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tow ball question


forestboy1978
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Interesting!

 

It arrives on Saturday. 

 

So putting the plate upside down changes from tension to compression. And shear of course. Distance from pivot point would be identical no matter which way round it was. Hmmm

 

I'm guessing this thing is about 10mm thick. Probably tested taking 30 tons day in day out. I'll take a look at it when it arrives. 

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5 hours ago, Conner said:

The problem is not with the plate itself. The tow bar is designed to have the load directly on the M16 bolts. This can be lowered by 2”. But when raised the forces change and load up the mounts on the tow bar.

To my simple mind- whether the plate is up or down the load placed on the M16s is the same? 

I get what you mean in that the M16s are very strong when being pulled directly but obvious shearing is a factor if vertical pressure is applied (whether from below or above)

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When we used to for towbars for Witter they stated. A drop plate can only be used as a drop plate. The towbar is designed to have the load either as designed or lower due to the fulcrum effect. I suppose it comes down to it being a “Drop plate” not a “raise plate”. If a customer wanted the ball higher we would supply adjustable ball. Or modify the trailer to suite.

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Do not use a drop plate to raise the height.

 

Its illegal & dangerous.

 

To those that say the forces are the same, you are wrong.

 

The issue is not the plates integrity.

 

If you cant see the forces are applied differently then you should not be giving advice.

 

When dropping the force on the towbar is UP to the chassis. When raising the height it is to pull the towbar away from the chassis.

 

The bolts create friction between bar & chassis. stretching the bolts reduces this friction.

 

Bars are heavily tested & only approved alterations (inc fitment & attachments) can be made to them.

Not even all bars can have a drop plate fitted.

 

I ask you this question.

 

When using a felling lever do you lift or lower the bar to create the forces you require?

Does it matter?

 

 

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14 minutes ago, Justme said:

Do not use a drop plate to raise the height.

 

Its illegal & dangerous.

 

To those that say the forces are the same, you are wrong.

 

The issue is not the plates integrity.

 

If you cant see the forces are applied differently then you should not be giving advice.

 

When dropping the force on the towbar is UP to the chassis. When raising the height it is to pull the towbar away from the chassis.

 

The bolts create friction between bar & chassis. stretching the bolts reduces this friction.

 

Bars are heavily tested & only approved alterations (inc fitment & attachments) can be made to them.

Not even all bars can have a drop plate fitted.

 

I ask you this question.

 

When using a felling lever do you lift or lower the bar to create the forces you require?

Does it matter?

 

 

hmm interesting,have thought about this a number of times over the years,more so with bigger timber,tend to lift more than ,;bearing down;    wrong?

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Draw me a diagram of the shear forces and bending moments and how they differ with the plate up or down.

The towball is still carrying a vertically applied load when static, and moving, more-so when braking.

Plus when moving it is subject to longitudinal acceleration forces, causing a bending moment in the plate carrying the towball.

I cannot see how these forces differ due  to the low or high mounting of the plate,

EXCEPT

If the towball was stupidly high it could concievably cause an overturning/lifting moment during braking, and perhaps dangerous when cornering? regardless of braking, but this should be more than counteracted by the excess downforce caused by the load on the trailer rotating the hitch downwards.

The mounting bolts should be engineered to withstand forces in any concievable direction.

I will now do some independant research.

Anyway, intuitively I imagine it has more to do with the stability of the towing vehicle, than any failure of the riser plate.

Regards,

Marcus

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2 hours ago, Justme said:

Do not use a drop plate to raise the height.

 

Its illegal & dangerous.

 

To those that say the forces are the same, you are wrong.

 

The issue is not the plates integrity.

 

 

 

 

 

I ask you this question.

 

When using a felling lever do you lift or lower the bar to create the forces you require?

Does it matter?

 

 

I lift ( no matter what size the timber )  It puts the lifting force near the outer edge if the trunk . If you push down its somewhere nearer the center giving less leverage .

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