just curious-

from an engineering standpoint... Which has better holding power, fine thread (NF) or corase thread (NC) ? What pro's and cons do both have?

Thanks in advance

 

guess theres no specific answer.

fine thread it is!

 

Interesting...there are two ways I can think of to look at it.

1) Fine threads are weaker because, since there are more threads there are more stress concentrations, therefore rendering it weaker. However, there is probably a fillet between the side of the thread and the bolt. A thread isn't completely squared, rather takes on more of a teepee shape (for lack of a better way to describe it).

2) Fine threads are stronger because, even though there are more threads and the possibility of more stress concentrations, if these stress concentrations are not very prevalent, then there are more threads to take the load applied to the bolt.

All in all, I remember 100% that you do not want shear force applied to a bolt. Tension is the best type of stress a bolt can see because that's what they're designed for.

Hopefully that makes some sense. Doubtfully though

 

There is no specific answer because there is not enough information. Determining which thread series to use depends on a bunch of things like, what material is being used, length of engagement , wall thickness, design of the part........ there are a lot of things to consider.

 

There are a "lot of things" to consider, but I will share my rules of thumb.

Fine thread bolts of the same size, typically have a larger thread root diameter. Hence they have a larger minimum cross section, and are stronger.... if you have a nice material to thread them into, like steel. If you are going into aluminum, I choose coarse thread, due to the fragility of small aluminum threads, and their propensity to gall and strip out. I use coarse thread in cast iron due to grain size effects.

Coarse thread will distribute the stress better into a threaded aluminum plate, fine thread will try to load all the stress into the first 2 or 3 threads, the neck down of the coarse thread will give a little and put the stress into the first 3 or 4 threads... that little change can add a lot of life to the joint.

Run some finite element analyses of a bolted joint and you will see what I am talking about.

 

with us.. i keep sucking the threads right out of the block with my tranny bolts... so grade 8 bolts are stronger than cast aluminum... is that what you were asking? hehe

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BigMoose &raquo;</TD></TR><TR><TD CLASS="quote">
Run some finite element analyses of a bolted joint and you will see what I am talking about.</TD></TR></TABLE>

Good call on this one. Run some FEA if you have access to a program and see what you come up with. You can vary between coarse and fine thread, and vary the load too if desired.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ****** &raquo;</TD></TR><TR><TD CLASS="quote">

Good call on this one. Run some FEA if you have access to a program and see what you come up with. You can vary between coarse and fine thread, and vary the load too if desired.</TD></TR></TABLE>

I dont have access to such programs wish I did though!

Most of the load is axial, with very minimal transverse load applied. The material is aluminum.

I appreciate all this input - it makes me want to go bug my university to get some new better engineering teachers.... dont get me started with the engineering program we have

Thanks for all of your replies!