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 > Adding scissor jacks for side to side leveling

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Huntindog

Phoenix AZ

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Posted: 08/29/21 04:04pm Link  |  Quote  |  Print  |  Notify Moderator

valhalla360 wrote:

Huntindog wrote:

It certainly is what cambering is. Do some googling as I did. There is more than one way to do it. But I found articles of some really big semi type stuff being cambered by welding. In addition at one time, Northwoods RV had a picture of welds on one of their frames stating it was cambering for more strength. I also toured the Palomino Sabre factory back in 2010 when I bought my Sabre. I took a lot of pics. One of them shows the cambering welds. I have that pic, but I haven't posted a pic in so long, I forgot how to do it

And welding certainly does change the way a length of steel feels.
I tried it and felt it it myself. If you still don't believe me.... Break out a welder and see for yourself.


Flatbed semi's, the beams are often cambered. If you see them running empty, the curve is easy to see but they are built for many tons of load. Far different from your average travel trailer.

I've seen a fair number of travel trailer frames and not seen cambering...at least not enough to visually see anything. They will sometimes reinforce where the axles connect but that's different from cambering.

I suspect what you are confusing is looking at the strength of flat sheets vs an I or box beam working together but that's different from cambering.


Google has a LOT of info on it. This was the first hit:

People also ask
What is a cambered chassis?
In the structural engineering world, camber is known as having a slight arc or bend induced in a beam. Positive camber is when there is a hump in the center of the beam, with its shape resembling a frown. ... Cambering beams allow smaller beams to be used in place of larger beams to support the same load.May 29, 2016.


Have you broken out your welder yet to see for yourself?

I encourage you to do so. All you need are a couple pieces of fairly long angle steel. I used 16 ga 1.5" x 2" x 10'. One you run weld beads on similar to the picture I posted of my Sabres frame. the other one is just your baseline piece. Run the beads and then compare the straightness, and feel of the cambered piece to the uncambered piece.This is the pic of some cambering welds on my 2010 Sabre: [IMG]https://i.imgur.com/9j3d5Zul.jpg "border=0"" border="0" alt="[image]"> [image]Click For Full-Size Image.[/img][/img]

Do this and then get back to me.



Huntindog
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vtraudt

Brighton, MI

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Posted: 08/29/21 04:35pm Link  |  Quote  |  Print  |  Notify Moderator

Huntindog wrote:


[IMG]https://i.imgur.com/9j3d5Zul.jpg "border=0"" border="0" alt="[image]"> [image]Click For Full-Size Image.[/img]


The few lines of surface welds induce some heat stress to the beam, which then bends up. This helps to end with a someone flat beam when load is applied and axles put underneath to push up.
It does NOT add any strenght. It only changes the bending line (crooked before weight, somewhat raight when loaded 'dry', somewhat crooked again when additional load is added (full tanks, food, storage, stuff on the rear bumper, stuff on the A frame, etc).

There may ONE very special/rare load condition when this beam is STRAIGHT. For practical terms, it will NEVER be straight. The amount of bending depends ONLY on a) the stiffness of the frame (fixed, and NOT influenced by the pre bending) b) the load and load distribution.

Lifting at the 2 rear corners (the front is already lifted at the corner, the A frame (front jack) lifts the 2 front corners, and all the static bending is/has taken place every time you put your front jack down, or hook up your trailer to the car), will add equal (but in reality less) than the normal static flex. Less, because A the axle is not in the middle of the lifting point and be the load is heavier on the front section ('tonque weight').

So lifting on the rear corners will ADD static bending (in the opposite direction. NO QUESTION.

The AMOUNT of bending could be the range (but opposite direction of the 'empty load' (the weight of the chassis itself, plus weight of the empty 'house'). In my case: 4400 lb weight empty, assumpe 2200 on 'rear' half. Lets call this the 'flat static' (assuming pre bend frame to make it 'flat' with this load). Now adding 120 gal of fluid (black, grey , fresh water) (on earth, roughly 1000 lbs) near the rear bumper. That ADDS 50% to the static bend.

Now we bounce it over a speed bump at 3 g. That is now an additional 2 g or 2000 lb near the rear bumber for a total of 3000 lbs. That is 1.5 TIMES the bending amount of the static 'assume flat with pre bent beam).

Now if we push UP the rear end of the empty trailer, that is 2200 lbs. This will result in roughly 50% LESS bending as the 'bump' with full tanks'.

Ditto, if the trailer is full (here: 7500 lbs, or 3750 on the rear portion), if we lift the rear, the bending is about equal to the amount exerienced during every 3G bump no the road (but only done once every time to jack it up, so say one per vacation, vs xxxx during driving).

