| Electronics > Mechanical & Automation Engineering |
| Screws meant for plastic. |
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| tooki:
--- Quote from: Shay on December 24, 2024, 10:41:08 am ---Thanks for your enlightenment. I’m used to think that self tapping screws and for both plastic and wood but not for metal or aluminium. Now I know it is more like a family. --- End quote --- Was that not obvious from reading the Wikipedia article about them?! Or did you quote the article without even skimming it first? On second thought, it’s obvious you didn’t read the article at all. And to reiterate: while wood screws (and others I listed above) do technically tap their own threads, we don’t call them self-tapping because there is no need to. So we really only say “self-tapping” for the situations where both self-tapping and machine screws exist, and 99% of the time that means metal. --- Quote from: Shay on December 24, 2024, 10:41:08 am ---It seems it is easy to know on AliExpress which screw is for plastic by looking at the thread angle and pitch and that there is no tip like screw used for wood. --- End quote --- Please read the page jfiresto linked above. It goes over the types and differences. It’s not just thread angle and pitch, it’s also the minor diameter and the thread shape. Screws for plastic exist both with pointy tips and with blunted tips. A quick glance is often not enough to determine what type of screw it is, and the AliExpress listings frequently don’t actually include enough speculations to make that determination. |
| T_guttata:
You can buy screws specifically for plastics from Bambulab: https://eu.store.bambulab.com/en-ch/collections/screws?page=2&srsltid=AfmBOoqLRPkW_e9v4lnm3wgKgp8yo24CU5kq1Uxu7a0htvpn761wkvd6 As with all parts from Bambu, quality is very good and price is fine. |
| Shay:
--- Quote from: tooki on December 24, 2024, 10:49:55 am --- --- Quote from: Shay on December 24, 2024, 10:41:08 am ---Thanks for your enlightenment. I’m used to think that self tapping screws and for both plastic and wood but not for metal or aluminium. Now I know it is more like a family. --- End quote --- Was that not obvious from reading the Wikipedia article about them?! Or did you quote the article without even skimming it first? On second thought, it’s obvious you didn’t read the article at all. And to reiterate: while wood screws (and others I listed above) do technically tap their own threads, we don’t call them self-tapping because there is no need to. So we really only say “self-tapping” for the situations where both self-tapping and machine screws exist, and 99% of the time that means metal. --- Quote from: Shay on December 24, 2024, 10:41:08 am ---It seems it is easy to know on AliExpress which screw is for plastic by looking at the thread angle and pitch and that there is no tip like screw used for wood. --- End quote --- Please read the page jfiresto linked above. It goes over the types and differences. It’s not just thread angle and pitch, it’s also the minor diameter and the thread shape. Screws for plastic exist both with pointy tips and with blunted tips. A quick glance is often not enough to determine what type of screw it is, and the AliExpress listings frequently don’t actually include enough speculations to make that determination. --- End quote --- Thank you for your detailed explanation. I admit I didn’t initially grasp the nuances of how self-tapping screws are categorized and how the terminology is used in different contexts, especially for metals. The distinction you’ve pointed out makes a lot more sense now, particularly why “self-tapping” is emphasized for screws intended for metal applications where machine screws are also an option. As for identifying screws for plastic, you’re absolutely right—relying solely on visual cues like thread pitch or the presence of a point can lead to mistakes, especially with incomplete specifications on marketplaces like AliExpress. I’ll take your advice and read through the linked page to better understand the differences in thread shapes and minor diameters. |
| WattsThat:
Another US source for similar hardware is https://www.microfasteners.com/ |
| CatalinaWOW:
Just to compound your difficulties, the selection of plastic screws by material type assumes insertion in new, molded material. Properties of many plastics change with aging, and of course 3D printed objects are also different. In many cases the pull out strength required is small. If you are working on older equipment it is wise to start with a smaller size screw, displacing the minimum material. If it doesn't hold adequately you can always move up. But if the plastic breaks when trying a screw that is too large for the current material properties the repair difficulty jumps a lot. In cases where more than the typical ten insertions have occurred and the hole is stripped the classic woodworking techniques of filling or shimming can work if done cautiously. The ten insertion limit can also be extended if you carefully align the screw with the existing displaced "threads". |
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