Serrated Flange Hex Nut with a Slot - A good idea? 2

[Hammer335i]

Friends,

I am looking at designing a grade 5 3/8" bolt assembly that needs a 1"x7/16" slot for horizontal adjustability (force will be in tension, perpendicular to the slot). I prefer the bolt to be secured with a standard serrated flange hex nut, but I am wondering if the limited amount of flange material will be enough to keep the serrated teeth engaged with the material at the edges of the slot and not become loose over time. i dont think it will pull through the slot, I am just worried it will loosen.

has anyone had any experience with this? Does any one recommend against this or am I okay?

Thanks,

Paul

 

[CoryPad]

Will you be preloading the system to something like half the proof load? If so, lose the serrations and there should be low tendency to loosen unless your joint is subject to high forces and many cycles. You should consider deformation of the part with the slot - there are calculators to determine contact area between the circular flange and the slot to avoid yielding.

 

[Tmoose]

Can you share pictures?

Do the parts loosen now?
How direct is the load path transferring the tensile load into surfaces being clamped, and what is the thickens of the clamped parts.
How tight is the fastener? What is the tensile load ?

 

[Hammer335i]

The parts are in the design process so I don't know if they would loosen up and I don't have any pictures. I am looking to see if I get a warning like "holy cow that is the dumbest thing I've ever heard of! don't do it!

 

[desertfox]

hi Again

Hammer please don't double post, or at least if you put a post in more then one forum then generate a link to the area where you want the most of the answers.

Here is my post from the deleted thread:-

Firstly your bolt tension must provide enough tensile force to generate a frictional force sufficient enough to prevent horizontal movement from the external force applied horizontally.
So let's assume you have a slotted bracket clamped to the floor with a vertical load of say 100N, if the coefficient of sliding friction at the base of the bracket is say 0.25, then a horizontal force of just over 25N will move your bracket even if you put a serrated washer under the nut at the top side of the bracket.
Secondly you need to calculate the surface area that the nut and washer are located on and divide this area into the tensile bolt force, the resulting compressive stress will tell you whether or not you've embedded the nut and washer into the top of the bracket, if embedment occurs you won't achieve the required tensile bolt load.
If you can provide some in depth information about the joint in question we might be able to help you further.

 

[paddingtongreen]

This type of connection is used in structural steel buildings and structures quite regularly using structural bolts with hardened washers, even in slip critical connections. I see no problem here with the bolt. I assume that stresses on the plies are fully compliant.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[Tmoose]

What is the tensile load in lbs or kg or stone?

How direct is the load path transferring the tensile load into surfaces being clamped.

http://www.spx.com/en/images/full20_21712CombiPro-standard-left.jpg

http://www.parts-recycling.com/Auto...1510-7-5HP-8-centrifugal-water-pump-photo.jpg

What is the thickness of the clamped parts.

http://www.mason-industries.com/masonind/_doc/pdf/h610v8.pdf

http://i01.i.aliimg.com/photo/v5/533845601/Stable_G3LM_Foot_Mounted_Helical_Gear_Motor.jpg

http://www.asia.ru/images/target/photo/50569629/DC_Traction_Foot_Motor.jpg

How tight is the fastener?

 

[Tmoose]

What is the OD of this flanged nut?
I am not at all comfortable tightening a nut that is supported only by two parallel edges to secure components I care about. Well, maybe it would be OK it it was a decorative panel attached to a slotted main structure of a cheap welding cart, etc from an overseas supplier. Even then I've been known to take all the supplied split lock washers and throw them in the trash, and assemble the cart with flat washers.

As others said I'd put a "large" "thick" washer between the nut flange and slotted part.
I put my efforts into specifying and applying sufficient clamping force to resist both loosening and even more important, shielding fasteners from load variations that cause fatigue failures.
I don't put much faith in anti-rotation devices, except possibly to make a bolted joint "fail safe" short term. A nylock nut could provide several rotations of resistance to spinning off if, due to improper installation, it loosened in service.
If forced to use a serrated nut I might include a feature on the large thick washer in a desperate attempt to keep it from rotating, removing that excuse for the serrated nut's eventual loosening. Maybe a flat on one edge of the washer to rest closely aligned to surface on the slotted component, parallel to the slot. Or Maybe an Oliver J Dragon tooth on the washer to engage the slot.

 

[paddingtongreen]

Peculiar opinions but nothing to quote.
The specification that covers structural steel joints in the USA is the RCSC Specification for Structural Joints Using ASTM A325 and A490 Bolts. Scroll down to section 3 to find when slotted holes are acceptable, Pretty much any time the shear is perpendicular to the slot. Link

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[paddingtongreen]

First sentence should have read, "Peculiar, opinions but nothing to quote."

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin