of the spindle and drill bit. During alignment, we use the rotating mandrel taper tip as close as possible to the intersection of the crosshairs drawn on the workpiece (e.g., ...). Figure 3 Using a magnifying glass, observe whether the cone tip and the width of the two lines are symmetrically aligned. If the symmetrical deviation between the cone tip and the line width reaches 0.02mm or more, it should be easily observed with the naked eye. For example, on a vernier caliper, each graduation is only 0.98mm. When one graduation line is perfectly aligned with a graduation line on the main scale, it can be clearly observed that the two graduation lines on its left and right deviate from the corresponding graduation lines on the main scale. This deviation is exactly 0.02mm. A magnifying glass can more clearly observe the 0.01mm deviation between the graduation lines. Therefore, when observing the symmetrical or overlapping state of the cone tip and the line width on the workpiece with a magnifying glass, the deviation accuracy can generally reach ±0.015mm, meaning the hole position accuracy can reach ±0.015mm. After centering the hole, use a center drill to drill the center hole at high speed (spindle speed 1000 rpm).

[0015] (III) Drilling Examples Example: Machining holes φ8 ±0.02 Quantity: 12 pieces First, mark the alignment lines and drill the center hole using a center drill. Then, use a 7.9mm twist drill for precision drilling. Because the allowance for precision reaming needs to be controlled within 0.08mm, the twist drill needs to be fine-finished to ensure the reaming allowance and the surface roughness of the hole. The method for finishing the twist drill is as follows: First, grind the two main cutting edges at the tip of the drill bit, grinding each main cutting edge to two angles: a first vertex angle of 100° and a second vertex angle of 100° (e.g., ...). Figure 4 , Figure 7To ensure even load distribution on both cutting edges and improve cutting stability, the length L of the first apex cutting edge is equal to the total length of the main cutting edge, and the length of the second apex cutting edge is 1 / 4 of the length of the first apex cutting edge. A 0.5mm radius arc is ground at the intersection of the main cutting edge and the helical side edge to provide a slight squeezing effect during cutting and good finishing. Finally, the rake and flank faces of the main cutting edge are ground with a fine grinding stone to refine the surface roughness to Ra 0.4µm, eliminating burrs on the cutting edge and reducing adhesion and friction during cutting. The feed rate during drilling should be controlled within 0.03 mm - 0.15 mm / revolution. A feed rate > 0.15 mm / revolution increases the Ra value, while a feed rate < 0.03 mm / revolution prevents smooth entry of the cutting edge and causes vibration. A cutting fluid primarily for lubrication and cooling should be used during drilling. After drilling, the hole diameter should be approximately 7.92 mm, and the surface roughness should reach Ra 6.4-3.2 μm. Because the hole diameter tolerance is small, and the spindle runout of a typical drilling rig generally exceeds the tolerance requirement, a hand-held taper reamer should be used. The hand-held reamer also requires edge grinding, with the reamer diameter controlled at Φ8 during grinding. 0 -0.15 (When the reaming allowance is approximately 0.08mm, the reamed hole diameter must be 0.02-0.04mm larger than the reamer diameter to meet the hole diameter requirements.) The cutting edge clearance angle is 0. ° to -5 ° The purpose is to remove the cutting edge from the hole wall, preventing scratches and reducing the likelihood of chatter marks. Grinding the flank face of the cutting edge improves the hole wall finish, refining the surface roughness to Ra 0.4µm, which can achieve a final surface roughness of Ra 1.6µm. When hand-reaming, the feed rate should be controlled at 0.3mm / revolution. Excessive feed rate increases the Ra value and the hole diameter, leading to out-of-tolerance issues. A cutting fluid primarily used for lubrication should be used during reaming. Note that the allowance during hand reaming should be controlled within 0.08mm. If the allowance exceeds 0.15mm, the reamed hole diameter will generally be 0.05mm larger than the reamer diameter, and the Ra value will increase.

[0016] Actual test results after processing: The hole diameter, roundness, and surface roughness of the hole are all qualified. The hole position accuracy is within 0.03mm. 11 pieces are qualified and 1 piece is out of tolerance by 0.01mm. The pass rate is 91.7%. If the hole position accuracy is set to 0.02mm, then 10 pieces are qualified and 2 pieces are out of tolerance (1 piece is out of tolerance by 0.02mm and the other piece is out of tolerance by 0.01mm). The pass rate is 83.3%.

