Technical materials on curing holiday syndrome

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The Spring Festival holiday ended yesterday, and I have returned to work. But I’m not in my best condition at all today; I feel anxious and restless, unable to calm down. This feeling must be what’s known as the \"holiday syndrome\". . How to overcome it? Since I’m not in the mood to work, let’s study some technical materials* – reviewing old knowledge helps gain new insights! Changing one’s mindset seems to be quite effective in curing the \"holiday syndrome\". . . Common mistakes and overlooked details in custom mechanical design:
I. Major errors that must be avoided in mechanical design
1. Designs that violate laws and regulations.
2. Designs that do not comply with contract terms or decisions made in meetings with clients or internal team members.
3. Designs lacking a basis for creation (excluding designs based on experience, feasible innovations, or inventions).
4. Designs that fail to meet functional and production capacity requirements.
5. Designs that cannot be disassembled or assembled.
6. Major errors in component selection.
7. Incorrect material selection for key components.
8. Significant errors in formulas and parameters used in calculations.
9. Errors in key dimensions, elevations, coordinates, etc.
10. Severe interference issues.
11. Excessive excess capacity in the equipment.
12. Safety hazards.
13. Other major errors.

II. Common mistakes that often occur in mechanical design
1. Non-compliance with drawing standards.
2. Insufficient calculations.
3. Inadequate technical and operational specifications (annotations on drawings).
4. Errors in material lists and component lists.
5. Difficulties in maintenance.
6. General collision issues.
7. Errors or insufficient specifications regarding tolerances, surface roughness, and geometric precision.
8. General dimension errors.
9. Errors in views.
10. Errors in text or wording (5 or more such errors count as one general error).
11. Other common errors.

III. Details that are easily overlooked in mechanical design
1. Designing lubrication points for rotating parts (manual or automatic).
2. Providing safety guards for rotating parts (including observation doors).
3. Designing lifting holes or lugs for components weighing more than 20 kilograms.
4. Designing adjustment bolts for positioning and load-bearing purposes at bearing seat locations.
5. Designing shims for connection surfaces that require height adjustments.
6. Designing dowels or retaining blocks for bolted connections.
7. Distinguishing between components welded on-site and those welded in a factory.
8. Indicating special welding requirements that are not standard.
9. Showing the direction of oil seals in sectional views.
10. Designing dual-nut systems to allow loosening of large components.
11. Indicating areas that should not be painted.
12. Showing the range of motion and trajectory of moving parts.
13. Ensuring safety in both operating and non-operating states.
14. Strengthening load-bearing areas (such as reinforcing ribs) while weakening non-load-bearing areas (such as weight-reducing holes).
15. Properly specifying linear tolerances, fit tolerances, and form and position tolerances.
16. Reasonably specifying surface roughness requirements.
17. Accurately drafting technical specifications.

IV. Specific examples:
1. Dual-nut anti-loosening mechanism: http://www.cmiw.cn/data/attachment/album/201902/14/154244vfqjnwyff4f2mqzv.jpg
A dual-screw anti-loosening mechanism should be used; the structure shown in Figure (a) is not acceptable. Instead, the structure shown in Figure (b) should be used, with a flat nut at the bottom and a thicker nut at the top. However, since a wrench cannot reach the flat nut at the bottom, it cannot be tightened properly. Therefore, a structure with two thick nuts, as shown in Figure (c), is necessary. 2. The two positioning pins should have different lengths. http://www.cmiw.cn/data/attachment/album/201902/14/154245xvpvmjepbprdbcmv.jpg When assembling large boxes, it is often necessary to use several positioning pins; it is not advisable to make all of them the same height, as shown in Figure A, because it is difficult to align multiple positioning pins at once when assembling the box. Instead, the positioning pins should have different lengths, as shown in Figure B, which makes it easier to align the box by first focusing on one of the positioning pins. 3. In gear drives, the proper arrangement of the large and small gears is important. http://www.cmiw.cn/data/attachment/album/201902/14/154245l1k1uggblb6vehih.jpg For ease of installation and to prevent step wear during gear operation, it is generally advisable to make the width of the small gear 5–10 mm greater than that of the large gear, as shown in Figure C. However, if the small gear is made of plastic, its tooth width should be smaller than that of the large gear, as shown in Figure D, in order to avoid the formation of indentations on the gears. 4. Frequently removed and reinstalled screw connections: http://www.cmiw.cn/data/attachment/album/201902/14/154246pzs1t21slidzs1s3.jpg The screw connection is shown in Figure A; its characteristic is that the screw is screwed directly into the threaded hole of the component to be connected, without the need for a nut. This type of connection has a simple and compact structure, and it is suitable for applications where bolt connections cannot be used. However, screw connections are not appropriate for situations involving high forces or frequent removal and reinstallation, as this can lead to wear of the threads and may result in the failure of the connected components. If frequent removal and reinstallation is necessary, then a double-headed bolt connection can be used, as shown in Figure B. The screwing depth should be H; when the threaded hole is made of steel or stainless steel, H≈d ； When the screw hole is made of cast iron, H=(1.25~1.5)d; when it is made of aluminum alloy, H=(1.5~2.5)d. For the threaded hole, H1=H+(2~2.5)p (where p is the thread pitch), and the drilling depth H2=H1+(0.5~1)d. 5. Intermediate coupling for the high-speed shaft: http://www.cmiw.cn/data/attachment/album/201902/14/154246bl8nxxlnpz4vltp8.jpg When installing a coupling at the end of the shaft that is rotating at high speed, the structure shown in Figure A should be avoided; instead, the length of the cantilever should be reduced. The greater the cantilever length, the greater the deformation and unbalanced forces. Therefore, when installing a coupling at the cantilever end, it is necessary not only to reduce the weight of the coupling but also to position it as close as possible to the bearing. 6. Machining of deep holes with small diameters: http://www.cmiw.cn/data/attachment/album/201902/14/154246fzpbp0f844p7fpvh.jpg Machining deep holes with small diameters is difficult, costly, and inefficient; it is not advisable to design deep, small-diameter lubrication holes on rotating shafts. As shown in Figure A, holes should be made as large as possible under feasible conditions. If necessary, holes of different diameters should be created, as shown in Figure B.