Just some perspective on the issue.

Huntindog

Phoenix AZ

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Posted: 08/29/21 05:04pm Link  |  Quote  |  Print  |  Notify Moderator

vtraudt wrote:

Huntindog wrote:


[IMG]https://i.imgur.com/9j3d5Zul.jpg "border=0"" border="0" alt="[image]"> [image]Click For Full-Size Image.[/img]


The few lines of surface welds induce some heat stress to the beam, which then bends up. This helps to end with a someone flat beam when load is applied and axles put underneath to push up.
It does NOT add any strenght. It only changes the bending line (crooked before weight, somewhat raight when loaded 'dry', somewhat crooked again when additional load is added (full tanks, food, storage, stuff on the rear bumper, stuff on the A frame, etc).

There may ONE very special/rare load condition when this beam is STRAIGHT. For practical terms, it will NEVER be straight. The amount of bending depends ONLY on a) the stiffness of the frame (fixed, and NOT influenced by the pre bending) b) the load and load distribution.

Lifting at the 2 rear corners (the front is already lifted at the corner, the A frame (front jack) lifts the 2 front corners, and all the static bending is/has taken place every time you put your front jack down, or hook up your trailer to the car), will add equal (but in reality less) than the normal static flex. Less, because A the axle is not in the middle of the lifting point and be the load is heavier on the front section ('tonque weight').

So lifting on the rear corners will ADD static bending (in the opposite direction. NO QUESTION.

The AMOUNT of bending could be the range (but opposite direction of the 'empty load' (the weight of the chassis itself, plus weight of the empty 'house'). In my case: 4400 lb weight empty, assumpe 2200 on 'rear' half. Lets call this the 'flat static' (assuming pre bend frame to make it 'flat' with this load). Now adding 120 gal of fluid (black, grey , fresh water) (on earth, roughly 1000 lbs) near the rear bumper. That ADDS 50% to the static bend.

Now we bounce it over a speed bump at 3 g. That is now an additional 2 g or 2000 lb near the rear bumber for a total of 3000 lbs. That is 1.5 TIMES the bending amount of the static 'assume flat with pre bent beam).

Now if we push UP the rear end of the empty trailer, that is 2200 lbs. This will result in roughly 50% LESS bending as the 'bump' with full tanks'.

Ditto, if the trailer is full (here: 7500 lbs, or 3750 on the rear portion), if we lift the rear, the bending is about equal to the amount exerienced during every 3G bump no the road (but only done once every time to jack it up, so say one per vacation, vs xxxx during driving).

Just some perspective on the issue.


Your perspective...... Why won't you try the experiment I suggested? Perhaps you do not want to see another perspective?

As for it not adding any strength, see the exerpt from my previous google quote:
Cambering beams allow smaller beams to be used in place of larger beams to support the same load.May 29, 2016.
(that is a very cost effective way of making an RV lighter.)

I am done here. It is obvious that you will not be detered.
As always, your money, your choice


vtraudt

Brighton, MI

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Posted: 08/29/21 05:06pm Link  |  Quote  |  Print  |  Notify Moderator

Huntindog wrote:


People also ask
What is a cambered chassis?
In the structural engineering world, camber is known as having a slight arc or bend induced in a beam.


Yes, cambered means using a pre bent beam.
Take a piece of steel, and bend it over your knee. Now it cambered.
Adding weight of top of that piece of steel, and it gets flatter (fi the pre bent was up).

Putting some welding lines on top of a piece of steel will induce stress, and bent the piece of steel. EVERY weld does that. That is why when welding pieces of steel together, the welder is using a certain sequence to equalized the bending if a straight, NOT bent work piece is desired at the end.

You could also use a TORCH and heat up one side of your beam, and then quench (to induce thermal stress). If you have a high carbon content steel, you could actual HARDEN that material (think knives and swords).

That bead of weld - while bending the beam for the intended purpose - does NOT make it stiffer. Sorry.

JRscooby

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Posted: 08/29/21 05:11pm Link  |  Quote  |  Print  |  Notify Moderator

vtraudt wrote:


Lifting at the 2 rear corners (the front is already lifted at the corner, the A frame (front jack) lifts the 2 front corners, and all the static bending is/has taken place every time you put your front jack down, or hook up your trailer to the car)



You must have some weird trailer. Other than the ones with floating tongue, any of the hundreds, if not thousands of trailers I have been around, jack the front up, the rear goes down. When pivot on the suspension, there is no force to flex the frame.

vtraudt

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Posted: 08/29/21 05:26pm Link  |  Quote  |  Print  |  Notify Moderator

JRscooby wrote:

vtraudt wrote:


Lifting at the 2 rear corners (the front is already lifted at the corner, the A frame (front jack) lifts the 2 front corners, and all the static bending is/has taken place every time you put your front jack down, or hook up your trailer to the car)



You must have some weird trailer. Other than the ones with floating tongue, any of the hundreds, if not thousands of trailers I have been around, jack the front up, the rear goes down. When pivot on the suspension, there is no force to flex the frame.