[0017] V. Key Points and Protected Aspects of This Application A method for drilling precision holes on a conventional drilling machine. Compared with other known methods, it can achieve the same positional accuracy and hole diameter accuracy, but the machining method is simple, practical, and easy to master. No special tooling or auxiliary devices are required during the machining process, which greatly reduces costs and labor time.

[0018] Key points and points to be protected: (a) Precise line marking To accurately determine the center position of a hole on a workpiece, it is essential to identify the scribing error of the scribing ruler. How do you find this error? Step 1: Find a standard pad with a thickness of H, coat it with cinnabar solution or copper sulfate solution, and let it dry. Adjust the scribing ruler to H / 2 and scribing a line segment a of approximately 10mm length on the pad (e.g., ...). Figure 1 Then flip the pad 180 degrees and draw a line segment b about 10mm long on the same scribing plane. The line segments a and b intersect by about 5mm. At this time, you can use a magnifying glass to observe whether the intersecting 5mm line segments completely overlap. You can also use a magnifying glass to observe and compare the width of the intersecting line segments with the width of the non-intersecting line segments.

[0019] If the intersection of two line segments does not completely overlap, adjust the scribing ruler and repeat step 1 until the width of the intersecting line segment is equal to or completely overlaps with the width of the non-intersecting line segment. This indicates that the scribing ruler's scale position at this point is the 10mm mark. Then, read the error between the vernier and main scale at the 10mm mark. This error is the scribing error of the ruler. The scribing error found using this method can be accurate to within 0.01mm. The theoretical basis is that a difference of 0.02mm between the vernier and main scale marks on a vernier caliper is easily distinguishable to the naked eye. Even with a magnifying glass, a 0.01mm error between the marks can be easily distinguished (see instructions for reading 0.01mm). Figure 5 , Figure 6 After eliminating the error of the scribing ruler, the scribing accuracy can reach 0.01mm.

[0020] (II) Finding the center of the hole Use a mandrel to align the tool on the drilling machine. Note that the mandrel used here is a mandrel with a tapered tip (e.g., ...). Figure 2 ).

[0021] Normally, tool alignment is achieved using the outer circle, taper tip, or punch of the mandrel. However, if the spindle's axis at rest deviates from its axis during rotation after wear, using the outer circle or taper tip Φ for tool alignment does not fully account for the offset caused by spindle wear and the offset between the drill bit axis and the spindle axis. This offset can typically be 0.005mm-0.03mm or more. To eliminate the adverse effects of spindle misalignment, we can use the taper tip of the mandrel during high-speed rotation (spindle speed above 800 rpm). During rapid spindle rotation, the trajectory of the taper tip is a very small circle close to a single point, and the center of this circle is the correct axis of the spindle.

[0022] During alignment, we make this dot as close as possible to the center line of the cross hole marked on the workpiece (e.g., Figure 2 Use a magnifying glass to observe whether the center of the dot coincides with the center of the two lines. If the deviation between the center of the dot and the center line of the lines reaches 0.02mm or more, this deviation can be easily observed with the naked eye. For example, consider the scale on a vernier caliper. Each scale mark on the vernier is only 0.98mm. When one scale mark is perfectly aligned with a scale mark on the main scale, it can be clearly observed that the two scale marks on its left and right deviate from the corresponding scale marks on the main scale. This deviation is exactly 0.02mm. A magnifying glass can further clearly observe the 0.01mm deviation between the scale marks. Therefore, when observing the alignment of the cone tip dot with the center line of the lines on the workpiece using a magnifying glass, the deviation accuracy can generally reach ±0.015mm. That is to say, the positional accuracy of the hole can reach ±0.015mm. After aligning the hole center, use a center drill to drill the center hole (spindle speed 1000 rpm).

[0023] (III) Sharpening of twist drills and hand reamers The re-grinding method is as follows: First, re-grind the two main cutting edges at the front end of the drill bit. Grind each main cutting edge to create two angles: a first vertex angle of 120° and a second vertex angle of 100° (e.g., ...). Figure 4 To ensure even load distribution on both cutting edges and improve cutting stability, the length L of the second apex cutting edge is 1 / 4 of the length of the first apex cutting edge. A 0.5mm radius arc is ground at the intersection of the main cutting edge and the helical side edge to provide a slight squeezing effect during cutting and good finishing. Finally, the flank face of the main cutting edge is ground with a fine grinding stone to refine the surface roughness to Ra 0.4µm, eliminating burrs on the cutting edge and reducing adhesion and friction during cutting. During drilling, the feed rate should be controlled between 0.03mm and 0.15mm / revolution. A feed rate > 0.15mm / revolution increases the Ra value, while a feed rate < 0.03mm / revolution prevents smooth entry of the cutting edge and causes vibration.

