Mini gantry crane

[robstaples]

I thought I'd show my latest completed project- don't get many-. I have a 10x10 beam down the center of my building (colored gray in upper part of picture) I wanted to be able to move my MMM and snowblower and other things in and out of the garage door. Tractor takes it the rest of the way. Because of limited height, I needed to be able to move it out of the way of the door (L39 is tall). I used 4 trolleys, two 2 ton to ride on the steel beam and two 1 ton to carry the hoist on the 6x10 inch beam. All the white is aluminum so I could move it easier. The red dolly connector is steel. I took the ratchet out of the electrical cord spring-driven coilers so they take up the tension continuously.
Rating: the winch is rated at 880 lb. My things to move are less than 700lbs. I was going to run a deflection test with a 2300 lb ironworker, but I thought why risk breaking things if I'm never going to lift that much. I followed the recent bridge crane thread and I know there is a safety limit risk.

I designed it to rely on shear strength of 1" AL plate for the tee joint. The welds are respectable on top and bottom but the picture shows the tight quarters. I sound defensive, don't I. I've follow all the welding discussions on this forum. The L bracket is just to plug the pull strain on the tee joint. If it flexed too much, I'll add a 45 degree brace on each side. So far so good.

 

[jimmysisson]

What's under the plywood on the floor?

Jim

 

[Jim Timber]

Floor looks like concrete to me.

A lot of those welds look really cold too. What process did you use on the aluminum?

 

[skyhook]

I beam looks like metal to me.

 

[robstaples]

The floor is concrete stained with a few years of clumsiness. The aluminum was welded with a new Lincoln Power Wave C300 set at MIG with 3/64 wire set on pulsed mig. It would go to 300 amps but heat controlled by wire speed . The machine was more difficult to master than I had expected. And I haven't. And the push pull gun was a mistake for me to buy. The 25 ft length just pinched the wire when I was 10ft from my machine. Live and learn. The horizontal welds at my welding bench were better. I take a picture today of the better welds.

 

[LD1]

The welds do concern me. But I'll try not to be too critical.

Potential weak spots I see are
1. Welds
2. How you attached aluminum beam to red trolley
3. The legs. With a 800# load I bet they will flex alot when moving. Or are those just ment to.move the EMPTY hoist out of the way? What size and wall thickness are those legs.
4. Adding to 3, the casters. Any resistance in them muts more side load on the legs. Those look pretty small in diameter. Ever try to run a caster over a small piece of gravel?

 

[ShowroomShine]

Yeah man thats a cool idea, but those welds look suspect.

 

[GPintheMitten]

I'm trying to understand how this works.

Does the white uprights and white beam slide to the right or left enough to get the garage entrance completely clear?

 

[robstaples]

Thanks for the interest and comments. The gantry moves left and right. To the right, it clears the door. To the left, further..25 total. My K. L39 is inside and the 10" beam clears the top of the roof but the trolleys don't. Your comments made me concerned to do a test. I tried to pick up my L39 to the limit of the electric hoist. I measured the height before and during the lift with a lift scale and a laser distance measurer. The lift maxed at 1000lb ( hydraulic scale accuracy ?? 0-5000lb). The center of the tee dropped 1/32" and the legs, on the casters, spread 1/8". seems ok.
Material used:
The legs are 3"x6"x1/4". 45s are 3x3x1/4". The H beam base of the tee is 10"x 6 and the cross is 8"x5?

The top and bottom welds were done at a bench. Better than the in place vertical welds.

The AL and steel(red) at jointed by 4 vertical grade 8 bolts 1/2 " and one web bolt.

The left right movement with load will need a freshly swept floor near the wheels and a decision based on what I'm trying to move. I thought I could temporarily brace the legs near the wheels together rigidly if it's heavy like my metal lathe

 

[GPintheMitten]

Very nice. Thanks for the additional info and pics.

 

[LD1]

The center of the tee dropped 1/32" and the legs, on the casters, spread 1/8". seems ok.
Material used:
The legs are 3"x6"x1/4". 45s are 3x3x1/4". The H beam base of the tee is 10"x 6 and the cross is 8"x5?

Okay until moved under a load. Then the game changes ALOT. THAT is my concern.

Dynamic loading is a WHOLE lot different animal than a static test. And where on the beam was the load placed that spread the legs 1/8"? was it in the middle? What happens if the load is closer to the door? What happens to your connection to the main beam if the load is all the way that way?

 

[Jim Timber]

Not to mention welding aluminum anneals it and it needs to be re-heat treated to achieve it's tempered strength.

