whit3rd wrote in news: snipped-for-privacy@googlegroups.com:
>> > On Friday, July 5, 2019 at 2:28:08 PM UTC-4,
>> > snipped-for-privacy@decadence.org wrote: ...
>
>> > Our lead tech has banned 1/4-20 from the shop floor in favor of
>> > 1/4-28.
>
>> * makes a lot of sense; holds better - so well that one would
>> think they would be reliable even in 1/8 steel panel (never tried
>> them in that thin of a panel.
>
> Doesn't make much sense, to me; that's a NF thread (NC is the
> 'standard') and can be jammed up by a tiny bit of grit, or minor
> thread dent. There's a REASON for coarse threads, and associated
> loose tolerances, in a variety of applications (like a clamp,
> where tightening the thing by a quarter inch can take five turns
> of a quarter-twenty, but seven of a quarter-twentyeight).
>
> If your shop were dealing with rust and sandblasting, the fine
> threads would drive you crazy.
>
You are one of the most accurate posters here.
I built hyper-hypothermia machines using stainless construction, but they bought regular zinc plated 1/4-20 x 1/2 screws that had six strikes on the head, but the friggin things twisted off like taffy. NOT grade 8 by any stretch.
My dad worked at Milacron, so I knew what a grade 8 bolt worked like.
These weren't it. The right stuff will SNAP OFF, and after a lot of overtorqueing. These were 'cheap chinese'. They didn't like me much after I told them they were ripped off, and it turned out that it was the VP of the place that made the buy.
I would use fine screws for rack modules and lab gear. Not field gear or say for the bot contest assembly stuff.
Coarse or fine threads... I would rinse clean any dust or grit blast media before putting a threaded screw with a threaded hole if it were at all possible. We used a really good brominated solvent that left zero residue.
I would take the extra moments to make a clean assembly using either pitch.