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OT Threads: fine vs course


 
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Machine249
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PostPosted: Fri Feb 08, 2013 11:44 am    Post subject: OT Threads: fine vs course Reply to specific post Reply with quote

What is the difference between fine threads and course threads? Apart from the obvious thread count. For instance, when would one be an advantage over the other. It seems to me that course threads would be stronger and therefor more desirable. Thanks for any input or opinions.
 
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Hec In Omaha
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PostPosted: Fri Feb 08, 2013 11:48 am    Post subject: Re: OT Threads: fine vs course Reply to specific post Reply with quote

Fine Threads have a higher Tensile Strength.
 
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Dean
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PostPosted: Fri Feb 08, 2013 11:54 am    Post subject: Re: OT Threads: fine vs course Reply to specific post Reply with quote

Fine threaded fasteners provide a higher clamping force for a given torque than course threaded fasteners.

Course threaded fasteners have a deeper thread engagement and are preferred for use in soft or brittle materials such as cast iron. They are also less expensive to manufacture.

Dean
 
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TheOldHokie
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PostPosted: Fri Feb 08, 2013 12:21 pm    Post subject: Re: OT Threads: fine vs course Reply to specific post Reply with quote

Machine249 wrote:
(quoted from post at 15:44:58 02/08/13) What is the difference between fine threads and course threads? Apart from the obvious thread count. For instance, when would one be an advantage over the other. It seems to me that course threads would be stronger and therefor more desirable. Thanks for any input or opinions.

Coarse Threads:
  • Coarse threads are commonly used where rapid assembly or disassembly is required.
  • If corrosion or damage from handling or use is likely.
  • They allow for easier starting with less cross threading.
  • In relatively low strength materials such as cast iron, aluminum, magnesium, brass, bronze, and plastic, coarse threads provide more resistance to stripping than fine or extra fine threads.
  • If subjected to heat, they are less likely to seize than fine threads.

Fine Threads:
  • Fine threads are commonly used for nuts and bolts in high strength applications.
  • While applications vary, in general, fine threads are approximately 10% stronger than coarse threads.
  • They have less of a tendency to loosen under vibration because the smaller lead or thread helix angle provides better wedging action when the assembly is tightened.
  • Fine threads are also used for fine adjustment and thin walled applications due to the shallower thread height.
  • Fine threads are generally easier to tap. Since the thread height is shallower, the chip load per tooth and chip volume are lower, resulting in less tapping torque and breakage, particularly in difficult to machine materials. Less chip volume also means that more lubrication will reach the cutting teeth resulting in longer tap life.
  • Fine threads require larger tap drill than for coarse threads, which improves the performance of the drill and tap
TOH
 
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Machine249
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PostPosted: Fri Feb 08, 2013 1:17 pm    Post subject: Re: OT Threads: fine vs course Reply to specific post Reply with quote

Thanks for the repies fellas. There is some very good information here. Something for me to keep in mind when fabricating and/or restoring parts. Thanks again.
 
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Del Huebner
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PostPosted: Fri Feb 08, 2013 3:02 pm    Post subject: Re: OT Threads: fine vs course Reply to specific post Reply with quote

Very good information, just printed a copy off for my notebook.
 
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John,PA
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PostPosted: Fri Feb 08, 2013 3:54 pm    Post subject: Re: OT Threads: fine vs course Reply to specific post Reply with quote

Fine threads are most common in aviation fastners. Howevers, what makes me nervous are 'dem ultra-lights and home builders.

John,PA A&E. EXPERIMENTAL equipment is all that is necessary for placards.
 
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Maineman
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PostPosted: Fri Feb 08, 2013 3:58 pm    Post subject: Re: OT Threads: fine vs course Reply to specific post Reply with quote

Boy, thought I could contribute something here!
But, oldhokie pretty much covered it!
I will add that there are also different classes of threads. And English thread standards are different than American. And European metric threads are different than American metric threads.

Not trying to show off, just trying to use some of that knowledge I gained over the years!

Joe
 
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Machine249
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PostPosted: Fri Feb 08, 2013 8:38 pm    Post subject: Re: OT Threads: fine vs course Reply to specific post Reply with quote

That's interesting Maineman. One of the things I really like about working on these old tractors is that everything is pretty well standard. These old tractors and my Harley are the only things I don't have to go back and forth to the tool box a hundred times to get the right wrench. I restored a Farmall a few years ago and you can take those 75% apart with just a 9/16" wrench.
 
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BMACK518N
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PostPosted: Sat Feb 09, 2013 9:23 am    Post subject: Re: OT Threads: fine vs course Reply to specific post Reply with quote

There are a few schools of thought on when to use a coarse vs fine thread. Most machines are engineered the way they are around those thoughts. Being in the bolt & nut business for over 37 years I've seen people make some bad choices in fastener selection even with best advise.
TOH has listed some good points regarding thread selection for your project.
Metric fasteners are another ball game. German vs Japanese fasteners can give you up to 4 different theads for one diameter, different wrench sizes for industrial vs automotive and it's a true learning lesson figuring out the bolt hardness. I would hate to be a true mechanic these days with the added expense of tooling up to do your job. As a fastener distributor I'm use to metric conversions, as an "American" I refuse to convert anything to metric.
At the end of the day would be believe fine thread fasteners are a nickle and a dime more than coarse thread. Just my two cents.
 
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TheOldHokie
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PostPosted: Sat Feb 09, 2013 1:44 pm    Post subject: Re: OT Threads: fine vs course Reply to specific post Reply with quote

BMACK518N wrote:
(quoted from post at 13:23:12 02/09/13)
Metric fasteners are another ball game. German vs Japanese fasteners can give you up to 4 different theads for one diameter, different wrench sizes for industrial vs automotive and it's a true learning lesson figuring out the bolt hardness. I would hate to be a true mechanic these days with the added expense of tooling up to do your job. As a fastener distributor I'm use to metric conversions, as an "American" I refuse to convert anything to metric.



Having spent 25 years of my career at NIST I have learned to appreciate the various standards of the world. DIN, JIS, and ISO all have metric fastener standards and they are all different Wink And the US manufacturers pick and choose what they like from all three Wink

In all fairness the United States ANSI standard for inch fasteners isn't any better. We had American National which was replaced by Unified but we still have some AN floating around in little tucked away corners. And of course there are UN and UNR thread forms and 3 classes of fit. Not to forget at least 5 different pipe thread profiles.....

TOH
 
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BMACK518N
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PostPosted: Sun Feb 10, 2013 9:29 am    Post subject: Re: OT Threads: fine vs course Reply to specific post Reply with quote

TOH,
You are so right, our own system was in bad shape for so long before some standards were set in place. Most people will never understand the machinists side like you do. My Dad was a jet mechanic all his life and had so many specialty taps and dies that when he passed away I gave them to a friend of his that was a machinist as I had no use for them. Irony of it all I was an ADJ in my short career in the Navy. I did keep one tool as a memory and that was a pair of safety wire pliers that I still have. Some people think I was born with this flat spot on my head. My Dad put it there after misusing many of his tools such as the safety wire pliers for cutting bicycle spokes. If nothing more than respect for tools I appreciate the common sense he passed on.
 
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