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dkaustin
04-11-2007, 06:54 PM
Came across this home-built gantry crane.

http://www.milwaukeeblimpworks.com/Gantry.html

It has some interesting features, but I am no structural engineer. Is this a good design, or is it a widow-maker?

What is your opinion, gentlemen?

bob_s
04-11-2007, 08:19 PM
Came across this home-built gantry crane.

http://www.milwaukeeblimpworks.com/Gantry.html

It has some interesting features, but I am no structural engineer. Is this a good design, or is it a widow-maker?

What is your opinion, gentlemen?


Based on the W4-13 I-beam data, with 1000 pound load in the middle of the 12 foot span, 13 pounds per foot for the beam load max stress should be 7500 psia.
Safety factor assuming nominal yield stress of 30000 psia is about 4.

speedsport
04-11-2007, 08:28 PM
I like it, when you are through with it please send to me, Thanks you.

bob_s
04-11-2007, 08:39 PM
Finally saw the cross headers, don't like the concentrated load on the jaws of the cross-member, there looks to be very little cross-sectioin holding onto the flange of the I-beam.
Better to have it supported from below, with the teeth on the cross-member preventing the rotation of the I-beam.

J Tiers
04-11-2007, 11:02 PM
I have to say I am not crazy-nuts about it.

The pipe columns are probably OK, but are minimally braced. They are probably susceptible to damage or bumps while loaded, which would cause a crash in the "right" conditions.

4" beam of any sort is edgy for 1000 lb. I did some calculations and table lookup for a similar fixed beam hoist. I decided that 5" was needed , and that was for a lesser span. But in my case I had a 3 foot cantilever, so that distorted my needs.

The beam may also need derating for twist.... I didn't calculate the span in flange widths.

I don't particularly like the Kee-Klamp construction, and the beam support looks a bit minimum also. One of the characteristics of a robust design is the relative lack of "limits", meaning that even if each support is not 100% sharing the load, it still is amply strong. I'd be a bit worried that design might need perfect conditions to maintain its de-rating from failure point.

Overall, it appears to be a minimum "just meet requirements" design. A commercial one of similar capacity would have more cross-bracing of the supports, and might use a different beam type.

Go look at some of the ganrty folks and see what they do. I think it will look a bit different.

wierdscience
04-11-2007, 11:39 PM
The adjustable tees are the weak link,so much so I would not have used them.They are most times made from cast aluminum or malleable iron niether of which is suitable for lifting equipment.

The beam and the legs are substantial enough to hold the load he is dealing with maybe even 2x's that,I would have prefered welded or bolted joints however.

Not to mention those tees start to add $$$ up quick.

ckelloug
04-12-2007, 12:30 AM
I haven't done any calculations on this and would have to shake some rust out of my brain to make them. I don't like the split cotter design as he calls it that connect the legs to the beam. It's hard to tell exactly what he's doing but it looks like it would be relatively easy to not properly tighten the bolt and have that joint slip thus shock loading the rest of the mount and collapsing the crane. It might be safe for trained personnel but as an implement for the machinery riggers I know, It's a lot safer to drill big holes in the I beam. Big bolts through I-beams in holes don't have a metastable "might carry the load" state when everything isn't perfectly tight. This thing looks apt to work fine on a good day and fail catastrophically on a bad day and the only way to tell the difference is to use a torque wrench. I also suspect that the legs aren't as stiff as I'd want but that's just an eye-ball based opinion, not a calculation.

Evan
04-12-2007, 01:07 AM
I hate web sites where the pics haven't been properly resized for the page. Those pics are HUGE, file size wise. Waste of my bandwidth and time.

dp
04-12-2007, 01:10 AM
I hate web sites where the pics haven't been properly resized for the page. Those pics are HUGE, file size wise. Waste of my bandwidth and time.

I never saw any pictures - they all stalled.

Swarf&Sparks
04-12-2007, 01:13 AM
Took 20 mins to load here and I'm on DSL!

