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Right.....Rip Into me then - update on Rear winch Mount


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Right,

Have taken much of the exellent advice re the new 2nd rear winch mount

From this prev post :

http://forums.lr4x4.com/index.php?showtopic=6950

.............Am here I am as at end of today ..................... :blink:

Much is tack welded (the gussets etc) but the main sides are seam welded up tho :rolleyes:

Before I weld everything up. :unsure:

1 Does it look sort of right strength wise ??, rememebr the winch pulls here from the TOP of the winch roller and it PTO Powered, the last unit did aself destruct (er ok, with my help) !

2 The top part will have a section welded into it picking up the 2 top threaded holes from left to right prob 40 mm deep.

3 The winch is bolted to this "Thing" with 4 bolts through the front face, 2 from the 40 plate at the base of the winch with the 3 gussets off it, and will have 2 more bolt holes on the top face plate when made and welded.

4. Yes ........some of it needs to be cleaned up yet ! :P .......... :P

5. I am also thinking of drilling some drain holes (say 40mm) acroos the bottom plate between the gussets for drainage, and a few back further where the gussets end ?...shouldn't make any differentce should it ?

6 The side plates are bolted from the very bottom (bottom of the chassis) up to the very top and end (top of the chassis) with a selection betweemN (holes to be drilled chassis will be "tubed"

Any futher idea mods suggestion fire away. Oh and before anyone says "Kin hell how much does that weigh - I can easily lift the unit (witrhout winch) with one hand, with winch erm, yeah ok gets a tad heavier but still liftable :P:P:P:P:P ........................................ :P

Go on then - let rip :lol:

RearWinch2ndunit-009Medium.jpg

RearWinch2ndunit-008Medium.jpg

RearWinch2ndunit-007Medium.jpg

RearWinch2ndunit-006Medium.jpg

RearWinch2ndunit-005Medium.jpg

RearWinch2ndunit-004Medium.jpg

RearWinch2ndunit-003Medium.jpg

RearWinch2ndunit-002Medium.jpg

RearWinch2ndunit-001Medium.jpg

And No, I don't wnat this to bend................ :lol:

And for thiose Sma*t A*ses who wonder why 2 earth leads

1. Welder

1 Plasma :P

Views please ?

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Mix of 5mm and 6mm.

Its not that heavy, ......less than say a typical front 'winch bumper', but I am planning to drill a number of 40mm ish +/- in the base tray back and front .....to aid getting the mud out of it ...which packed into the old design and proved a swine to get out even with a pressure washer :lol:

Shoving the whole lot on the 90 for a test fit only saw a 1/2 inch drop at the rear....and I'm on very light poundage springs....

mind you the old winch tray was made from far thick materials, and prob weighed around the same weight (8-10mm plus 5mm and 6mm !) but design was not up to the forces involved...and I am just a tad hacked off that the 1st unit self destructed and I have had to do all of this....

Teach me not to rush things now and again, at the time I was unsure but was up against the clock, proved to be a big error of judgement, BishBoshs help means this should be more than strong enough, and I am also going to build in the dixon bate adjustable towhitch system, so I can just change over from D Ring recovery hook to Dixon B adjustable tow hitch with about 8 bolts only rtaher than a major swap around..

Ho hum thats more work then :huh:

Nige

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Nige,

As I said in the earlier post, most of the load is going to be applied near the top winch mount bolts (because that is where the rope is pulling).

With you earlier posts, you have been concentrating at the level below the winch, which was the wrong place. You have reduced the weight there now, from material which is/was not going to take much load.

Where you should have concentrated, is at the top. That pi$$y little flange above the rope slot has to act as a beam to carry most of the rope load, from the top winch mount bolts, out to the massive side plates and to the bolts which connect the side plates to the chassis rails.

How the forces and stresses will be distributed is somewhat complex, but you should visualise the structure that you are fabricating as a beam spanning across the side plates, to which the winch is bolted. When the rope is pulling from one side of the drum, most of the tension in the rope will be applied to the beam at the position of the top bolt nearest the rope. The will be a much smaller load near the bottom bolt on that same side.

Now look at what part of the structure contributes to that beam? That is what you must understand!!!

