Winch Bolts

[proskier101]

if he has to buy new bolts why not just buy grade 8 anyways????

its an upgrade so why not do it?

 

[Stumpalump]

if he has to buy new bolts why not just buy grade 8 anyways????

its an upgrade so why not do it?

Urban legend that grade 5 will strech or flex more before breaking I guess.

 

[CJ~Abuzer]

I have the Smittybuilt XRC8 and it has been installed on a C4x4 trailblazer bumper since September of 2007. It has been used numerous times since then, on vehicles ranging from Wranglers to 3/4 ton FS Chevys, and even a 1953 panel on 44s. I mounted it with the bolts that accompanied the winch and I have never had an issue.

 

[5-90]

Urban legend that grade 5 will strech or flex more before breaking I guess.

If it's an "urban legend," i've verified it experimentally.

"Strong" in steel also comes out to mean "brittle" - meaning that the more you harden a fastener, the more "dramatic its failure mode becomes" (less stretching, more snapping.) Look up stress/strain plots for steels of various hardnesses or various strength specifications, you'll see what I mean.

Washers are graded like bolts - but there are also washers that are just listed as "hardened" - they're usually black oxide coated, and about three times as thick as the regular flat washers. If you can find those (check an MRO house,) they're what you want.

I will, however, go with not getting bolts from China - they still haven't got the hang of heat treatment. Japan, Germany, Taiwan, and - oddly - England make about the only offshore screws I like to use. Hong Kong isn't too bad, but I'd put it somewhere between China and Taiwan.

Japan, Germany, & Taiwan usually "through-harden" their fasteners, vice the more typical "case harden" that is being referred to (with the "surface harden only" you see when you grind through.) Case hardening has its uses - but it's not here. You case harden when you need high surface strength with high inner ductility - with winch mounting, you need full strength all the way through the body of the fastener.

 

[Stumpalump]

Shear and tension strength is greater on grade 8. When would ever using a grade 5 be better than using a grade 8 except in cost?
http://www.rockcrawler.com/techreports/fasteners/index.asp

 

[proskier101]

the only thing i get about the argument against grade 8 is that when they break they REALLY BREAK! (kinda like steel winch line vs synthetic)

at least thats what i got out of 5-90 first paragraph


but what is the breaking point? how much higher than grade 5? sure people have bent grande 5 and broke grade 5 abd it saved something and caused less stress...but how many acutally broke or bent grade 8?

 

[BADaXJ]

FWIW, i use grade 8 on pretty much everything, including my winch. i have yet to even come close to a failure on any of them... i have yet to even see one bend. if my winch bolts fail, the fairlead mount is going to slow it down and i don't think it'll go too far. if it were me i'd go grade eight. there is plenty of merit to what 5-90 is saying but i'd rather avoid the failure in the first place than have a mild failure. plus, grade fives rust and strip out sooner in my experience which is a big factor for me up here in the rust belt. nothing more frustrating than trying to remove a rusted grade 5 only to have it relatively easily twist right off leaving the rest in the nut.

 

[Tommy4949]

You also said that the washers are deformed and being pulled into the mounting holes in your bumper, are those holes alot bigger than your mounting bolts?

They had no side to side play, but the holes in the bumper are slotted. I slide the winch all the way forward so I could get the grill assembly back in and out easier. They started pulling through on the back side of the winch though the slot.

 

[BADaXJ]

sounds like the washers pulled through and then things loosened up. get a couple different size hardened washers and stack them in a pyramid fashion so they will be stonger.
(smallest one against the head of the bolt, biggest one against the slot)

 

[5-90]

the only thing i get about the argument against grade 8 is that when they break they REALLY BREAK! (kinda like steel winch line vs synthetic)

at least thats what i got out of 5-90 first paragraph


but what is the breaking point? how much higher than grade 5? sure people have bent grande 5 and broke grade 5 abd it saved something and caused less stress...but how many acutally broke or bent grade 8?

Without actually looking it up (honestly, I don't feel like digging out that notebook right now...) I seem to recall that the SAE5s are H&T to 150ksi, and the SAE8 to 180ksi. That's 150,000 or 180,000 pounds per square inch for ultimate tensile strength - the elastic limit will be somewhat lower, and the ultimate shear strength is usually considered to be about 75% of that (or 112.5ksi/135ksi.)

Why do I call out per square inch so sharply? Because not many threaded fasteners have a cross-sectional area of exactly one square inch. Typically, you calculate the area using the minor diameter of the threaded portion (unless you're loading in shear, and loading "on the grip" - or unthreaded shank end.) For, say, a 3/8"-16 screw, you're looking at a minor diameter of 5/16", or .3125" (nominal.)

