Scaffold pole strength.
Discussion
I want a "gantry" in the garage from which I can hang a chain block as an engine hoist. Small section RSJ would be ideal, but they seem to be eye-wateringly expensive. A bit of lateral thinking later and I came up with the idea of using two scaffold poles clamped together at each end.
I fed the measurements (ten foot span, two inch dia, 4mm wall, 180KG load) into a couple of web deflection calculators and got the rather eye opening result of nineteen inches of deflection for one pole (presumably half that for two parallel poles). This can't be right, can it?
I'm just imagining my 90KG body weight stood in the middle of a 10' pole, and I wouldn't expect much, if any, movement at all.
So, are scaffold poles a bit limp-wristed or are the "calculators" wrong?
I fed the measurements (ten foot span, two inch dia, 4mm wall, 180KG load) into a couple of web deflection calculators and got the rather eye opening result of nineteen inches of deflection for one pole (presumably half that for two parallel poles). This can't be right, can it?
I'm just imagining my 90KG body weight stood in the middle of a 10' pole, and I wouldn't expect much, if any, movement at all.
So, are scaffold poles a bit limp-wristed or are the "calculators" wrong?
I wedged the roof beams above the double thickness wall pillars the hung 2 short lengths of scaffold tube lengthways across 2 roof beams and hung a transvers piece of tube across them so I had for and aft movement as well as some side to side.
Using a standard wire hand ratchet hooked to U clams, with that lot i could lift any engine out with no noticeable flex in the garage roof.
Another option is to use acrojacks to support the roof beams
Using a standard wire hand ratchet hooked to U clams, with that lot i could lift any engine out with no noticeable flex in the garage roof.
Another option is to use acrojacks to support the roof beams
I think you'd be surprised at how much a 10 foot scaffold pole would flex if you stood in the middle of it with only the ends supported. When used for their intended purpose the long ones are either centrally supported (either with a vertical, some form of triangulation or a ladder beam) or purely used as uprights.
You really need vertical height to your construction to make it rigid. Welding two poles together and then positioning them such that they're above one-another might work. Side-by-side or simply bound together at the ends, you'll still get a fair bit of deflection. If you go for a ladder beam, remember it must be mounted in the vertical plane not horizontally or it wont work.
Personally, I'd use an RSJ. You should be able to get one that'll do the job for around £50 a meter.
You really need vertical height to your construction to make it rigid. Welding two poles together and then positioning them such that they're above one-another might work. Side-by-side or simply bound together at the ends, you'll still get a fair bit of deflection. If you go for a ladder beam, remember it must be mounted in the vertical plane not horizontally or it wont work.
Personally, I'd use an RSJ. You should be able to get one that'll do the job for around £50 a meter.
Edited by kambites on Thursday 14th January 10:32
Engine hoists are only £100 to £150, so to be harsh for a moment what does a home built gantry get you that a designed, tested & warranted engine hoist doesn't?
WRT to welding scaffold tubes, to get the structural performance your calcs assume you'd need to either fully weld the length, and they're galvanised so that will have to come off first, or put a lot of tube clamps on. Plus you'd also have to horizontally restrain each end so the load doesn't over turn the "beam", which is likely as the engine's centre of gravity will change as it rotates out of the car and you will have the devils own job keeping this vertically under the axis of the "beam"as your lift progresses. The RSJ would be the way to go, but you'd need to add padstones at each end so the RSJ doesn't crush the wall locally. Oh, and test it with something that doesn't matter first (water barrel, bags of sand etc)
WRT to welding scaffold tubes, to get the structural performance your calcs assume you'd need to either fully weld the length, and they're galvanised so that will have to come off first, or put a lot of tube clamps on. Plus you'd also have to horizontally restrain each end so the load doesn't over turn the "beam", which is likely as the engine's centre of gravity will change as it rotates out of the car and you will have the devils own job keeping this vertically under the axis of the "beam"as your lift progresses. The RSJ would be the way to go, but you'd need to add padstones at each end so the RSJ doesn't crush the wall locally. Oh, and test it with something that doesn't matter first (water barrel, bags of sand etc)
Collectingbrass said:
Engine hoists are only £100 to £150, so to be harsh for a moment what does a home built gantry get you that a designed, tested & warranted engine hoist doesn't?
