crane uprate - where would you add some metal ?

Stueeee you are of course quite right about the purpose of the mid castors

Incidentally as regards the angle of the axle of the fixed front castors, on the 1 ton Draper they are mounted at an angle to the leg so that the axle is correctly aligned with forward travel. My modified SGS also has the mounting angled for forward travel. But even with the forward castors fixed, the rear swivelling castors do permit one to manoeuvre the whole crane around in a turn with the aforesaid 6 ft metal pole lever, of course lowers the  machine so it sits on the legs before doing turning manoeuvres

Edited By Adam Harris on 10/02/2021 15:01:45

Edited By Adam Harris on 10/02/2021 15:15:44

As an abstract exercise, comparing the two designs indicates where the makers think the weak points are:
- Top jib reinforced by triangulation around the upper ram pivot
- Two tension stays at rear to reduce risk of vertical post tilting sideways

The problem with using the hydraulics as a load limiter is the extendable jib surely? If the ram is sized for max load with short jib, then it can potentially overstress when extended.

(No qualifications to back this up apart from decades old physics A level and youthful misadventures with farm machinery, you have been warned)

Whilst I concurr with the idea that beefing it up is a. not worth it and b. potentially hazardous I do think that providing a system like this is tested afterwards and that could be quite simply done the hazard could be avoided.

All one has to do is decide on the aimed for maximum load, add in the required safety factor and load it to that figure. The load need not be taken more than an inch above ground so nothing much would happen in the event of a failure. I woud suggest this be done on home built systems too. It's no different to doing boiler tests at twice working pressure. If it doesn't break you know you are safe at half the loading, if it does well you wouldn't want to use it anyway.

So essentially if you must alter anything like this engine hoist, test it first in a way that it can fail in a safe way.

regards Martin

Adrian -

The manufacturers do tell users the maximum SWL at the different settings but might discreetly design them so that they will withstand some abuse and will "fail safe".

Martin -

"An inch above the ground... " Commercial crane-handling courses teach always to ease the load just off the floor, and pause to ensure all is correct before further lifting and moving. Usually if that shows anything at all, it is as simple as adjusting the slings for balance. And that is for normal operation, not just for load-testing the lifting equipment.

It is no bad thing to follow such practices in our own workshops - whether the hoist is lifting a brand-new 6" lathe onto its cabinet or taking the strain when you are changing one of its heavy chucks.

Hi, when I did my wheeled mobile crane course, (every three years) just easing the load off the ground was always emphasised to check everything was OK before the full lift and when contract lifts were on site, they always did the same, and of course a good banksman would guide you to do this and check before giving you the OK to carry on.

The big difference between a crane and these engine hoists, is a good crane operator can lift the load truely vertical, whereas these engine hoists lift in an arc, so the best position for the boom to be when taking the strain, is horizontal, but of course that is not always possible.

Regards Nick.

The angle of the OP's castors may be intended to prevent the crane moving or being moved under load.

Speaking as someone who has moved a crane with a Pontiac big block v8 on the jib, running a wheel into a 1/4" af nut hiding on the floor will fix any constipation problems you may have had. It's surprising how much 250kg can bob up and down.

One thing to be aware of with any lifting operation using a crane, including the type under discussion, is that as soon as the load is off the floor the mass of the load is effectively at the end of the boom where the fall attaches. In the case of an engine hoist that means the mass of your 200kg lathe you're lifting is now in effect about 1.5 metres in the air. Move it at your own peril!

Reg

What I was proposing was a failure test. Actually try and break it with a larger load than you are going to use in anger but in a way that causes no risk to you. But perhaps you realised that.

regards Martin

PS looks like this one will run and run. Maybe I should pose a wacky idea just for the entertainment value.

Edited By Martin Kyte on 10/02/2021 21:00:58

Hi,Could you please explain why the mass would appear to be 1.5m off the floor ,if say you’d only lifted it 10mm.

Maurice

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

The weight of the load is at the hook but the mass is where it was. The force moves not the mass.

regards Martin

Martyn

Nice point which many people are unaware of and hence it gets misused, that mass is different to weight.

Mass = Density x Volume

Weight = Mass x gravity

Essentially on Earth Mass = Weight. However on the moon the mass of an object remains the same but its weight is much lower due to the lower gravity.

Dave

Hi Martin, agreed and that's why I said weight, which is the effect I believe Reg was talking about.

Regards Nick.

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

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

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

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.