Workshop crane project

[Sonic EscapeParticipant @sonicescape38234]

I’m aware of the risks. Now I have a cold but this weekend I’ll lift the machine only 2-3cm. To see how the structure behaves. Then maybe I’ll move it a little. And that’s it. I need to clean the garage first. This might be more complicated than building this thing.

I have to give it a try anyway. I can’t just throw it away. It is too pretty. However if I don’t post nothing next week that means there is no Wi-Fi in the hospital 🙂

[Robert Atkinson 2Participant @robertatkinson2]

To put the risk in perspective the load is only going to be lifted a inch or tw so is unlokely to tip over or injure anyone if it does fall. The biggest risk for tipping is inertia and a sudden stop such as a castor hitting a bit of metal on the floor. Answer to that is makesure the path is clear of debris and damage and move it slowly.
The joints are grossly over-engineered. Even if one of the mitered joints failed the braces would probably hold the load and at least hold the frame together until the load dropped the couple of inches to the floor.
Compare this to a machine mart folding engine crane. Lots of non-failsafe welds in one of those.

Robert G8RPI (normally the one pointing out the dangers)

[Sonic Escape]

On Sonic Escape Said:

…
One chain block for the two back lifting points and the other block for the front. For some reason the chain blocks manufacturer disagrees with my plan …

 

Helps I think to ask ‘what could possibly go wrong?’ when the instructions advise against something.  Understanding risks helps avoid them, and guides those who might need to tackle a tricky job.   Relying on luck isn’t smart, whilst preparing for the worst can avoid much unpleasantness.   For example, a common cause of crush accidents is people instinctively reacting to a heavy toppling object by trying to push it back.   Thinking ahead suggests it’s much better to jump out of the way because broken things are almost always far less trouble than broken people.

A couple of issues come to mind with doing a lift with two hoists.

• The object may hit something or overbalance by rolling on the axis between two lifting points.  (Sonic may have allowed for that risk: he mentions having two back lifting points and one at the front, which should stop rotation.)
• When one hoist lifts higher than the other, the weight of the object isn’t shared equally between them.
  • Therefore either hoist has to be capable of supporting the full load on its own.   Lifting a 1000kg object with two 750kg hoists is dangerous because one of them might be overloaded by an operator error or mechanical fault that causes an imbalance.
  • Even if both hoists are strong enough, the load transferred to the structure is also unbalanced, so it might be overloaded or topple.  In the diagram, a tilted 1000kg object puts more strain on chain a, and less on chain b, and the unbalance causes the whole frame to want to turn counter-clockwise.  Whether the structure topples or not depends on where the centre of gravity ends up.

If the mass of the structure, plus the structure’s material and the joint types are known, strength and stability can both be predicted.  More usually, a crane is designed to lift a given mass safely, with the engineer calculating materials and form as necessary to do the job.  A proper design would consider everything, for example my diagram ignores foot pressure, column buckling, strut bending and assumes a perfect ground.

That said, I’m not against Sonic’s practical approach because I detect he’s doing enough risk management to avoid injury in the event his crane breaks, and he’s acknowledged the comments.   I have less confidence in certain others who puts stuff like this on the internet as a done deal, especially those who can’t cope with criticism!

Dave

[DiogenesParticipant @diogenes]

👍 Robert Atkinson

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I don’t agree that those 45 degree joints should not be used, however, if the welding is of a very low standard, the welds are likely to fail, but it’s nothing to do with the joint design. To say the welds should not be taking all of the load is nonsense, but they do have to be structurally sound, if you look at the photo below, you will see the horizontal I beams are bolted to the columns, but all the end plates for the bolts are welded to the ends of the I beams, therefore all the loading on the beams is taken by the welds, the bolts only take the clamping load of the end plates to the columns, producing enough friction between the end plates and the columns to carry the load down to the ground. So if any of you are worried about welds taking all the loads, don’t got into buildings with a steel structure like this was designed. (This one was in the process of demolition)

I can’t see anything really wrong with Sonics frame design, although the welding could have been a lot better, but I’ve seen some much more atrocious welding than his, which hasn’t failed, but even so, one should not get complacent about such things. It is unlikely that his frame will topple, as all his load will be inside, and if he lifts it just a small amount and something fails, it will just land back down on the ground in all probability. He should though, have someone else operating the other chain block, and they should both lift at the same time.

