How to ease out a hardened shackle to fit over a standard scaffolding pole

[GreensandsParticipant @greensands]

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I am currently using a length of nominal 44mm O/D scaffolding pole as an overhead gantry system for my model engineering purposes and have been gifted a shackle complete with a suspension hook which on the face of things should be an ideal match for the pole. Unfortunately the I/D of the shackle measures 39.26mm as opposed to the 44.3mm of the pole. Health & Safety orientated members look away now, but how would it be possible (or advisable) to ease out the I/D of the shackle to give a sliding fit over the pole? A form of angle grinder perhaps?

With the new design of the website I seem to have lost the art of posting photos onto the forum. Can someone please tell me how this is done?

[JohnFParticipant @johnf59703]

As far as H & S is concerned always take heed !  However you should consider what weight you are likely to lift and I would think its probable the shackle will be far stronger than the scaffold pole you are using ???  Usual caveat’s apply here !

Photo’s – when you create a post or reply there is an icon at the far right of the legend – box with a mountain in it, hover on this and it says “inset image” and away you go.

John

[JasonBModerator @jasonb]

Clamp to mill table, ctr it up and use a boring head to open up the size. Faceplate on the lathe if no mill. Carbide tool in both cases.

[Pete RimmerParticipant @peterimmer30576]

A 2 Tonne D shackle with 1.5″ jaw opening is £9 from Zoro (ZT1024832X). Hang that on your scaffold tube and hang your one from it.

[JasonBModerator @jasonb]

Peter how will that fit on to 44mm 1 3/4″ Pole

[Keith LongParticipant @keithlong89920]

Greensands – just to point out that at 44mm o.d. you haven’t got a standard scaffold pole, the od of those is 48.3mm. It sounds more as though you’ve got a length of (probably) 1.5inch NB pipe.

Not trying to be picky but if you decide eventually to buy another shackle or fitting you could wind up with the wrong size.

I’m reasonably familiar with scaffold tube from theatre work as it used for lighting bars and general rigging – we’ve also got 1.5 in NB pipe in the central heating system and that can cause confusion when the scaff. clamps don’t fit!

[GreensandsParticipant @greensands]

I have attached a photo of the shackle in question.  I had not thought in terms of using a carbide tipped tool but will certainlty put it up in the 4-jaw and give it a go.

 

[John Doe 2Participant @johndoe2]

I am sure you know what you are doing but I would be careful here.

Cutting or filing that shackle could weaken it and/or introduce stress risers, which might cause it to fail one day.

For your current purpose a shackle failure might be benign, but years from now when you have forgotten all about it, you might use that shackle in a more safety critical role or for a larger weight.

Surely not worth the risk – just buy a known good make of shackle of the right size. If this one fails and causes injury after resizing it, you might wish you had spent the money ?

[DC31kParticipant @dc31k]

Where do you get the idea that the shackle is hardened? Have you confirmed this by rubbing it with a file?

Squeeze the tube in a vice to make it elliptical, with minor axis to fit the shackle.

By doing so, you will increase the second moment of area in the direction of the lifting force and thus increase the capacity of your crane.

[Mick B1Participant @mickb1]

Why not turn a suitable solid extension to fit inside the (alleged) scaffolding pole at one end (with clamping screw[s] to suit) and a fit for the shackle on t’other – possibly with a groove to locate the shackle loop and a retaining clamp and screw?

[Martin ConnellyParticipant @martinconnelly55370]

Machining away some of the inside may cause the shackle to bow outwards or inwards afterwards and require that it is then in need of bending as well to get the bolt back in. It does all sound a bit iffy to me and I would go along with John Doe 2, buy something that fits to start with. A quick check on Ebay tells me I can buy a 4.75t shackle with an internal diameter of 48mm for less than £9.

I imagine you are not lifting much as the strength of scaffold poles is not very good over a long, unsupported span which is why scaffolders have to use Warren Girder type scaffold truss beams for spanning over anything over a metre or two wide. If you are using NB pipe and it has a welded seam I would not use it for lifting at all. Same as if it is not stainless or galvanized. Internal corrosion can be a problem.

Martin C

[JasonB]

On JasonB Said:

Peter how will that fit on to 44mm 1 3/4″ Pole

It won’t, my mistake early morning post. Buy the correct one for 11 quid.

[GreensandsParticipant @greensands]

Well, for what it is worth I have taken up Jason’s idea and turned to size using a carbide tipped tool and the shackle mounted in the 4-jaw. No issues, no panic moments and I now have the required sliding fit. Sharp edges removed using a half round file. Probably will be kept under the bench and held in reserve.

 

 

[File HandleParticipant @filehandle]

A blacksmith solution is probably best  hammer it on the beak of an anvil rather than cutting away metal.

[Nigel Graham 2Participant @nigelgraham2]

I’d never even consider trying to modify a shackle, either by cutting it or by bending it.

Machining it at all will obviously weaken it but not at all predictably, and bending it even if more scientifically than bodging it with a big hammer, would ensure the pin will no longer fit correctly – so scrapping it.

Buy a shackle that fits correctly – take a sample of the tube and that hook to the stockist to test for fit.

Lifting-tackle is not ever so expensive, and it’s not worth taking risks with it.

 

 

[Michael GilliganParticipant @michaelgilligan61133]

Nigel

We don’t know how Greensands is using any of this gear, or at what loadings, … but I suspect that the tube is being used as a substitute for an overhead rail.

Without the detail, and lacking the analytical tools, I suggest [gut-feeling] that the tube would fail long before the modified shackle … and also that the substantially larger contact patch will decrease, rather than increase, the risk of risk of indenting the tube.

Obviously all of this project is outside normal ‘lifting & handling’ regulations, but if Greensands is happy with that, so be it !!

The machining looks well-done, and the modified shackle may [for all we know] still have an enormous safety margin when loaded as he intends.

 

Note: I am happy to retract any or all of the above if/when the configuration is disclosed.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

[ PostScript ]

If there happens to be a Safe Working Load mark on that shackle: it should, of course, be obliterated now that the shackle is modified.

MichaelG.

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Edit: __ as a quick unverified check, this is worth a look

https://www.engineeringtoolbox.com/shackels-safe-load-d_1696.html

 

[jaCK HobsonParticipant @jackhobson50760]

“Health & Safety orientated members look away now”. That didn’t work!

 

Nice result.

[Nigel Graham 2Participant @nigelgraham2]

Well, obviously we don’t know all the criteria in Greensand’s application – including the maximum mass he wants to lift, and the span and supporting arrangement of the beam.

Even so, although his modified shackle may be fine there, for any other purpose it is effectively scrap.

The turning seems to have retained roughly 2/3 of the diameter of the bar. That would make me think the shackle’s maximum SWL is now about half original by area alone (4/9). What it has actually become by shape effects, is another matter. At least the outline has given smooth transitions from machined to uncut surfaces towards the pin.

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Jack – It certainly didn’t! 🙂

[JasonBModerator @jasonb]

Can’t follow your maths there Nigel, maybe 2/3 reduction in one direction but nothing taken off in the other direction so only a 30% reduction in area though to me it looks less than 1/3, say 1/4 which would be a 20% reduction in CSA

[Michael GilliganParticipant @michaelgilligan61133]

If Greensands would be so kind as to measure the present minimum thickness of the modified shackle, we could confidently assume that treating that as its new ‘diameter’ would give an additional margin of safety.

… see the tabulation that I linked earlier [or do the maths if you prefer, Nigel]

MichaelG.

[Author]

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