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Single Point Lift @ 45 Degrees

10/17/2017 3:21 AM

Hello,

I am currently designing a rectangular box enclosure, approx. 1.5m long weighing ~35kg.

The box will be lifted using a crane via a single lifting point on the box. When the box is lifted, it needs to tilt and rest at 45 degrees whilst in the air.

How do I calculate how far I need to place the lifting point/eyebolt in front of the centre of gravity for the box to sit at 45 degrees during lifting?

Thanks,

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#1

Re: Single Point Lift @ 45 degrees

10/17/2017 3:44 AM

You make a harness to hold the box at 45° ....A rectangular box supported by one point would not be stable...

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#2
In reply to #1

Re: Single Point Lift @ 45 degrees

10/17/2017 4:13 AM

Thanks for the reply.

unfortunately, due to constraints on the design of the box a harness is not suitable for this application.

I really need to know at what distance past the CofG the box could be lifted at 45°.

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#3

Re: Single Point Lift @ 45 degrees

10/17/2017 4:30 AM

If the box is a reasonable height and you determine the height from CoG to the top face, by simple geometry the point is same distance along fom the CoG.

If the height is negligible SE has already given you the answer - it's unstable. But can't somebody put a hand on it hold it at 45deg? For total weight 35kg the force needed is minimal.

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#16
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Re: Single Point Lift @ 45 degrees

10/18/2017 8:11 AM

A 4 point lift at the corners would stabilize it. Weight is so low that the harness could be very short as well.

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#17
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Re: Single Point Lift @ 45 degrees

10/18/2017 8:32 AM

But the OP stipulated that it had to be a single-point lift.

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#4

Re: Single Point Lift @ 45 degrees

10/17/2017 5:31 AM

Here's the construction (side elevation). Either draw it to scale, or use trigonometry.

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#5
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Re: Single Point Lift @ 45 degrees

10/17/2017 5:36 AM

Perfect, finally got my head around it thanks!

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#6
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Re: Single Point Lift @ 45 degrees

10/17/2017 10:46 AM

This presumes the box is of uniform density.

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#7
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Re: Single Point Lift @ 45 degrees

10/17/2017 10:50 AM

Quite. But as long as the position of the C of G can be established (and is fixed) the same method applies.

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#9
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Re: Single Point Lift @ 45 degrees

10/17/2017 11:31 AM

Agreed, CoG is not necessarily the center of pressure.

As well, we don't know if the box contains dry sand at 30% available volume (or the like), thus complicating the CoG at the lift angle of 45° when the angle of repose of the contents is considered.

We also don't know the tolerance of the stated target of 45°. ± 5°?

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#8
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Re: Single Point Lift @ 45 degrees

10/17/2017 11:07 AM

When you say uniform density, do you mean density does not vary due to the box contents moving about, or varies from point to point but is fixed? In the latter case you can still locate the CoG, so the method works.

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#10
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Re: Single Point Lift @ 45 degrees

10/17/2017 12:27 PM

How is the lifting point not at the corner of the box? Does this allow for a non-uniform box?

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#11
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Re: Single Point Lift @ 45 degrees

10/17/2017 1:13 PM

Lifting point would only be corner for 45deg for e.g. a square side elevation with central C of G.

Also box C of G must be fixed and locateable.

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#12

Re: Single Point Lift @ 45 degrees

10/17/2017 4:19 PM

Just slap an eye bolt somewhere on the top, lift it slightly and fill it with ballast until it tilts to the correct angle.

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#13
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Re: Single Point Lift @ 45 degrees

10/17/2017 4:40 PM

Isn't that cheating on the final exam?

I was going to say "ballast it Lyn", but that not be taken as a jokiepoo.

How we all, all of a sudden jumped on this guy's homework like ducks on the last bug of June?

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#14
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Re: Single Point Lift @ 45 degrees

10/17/2017 5:34 PM

I didn't, "explain in detail" and I didn't "show my work" and I didn't, "explain my thought processes".

Hell, I already worked it out three different ways in my mind!

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#18
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Re: Single Point Lift @ 45 degrees

10/18/2017 10:45 AM

OK, then you get an "A".

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#15

Re: Single Point Lift @ 45 degrees

10/18/2017 6:43 AM

Lift it from the middle then keep adding weights until it is at the right angle, assuming it's made of metal, use magnets. I commend this to the house for approval thank you.

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#19

Re: Single Point Lift @ 45 Degrees

10/18/2017 2:29 PM

Tune lift point to required precision.

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#20
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Re: Single Point Lift @ 45 Degrees

10/18/2017 5:47 PM

" The box will be lifted using a crane via a single lifting point on the box "

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#22
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Re: Single Point Lift @ 45 Degrees

10/19/2017 10:40 AM

"...using a crane..."

This is a source of brow furrowing. A crane, for lifting ≅ 35 kg? How about a pulley and a clothesline rope and a high school kid?

Prolly just semantics.

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#24
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Re: Single Point Lift @ 45 Degrees

10/19/2017 10:43 AM

Could be a derrick taking it up 20 stories - who knows?

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#21

Re: Single Point Lift @ 45 Degrees

10/18/2017 7:32 PM

I doubt that we'll ever hear from MechDesEng88, until he has another homework problem he wants the forum to solve.

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#23
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Re: Single Point Lift @ 45 Degrees

10/19/2017 10:40 AM

I concur.

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#25

Re: Single Point Lift @ 45 Degrees

10/19/2017 2:17 PM

Wow, this is first time I’ve posted a comment on a forum and the range of answers is impressive. A word of advise for the people who left silly comments after I clearly stated that my question had been answered, stop wasting your time and keep it on topic. Don’t bring the professional status of this site down with pathetic statements. I concur you have been reported. Good day

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#26
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Re: Single Point Lift @ 45 Degrees

10/19/2017 2:27 PM

Farewell - and please take your head-up-where-the-sun-don't-shine attitude with you. Don't you recognize a little gentle persiflage when you read it?

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#27
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Re: Single Point Lift @ 45 Degrees

10/19/2017 2:55 PM

You came to the forum for help, we did not solicit you.

It is your job to separate the wheat from the chaff, and not complain about the quality of the crop.

First time posters are not taken seriously when they, on their first visit after getting plenty of help with their homework, offer advice. Not good form!

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#28
In reply to #27

Re: Single Point Lift @ 45 Degrees

10/19/2017 7:42 PM

It’s your job to keep replies on this forum to the point and assist the person looking for help. It’s not about making snidey comments about the persons intentions and making people feel unwelcome.

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#29
In reply to #28

Re: Single Point Lift @ 45 Degrees

10/20/2017 4:59 AM

Out of interest what was the purpose of this question? It's quite unusual to want a load to be lifted at an angle, mostly we try to lift the load parallel to the ground.

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#30
In reply to #29

Re: Single Point Lift @ 45 Degrees

10/20/2017 5:14 AM

The rectangular box is interfacing within a larger static box located at 45º.

Hence when craning it in, the rectangular box being lifted should ideally be at the same angle as the interface.

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#31
In reply to #25

Re: Single Point Lift @ 45 Degrees

10/20/2017 12:11 PM

Might we ask the reason for this 45 degree inclination of the box during the lift?

Never mind, I see you just answered that.

Good luck. If you are just lifting this box, then weight shift is not an issue.

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