Regards Nick.

[RainbowsParticipant @rainbows]

I thought I’d mention those castors are very unlikely to evenly spread the load unless on a dead flat surface. Like a chair on a wonky floor, trolleys like to rest on 3 wheels. The castor wheels will give some squidge to help divide the load but if any individual wheel can’t take 1/3 or 1/2 the load it could be liable to collapse under load.

If the current plan is to just raise the machine onto rollers though then its a simple fix to just rest the crane on wooden beams to bypass the castors. Small commercial gantry cranes often have screw jacks built in to do the same.

 

As long as you position your body as if the crane could collapse at any moment, and always remember not to try and catch falling objects the chance of damage to people (but not property) should be minor. As mentioned swap that rope out for a sling though I don’t love its chances

[duncan webster 1Participant @duncanwebster1]

In response to SOD, the main railway works had overhead cranes with 2 crabs on one bridge so that locos could be lifted from both ends. These crabs lifted independently, but were controlled by people who knew what they were doing. The situation in SOD’s sketch would not be allowed to occur. They didn’t just lift by a few inches either, they could lift a complete loco high enough to travel over the other locos in the shop.

Even when I worked on a narrow gauge railway we had an overhead fixed beam with 2 runners and 2 chain blocks to lift locos. Hard work with hand chain blocks I assure you.

[jaCK HobsonParticipant @jackhobson50760]

It does look healthily over-engineered.

Another thing – It is not going to get much use near it’s max weight. This is very unlikely to fail due to fatigue. Just go lift the heaviest thing first with suitable caution as a proof test – if it survives then lighter things should be pretty safe.

I can imagine all sorts of theoretical arguments against this statement – like dynamic loading if the crane is involved in a red bull downhill race with even quite a light weight mill. But in practice – that thing looks solid!

Bad looking welds can be quite strong. Good looking welds can be weak. Hanging off the weld and ‘feeling’ is a useful test in a home workshop.

It is all mild steel. I’d expect the majority of fail modes are not very catastrophic – a joint pops, the machine settles down the 1″ it been lifted, the crane still takes some load.

Load distribution very much depends on ability of structure to conform to the surface – and that is mainly the flatness of surface and compliance of rubber wheels. The reason for so many castors is that it is to protect the tiled surface – which is pretty flat – flat enough for compliance to play a significant factor. I wouldn’t have bothered but I can see the point.

If those tiles are not well supported (spot dabs instead of even cover of cement) and well laid (flat) then they will crack whatever – as soon as 1.5t machine is carefully put down on them.

But I don’t really know what I’m talking about.

[JasonBModerator @jasonb]

If there was a worry about the load being unstable when the crane is moved a very simple solution would be to drill  4  vertical holes through the bottom rails so that two pieces of 100 x 50 box section could be bolted to the underside.

Lift load,  slide box sections into place and bolt to the bottom rails and then lower the load onto the box sections. That way you just have the load on a dolly with no risk of it swinging about. When you have it in position just raise off the box section enough to remove them and lower to the ground.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi JasonB, that’s a good idea about bolting box sections on, and landing the machine on to them for moving, but I think he would have to take two of his casters out of the middle sections on each side, and then move the other ones to the central position, as I think they may prevent the casters swivelling, though he may have enough room to move the two of them to the middle.

Regards Nick.

[JasonBModerator @jasonb]

Yes, might have to arrange things so the bottoms of the supports are flush with the underside of the frame, maybe plate the ends and tap then bolts in from the sides. Or weld some angle onto the ends so they just sit on the tops but lower. As he says a front cross member is to be added that would replace that so only really one extra member to add.

[Sonic EscapeParticipant @sonicescape38234]

Today I made a first lifting test. And surprise, the top of the machine is very long on the back and there is no space left for the chain block.