Mike W
04-12-2007, 02:05 AM
It took me 2.5 minutes to download on cable.

matador
04-12-2007, 03:28 AM
Am I the only one that thinks it's comical that the guy uses an engine crane to assemble his "crane"?The engine lift looks stronger than his version.
I certainly wouldn't stand under it with a load on it.It looks to me like it could quite easily collapse sideways.Just my $0.02.

Forrest Addy
04-12-2007, 03:44 AM
I'm not thrilled either wih the design or the choice of materials.

It's clear the builder didn't consider leg buckling in that skinny pipe as a threat to safety. My handy books discuss aspects like slenderness ratios, load eccentricities, etc that were clearly not taken into account as an engineering preliminary.

Black iron pipe is made to bend and yield to survive a couple of freeze/thaw cycles and structural settling. It's not intended as a structural steel. Structural steel tubing has almost double the mechanical properties per square inch of Sch 40 iron pipe.

Those Kee fittings are intended for hand railing and light scaffolding not elements in a crane design. They're made of malleable iron. "Malleable" needs to be explained. Malleable refers to ductility under the hammer; the ability of the material to flow and yield without fracturing under sufficient load. Cast iron has practically zero malleability (less than 1% to failure) whereas pipe steel has considerable (maybe 35%). Ductility of malleabliity of malleable iron is about 5%. I would NOT Kee fittings for scructure bearing suspended loads.

The skepticism expressed above about the beam suspension is well founded.

I have no complaint about the choice of beam except I failed to notice what arrangement was made to prevent the crane from tilppng uncontrollably should a load be pushed from the supported part of the beam to the cantileavered end.

This "crane" is a classic case of a fellow having a bad idea who turned it into a bad design. He not only executed it neatly but published it on the internet where only truth and beauty may be found. It makes me shudder. I'd use it in an engineering statics class as an example of a bad design.

Want to make a good portable home shop crane? Take your inspiration from Wallace Gantry and use similar materials. Weight in hand portable apparatus is always a factor. If the proper materials are chosen a 2 ton working capacity adjustable height home shop crane with a safety hoist trolley and foot casters. It can be designed so it has a center span of 10 feet, a working height under the beam of 11 feet, and no part of it will be more than a one man load to assemble and erect. Plus it will be well designed and made of the right materials. If challenged, it will meet safety requirements and pass overload tests on an adverse surface. It will not be cheap. Cheap and safe are concepts that don't go well together in hoisting apparatus.

Your Old Dog
04-12-2007, 06:45 AM
I hate web sites where the pics haven't been properly resized for the page. Those pics are HUGE, file size wise. Waste of my bandwidth and time.

I'm on a high speed cable connect. The first little picture came through and properties said it was of 700K and I could barely make it out! I gave up on the rest after waiting for that one.

As for the design, no engineer here but that looks like where mankind may have started with the gantry designs, not where they should have left off :D

pressurerelief
04-12-2007, 07:47 AM
Looking at this is "Crane" is eye opening to say the least. If the Kee Klamp people saw it, they would be going to the legal dept. to design a new sticker on unintended uses. I do not believe there is any published data from kee klamp for this type of application so "doing the math" is going to be improbable if not impossible.

Personally I would not load something constructed like this to more than a couple of hundred pounds. Kind of like a third hand, but who needs one when, as pointed out, he already has an engine lift.

Look in the Darwin Awards next year, he may be in the running.

PTSideshow
04-12-2007, 08:03 AM
Reminds me of the old style home made ones the local headstone maker used on his yard and truck. He did say in his description that you have to counterweight the other end when using it with the load at the end.
I still don't see how that can be any more help getting something into a basement than the engine hoist frame with a winch on it. Unless he can access his basement with a straight down drop. I wouldn't use it.