The tensile stress area is then ~.0767 quare inches, so the tensile load that may be applied (as an absolute figure) is ~11,504/13,805 pounds per bolt.

Therefore, multiply by four (four bolts,) and you get 46,016/55,220 pounds of tensile stress, or 34,512/41,415 pounds of shear stress (over all four bolts.) That's assuming the bolts are loaded in "single shear," instead of "double shear" (two shear planes through the shank, instead of just one.)

Most winches aren't even rated that high, using the SAE5 numbers. Yes, you're looking at the preload on the fastener (at what, 35 pound-feet? That means that the fastener is "preloaded" to something like 20% of its ultimate strength, assuming a 3/8"-16 thread. So, that's 36,812/44,176 pounds in tension, or 27,609/33,132 pounds in shear. Still doing well...)

So you see, we're still doing well with fastener strength. Yes, you have more overage using SAE8 instead of SAE5 - but failure modes are more drastic for harder steels - which is why I'm not suggesting them, or just "backing them up" with SAE5 screws. Assuming you're torquing the SAE8 screws in opposite corners to 35 pound-feet, I'd torque the SAE5s to about 30 pound-feet - the SAE8s should still fail first (since they're bearing the brunt of the load,) but the SAE5 bolts will still have room to stretch while the SAE8s are snapping. You can use SAE8 nuts and hardened washers all around, since it's the bolts that are loaded, and the bolts that will fail first.

I know this is a lot - but it's the "simple" version, as I don't have my references to hand and I'm about to head out the door...

 

[Tommy4949]

Without actually looking it up (honestly, I don't feel like digging out that notebook right now...) I seem to recall that the SAE5s are H&T to 150ksi, and the SAE8 to 180ksi. That's 150,000 or 180,000 pounds per square inch for ultimate tensile strength - the elastic limit will be somewhat lower, and the ultimate shear strength is usually considered to be about 75% of that (or 112.5ksi/135ksi.)

Why do I call out per square inch so sharply? Because not many threaded fasteners have a cross-sectional area of exactly one square inch. Typically, you calculate the area using the minor diameter of the threaded portion (unless you're loading in shear, and loading "on the grip" - or unthreaded shank end.) For, say, a 3/8"-16 screw, you're looking at a minor diameter of 5/16", or .3125" (nominal.)

The tensile stress area is then ~.0767 quare inches, so the tensile load that may be applied (as an absolute figure) is ~11,504/13,805 pounds per bolt.

Therefore, multiply by four (four bolts,) and you get 46,016/55,220 pounds of tensile stress, or 34,512/41,415 pounds of shear stress (over all four bolts.) That's assuming the bolts are loaded in "single shear," instead of "double shear" (two shear planes through the shank, instead of just one.)

Most winches aren't even rated that high, using the SAE5 numbers. Yes, you're looking at the preload on the fastener (at what, 35 pound-feet? That means that the fastener is "preloaded" to something like 20% of its ultimate strength, assuming a 3/8"-16 thread. So, that's 36,812/44,176 pounds in tension, or 27,609/33,132 pounds in shear. Still doing well...)

So you see, we're still doing well with fastener strength. Yes, you have more overage using SAE8 instead of SAE5 - but failure modes are more drastic for harder steels - which is why I'm not suggesting them, or just "backing them up" with SAE5 screws. Assuming you're torquing the SAE8 screws in opposite corners to 35 pound-feet, I'd torque the SAE5s to about 30 pound-feet - the SAE8s should still fail first (since they're bearing the brunt of the load,) but the SAE5 bolts will still have room to stretch while the SAE8s are snapping. You can use SAE8 nuts and hardened washers all around, since it's the bolts that are loaded, and the bolts that will fail first.

I know this is a lot - but it's the "simple" version, as I don't have my references to hand and I'm about to head out the door...

Wow thanks a lot. Assuming you are correct in your calculations, if not the exact numbers, I have just learned a great deal in just this one reply. I have always believed you can read more in a short mathematical formula than in a whole page of written words, if you affluent in the language of numbers that is.

 

[5-90]

Wow thanks a lot. Assuming you are correct in your calculations, if not the exact numbers, I have just learned a great deal in just this one reply. I have always believed you can read more in a short mathematical formula than in a whole page of written words, if you affluent in the language of numbers that is.

You're welcome. I'm fairly sure the basic numbers are accurate - but I know the maths are accurate, even if the numbers are not, so it still shows the process (I did learn in Logic years ago that "A correct conclusion drawn from a false premise is false." The numbers I used were more for illustrative purposes than anything else.)

