[just_cruizin]

Don't forget when using 2 points you have to de-rate them for the angle of the pull.

On Zook-Fan point about other vehicles, that really is irrelevant as the mass/momentum of the Recovery is limited to the lightest vehicle. What does need to be considered though is the suction force on a stuck vehicle. Can be multiple times the mass of the vehicle.

Getting testing is the critical point here. I had the bolts I make for the body lifts tested for purely that point. You done need to get more then one item done though.

[frak]

Many moons ago i studied mech engineering (and became a computer programmer of course!) Of which engineerimg design was a large chunk as you would expect.

You comment about safety factor (2.5 i think it was) gave me a funny feeling as from what i remembered that was around what you use for a more static load.

I dont have my deisgn text books handy given i am in melbourne right now for work, but i suggest looking at this link which gives some standard factors of safety for various things
http://www.engineeringtoolbox.com/facto ... _1624.html

They suggest 9 as the fos for a lofting hook for example whichbis morr what i was expecting you to say.

I goimg to assume that that you are calculating stresses on bolt holes and welds etc. (In which case apologies for stating somebobviousnthings though really just some highlights)

As for tearimg at then chassis (ie crush failure aroumd the bolt hole that looks like a tear) failimg that way it can be dealt with bu longer plates and more bolts. If people worry about faulure of the chaasis rails itself they gets more complicated of course.

The stesses from two points is pretty big and more so the closer to the points the mid point of the triangle is when ising both at once. Basic truss design calcs as was pointed out the two angled tensile stresses will create a compressive load between both chassis rails.(assuming cable from both points point in of course)


Makes your design job harder. Lot of people dont think about this in practice

Would be less risk for you to sell single tow hooks with two mount options and clearly state designed for use singly (could be stamped on it in fact)

At least then when somebody uses a terribly shallow angle and translates a single 3t tow force into a 10t compressive load between the rails and bends their chassis and/or tour tow hooks it is harder for the lawyer to successfully blame you.

Hope that makes sense and good luck with it.

[frak]

Oops bolt hole failure tear would be a tensile failure. Squashimg the bolt would be compressive failure. Snapping bolt would be sheer failure. Been a a while and hadnlate night last night...

[30ONA]

Thanks Frak. FOS 2.5 is with one point, it is 4 with two points. But a test could prove otherwise. Also this FOS could be well above what the chassis can take. I currently have then mounted behind the front body mounts so to force the two trails together in a twin connection recovery, you would need to bend the one odd the chassis, bend the cross member and the body. I'll look at a long crush tube but I don't think it necessary. I have crush tubes in the chassis already for the mounts.

I also have three bolts at the moment, this is without drilling any new holes as that was part of my scope. 2x M18 grade 8.8 and 1x M16 grade 8.8

[got_bar_work]

My suggestion would be look at making plates that standard hooks could mount to. I would want a hook to open up or snap over a plate with a hole and shackle to rip out of the chassis still attached to the end of the strap. I wouldnt even think of 2 mounts unless it comes with a new crossmember. There is no strength in the end of a gv chassis.
U could feed a big plate with tapped holes down the end of the chassis opening . That way its a plate ever side of the chassis wall . Bolts are only in tension then . Friction of the clamping plates is what is holding sheer.

[30ONA]

Yes. But requires drilling of the chassis.

[got_bar_work]

Nothing wrong with that. That part of the chassis is doing sfa but holding a bumper and is going to be sandwiched betweeen 2 thick steel plates . Its the best way of bolting anything to a chassis. Its how every truck is held together . Heaps of bull bars are designed to be fitted like that.

[30ONA]

Found this http://www.3dcadbrowser.com/download.aspx?3dmodel=78287
Doesn't help me as it is a different chassis but could help others.

[30ONA]

Does anyone have good pictures of the end of the chassis with and without the bumper and reinforcing bar attached?

[got_bar_work]

My chassis is about 20mm shorter .it was damaged in a crash. Was trimed back to refit the steel bumper

[bogga]

Call me paranoid but when my bar was built I didn't like the idea of heavy winching off the stock chassis mounts.

The winch base plate is 10mm and sits on top of the crossmember tube between chassis rails. There is another tube inside of this for added strength. Two sleeves were welded through the tube so the rear of the plate can be bolted on to the crossmember in two places as well as the stock chassis mounts. Recovery points are on the bar.

[30ONA]

In that first photo looking down the chassis, how far back it's that gusset?

[bogga]

30ONA wrote:

In that first photo looking down the chassis, how far back it's that gusset?

Through the crossmember?