Almost 4.26 minutes on highspeed cable LOL

Evan
04-12-2007, 08:44 AM
Kee Klamps are designed for load bearing applications and the manufacturer provides load bearing technical data for the product. The 1 1/2" size used is rated from 5000 to 7000 lbs depending on configuration. The clamping system isn't the weak point.

More important is the stability of that length of sched 40 pipe considered as a slender member under compression. This especially applies to the point on the legs where the triangulated portion is supported by a single member. This is a stress concentration point and is liable to high bending loads at this point if the unit is subject to moving side loads. In particular, if the load, an engine for example, were to be picked so that it were to swing it could place high loads on that junction of the legs.

Also, if used to pick a load off the cantilevered end the entire load falls on only the pair of legs at that end. The legs at the back won't be supporting any load and will be in tension to the counterweight he mentioned. He doesn't give details of how he intends to counterweight the system but it must either mean adding load at the far end or otherwise restraining the rear legs at the bottom placing them in tension.

Also of concern is the stability if a load is moved on the trolley along the beam projection and anything causes the trolley to stop suddenly. All of the fore/aft load falls on only the front upper triangulation joint if the back legs are in tension and not anchored.

As the device is meant to be used with a moving load static load calculations are of no use in determining safety factors. Dynamic loading is a very different kettle of fish and not something that even an experienced shade tree mechanic is likely to be able to do.

Note that I take care not to walk under the lifting boom on my Land Rover. :D

dkaustin
04-12-2007, 09:25 AM
Thanks to all who replied. A real eye-opener!

pcarpenter
04-12-2007, 10:28 AM
This is $600 when its not on sale. I wonder what all the hardware cost the guy who built the other one.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=41188

Say what you will about it being an HF product. Even if you derated it to 1000 pounds too, you are buying something ready for assembly that should do the same job. Now...as for one man assembly and disassembly I dunno. I would leave it assembled and park it. At an almost 8' span, you could park the nose of a car under it or let it hover over your lathe or something like that to reduce its space hogging attributes to a minimum.

paul

A.K. Boomer
04-12-2007, 11:56 AM
All I needed to read was that the legs are built from black pipe, why anybody would build anything other than running a gas line from black pipe i cannot comprehend -- ok maybe a birdfeeder post if you dont mind the rust,


the more i read the more i started thinking of how it reminded me of Evans post pounder... the difference is Evans pounding posts and this guys moving around thousands of dollars worth of equipment, I believe the word that would sum it up best came from a bloke named Curly, ---- Ynaahhhaaa, woop,woop woop,arf,arf,soytenly,knuck,knuck,knuck...

J Tiers
04-12-2007, 01:25 PM
More important is the stability of that length of sched 40 pipe considered as a slender member under compression. This especially applies to the point on the legs where the triangulated portion is supported by a single member. This is a stress concentration point and is liable to high bending loads at this point if the unit is subject to moving side loads. In particular, if the load, an engine for example, were to be picked so that it were to swing it could place high loads on that junction of the legs.

Good point, and it is actually worse than that.... The triangle provides some help against the slender column issue, BUT ONLY IN ONE DIRECTION. The other way, at 90 deg to the beam, it simply may add some bending strength, how much depending on its end connections.



Also, if used to pick a load off the cantilevered end the entire load falls on only the pair of legs at that end. The legs at the back won't be supporting any load and will be in tension to the counterweight he mentioned. He doesn't give details of how he intends to counterweight the system but it must either mean adding load at the far end or otherwise restraining the rear legs at the bottom placing them in tension.

Again, good point, and it may be actually even worse than that, depending on how the counterweight is supported. If hung from the beam, at the far end, or from the legs, its one thing. But if hung from the middle somewhere, as might be natural, it ADDS TO the load on the near-side legs.



Also of concern is the stability if a load is moved on the trolley along the beam projection and anything causes the trolley to stop suddenly. All of the fore/aft load falls on only the front upper triangulation joint if the back legs are in tension and not anchored.


yet another good point.......