Just remember to use the minor diameter of the threaded fastener (diameter at the thread root - another reason I picked 3/8"-16. It's easier, and I know offhand that the minor is 5/16"...) when calculating tension and stress loads, with the caveat that loading a fastener in shear "on the grip" is both effectively stronger (no thread groove) and physically stronger (more material.) However, it does take a bit more design to accomplish, usually.

 

[Stumpalump]

Hey 5-90, Can you refresh us on whats the best to use as far as fine vs coarse threads go and when to use them?

 

[5-90]

Hey 5-90, Can you refresh us on whats the best to use as far as fine vs coarse threads go and when to use them?

I could assume you're being a smartass, but there are some who would benefit...

Fine threads tend to be stronger (larger major diameter) from a point of tensile or shear stress, but the threads - being thinner at the root - can pull out more easily. Fine threaded fasteners should only be used in wrought stock or in combination with nuts (castings? Don't bother.)

Coarse threads are for castings, or for other materials with an amourphous grain structure (this includes wood - note that wood screws have a fairly coarse thread pitch.) Coarse threads can also be used for fasteners that need to be removed relatively often, since it's less work to back out an inch of 18-pitch threads than an inch of 24-pitch threads.

This doesn't even take into account the various "special" pitches - UN8 (8tpi,) UN12 (12tpi,) UN16 (16tpi,) or UNEF (UNified Extra Fine) or UNEC (UNified Extra Coarse.) These tend to have specific industrial uses.

And, different thread forms - like Acme (power transmission and clamping. Check the operating rod on your bench vise - I'll bet it's an Acme thread,) square thread (extra-heavy-duty power transmission,) buttress thread (one-way clamping - steep on one side, gentle on the other,) Whitworth (55* included angle with rounded crest and root, vice the 60* Unified pattern with sharp crest & root,) and the like.

Short form? Use fine threads when you're going to thread into a nut, or when you're forming a hole in billet stock (like machining from a bar or plate that was rolled to form.) Use coarse threads in cast stock, or when you need to install and remove relatively often.

There's a reason that the U-joint strap screws at the axle are 1/4"-28...

 

[WB9YZU]

I have never had a winch bolt come loose, and they are grade 5.

Winches should be mounted so that the bolts are in sheer, not stretch. So instead of "Face" mounting it like I have seen folks do:

|O------------->

The whole thing should be mounted in sheer as thus:
O-------------->
---

You could also do this as it puts the bolts in neither stretch or sheer:
O|-------------->

The holes should be the size of the hardware. Washers should be there to prevent the bolt from digging into the base metal, not to make up for too big a hole/too small of hardware. Torque hardware to manufactures specification.

If you decide to use Grade 8 hardware, there is no downside except a very minor cost difference.

Ron

 

[Stumpalump]

I could assume you're being a smartass, but there are some who would benefit...

.

Never have and never will be a smart ass on the tech forums or when sombody genuinly needs help. I kinda had the basics but thought this would be a perfect place for you to explain it best and expand any general knowlege we had. So if I want threads in a piece of square 3/16 mild steel tube to bolt a skid plate to I should use fine threads. Thanks

 

[5-90]

Never have and never will be a smart ass on the tech forums or when sombody genuinly needs help. I kinda had the basics but thought this would be a perfect place for you to explain it best and expand any general knowlege we had. So if I want threads in a piece of square 3/16 mild steel tube to bolt a skid plate to I should use fine threads. Thanks

I wanted to make sure - you do, after all, have something of a reputation (not what I've heard from others, I try to form my own opinions...)

You are essentially correct. That said, however, bear in mind also that the rule of thumb is a minimum of three threads' worth of engagement (on a 5/16"-24, you want a bare minimum of 1/8" wall thickness to work with) to not need a nut. Of course, this will increase based upon various loading factors - how much tension you expect on the join static weight, et al.

Better still is one full diameter (nominal) of engagement - using the 5/16"-24 example above, you want 5/16" of wall for serious loading (major tension load, mainly. Compressive is less of a problem anyhow - since the screws locate the thing in that case - and shear depends mainly upon screw minor diameter.)

Yes, this applies to wrought stock (mill-rolled structural shapes, mainly.) If you're working with cast stock (with an amourphous grain structure,) you're looking at one-and-one-half to two full times the nominal diameter of the fastener, if you're threading into the part (full engagement through the body of the nut, if you're using a nut, with wrought or cast stock. Two nuts' worth if you're using jam nuts, since they're thinner than full hex nuts.)

I gotta do that fastener primer I'm thinking about one of these days. BillAVista did a good job on his, but it could use expanding and a little more "simple engineering" could be presented with the work, I think.