When is it necessary to incorporate a tapped hole versus a drilled hole?

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Discussion Overview

The discussion centers around the necessity of incorporating tapped holes versus drilled holes in mechanical assemblies, particularly in contexts where components may be disassembled and the material properties of the components are considered. The scope includes practical applications and considerations in engineering design.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants suggest that threaded holes are preferable if the assembly will be disassembled regularly, as they can simplify assembly and reduce part count.
  • Others argue that threaded holes may be necessary if the base material is soft or if there is insufficient material to support threads and bolt pull-out strength.
  • One participant questions the relevance of vacuum conditions, seeking clarification on whether threading is required for sealing or if it relates to the holding mechanism of nuts and bolts.
  • Another viewpoint emphasizes that using a bolt/nut assembly can be advantageous in terms of repairability and the ability to use stronger fasteners than the base material, particularly when considering the distribution of forces and potential stripping of threads.
  • It is noted that threaded holes are often used in situations where space constraints limit the use of nuts.

Areas of Agreement / Disagreement

Participants express differing opinions on the necessity of threaded holes versus nuts and washers, with no clear consensus reached. Various factors such as material properties, assembly frequency, and repair considerations are debated.

Contextual Notes

Participants mention specific conditions under which either method may be preferred, but these conditions are not universally agreed upon, indicating a reliance on context-specific factors that may vary by application.

Who May Find This Useful

Engineers and designers involved in mechanical assembly, materials selection, and fastener design may find this discussion relevant to their work.

EulersFormula
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If I need bolt holes drilled into a component and I have nuts available, is it ever necessary to have the machinist thread the holes if the system will not be exposed to vacuum conditions?
 
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Yes.
If your assembly will be disassembled regularly, I like to have threaded holes, not nuts+washers.
If you wish to reduce the part count of your assembly.
If the amount of material is not sufficient to support threads and bolt pull-out strength.
If the base material is soft (like aluminum) and would be subject to eventual thread damage.
I'm sure there are many other reasons.
 
What significance is the vacuum conditions? Are you threading to create a seal, or is there some reason I do not understand, in how a nut and bolt hold, that requires vacuum?
 
If parts are cheap and labor is expensive (as is usually the case), or if the force which the fasteners are withstanding is fairly high, I would suggest a bolt/washer/lockwasher/nut assembly. The washer distributes the force over a wider area on the surface (sparing the part) and the lockwasher keeps the nut from unthreading due to vibrations. There are two advantages to this setup:
1. If the thread strips on either the bolt or the nut, you can change those rather than drilling out the threaded hole and retapping it or resorting to expensive helical inserts.
2. You can use stronger fasteners than the base material, assuming relatively small shear forces or enough distance from the bolt to the next component or the edge of the plate (so that the plate can withstand the shear forces).

Where I work, we usually use threaded holes only where there is only enough space on the other side for a low-profile nut (which, with a threaded hole, can act as a locknut), or not enough space for anything at all.
 

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