I don't think pipe is bad in and of itself. But it needs to be used intelligently, which I agree is NOT done in that design. '

Anything at all that is different from the perfect static condition, and there may be an issue causing it to drop the load by buckling.

bob_s
04-12-2007, 02:46 PM
Actually the legs are of the least worry. The buckling load for a 9 foot long 1 1/4" schedule 40 steel pipe is 4950 pounds.

Even if you put the 1000# directly over two of the legs the load would only be
about 570# (539/cos(angle) estimated to be about 18.4*)

Evan
04-12-2007, 02:56 PM
The buckling load for a 9 foot long 1 1/4" schedule 40 steel pipe is 4950 pounds.

That's static load. As I said, this must be analyzed as a dynamic load situation. That especially affects the buckling tendency of slender members in compression. Static load values assume no motion induced forces.

bob_s
04-12-2007, 03:04 PM
Even if you lift at 1G in excess of gravity, you will only double the load!

Ain't no way with a manual hoist even a gorilla will be able to do that!

Evan
04-12-2007, 03:13 PM
I'm not talking about lifting speed. I'm talking about the possibility of the load swinging and maybe even striking the legs. Even if the load doesn't strike anything it isn't difficult for a swinging load to double the gee forces in a periodic manner and it could also transfer most or all of that load to just one leg instead of all four. Also, what happens if the operator leans or pushes on one of the legs as the load is swinging? A slender member under compression is very vulnerable to small side loads which may induce buckling.

Too_Many_Tools
04-12-2007, 09:25 PM
This is $600 when its not on sale. I wonder what all the hardware cost the guy who built the other one.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=41188

Say what you will about it being an HF product. Even if you derated it to 1000 pounds too, you are buying something ready for assembly that should do the same job. Now...as for one man assembly and disassembly I dunno. I would leave it assembled and park it. At an almost 8' span, you could park the nose of a car under it or let it hover over your lathe or something like that to reduce its space hogging attributes to a minimum.

paul

Seen we have a number of experienced eyes on this subject, what do you think of the HF offering?

TMT

Too_Many_Tools
04-12-2007, 09:28 PM
Want to make a good portable home shop crane? Take your inspiration from Wallace Gantry and use similar materials. Weight in hand portable apparatus is always a factor. If the proper materials are chosen a 2 ton working capacity adjustable height home shop crane with a safety hoist trolley and foot casters. It can be designed so it has a center span of 10 feet, a working height under the beam of 11 feet, and no part of it will be more than a one man load to assemble and erect. Plus it will be well designed and made of the right materials. If challenged, it will meet safety requirements and pass overload tests on an adverse surface. It will not be cheap. Cheap and safe are concepts that don't go well together in hoisting apparatus.

Good point.

Has anyone seen a good homemade copy of the Wallace gantry?

If so, pictures please.

TMT

Duct Taper
04-12-2007, 09:40 PM
Check out the Bushman site for specs and ideas on how strong you have to make a crane before you even start.

http://www.bushman.com/prod_gcran.asp

aboard_epsilon
04-12-2007, 09:52 PM
Good point.

Has anyone seen a good homemade copy of the Wallace gantry?

If so, pictures please.

TMT

how about this i made in a hell of a hurry 2004

http://bbs.homeshopmachinist.net/showthread.php?t=8834&highlight=shipman+gantry

fully portable

not tested scientificaly for weight ...but it has lifted over 1.5 tons...without any visual deflection...reckon it's ok up to two tons with chains across the bottom of the legs ..

wouldnt chance any more on it .

drawings here

http://bbs.homeshopmachinist.net/showthread.php?t=8858&page=2&highlight=gantry+mark

all the best..mark

J Tiers
04-12-2007, 11:48 PM
The HF one is a whole lot stronger than the Kee-Klamp one, at least than as much of that one as I had patience to wait for on dialup.

I'd still worry about a load being rolled sideways along the beam and stopping suddenly, or hitting the end support. The bracing there seems short of the strength of the rest of it against pure downward loads.

