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elisua
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What is stronger and better for continuous movement? Screws or pins for a mechanical component made of titanium Ti-6Al-4V
In summary, screws and pins are both fasteners used to join materials, but they serve different purposes and offer distinct advantages. Screws provide strong, threaded connections that allow for adjustable tension and are suitable for applications requiring a tight fit. Pins, on the other hand, are typically used for alignment or to secure components in place without the need for a threaded hole, offering ease of assembly and disassembly. The choice between screws and pins depends on the specific requirements of the application, including load, strength, and ease of maintenance.
- #2
berkeman
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Welcome to PF.
Do you mean bolts (or machine screws) versus pins? Can you be more specific in what the fastened joints look like?
Do you mean bolts (or machine screws) versus pins? Can you be more specific in what the fastened joints look like?
- #3
elisua
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This is a design concept for a fully titanium mechanical device that will be implanted in a patient. It needs to be determined in screws or pins could be placed where I highlighted in red. For purposes of being able to sustain patient daily motion, weight, torsion, I'd want to get some insight to see if overall it would be better to use screws instead of pins.
Still this is in the design concept phase, but just want to know do that I move forward in the best possible way.
Still this is in the design concept phase, but just want to know do that I move forward in the best possible way.
- #4
Bystander
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- #5
Benjamin Calloway
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As far as weight and torsion capabilities, a cylindrical pin and the unthreaded shank length of a bolt have the same geometry, so both would be acceptable in that respect. The reentrant edge of a screw or bolt with a flanged head would cause a stress concentration, so if that's a concern, you might choose to use some unflanged pin. As far as sustaining cycles from motion, vibration, etc., that depends on how you'd plan to secure the pin or bolt. Pins are more readily able to be permanently secured from what I've seen.
- #6
berkeman
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Thanks for the drawing. I'm pretty familiar with human A&P, but I'm having a hard time picturing where I would place that in a patient (Pt). Can you say more about the application? What are the expected stresses on those pinned joints? What is the range of motion for those joints? What is the mechanism of lubrication of those moving joints?elisua said:
And what medical safety standards are you designing this to? 14971, 10993, 62304, and 13485?
https://www.in2being.com/iso-medical-device-standards/
- #7
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If you use a shoulder bolt, there is no real difference compared to a pin. The shoulder bolt is just a pin with its own locking mechanism. The real question is therefore: How will the pin be secured and how does this locking and positioning system compare with a screw and nut?
- #8
berkeman
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Except a pin cannot loosen once it is flanged, right? A bolt can loosen unless it uses a lock washer or similar add-on. Still, I'm not sure how this all applies to implanting this inside a Pt and the medical safety standards...jack action said:
- #9
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How are those flanges made or held in place though? A rivet? Interference fit? A circlip? A cotter pin? A set screw? A nut on a threaded end is just another way of locating the pin.berkeman said:
If I understood the drawing correctly some sort of clevis pin is needed (Should it be allowed to rotate?), not a bolt or a screw. The locating mechanism is really what needs to be determined.
https://en.wikipedia.org/wiki/Clevis_fastener#Clevis_pin said:
- #10
Flyboy
Gold Member
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… huh. Is it possible to TIG weld the pin ends in place before implantation? Or is that connection one that must be made during the procedure?
FAQ: Screws versus pins
1. What are the main differences between screws and pins?
Screws are fasteners that are designed to create a strong, permanent connection by being threaded into materials. They provide a clamping force and can be easily removed and reused. Pins, on the other hand, are generally used to align or hold parts together temporarily. They do not provide the same level of clamping force and are often used in applications where parts need to be disassembled frequently.
2. When should I use screws instead of pins?
Screws should be used when a strong, permanent connection is required, especially in applications that need to bear weight or resist shear forces. They are ideal for joining materials where a secure hold is necessary, such as in woodworking or metal fabrication. Pins are better suited for applications where parts need to be frequently assembled and disassembled, or where alignment is more important than a strong hold.
3. Are screws stronger than pins?
Generally, screws are considered stronger than pins because they create a tighter grip through their threading, which allows them to withstand greater loads and resist loosening over time. Pins, while useful for alignment and temporary connections, do not provide the same level of strength and are more prone to shear failure under heavy loads.
4. Can I replace screws with pins in my project?
It depends on the specific requirements of your project. If the application requires a strong, permanent connection, replacing screws with pins may not be advisable as pins do not provide the same clamping force. However, if the application is more about alignment or allows for easy disassembly, pins can be a suitable alternative.
5. What are the common types of screws and pins used in construction?
Common types of screws include wood screws, machine screws, sheet metal screws, and self-tapping screws, each designed for specific materials and applications. Common types of pins include dowel pins, cotter pins, and clevis pins, which are often used for alignment and temporary fastening in various construction and mechanical applications.