question on the fine threads

[caseydog]

Being a retired mechanical engineer as I work on items I ask the question why did they design this that way, guess it is a curse of the profession. I am intrigued by the use of fine threaded bolts on the older tractors. My experience has been only a 51 VAI, 52 DC and now 42 SC, but I find time and again the use of fine threaded fasteners. Any one have an opinion on why they used them so much as in my years of engineering I hardly ever specified fine thread fasteners. I do know after they have set for many many years they are tough to get lose.
Thank you for any opinions

 

[oldproudvet]

In the aviation/high performance/older automotive world fine threaded fasteners are a higher quality (in the sense of ability to hold torque) similar to a grade 8 bolt. Fine thread is always used in high stress connecting rod fasteners, for example, where the bolt will stretch to give you the needed clamping power. So it's not the simple squeeze of the nut. (they are not reusable for that reason) Torque charts will show the difference in the clamping power (not the right word I know). Ford, back in the 30s was always known for their light weight frames they were able to use because of the quality of their steel. They introduced tungsten into the steel mix in the teens for their model T frames. The majority of their fasteners in any critical location were always fine threaded high quality fasteners. Newer manufacturing techniques don't require this type of fastener for production materials......My 2 bits, w/o digging into the old files for proper research. I'm sure many opinions will surface here.......

 

[DKase]

I can understand the National Course, and National Fine. The fine threads do hold more, but why so many different sizes? Take for instance the 3/8 bolt size. It can come in 17 different thread pitches. 10,14,18,20,22,26,27,28,30,32,36,40,48,56,64,72,and 80 threads per inch! Why? That is just nuts!

 

[case1939]

Case used a lot of fine threads bolt's on a lot of there implement's also.

 

[RJKeith]

Fine threads are also called SAE (Society of automotive engineers) threads. My guess is the shallower slope of the thread means more force on the nut/bolt to work loose. Sine of the angle of the thread is smaller.

 

[Bhunt]

I worked 30 years on aircraft nothing but fine thread fasteners & rivets. Old is absolutely correct fine thread has a higher load rateing and fine thread is less likely to come loose. Yea im reworking an sc there are numerus different thread pitch configurations throughout it. Interestingly enough the head studs have course thread in the deck and fine thread on the head.The front implement clamps are course in the chassis and fine in the clamp.
Byron

 

[oldmisterbill]

Years ago we were having problems with a machine at work. Our suppliers were Bowman fasteners. They wanted to give a 1day course on installing fasteners(nuts & bolts), !st thought whats the big dealon putting a nut on a bolt? Well itsmostly about clamping force. They had a hydraulic cylinder with a hole in the center allowing us to tighten a nut&bolt and measure how tight it clamped. After 7 hours we weren't bored at all learned steady for 7 hours about "tightening a bolt" Definatley mor clamp pressure from a fine thread. Lube a thread and it will tighten better under the same torque,will not loosen as easy,every time a nut and bolt is reused it looses clamping force. Now I lube almost every thread I install. No nylock nuts (equal to a grade 2) more than we can write about on this forum. But if you want a quality fastener that will hold use a fine thread. And for us "olds" clamp force is correct.Yes grade is important and also watch for "counterfit fasteners coming form over seas withfake logos on the head. Logos are trade marks and also warrenty the quality of the fastener. Buy your fasteners from a reputable supplier. BE safe!! A poor quality fastener can be deadly. Mr Bill

 

[oleclint]

Fine threads on Case s. It seemed to me that it was very stupid of the engineers to use fine threads on the battery cover lid on DC tractors. Maybe other models too. Nothing special needed for strength there. Let a little battery acid run down on them , then fight the fine thread wing nuts to remove them. No wonder the battery never got checked until it went dead. Rant over. clint