HF stuff has a way of looking worse in person. I saw one when I was looking for some little item they were sold out of (chip brushes, probably), and it isn't as nice in person, or at least the one I saw was not.

dp
04-13-2007, 02:29 AM
If anyone needs an example of the failure modes of this contraption they need only substitute schedule 40 PVC for the iron pipe and hang a load on it. The whole rig will quickly fail leaving one to imagine the matter of scale of the forces required to fail the exihibit.

Having yarded a lot of engines out of cars over the years I have to agree with Evan that this is not a good solution for dynamically shifting loads. Particularly when the transmission accumulator hangs on a heater hose while the operator is reefing on the chainfall while watching the clearance of the starter motor. Unintended forces build quickly and release faster.

I know a widow maker when I see one.

bob_s
04-13-2007, 08:50 AM
Seen we have a number of experienced eyes on this subject, what do you think of the HF offering?

TMT

The HF gantry appears to use a lighter I-beam than the home brew (specs say 2 7/8 in wide flange). They rate it at 2000# lift capacity, due to the more rigid end supports on the columns. It also seems to have a very narrow foot print perpendicular to the beam. Note that the Wallace gantry of the same capacity has a minimum foot print of 6.5', and lists a work envelope of +-7.5* on the lift itself, so expect that the work envelope of the HF to be smaller still.

Evan
04-13-2007, 10:47 AM
For any design that includes columns in compression there is a very important concept that governs the strength and stability of the structure. It's called the slenderness ratio.

It is the ratio of the column diameter to the length. The failure mode of a loaded column is dependent on this ratio and the applicable ratio for a material varies depending on the Young's modulus of a material. Young's modulus describes the stiffness property of a material.

There are three main ways that a column in compression will fail and which way it fails is dependent on the slenderness ratio for the particular material. These failure modes are not precisely defined by the slenderness ratio and as the slenderness ratio increases the mode graduates from the previous to the next.

A loaded column can fail by pure compression failure of the material as the stress exceeds the ultimate yield strength of the material. This is the failure mode for short, fat, low ratio columns.

An intermediate failure mode for somewhat taller and more slender columns is called kneeling. The column fails in an inelastic manner by buckling at a defined point when the yield strength is exceeded. This occurs near the compressive limit of the material but is characterized by a sideways displacement at the failure point.

For a slender column the failure mode is buckling in an elastic manner. Long before the yield strength of the material is reached the column will elastically bend over the entire length of the column. This failure mode is independent of the compressive yield strength and is defined by the stiffness (Young's modulus) of the material. It is a situation where the resonant frequency of the member reduces as load is applied until it reaches zero. Near zero resonant frequency the column is extremely sensitive to small forces applied perpendicular to the column as well as any existing bending loads that are applied by the structural design.

Side loads on a slender column are of particular importance. Because slender column failure is dependent on resonant frequency any displacement of the column sideways is in effect "plucking" the column like a guitar string and exciting it at whatever it's current resonant frequency is. The lower the resonant frequency of a long thin member the easier it is to displace and the larger the excursion that results from an applied force. As the column is displaced the compressive force vector no longer acts through the neutral axis. It rapidly moves non-linearly so that the compressive load increases on one side and is relieved on the other. This very rapidly overloads the material on the compressive side beyond the ultimate compressive limit and it buckles.

The slenderness ratio zones vary with material. The three materials of most concern to most HSM's are steel, aluminum and wood.

Here are the ratios of interest for each material.



SR=Slenderness Ratio=length/radius
(radius is from neutral axis to most distant fiber radially)

Failure mode: Ultimate Intermediate Buckling
yield inelastic
limit
Structural Steel SR < 40 40 < SR < 150 SR > 150

Aluminum 6061 - T6 SR < 9.5 9.5 < SR < 66 SR > 66

Aluminum 2014 - T6 SR < 12 12 < SR < 55 SR > 55

Wood SR < 11 11 < SR < (18 - 30) SR>(18 - 30)


Note: The radius used is properly the radius of gyration. For members that are mainly bilaterally symmetrical around the long axis such as common beams and tubes the radius to the most distant fiber will suffice. This isn't an exact calculation. If the beam is significantly asymmetrical (rectangular, L shaped etc) then the calculation of radius of gyration should be made.

