crane uprate – where would you add some metal ?

[Maurice TaylorParticipant @mauricetaylor82093]

Posted by Nicholas Farr on 10/02/2021 21:56:39:

Hi Maurice, so you lift 1 tonne just off the floor, then that 1 tonne is transferred to the hook and then the pivot pin in the end of the boom. i.e. the weight of an object is on whatever is holding it, imagine you have a bag of shopping on a set of scales and you pick it up, all the weight of the bag and shopping is then in your hand and the scales return to zero.

Regards Nick.

Edited By Nicholas Farr on 10/02/2021 22:14:59

Hi,thanks for your reply.I agree with what you say.I still don’t understand how the 200kg load in Reg’s post is 1.5m in the air if it only just off the floor.If the 200kg was 1.5m in the air, the base of the load would be 1.5m from the floor,then you would move at your peril.

If it was just off the floor ,you would only need to stop it swinging. I’ve done this with a 250kg engine and gearbox

Maurice

[Martin KyteParticipant @martinkyte99762]

Posted by Maurice Taylor on 11/02/2021 10:07:09:

Posted by Nicholas Farr on 10/02/2021 21:56:39:

Hi Maurice, so you lift 1 tonne just off the floor, then that 1 tonne is transferred to the hook and then the pivot pin in the end of the boom. i.e. the weight of an object is on whatever is holding it, imagine you have a bag of shopping on a set of scales and you pick it up, all the weight of the bag and shopping is then in your hand and the scales return to zero.

Regards Nick.

Edited By Nicholas Farr on 10/02/2021 22:14:59

Hi,thanks for your reply.I agree with what you say.I still don’t understand how the 200kg load in Reg’s post is 1.5m in the air if it only just off the floor.If the 200kg was 1.5m in the air, the base of the load would be 1.5m from the floor,then you would move at your peril.

If it was just off the floor ,you would only need to stop it swinging. I’ve done this with a 250kg engine and gearbox

Maurice

Reg has stated it wrong or at least loosely. The force moves the mass stays put. KIlogrammes is mass Newtons is force. The language is confusing at times. 200g Newtons appears at the hook the 200kg mass is still suspended just above the ground.

We loosely talk about the load being carried and the loading on the hook making no direct reference to forces or mass.

regards Martin

[not done it yetParticipant @notdoneityet]

In a state of equilibrium, the weight of the object (a function of mass and gravitation field strength) will have to be exactly opposed by a an equal force – or the mass would accelerate. This is all according to Newton’s Laws of Linear Motion.

[Martin KyteParticipant @martinkyte99762]

Posted by not done it yet on 11/02/2021 12:53:59:

In a state of equilibrium, the weight of the object (a function of mass and gravitation field strength) will have to be exactly opposed by a an equal force – or the mass would accelerate. This is all according to Newton’s Laws of Linear Motion.

? and the point is

regards Martin

[gerry maddenParticipant @gerrymadden53711]

Right then, now that all the dust has settled I thought I'd send a few words in response. First of all thanks all for you advice and comment. Perhaps I should have added that I'm not a completely wet-behind-the-ears erk and I do deal with very heavilly loaded structures on a daily basis. So no need to worry about safety.

Many suggested that devices like this are 'pared to the bone to minimise cost'. This is clearly not the case with this crane which exhibits all the signs of component standardisation for economies of scale. A great example of this is the main hinge bracket which is 3/4 of an inch wider that the main beam that sits in it. (It looked so awful I put plastic spacers in the gap to make sure the beam didn't slide about!) So clearly this cranes main post is used in a bigger capacity model. Then there's things like the bolts that are either too long or too short so that the threads become load-bearing in shear. …Not to mention standard soft and thin washers that don't reach the side walls of the box sections so don't spread the loads into the structure in a proper and decent way.

As I said in my original post, I hadn't done any calculations. But one only has to 'look' at the crane to see that exceeding the rated load by 10% wouldn't be a disaster and that with some effort and judicious application of bits of scrap, probably 50% more might be safely achievable. I'm not sure I would ever need this much though. I suppose I just hoped that someone else had already done this exercise and would be able to say from experience what worked for them.

What astounded me the most if I'm honest was that I got more warnings about safety than others who asking about electrical wiring issues! Come on its only a simple crane, and as some pointed out, so easy to test with bags of sand.

Gerry

[noel shelleyParticipant @noelshelley55608]

There has been an analogy to boiler testing as a way of testing with a proof load ! The design of the boiler will have a safety factor of between 6 and 10, before the test is done. Altering a crane that has a low safety factor to start with and then using a proof load of 1.5X is NOT a good plan. A proof load of 4x is a safer plan though I doubt a cheap crane would take it, proving that under real conditions of rough or uneven surface It can soon go very wrong. Good luck. Noel.

[Former MemberParticipant @formermember12892]

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