I don’t know why I didn’t noticed this before. Because of this I mounted the chain block in this unusual way. Then I started to lift the front. By the way, never buy cheap chain blocks. They work fine with no load. But once there is a weight the chain gets stuck all the time. It is almost impossible to use them. And no amount of lubrication helps.

The good news is that after I lifted only the front of the mill just 1cm I was able to move the machine! I pulled it 10cm without to much effort. So there is no need to lift it completely. It seems that 1200kg is not a huge weight. The frame feels super solid. And the castors are ok. Tomorrow I’ll move the mill a few meters to the left to wash it. That oil that spilled all over the place is smelly. And in a closed space I think it will be unpleasant.

 

[duncan webster 1Participant @duncanwebster1]

The attachment between single hook and sling at the back is certainly below the centre of gravity, this is not good, the cg must be below a line drawn between the 2 hooks, and I’d say well below, or it is likely to topple.

Can you move the chain blocks round 90 degrees so they are either side rather than front and back?

And put the slings inboard of the feet so they can’t slip out

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Duncan, the cg must be below the lifting point, and his lifting point is still at the top of his frame, where his sling is over. His chain block hook, is in effect, in the same place as two links in the lifting chain would be, if the chain block hook was at the top. Seeing as the sling ends are on opposite sides of part of the machine, should also stop it from toppling, but it would be better if the sling was choked over the top of the frame, and a shackle used to joint the two sling loops and hang the chain block on.

Regards Nick.

[jaCK HobsonParticipant @jackhobson50760]

Good job. I like to move my 750kg grinder around by leaving a bit touching the floor and then rocking it around maybe 10cm at a time just like that. Well, until I put it on castors. Big things scare me. Yesterday I was looking at a cherry tree I want to cut down and imagining how big it would be laid down – it also gives me the willies. Things don’t have to go too much wrong to go very wrong.

[Nicholas Farr]

On Nicholas Farr Said:

Hi, I don’t agree that those 45 degree joints should not be used, however, if the welding is of a very low standard, the welds are likely to fail, but it’s nothing to do with the joint design. To say the welds should not be taking all of the load is nonsense, but they do have to be structurally sound, …

 

… He should though, have someone else operating the other chain block, and they should both lift at the same time.

Regards Nick.

Nick has misunderstood the point.  I’m saying that, if circumstances permit it, a structural configuration that doesn’t need a weld at all is a better choice than one that requires the weld to be in good order.    Whilst it’s true that well-made welds can be as strong as the metal they join, we also know that welding isn’t always done well, and that it’s difficult to test without special equipment.

Nick admits that welds do have to be structurally sound.   Unfortunately Sonic’s photos, skill-level and inability to test welds mean that’s doubtful in this case.   That being so, replacing the crane’s top with a door lintel design, is a simple safety improvement, and I suggest there’s no good reason for not doing it.   Given a straight choice between a strong configuration and a weak one, a structural engineer will go strong.

Joints in steel frame buildings are a different problem: and, Nick’s advice they are OK is misplaced, because they do collapse:

 

Ditto misunderstanding with the dual lift problem.  A safe dual lift requires requires two coordinated operators who understand what they’re doing.     The chain lift manufacturer’s instructions tell ordinary customers not to do dual lifts because it’s unlikely ordinary customers understand dynamics.  Here’s an example of the professionals getting it wrong!

https://youtu.be/8_nTLIuk6Hk

Saying stuff is OK if done properly isn’t good enough, because it assumes ‘done properly’ is sorted, when there’s a chance, it isn’t.  The ‘if’ cannot be ignored, and assumptions are always dangerous.    Better, I think, to engage brain and establish clearly what ‘doing it properly’ requires.   Identify the risks, and mitigate them.   If a structure can break due a faulty weld, is there a way of not relying on the weld by using a different geometry?  In Sonic’s case, the answer is yes.

Structural Engineering is ‘quite interesting’.   I recommend the book ‘Why Buildings Fall Down‘ as a non-mathematical insight.