J Tiers
04-13-2007, 12:45 PM
The "Blimpworks guy" TOOK DOWN THE SITE as he said people he believed convinced him the design was unsafe......


Sorry..

People whose experience and judgement I respect have convinced me that the gantry crane design previously shown on this page is unsafe. Until the design issues are resolved, I am withdrawing the page.


As far as the HF.............


The HF gantry appears to use a lighter I-beam than the home brew (specs say 2 7/8 in wide flange). They rate it at 2000# lift capacity, due to the more rigid end supports on the columns.

And, it is only 94" between the columns, not the 12 feet that I think I recall from the Blimpworks one. That difference makes a LOT of difference.

ckelloug
04-13-2007, 05:40 PM
Evan,

The text of your description of column failure mode differences due to the slenderness ratio was more clear than most textbooks I've ever had on anything. It's an asset. Congratulations on such a well worded description.

For all the grief you get about the "Evan Wall", I must say that I would be extremely displeased if I ever was thrown against a physically manifested wall built by you. Such a wall would be indestructible. Since Young's modulus is symbolized by E, we can just call it Evan's modulus here today.

wierdscience
04-13-2007, 10:55 PM
One point that I don't think has been addressed here is the use of A-frame lifting devices for transporting.It's a bad idea.

If you have a load suspended and are rolling it along on the floor and sudden movement can cause the A-frame to stop suddenly with the load still moving.Depending on the load and it's distance off the floor relative to the height of the A-frame it could mean a wild swing or a sudden flip.

I once saw an A-frame with penumatic wheels on the legs,shortly after I saw the same frame on it's side with the load it was carrying on the ground.The owner said "it happened really quick,like it was spring loaded,the wheels just shot out from under it!".....Duh?:D

A-frames are best rolled or assembled in place over the load,the load lifted and lowered onto some suitable transport device.

I have a small A-frame on wheels at work that I use to pick motors and gearboxes in the field.It has wheels on all four legs to allow rolling into position.Once the load is lifted supports can be placed across the base rails of the frame under the load and the majority of the load lowered onto the supports,it can then be transported safely since the GC is now near the ground and the pendulem effect is nill.

Black pipe is acceptible,if used correctly,proper material will not compensate for poor design.Blackiron pipe is commonly used by the shipload for structural members everday in my area in sizes 1/2 to 60" for everything from support columns to oil platforms.

Most comoon seen here is A-53 continous seam same as the pipe used in the hoist.

Personally I like square tubing for it's added column strength and ease of fabrication,but I have no problems with black pipe in a pinch.

wierdscience
04-13-2007, 11:01 PM
Deleted duplicate post-

Charles Ping
04-16-2007, 06:12 AM
I've been away so missed the blimpworks design before it was taken down - all useful discussion though.

Not being confident enough to design one from scratch I came across this site:
http://www.synthx.com/products/index.php?cat_id=3&catname=Cranes%20&%20Lifting
Having some Paypal surplus funds I bought the plans - which appear to be much better than the drawing on the cover would suggest.

Anybody else looked at them?
The t&c's forbid me from distributing them.
In summary there are a number of options around span, height and capacity.
As an example a load capacity of up to 5000lbs, span of 12ft and up to 11.5 ft height uses 3.5" square for the uprights with 2"x2" angle braces, channel section bases and and 7" I beam. The devil, of course, is in the detail, and such elements as brace length, base length (which are specified and vary with load capacity) and construction/welding details are listed.

Seems fairly robust from my amateur viewpoint and good value (and no, I don't know the company)


Charles