[30ONA]

Today I was at a lifting shop getting some new shackles. Had a chat to them and looked at their testing bed. They are happy to do testing on an hourly rate. I'm going to revisit my design, ger some chassis rails from a wreckers an set up a test rig.

Target WLL 8T to match the straps. Thinking about doing 1x proof load to 8T, then another 49 times for good measure. If it's still working I'll take it to failure. I don't mean break it, but failure as in the moment one of the components elongated.

Thoughts...

[bumstein]

Do it. That's my thoughts!

Report back

[Gwagensteve]

I've read this over a few times and given it quite a bit of thought. I might be overthinking it, but It just doesn't sit right.

I'll leave the final test to failure aside for now.

If you want a WLL of 8T, you have to test above this but whatever FOS you deem appropriate - if it's 2.5, you need to test to 20T. Testing for 8T means you have no FOS. In practice, that means maybe the strap breaks, maybe the recovery point breaks. That's less than ideal. Maybe it will take 8T when loaded in a jig but only 5T when loaded at a steep angle. Maybe it will take 8T 50 times loaded straight but only 8T once when loaded at an angle. If your test load is very close to the failure limit of the other equipment in the system, these are important considerations.

So to take into account the test to failure - is this going to be in a straight pull or in the weakest orientation the recovery point could be loaded? (I say this with reference to the load charts for eye bolts - they're not rated for the same WLL at all angles)

What if the chassis starts to deform but the recovery point itself is sound?

I guess what I'm getting at is that you can test under the most favourable conditions to confirm your assumptions/design, or you can test under the least favourable conditions to learn whether the design is adequate in the field.

another consideration is that whilst starting your assumptions with 8T is fine for snatching, what of winching? Seems all the kiddies are running 85740383947lb winches these days and if it doesn't move, they'll go straight for the snatch block. The resulting high and sustained load could be applied at almost any angle (unlike snatching)

If this is to be a commercially available product, in the event of a failure or accident involving loss or injury, the quality and circumstances of the design verification and testing you undertook will be heavily scrutinised. We used to have a forensic metallurgist who worked out of our laboratory at work. This stuff gets heavy.

[30ONA]

It's just for me at this stage. So not too concerned about legal issues, I just don't want tutto bend my chassis or hurt anyone. I would expect suitable operation guidelines at sale will cover this, but I would check with a lawyer if I ever sell them. And more testing will be needed, angles etc. But I'm at the point where I need some quantitative data to determine if I go any further.

I don't disagree with your comments. But if I had enough money to test at all angles now I wouldn't be driving a Suzuki.

Regarding FOS. This will be determined after all the cyclist tests. I'm going for a minimum of 2. This means the strap will fail first. That's the goal. Strap testing I've seen barely makes it to 8t for 8t rated straps. Otherwise if I fail it first I can't do the cyclic tests. I'll decide on progress once the failure limit is seen.

[Gwagensteve]

I'll still say you need to disregard snatching as the scenario which will fail the recovery point, start worrying about winch loads.

If this is genuinely for yourself, on the other side of your mock chassis, set two welded crush sleeves through the chassis and bolt a commercially available tow hook through the chassis, torquing the bolts to spec for that diameter. (likely to be 12mm) and test that.

A $20 tow hook, two crush sleeves and an hour of a welder's time might stack up very favourably compared to the design work and liability you're trying to work around.

Steve.

[30ONA]

I'm not sure what your getting at testing the hooks. My new design will accommodate a hook our a shackle but the intended purpose is for recovery not winching

[Gwagensteve]

I think you're missing my point.

The vehicle recovering you might be snatching or winching as appropriate.

The "hook" I'm referring to is a generic rated bolt-in tow hook as is available from any 4WD accessory reseller. Considering the work you're going to, you'd want to be sure you were coming up with a better solution than welding in 2 crush sleeves through the chassis and bolting a hook like this



Obviously that's not a commercially saleable offering, but its perfectly acceptable for your own use.

[30ONA]

Nice and simple idea, but I don't think the numbers work. Nup 2x M12 8.8grade shear at 8t when paired. WLL odd the hook is 4.5t anyway.

Looking at the"rated" points for more common vehicles, they only have aWLL of 5t. So if I down rate mine to 5t FOS goes up. These ones are tested on a jig, I'm going to do mine on an actual chassis rail. In short this will also rate the chassis which no one else has done ( that I can find)

[Gwagensteve]

Literally thousands and thousands of vehicles much heavier than a GV have been recovered with those hooks for probably 40
years. The bolts rip out of what they're bolted to before the bolts fail.

If there's a reason a generic recovery hook can't be installed by all means engineer a solution that fits, but you know, first principles and all.

Chexk the bolt diameter for yourself. They might be bigger than 12mm.