I can certainly appreciate the intentions of this project, but I would've bolted the T connection and used steel brackets on the corners for the legs and uprights. Aluminum is much easier to bend and set, where steel will flex and more readily return to it's original shape.

 

[robstaples]

LD1, In the simple load test, the winch was about 2ft from the door end. There may have been some compression in the rubber covered casters. Cast iron centers. What I don't know is how much force to rip the flange off of the top of the web. That would be a probable failure mode for the main beam. The grade 8 bolts won't be the weak point. There will be a interesting dynamic of the gantry on rollers and a heavy load that I push when suspended. The load will pull the gantry. But if I lift something heavy only fractions off the floor, it should minimize risk.

 

[Jim Timber]

What I don't know is how much force to rip the flange off of the top of the web. That would be a probable failure mode for the main beam.

You think the red end is the weak point??

If you're only lifting things inches off the floor, then failure isn't a big deal. Sure, a lathe or mill won't like being dropped, a surface grinder could be ruined, and toes do crush pretty easily - but no one's likely going to die.

What if you're trying to put a mower in a pickup? You didn't get the mower high enough (because they don't balance for crap), and you smack it with the tailgate causing it to flip over in an unsupported direction - then that starts the whole thing swinging. Now what?

What if that swinging mower makes the legs spread out and the garage door side of the main beam goes down, then the load goes flying at the truck, but you're standing between them? Then what? Can you handle 500# coming at you with the force of gravity. I know I can't.

Static loads are the lowest importance when figuring what's safe. Dynamic loads are why cranes have safety factors of 5:1. Gravity can be a cruel master. I have two crushed toes because an 840# beam decided it didn't want to play nice while hovering 2" above the floor. I should've been wearing steel toes too. My cross to bear. My second toe next to my big toe doesn't bend in the middle anymore because of that mistake.

 

[robstaples]

Jim, Thanks for your feedback. No, the white end.- Aluminum is the weak link. Your comments lead me to think about adding a 1/2" steel plate under the tee joint bolted thru both members on 3 sides. That would leave the top of the legs as the weakest joints. I'm seriously considering thsee additions. Thanks. Rob

 

[Jim Timber]

Having built my own crane, and having a 5,000# load shift when a strap slipped - I take these projects very seriously. The engineer I was bouncing ideas off of when I built it was giving me a 2K safe limit before finding out I was tying all my columns into the building's walls at 2 points. His concern was always "what if it shifts?" Now that I have 6 years use of that crane, and countless wiggling loads (usually just weldments that aren't well hooked), I've come to realize what he was trying to beat so deeply into my head. We can't plan for best case scenarios. We have to look at what's the worst thing that might happen - will the crane survive it, and will we?

700# isn't a lot of weight in the grand scheme, but it's enough to change your life. I just want what Dave wanted for me: that you stay safe. Crane's are handier than sliced bread. When you get used to having it, you'll use it all the time.

You might be able to sneak some L brackets in on the web of your T and not lose much travel of the dolly. If that joint holds, then the next concern is the short side of the T twisting and spitting the feet fore or aft along the same line as the long leg. Side to side bowing that you're measuring isn't the failure mode I'd be worried about (it might not even be what you're actually measuring either). I'd look at how the short side of the T is reacting to the load and adjust the strategy accordingly. If it's twisting in the horizontal plane, then boxing it or adding another stiffener along it's length would be needed.

I was looking for pics of how my runway trollies are bolted to the web of my bridge to give you an idea about bracing, but I don't have it on the web. I did find the x-ray and pin shots (I'll spare ya the icky feet).

As for your 30' push-pull gun - you need to unfurl it before use. I have a 35' Miller and it's a pain to use because of how much extra leads I have. I tig all my aluminum instead. I've probably run a pound of wire through the PP rig in 5 years of owning it. When I move and start doing dock repairs, I expect it'll be a lot more useful.

 

[Walker1]

As a pro welder I wouldn't work under it should have used bolted connections. You might consider retro fitting some bolted bracket on each of your aluminum joints.

 

[Coyote machine]

I'm not clear on why you only have the two legs by the garage door? Is there no way to have 2 more where your current T joint is located? Even if they were roll into place for support just when using the crane, then roll away after use?

 

[Jim Timber]

Can't load in/out of a trailer or truck bed if the middle is blocked.

I think the concept is good, but the materials/construction/assembly needs a little tweaking.

 

[Sodo]

That should be handy. I like your scale too.

I think you should proof it to a good amount beyond 1000 lbs. can do it in increments, & don't lift the test weight high, lift it so it can only fall 1/2 inch. Watch the paint on all the welds. Nows a good time because the paint is easy to monitor.

Agree the casters look undersized. What are they rated at? Maybe double them on a walking beam?