A good approximation is, The top flange, the corner gussets (between the top flange and the side plates) and a portion of the vertical plate between the probably extending no further down than the bottom of the rope slot.

Except for the part of the side plates from the ends of the beam to the chassis mounting bolts, most of the rest of the structure is doing little more than taking up space.

Now that is not a very strong beam, particularly the section above the rope slot. Also because the section of this beam changes dramatically where the rope slot is, there will be considerable stress concentration where the stiffness changes.

IMHO, you need to do something to be able to withstand the bending loads on that top flange.

The vertical plate below the rope slot and the stiffener below the winch are not going to take much load from that top flange, until the top flange bends considerably.

I wish that I could know where the side plates will bolt to the chassis, as that would allow a better visualisation as to how it will perform. Remember that the load has go get from the top flange to the chassis mounting bolts.

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John,

Ok ta for the input.

I was planning to have a big plate say approx 28 inches wide by say 3 inches deep bolted right across the top from left to right, bolts through the forward facing flange on the winch plate, through to the side plates all again bolted through. and the winch itself has the 2 bolts showing at the top, these would eqaully be then used ?

Didn't know if you had spotted this in the post above, ?, would this not make the top hugely stronger ?

The side plates are high enough that when fitted the shape of the curve in the 90s chassis will mean the side plates will have bolts from the bottom of the chassis, which then go through the lowest part of the paltes, and as the90s chassis moves upwards the rear of the side plates will have bolts at the top, and these will bolt through the top of the chassis..

In effect the chassis and the side plates will be bolted top and bottom of the side plates and the chassis prob around 8 each side, plus the rear crossmember tow mount bolts (4) and the bolts going up through the bottom of the cHassis (4)

Re the above what thoughts now ? <gulp>

Nige

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I am not sure I totally agree Bush - the stiffness of the side gussets in the horizontal plane will attract the load directly from the bolt positions. I think you coud cut the thing in half vertically down the middle and not lose a massive amount of bending strength - it is peforming like two stiff cantilevers IMHO. When the bolts are loaded asymmetrically however you then have to think about torsion, but even then I think the assembly is pretty good....

Well, lunchtime came around so I threw this together:

Deformedshape.jpg

This is with 6 tonnes acting uniformly over the four bolt positions. Max deformation is 1.4mm so don't panic at the exaggerated scale. I have assumed it is welded to the chassis along the full perimeter of the sides.

Obviously a lot of assumtions on geometry - scaled sort of off your pictures with the bolt pitch of 10" as a guide and everything is 20mm 6mm plate :lol: . Couldn't be bothered to model the letter box - it won't make much difference to this model and I also didn't have time to model the bottom half of the assembly. The mesh is un-refined too so no picking holes :blink:

This one is with all the load on the top two bolts - displacement is 1.6mm.

Deformedshapetopbolts.jpg

A few things are pretty evident from this model:

1. If you can, get a stiffener on the left hand side of the letterbox like you have on the right. If you can't get it on the winch side of the plate put it on the other side. (On the "other sied" a piece of angle toes down would be good...) This would also help point 2:

2. Put the gussets on the rearward facing "lip" that I suggested before to stop it un-folding as the pictures show.

3. The lower gussets would have been better with the inner corner cut out to allow drainage :ph34r: - a 25 x 25mm chamfer would have little detrimental effect on performance.

4. The additional stiffening below the winch to the Southdown tray is a good thing. However, you could probably have got away without it. Drain holes in the Southdown plate should not be a problem as long as the pitch of the holes is at least 3 diameters. To be honest, one in each of the rear corners should be enough - leave at least 1.5 diameters to the edge of the plate though.

CAVEAT: This has been thrown together in a one hour lunch break when I was repeatedly interrupted and distracted by graduates asking questions. There has been no caluation applied to this. The geomtrey and plate sizes have all been estimated from unscaled photographs. In a nutshell - if you break it again Nige it is your own fault!! :ph34r:

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Now that my brain is not bemused by alcohol …….. I’ll try to say something sensible …….. yes, I know, that will be a first...... :D

We concentrate on making super strong winch mounts, both front and rear, but eventually you must reach a point when the mount becomes stronger then the chassis.