[0024] When using a hand reamer for grinding, the reamer diameter D will be larger than the reamer diameter because the diameter of the hole after reaming will be larger. The amount of this difference will vary depending on the reaming allowance and the difference in hole diameter. Generally, a reaming allowance of one percent of the hole diameter is appropriate. The purpose of using a cutting edge clearance angle of 0° to -5° is to remove the cutting edge from the hole wall, so as not to scratch the hole wall and to reduce the likelihood of chatter marks. Grinding the back face of the cutting edge is to improve the surface finish of the hole wall and refine the surface roughness to Ra0.4um, which can make the surface roughness of the machined hole reach Ra1.6um.

[0025] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for drilling precision holes using a conventional drilling machine, characterized by machining... The steps are as follows: Step 1: Draw precise lines Find the scribing error of the scribing ruler, accurately scribing two lines on the machined surface of the workpiece to form a cross. The intersection of the cross is determined as the center position of the hole to be drilled on the workpiece. Step 2: Align the hole center Clamp the workpiece with a flat-jaw vise on the worktable of the drilling machine. Take a mandrel with a tapered tip and clamp it on the spindle. Rotate the tapered tip of the mandrel to approach the intersection of the cross lines on the workpiece. Observe from the direction of the horizontal and vertical lines respectively to see if the tapered tip corresponds to the middle position of the intersection of the horizontal and vertical lines. If it corresponds, the spindle has no deviation. If it does not correspond, adjust the position of the flat-jaw vise according to the offset of the tapered tip until the tapered tip corresponds to the middle position of the intersection of the horizontal and vertical lines. Step 3: Grind the twist drill and hand reamer, then drill and ream the hole.

2. The method for drilling precision holes with a conventional drilling machine according to claim 1, characterized in that: In step 1, the method for identifying line drawing errors is as follows: Step 1.1: Take a standard pad block with a thickness of H, apply colored paint, adjust the scribing ruler to H / 2, and draw a line segment a on the pad block. Then flip the pad block over and draw another line segment b on the same scribing plane. Line segments a and b should at least partially overlap. Then observe whether the width of the overlapping part of the line segment is equal to the width of the non-overlapping part of the line segment a / b. If they are equal, it means that line segments a and b are at the same height, and the scribing ruler meets the accuracy requirements for use. If line segments a and b are at different heights, adjust the scribing ruler and repeat step 1.1 until line segments a and b are at the same height. At this point, the height of line segments a and b is H / 2, and the vernier of the scribing ruler is not at the H / 2 mark, indicating that the scribing ruler has an error. This error is the scribing error of the scribing ruler.

3. The method for drilling precision holes with a conventional drilling machine according to claim 1, characterized in that: The twist drill has two main cutting edges and a helical side cutting edge. The main cutting edges are connected to the helical side cutting edge. In step 3, the method for grinding the twist drill is as follows: First, grind the two main cutting edges at the front of the drill bit. Each main cutting edge has two cutting sections. The first apex angle is formed between the adjacent cutting sections of the two main cutting edges, and the second apex angle is formed between the opposite cutting sections of the two main cutting edges. The first apex angle is greater than the second apex angle. Use an oilstone to grind an arc at the intersection of the main cutting edge and the spiral side edge, so that the twist drill has a squeezing effect and a finishing effect when cutting. Finally, use a fine grinding stone to grind the front and rear faces of the two main cutting edges to remove burrs on the cutting edges.

4. The method for drilling precision holes with a conventional drilling machine according to claim 3, characterized in that: The reaming allowance after drilling is one percent of the hole diameter.

5. The method for drilling precision holes with a conventional drilling machine according to claim 3, characterized in that: In step 3, when grinding twist drills and hand reamers, ensure that the back angle of the cutting edge of the hand reamer is 0° to -5° so that the cutting edge does not scratch the hole wall when it is removed from the hole wall and is less likely to produce chatter marks.

6. The method for drilling precision holes with a conventional drilling machine according to claim 3, characterized in that: In step 3, the feed rate during drilling is controlled at 0.03 mm - 0.15 mm / revolution.

7. The method for drilling precision holes with a conventional drilling machine according to claim 3, characterized in that: In step 3, the first vertex angle is 120°, the second vertex angle is 100°, the total length of each main cutting edge is L, the length of the opposite cutting section of the two main cutting edges is 1 / 4L, and the arc at the intersection of the main cutting edge and the helical side edge is an arc of r0.5mm.

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