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Discussion Starter #1
Hey all,

I know there are about eleventybillion gantry crane threads between Pirate, shop floor talk, home shop machinist, garage journal, etc., but I actually want to finish a few engineering calculations for this thing.

I currently go to school for mechanical engineering, so really, this should be a piece of cake. I however, do not have my mechanics of materials books on hand to get the correct formulas and frankly, I just don't remember EVERY little thing I learned.

I have already looked at the Wallace and Vestil gantry cranes and started with some of their dimensions for the approximate size I want, as well as the size of I-beam that I need.
I am going to have a 10' span, adjustable height 9'-11', 6.5' tread, 8" casters and am building this to hold 3 tons. Although it will most likely never see that, I may come close when I move some big machines in.

I remembered enough/ used some calculators on engineering edge, to ultimately determine that the beam I want is an S10x25.4, which has an adequate safety of factor built in.

The only thing I am a bit uncertain about is the tube for the uprights.
The design will most likely be a cross between the Wallace and Vestil, having the I-beam connected to the tube, and then having two pieces jut out from each tubular leg.
Or I may just have the uprights go to a flat bottom piece.

My question is, what is the max axial compressive load that a 3.5"x3/16"x8' piece of square tubing can handle?
I found this column load chart from this nifty website and on page 11 it says that it is 44kips, which would equal 22 tons.
Is that right?
I also know that the angle of the legs will change things, but I'm not worried about that right now.

Thanks in advance!
 

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I don't think Column loading is going to be your hang up, nor will the pure compressive force for 3.5" square. You've got to take into account the bending moments that gets transferred from the fixed ends of the main beam across the top as well. You will have casters on the base, so the two pieces will not be tied together. It'll be like walking on hardwood floors in socks. You will have to have stiffness in the up-rights as well to keep them from splitting apart under load and moving around.

Just for grins - 3.5" x 3/16" square tube, with a yield of 36000 psi, will handle roughly 90,000 lbs. This tube will work for your up-rights, but you'll need bracing.
 

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Discussion Starter #3
Bringing this back from the dead.
I posted pics in another thread and got some questions about it, so I figured I would show the build up of it.

I will edit this later to add the exact materials used, I do not have my list with me at the moment.
I will also add more detailed pics if they are requested, as I kinda got in a hurry to finish it and pictures took a hold.

I researched different designs on the market, mostly Wallace and Vestil and I kinda incorporated those two and my own designs into one.

With what I remember from my MEM classes, I did some calculations and with a safety factor of approximately 3, the structure is good to around 4.5 tons.

NOW, the casters are only rated at 1 ton each, so they are the limiting factor in the design.
This thing will also most likely NEVER EVER see more than 2 tons.

So far I have used it to lift a Bridgeport, Grobe saw, ass end of my jeep, motor, and other things like that.

Here is the build though!

The dimly lit space I worked in before moving everything.


The materials after final cuts.


Drilling mounting flange holes.


Holes and flange plate.


Cutting the angled legs.


Making sure it's all even.


Laying it out.


Clamping it all together.




Welding the uprights.
 

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Discussion Starter #4






All together!






Shitty dark picture of the Bridgeport hanging from it. Saw no visible deflection at all.


Jeep.


Engine.
 

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Discussion Starter #7
Nice! How do you adjust the height?
Thanks. Currently I just use a floor jack to raise it up one side at a time. The clearances are pretty tight, but it extends quite smoothly for being so heavy.

I do however have a little 'system' on paper that should allow me to use the hoist itself to raise it up.
Would look something like this.


That turned out very nice.. great job :beer:
Thank you very much, it wasn't all that difficult to make and comes in handy a lot.
I've seen some of your threads with your shop stuff, you have got quite the setup yourself. :smokin:


I first mocked it up in Google Sketchup to get a visual reference as to how it would look when done.
But, I'm drawing it up in Solidworks now so I can do an FEA on it.
I can post up the files when it's all done.
 

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Discussion Starter #10 (Edited)
thats a pretty awesome idea. i dont think you need the pulleys though. just hook the ends of the cable directly to the bottom where the pulleys are. no?
Thanks. I thought the same thing too at first.
The uprights are bolted directly to the i-beam....So it would just be pulling on itself, doing nothing.
By attaching it the stationary legs, when I start putting tension on the cable, it will start lifting the uprights.
Just stare at it for a couple minutes, you'll see it. :laughing:

Edit: Your edit was faster than my response... lol
 

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Thanks. I thought the same thing too at first.
The uprights are bolted directly to the i-beam....So it would just be pulling on itself, doing nothing.
By attaching it the stationary legs, when I start putting tension on the cable, it will start lifting the uprights.
Just stare at it for a couple minutes, you'll see it. :laughing:

Edit: Your edit was faster than my response... lol
ha. yea, i typed it, and then realized my it wasn't going to work. i wonder how hard that's going to try to collapse the legs inward toward each other. worst case scenario, just throw a 2x4 in between thats the right length.
 