[rustyzook]

I had then on both of my old 4runners, we used to play tugg of war and never pulled any off the car, in hindsight young stupid me wasn't very smart.

But I can confirm the bolts don't snap with a 2.4 4runner trying to pull against a 4.2td gq. I don't recommend trying that as it's plain frigging stupid! And the bolts that came with mine were a 13mm high tensile shaft. From memory.

[30ONA]

Done.

[fordem]

So what are those rated for? Aren't they spaced down from the rails quite a bit? Are the threaded inserts on the rails designed to withstand a dynamic load toward the front of the vehicle or the vertical load of the vehicle downward on to the cross member? Are you using the original bolts? Are they high tensile bolts? Are they long enough to accept the thickness of the recovery point and still thread far enough into the insert on the rail?

[30ONA]

So what are those rated for?
They are not currently rated. I would want them tested first to confirm my calculations. I'v run out of time and money right now for testing. I needed to have them fitted for an event in 4 weeks. But on paper when used with all the correct gear and used as a pair they are capable of at least 8T of force as which point the bolts will shear. However in practice I doublt this would be the failure mechanisim. This is because there are so many variable in play. This also assumes using 4.7T shackles on the recovery points and a 5m long 12T equalizer. But this is because I designed them for 8T I want the snatch strap to fail first, 5T snatch strap. So I have engineered the strap to fail first.

Are the threaded inserts on the rails designed to withstand a dynamic load toward the front of the vehicle or the vertical load of the vehicle downward on to the cross member?
Probably not. I would guess the were designed to hold the cross member to the chassis.

Are you using the original bolts?
No

Are they high tensile bolts?
Yes, 8.8 the equivalent of the automotive ones already on the car.

Are they long enough to accept the thickness of the recovery point and still thread far enough into the insert on the rail?
The existing bolts are not. I'v bought longer bolts (M12*160 from memory and cut them down. They have the same length of thread as the originals and a 14mm longer shaft to accommodate the recovery point.

Also not in the photos is the front sump guard, I have to hack the corners off before I could re-fit it because in now clashed with the recovery points. It bolts from the cross member back to the next cross member.

[Gwagensteve]

Baby/bathwater, nose/face, wood/trees etc.

This boggles my mind. All of the time and effort you’ve put into this and now you’re repurposing a factory connection to to a job it wasn’t designed to do and you’re left with an inaccessible recovery point that’s still reliant on 2x12mm bolts, isn’t rated, and is potentially compromising the thing that holds the front of the car together.

Many of the commercial recovery points suffer from the same problem of being inaccessible if the car is actually bogged, so you’re not alone there, but few use critical suspension connections for mounting.

Whilst I know you’re trying to avoid bolt failure but it’s hard to imagine a location where bolt failure would be more critical or inconvenient as it would render the vehicle undrivable.

[rexhunta]

1 small thing, if you're planning on doing any comps ( especially WA side in Modified or Licenced class ) all points must be tested, stamped and approved, and must have 2 each end.

Not sure what over east is like, but it's a small thing that comes up regularly at scrutineering and the amount of vehicle you see get knocked back.

I know a few guys down here have had bullivants or beaver mining test their recovery stuff to be stamped and tested.

[30ONA]

This location looks the strongest to me out of they options available. The alternative was a high mount through the bumper rendering the car roadworthy and into thin plate that cannot handle the forces.

Does not need testing for my purposes. If I stamp it 1T is it rated even if I think it's designed for more? There would need to be very specific requirements about ratings there is no regulation on the method of testing so the rating is meaningless.

[30ONA]

Gwagensteve wrote:

Baby/bathwater, nose/face, wood/trees etc.

This boggles my mind. All of the time and effort you’ve put into this and now you’re repurposing a factory connection to to a job it wasn’t designed to do and you’re left with an inaccessible recovery point that’s still reliant on 2x12mm bolts, isn’t rated, and is potentially compromising the thing that holds the front of the car together.

Many of the commercial recovery points suffer from the same problem of being inaccessible if the car is actually bogged, so you’re not alone there, but few use critical suspension connections for mounting.

Whilst I know you’re trying to avoid bolt failure but it’s hard to imagine a location where bolt failure would be more critical or inconvenient as it would render the vehicle undrivable.

Perhaps the time and effort lead me to exactly this point.
The rating is only as good as the testing and method so if I do test it I'll keep it to myself because I'm sure I'll do the wrong too.
Your assuming accessibility based on being bogged in the front. This will not always be the case.
The vehicle would be drivable to a garage as there are 8 bolts holding the cross member. Also as I said the strap has a much lower load rating so the likelihood is very low.
In short Steve there will never be a perfect solution. To anything.