Just how strong is the LR chassis when subjected to the winching stresses that we place upon it ? I would much rather see the winch mount break than something to give on the chassis……….. which in turn is probably a much harder fix. I’ve heard in the past that the front is 12 tons ……….. but I have also heard that it is 6 tons ……. are there definitive figures ? …………… after all its only 2 or 3 mm thick box section

Certainly Nige, it looks plenty strong enough to me …………..but then again I would need to see it in position to provide the full mechanical picture.

I suppose that adding a strong winch structure in the correct manner would add to the to strength of the that part of the chassis ……….. :unsure:

Hmmmmmmm…….. the rambling thoughts of a madman……….. :rolleyes:

Ian

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...I was planning to have a big plate say approx 28 inches wide by say 3 inches deep bolted right across the top from left to right, bolts through the forward facing flange on the winch plate, through to the side plates all again bolted through. and the winch itself has the 2 bolts showing at the top...

The plate will help, but it would be better if welded.

I saw the extra tapped holes in the winch and the bolts through the lower stiffener to the winch - I don't see the extra bolts at the bottom stiffener helping much. The extra bolts at the top will help with the bolted in plate, but would not be necessary if the plate was welded in instead of bolted in.

...the side plates will have bolts from the bottom of the chassis, which then go through the lowest part of the paltes, and as the90s chassis moves upwards the rear of the side plates will have bolts at the top, and these will bolt through the top of the chassis...

If I understand this correctly, these bolts will take most of the load and should be fine.

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I am not sure I totally agree Bush - the stiffness of the side gussets in the horizontal plane will attract the load directly from the bolt positions...

True. The load has no alternative.

...I think you coud cut the thing in half vertically down the middle and not lose a massive amount of bending strength...

Again true, because the actual frame has so little bending strength there now. But your FEA model does not capture this problem.

...it is peforming like two stiff cantilevers IMHO...

Agreed, that is what it is. But that does not make it a good solution!

...When the bolts are loaded asymmetrically however you then have to think about torsion, but even then I think the assembly is pretty good...

The worst case will be when the rope is against one of the cheek plates of the winch drum.

Then it would be reasonable to assume most (if not all) of the rope load applied at one of the top bolts. The cantilever on that side has to take all of the load because there is little bending strength from the flange above the rope opening. This is the problem that I have with the design, and it is worse than your FEA model.

...I have assumed it is welded to the chassis along the full perimeter of the sides...

IMHO, this assumption makes the model behave better than it would if constrained more like the real thing.

...Couldn't be bothered to model the letter box - it won't make much difference to this model...

I dissagree.

It is obvious from the deformed model that the plate, which would not be there if the rope slot was included in the model, is contributing to the bending strength.

I suggest, if the slot was there and the constraints at the side plates were more like the bolts that Nige is intending to use, and the load is applied at one of the top bolts, then it will not perform so well.

I still maintain that it should have better bending strength across the top of the rope slot. That would make a better winch cradle IMHO.

Nige's problem is that he does not want, for whatever reason (and they may be valid reasons for all I know) to put the plate where it will do the most good and is paying the penalty.

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Looks like it should do the job,

I would be tempted to make a back gaurd for the winch to replace the 2 bits of threaded bar to keep the rope where it should be on side pulls.

You could also tie this in to the rest of the winch mount, this would place a lot of load on the winch itself but it should stop the deformationshown in the CGI.

The question i do have to ask is why not just fab up a new rear x-member that is up to the job?, it'd probably be lighter overall.

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The question i do have to ask is why not just fab up a new rear x-member that is up to the job?, it'd probably be lighter overall.

Erm Good Point :blink:

Erm, how about "I'm trying to get in tune wiv me femine side, ...so doing what women do, ...making a easy job difficult ....and being bl**dy minded :D ? "

Actually its more Bl**dy mindedness, I started it and I'll finish it :angry: Humpfh

Or a combo of the 2 :lol:

Nige

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If it is to be bolted throught the chassis then Bush is right - torsional effects could cause significant deformations. You will need to add vertical stiffeners eaither side of the bolt holes to stop the plates bending.

The suggestion to add more bending capacity across the front of the winch is a good one. Just make sure it is adequately stiffened to prevent buckling. A piece of 50 x 5 EA should do the trick if you can fit it in. I also agree that it should be welded in. Bolts will allow too much rotation before they can pick up load in this application I think.

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