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Thanks. Currently I just use a floor jack to raise it up one side at a time. The clearances are pretty tight, but it extends quite smoothly for being so heavy.

I do however have a little 'system' on paper that should allow me to use the hoist itself to raise it up.
Would look something like this.
I dont think that would work too well as you are applying a force downward on the gantry as you are trying to lift it.
Do a FBD, I don't think it will work.
 

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yes it will work, forget FBD's. there will be less cable length as it is drawn it, only option is for the uprights to move up. I've seen systems like this before:)
 

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Good job for sure! If you need some help with the calcs let me know. FEA isn't really needed for something like this but it is a nice tool to check with.

FBD's are the most important aspect to analysis.
 

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Slick idea on that cable system.. sort of like a forklift mast.. using the chain to pull the mast extension up..
 

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I really like your design, I will likely be building something extremely similar. Few questions if you don't mind.

How did you decide on a leg angle and tread width? Your legs look to be about 60 degrees and come up almost to the beam when at mid height. Is this more desirable vs having the legs at a shallower angle and having straight tube up a couple feet?

Does the location of the pins in the side matter ( relative to the intersection of the legs)?

Did you notch the legs or the receiver tube for the horizontal tie in at the bottom? Would you notch the receiver tube for the legs or did you just weld them to the surface? I would think notching could weaken the overall structure but at the same time make a stronger joint.


Thanks a bunch, I will post up some pics when I get started.
 

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Discussion Starter #19
yes it will work, forget FBD's. there will be less cable length as it is drawn it, only option is for the uprights to move up. I've seen systems like this before:)
Exactly!

Good job for sure! If you need some help with the calcs let me know. FEA isn't really needed for something like this but it is a nice tool to check with.

FBD's are the most important aspect to analysis.
That is very true. FBD's are the most important aspect in life... :engineeringdork: :laughing:

Thanks for the offer, I may take you up on it.

what if you had a smaller winch on a roof truss and a hook welded in the center of your crane.
That would obviously be the best and easiest way to do this.
But the roof truss of the building is lower than the maximum height of the crane...so no go.

HTF does that cable system work? :confused:
See Nissan Nick above and BESRK below. :flipoff2:

Slick idea on that cable system.. sort of like a forklift mast.. using the chain to pull the mast extension up..
Yes sir, that is pretty much the idea.
Although it is fairly :mr-t: to have the cable running from side to side like that while raising it, it is a lot cheaper than putting separate hydraulic or air cylinders on each leg to raise it, and faster than the floor jack.


I really like your design, I will likely be building something extremely similar. Few questions if you don't mind.

How did you decide on a leg angle and tread width? Your legs look to be about 60 degrees and come up almost to the beam when at mid height. Is this more desirable vs having the legs at a shallower angle and having straight tube up a couple feet?

The tread with was determined by what is standard on the market today.
Take a look at the charts on these two websites.
Vestil Gantry Cranes
Wallace Gantry Cranes

I followed the specifications for the 5 ton model on the Wallace site.
Tread=6'6"

I will get back to you with the angle tonight.
I misplaced my original drawing somewhere and haven't been around much to take the measurements.

You can indeed make the angle shallower and have more tube straight up than what I have.
If you look at the Wallace cranes, that is exactly how they are built.
The Vestils on the other hand, are close to mid height.
For the tread I wanted, and the heights I was working with, that just happened to be where they ended up.
It also just gives it a more secure feeling when I do raise it higher though.


Does the location of the pins in the side matter ( relative to the intersection of the legs)?

Not that I know of.
You obviously wouldn't want to drill a hole 1/16" above the very bottom edge.
Those two are spaced evenly from edge to edge.
Although those pictures only show one pin per side, it normally has two pins per side as an extra precaution.

Did you notch the legs or the receiver tube for the horizontal tie in at the bottom? Would you notch the receiver tube for the legs or did you just weld them to the surface? I would think notching could weaken the overall structure but at the same time make a stronger joint.

I did not do any notching at all. Only what you see in the pictures.
I would just weld them. If you feel you need more support, then you can always add some fishplates over each joint.

This is also not something to tackle if you aren't 100% confident in your welds.


Thanks a bunch, I will post up some pics when I get started

Not a problem man, I would definitely like to see them! .
 

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Did you get the materials list rounded up? Figured I would bump this for a great build and to see if you had a list. Looking at building something just like this.
 
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