Dave

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Dave, sorry but your lintel idea is no guarantee it won’t fail if the welds are not good enough, so there is no way it can be said that it’s really any safer. I think your comparison of a duel lift with Sonic’s frame, doesn’t cut it, the two cranes were most likely slewing past the point of balance, and of course the barge they were on would very easily roll, once they passed the point of balance, which is something Sonic’s frame wouldn’t do, as the weight is all inside its footprint. He is only intending to lift his machine just clear of the ground, so it’s not likely to topple, unless he intends to go down a hill with it.

Yes buildings do fail, but it’s a very small amount, compared to the many thousands that don’t, the one in my photo was in use for 42 years, but it wasn’t demolished because of any structural issues, but its working life had finished, and there was no more use for it, and the building which this one was an extension was at least 10 years or so older, and was also demolished at the same time.

There are numerous reasons why buildings fail, but not all of them are through bad workmanship, bad design and or overloading are sometimes to blame.

Regards Nick.

[Tim StevensParticipant @timstevens64731]

I have to take issue with the sketch used by S.O.D several posts back. He shows a length of bar hanging below a table from two cords, one longer than the other. No problem so far, but if I read it right, this is supposed to create a moment tending to rotate the table to the left.

It is a long time since I did my Physics A level, but what I see is a force down each of the cords, both pulling the table-top downwards. Each force is in line, exactly, with the cord, isn’t it? And the result is to pull the left table-leg downwards and the right table-leg downwards. These forces might be different but I don’t see how the overturning will be effected.

Can someone put me, or him, right, please?

Cheers, Tim

[Nicholas Farr]

On Nicholas Farr Said:

Hi Duncan, the cg must be below the lifting point, and his lifting point is still at the top of his frame, where his sling is over. His chain block hook, is in effect, in the same place as two links in the lifting chain would be, if the chain block hook was at the top. Seeing as the sling ends are on opposite sides of part of the machine, should also stop it from toppling, but it would be better if the sling was choked over the top of the frame, and a shackle used to joint the two sling loops and hang the chain block on.

Regards Nick.

The machine can rotate around the bottom hooks, so the hooks would be better above the CG. Imagine if he just had 2 eye bolts in the base with the chain blocks attached. Having the short sling at the back is similar to having a long eye bolt. I will admit that the sling around the overarm will tend to stop it toppling, but it is all less than ideal. Why not just put the slings and chain blocks at the side, although the top cross pieces look to be of smaller section on the sides

With a very short strap around the top back cross member so that the top hook is nearly  touching it looks possible to get the chain block above the overarm, which would be altogether better

[Mark RandParticipant @markrand96270]

@sonicescape38234 is lifting the mill by 10cm / 4″ it doesn’t matter if the slings slip, a sling or rope breaks or the whole assembly falls into a pile of matchwood. No harm will be done (other than to the odd paving brick 🙂 ).

If you want a slightly more secure setup, loop the purple sling around the hook and the green sling around the frame, this adds greatly to the stability.

[Sonic EscapeParticipant @sonicescape38234]

Last week I lifted the milling machine about 10cm and I tried to move it. No chance! There is too much friction from the 8 rubber castors. Also I felt that the hanging machine acts like those seismic dampers in tall building and it is opposing the movement.

But I found another way to move it. I can lift only the front of the mill. And then I push it from the back with a lever. I can move it up to 50cm. Then I lower it down, move the frame 50cm and repeat. It is slow but very easy and safe. In the garage I’ll add a metal plate under the lever to don’t crack the floor tiles.

If the plan to move the machine on wheels failed, the lifting of heavy items from the workbench works very well. The frame can slide over the workbench as planned. Here I’m lifting a ~100kg rotary table.

It is very easy to lower it into a wheelbarrow and move it into the new shed. There I mounted the second chain block to unload the wheelbarrow.

 

[OldironParticipant @oldiron]

Looks like you need to change the wheels for the hard plastic type. You can get these up to a 700Kg load capacity each. Not sure how 8 wheels react to each other when loaded. Maybe 4 would be better. The rubber wheels will all have a flat on the bottom when heavily loaded. Will be almost impossible to move.  The frame looks good though.

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