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| Solder dots around mounting hole - what are they for? |
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| VK3DRB:
--- Quote from: KE5FX on October 23, 2023, 11:53:35 pm --- --- Quote from: nctnico on October 23, 2023, 10:11:02 am ---It is an interesting subject. I would like to see some numbers about how much FR4 'flows' though. I have not been able to find those -yet-. I doubt it is a large amount though otherwise screws would get lose over time by themselves. --- End quote --- It's hard to generalize about "FR4" other than to say that it is made of some sort of fire-retardant material with an Er somewhere near 4. But I've seen a lot of TO-3 mounting screws that have loosened over time. Far too many to think that most PCB laminates -- or more likely, prepregs -- don't cold-flow to some extent. --- End quote --- That's because they are mounted poorly. Heat/cold cycles can loosen screws that don't have appropriate spring washers on them over time. Loctite can also prevent movement. |
| wraper:
--- Quote from: VK3DRB on October 26, 2023, 07:31:45 am ---That's because they are mounted poorly. Heat/cold cycles can loosen screws that don't have appropriate spring washers on them over time. Loctite can also prevent movement. --- End quote --- Spring washers are among the most useless things that can be used for prevent screw from loosening though. https://ntrs.nasa.gov/citations/19900009424 --- Quote ---The typical lockwasher serves as a spring while the bolt is being tightened. However, the washer is normally flat by the time the bolt is fully torqued. At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a lockwasher of this type is useless for locking. --- End quote --- |
| thm_w:
--- Quote from: VK3DRB on October 26, 2023, 07:27:25 am ---Having solder on these vias is pure stupidity. --- End quote --- Its not vias, its just a pad, and it could be necessary in this case as the board appears to be OSP, as we discussed above. --- Quote from: wraper on October 26, 2023, 11:55:47 am --- --- Quote from: VK3DRB on October 26, 2023, 07:31:45 am ---That's because they are mounted poorly. Heat/cold cycles can loosen screws that don't have appropriate spring washers on them over time. Loctite can also prevent movement. --- End quote --- Spring washers are among the most useless things that can be used for prevent screw from loosening though. https://ntrs.nasa.gov/citations/19900009424 --- Quote ---The typical lockwasher serves as a spring while the bolt is being tightened. However, the washer is normally flat by the time the bolt is fully torqued. At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a lockwasher of this type is useless for locking. --- End quote --- --- End quote --- They work better than a plain washer, that NASA quote is a bit deceiving. They still don't work that well though (skip to 1:40): |
| SiliconWizard:
--- Quote from: wraper on October 26, 2023, 11:55:47 am --- --- Quote from: VK3DRB on October 26, 2023, 07:31:45 am ---That's because they are mounted poorly. Heat/cold cycles can loosen screws that don't have appropriate spring washers on them over time. Loctite can also prevent movement. --- End quote --- Spring washers are among the most useless things that can be used for prevent screw from loosening though. https://ntrs.nasa.gov/citations/19900009424 --- End quote --- Nice reading. Well recommended. |
| VK3DRB:
--- Quote from: SiliconWizard on October 26, 2023, 09:23:51 pm --- --- Quote from: wraper on October 26, 2023, 11:55:47 am --- --- Quote from: VK3DRB on October 26, 2023, 07:31:45 am ---That's because they are mounted poorly. Heat/cold cycles can loosen screws that don't have appropriate spring washers on them over time. Loctite can also prevent movement. --- End quote --- Spring washers are among the most useless things that can be used for prevent screw from loosening though. https://ntrs.nasa.gov/citations/19900009424 --- End quote --- Nice reading. Well recommended. --- End quote --- Good doco. They mentioned nyloc nuts which have the greatest efficacy. It is a safety requirement in Australia that earthed chassis terminals have a nyloc nut securing the earth wire to the chassis and NO star washer between the lug and the chassis. I have also used nylocs on circuit boards where something must frame earthed. Another point is that over time, metallic bonds are formed on threads and other mating metals over time, making them more diffucult to remove or shake loose. A bloke came around here to buy my 30-year old 7' x 4' trailer earlier this year. The trailer had an oversized ball, which prevented theft. So he had to remove the 2 inch ball from his 4WD and put my 2.5 inch ball on. Trouble is the old ball had been left untouched in his 4WD for 25 years. To remove it, no amount of WD40 could shift it. I did not want to use a blow torch near a fuel tank or the greasy underside of his vehicle. A large pipe wrench with an extension handle could not budge it. What worked was putting the pipe wrench on the nut and backing the 4WD into a large power pole. The heavy duty pipe wrench handle was actually flexing. Eventually it released with an almighty BANG. Looking at the threads, I don't think rust played a big part. It was more likely the metallic bonds in the thread which had formed over 25 years. Anyone who has left metallic gauge blocks up against each other for a few weeks will know how strong these bonds can become. |
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