Studs & Nut Standards for Stripping Nut

[SalCas]

Good day everyone,

I would like some support regarding standards between bolts and nuts to see if I can fix an issue I'm having at the moment. The issue is that on a plastic base with 4 studs "perpendicular" to the base keep getting its nuts either stuck or the nuts end up breaking the stud when trying to remove them. They're both 18-8 stainless steel and both have an M8x1.25 thread. The issue here that I believe is causing this is the fact that the studs aren't entirely perpendicular to the base, they're slightly angled, varying from 87 to 89 degrees, all leaning to the same side. Now, the tool we utilize to assemble the nuts is fixed to be perpendicular to the ground, this in conjuction with the angles of the studs, is most likely what's causing my issues with the stripping nuts.

I follow drawings that call out specific dimensions and the supplier of the bases also follows one for this same base, and the drawing doesn't call out any sort of perpendicularity on the stud, so adding some form of standard here or having a guide to follow to call out some sort of tolerance that exists already would be very helpful.

I would like to know if there's any standard or guide out there that I can follow regarding bolt/stud perpendicularity or anything that can solve my issue, the base is a molded plastic that wraps around the base of the studs, and during the cooling process is when the studs all tend to lean over, causing these angles on them.

Thanks in advance.

 

[chez311]

How are these nuts/studs being driven in/out? Stainless on stainless fasteners will gall and seize very quickly when driven without lubricant or coatings, especially when driven at high speed (

https://www.youtube.com/watch?v=TQGM3Tip53g

). They likely start galling to some degree even when any amount of static torque is applied. I am very skeptical that perpendicularity is your only issue here.

I would like to know if there's any standard or guide out there that I can follow regarding bolt/stud perpendicularity or anything that can solve my issue

Not likely. Does the drawing have geometric tolerances applied like position? If so position controls perpendicularity within the specified position tolerance. Either way - revise the drawing and either apply your desired perpendicularity tolerance/refinement.

 

[SalCas]

We are using a high speed driver, similar to a Dremel tool, but larger. Its mounted in a specific manner that it stays upright with the die facing down, so its very likely that the galling is happening due to this, upon looking back, it seems that these issues started becoming more common after we applied this assembly method to our manufacturing process.

Now, seeing the video you sent I can say that that finish definitely would help on the mechanical side of things, some antiseize might also be a possible solution, but the issue is that these studs will undergo high currents, so I'm not sure how both of these options would fare against this, of if they will interfere.

 

[chez311]

You're probably talking about a DC Nut Runner or similar. They can get up to blinding speeds - I've even seen galling issues when switching to these high speed methods before because production wants to crank them up as high as they can go, turn them down a bit and voila issue solved.

Your case is a little more troublesome as slowing the speed down will absolutely help but will not solve it altogether - you're probably going to have some amount of galling issues even if you run them down by hand. It might not even be during assembly but upon removal during service where you notice it as during assembly you were able to apply enough dynamic torque to overcome it. This might be acceptable, but if possible a lubricant, thin film coating*, or at the very least using different grades of stainless on the nut and bolt. Also not sure how critical this connection is, but keep in mind that galling essentially increases your thread friction thereby decreasing your preload.

*I didn't mean to endorse the specific one in the video - theres a multitude out there, usually PTFE based, I doubt anything PTFE based would have any electrical effects but that would be something to discuss with the coating suppliers.