What it gets me is lifting capacity that's hidden in the roof of the garage rather than a huge collection of (99.9% of the time) scrap iron that I'd have to store in the garage and which I would be guaranteed to bark my shins on every time I went in there!Collectingbrass said:
Stuff about welding and CofGs
I take your point about welding galvanised stuff and adequate support, but I wasn't intending to do any welding and the support is already sorted. I was just surprised that thick wall tubing was so flexible. However, I suppose in its primary use that flexibility is not an issue as it can be braced. My proposed use would have precluded bracing due to the welding issues and/or the cost of the necessary additional material, putting it within a gnat's of the cost of an RSJ. Yes, I'm from Yorkshire and hence I am toying with this quandary at the moment.
It's looking more and more like the engine & gearbox Is going to need removal from my Seven.
Engine crane or gantry, that is the question.
I see the disadvantage of storing a crane, but on the plus side the e & g could be wheeled to the strip down bench.
The gantry, once fitted, can remain in position.
If I go for the gantry I'll go for oblong box section. []
Paul G
It's looking more and more like the engine & gearbox Is going to need removal from my Seven.
Engine crane or gantry, that is the question.
I see the disadvantage of storing a crane, but on the plus side the e & g could be wheeled to the strip down bench.
The gantry, once fitted, can remain in position.
If I go for the gantry I'll go for oblong box section. []
Paul G
cmsapms said:
Collectingbrass said:
Engine hoists are only £100 to £150, so to be harsh for a moment what does a home built gantry get you that a designed, tested & warranted engine hoist doesn't?
What it gets me is lifting capacity that's hidden in the roof of the garage rather than a huge collection of (99.9% of the time) scrap iron that I'd have to store in the garage and which I would be guaranteed to bark my shins on every time I went in there!Collectingbrass said:
Stuff about welding and CofGs
I take your point about welding galvanised stuff and adequate support, but I wasn't intending to do any welding and the support is already sorted. I was just surprised that thick wall tubing was so flexible. However, I suppose in its primary use that flexibility is not an issue as it can be braced. My proposed use would have precluded bracing due to the welding issues and/or the cost of the necessary additional material, putting it within a gnat's of the cost of an RSJ. Yes, I'm from Yorkshire and hence (1) We're like normal Tykes, but shillings and white five pound notes are still legal tender as we have so many still on hand...
finishing touch said:
I am toying with this quandary at the moment.
It's looking more and more like the engine & gearbox Is going to need removal from my Seven.
Paul G
I'm in the same boat. My seven's gearbox is in dire need of a rebuild. So the engine/box needs to come out. When I've had the engine out on previous occasions I've been doing work on it, so could remove the head in situ and then lift the bottom end out by hand. Now I'm a bit older I'm not sure my back will thank me for doing that and, anyway, I don't need/want to split the engine this time.It's looking more and more like the engine & gearbox Is going to need removal from my Seven.
Paul G
I'm going to arrange for the gantry to extend over the top of the workbench so that, with the help of a trolley arrangement on the RSJ, I can lift the engine from the car, move it sideways and lower it onto the bench.
Collectingbrass said:
As an East Yorkshire (1) tightwad myself I would at this point be thinking long and hard about how often I really would use the gantry and whether treating Ebay, Gumtree et al as a hire shop (buy it, use it, sell it) might not be the better idea, especially if really it is a one off for a restoration project...
(1) We're like normal Tykes, but shillings and white five pound notes are still legal tender as we have so many still on hand...
Trouble is, I'm an inveterate tinkerer, so engine removal is a fairly frequent occurrence. I've hired engine cranes before and find that they have as many limitations as advantages. (1) We're like normal Tykes, but shillings and white five pound notes are still legal tender as we have so many still on hand...
Paul S
cmsapms said:
I was just surprised that thick wall tubing was so flexible.
The walls may be thick, but the effective diameter is small compared to the average RSJ and that makes a massive difference (more correctly, the area moment of inertia).The bending stiffness of a tube increases with a fourth power of the diameter, i.e. double the diameter and you get a sixteen-fold increase in stiffness.
sometimes the delivery charge is more expensive....cmsapms said:
... rather than a huge collection of (99.9% of the time) scrap iron that I'd have to store in the garage and which I would be guaranteed to bark my shins on every time I went in there!
Reminds me of the joke, if that's the right word, of:Q. Where's the best place to store an engine hoist? A. At a mate's!
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