You are correct (if you put your trailer into a no gravity zone (like outer space). You are my first alien contact on RV.Net.

If you would bring your trailer here on earth, gravity does do its bending thing, if you like it or not. In fact EVERYTHING on earth is bent (past tense), sometimes just bent into a straight line (I know, this will bend (present tense) your brain; double pun intended (yes, gravity bends even the stiffes brain on earth!).

vtraudt

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Posted: 08/29/21 05:38pm Link  |  Quote  |  Print  |  Notify Moderator

Huntindog wrote:


As for it not adding any strength, see the exerpt from my previous google quote:
Cambering beams allow smaller beams to be used in place of larger beams to support the same load.May 29, 2016.
(that is a very cost effective way of making an RV lighter.)


Yes, allow smaller beams to be used in place of a larger beam so support the same load. Reason: the beam was BENT UP, adding load flattens it to be used with the 'house'. It was BENT DOWN by the load of the house to be flat again. It did NOT make the beam STIFFER. It did NOT (and your article nowhere states it since it is NOT true) reduce the bending. The beam was just crooked to start ("cambered") and then flexed down (bent) by the weight. The amount would have been teh same if they had started with a straight beem, the beam would then flex down by the weight of the house, by the same amount. Quite simple physics (here: stiffness of a beam as calculated by moment of inertial (simple example: rectangle shape beam: https://wesbeam.com/Wesbeam/media/Images/Blog%20images/2019-08-27_14-10-28.png).

JRscooby

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Posted: 08/30/21 05:31am Link  |  Quote  |  Print  |  Notify Moderator

vtraudt wrote:



You are correct (if you put your trailer into a no gravity zone (like outer space). You are my first alien contact on RV.Net.

If you would bring your trailer here on earth, gravity does do its bending thing, if you like it or not. In fact EVERYTHING on earth is bent (past tense), sometimes just bent into a straight line (I know, this will bend (present tense) your brain; double pun intended (yes, gravity bends even the stiffes brain on earth!).


This sounds like somebody educated beyond their intelligence, or acting stupid. Over the years I have bent a lot of steel, (most, but not all on purpose). I have had some sag under own weight when lifting 1 end.
But even a super light duty, like a garden cart, when loaded to capacity, you lift the tongue, the back goes down, but nothing bends. (If it did, you could not tow it without it bending.)

vtraudt

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Posted: 08/30/21 06:21am Link  |  Quote  |  Print  |  Notify Moderator

JRscooby wrote:

vtraudt wrote:



You are correct (if you put your trailer into a no gravity zone (like outer space). You are my first alien contact on RV.Net.

If you would bring your trailer here on earth, gravity does do its bending thing, if you like it or not. In fact EVERYTHING on earth is bent (past tense), sometimes just bent into a straight line (I know, this will bend (present tense) your brain; double pun intended (yes, gravity bends even the stiffes brain on earth!).


This sounds like somebody educated beyond their intelligence, or acting stupid. Over the years I have bent a lot of steel, (most, but not all on purpose). I have had some sag under own weight when lifting 1 end.
But even a super light duty, like a garden cart, when loaded to capacity, you lift the tongue, the back goes down, but nothing bends. (If it did, you could not tow it without it bending.)


Who is talking about raising the tonque? if you raise or lower the tonque, the bending does not change (yes, it is bent if a load is applied). But if gravity is present, your tonque is actually pushing UP the A frame. If you want to test it (the amount of bend), balance out the trailer (for example put a lot of weight on the rear until the tonque just lifts up. Now check how much your rear has gone down. That is about the amount your front is sagging. Note: you would need to put jacks under the center (axles) to prevent your suspension to go down.

But the concept of a beam bending, the force that act upon the beam, bending stiffness, moment of inertia, forces from acceleration, etc is very much beyond the grasp of the most of the members of this forum, and not (I realize it finally) suited for discussion here.

Grit dog

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Posted: 08/30/21 08:20am Link  |  Quote  |  Print  |  Notify Moderator

So have you tried jacking up your trailer or is this just a theoretical discussion on steel beam design?


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