Nice looking setup. I would suggest getting a trolley for your beam, it will help gain some head room or a shorter sling. As for the casters , adding some full size gussets would make me feel better. Best part is the writing on the beam.

 

Thanks man, I have a trolley but only one so when i lifted the sheetmetal brake i needed to lift from both ends so didn't use it. Yea I am with you, feel like the bottom needs something for sure.

 

Nice build on the crane, I would tie the new extensions together at the bottom on each side for added strength....

 

How about a cross brace fro the bottom of the main base to the bottom on the opposite of the extension just a bolt in piece. This would like a X when done and you would not have take anything a part. That would lock them in to place and still be able to be removed.

 

I have used it 2-3 times so far like it is, but only light weight (700 lb was the heaviest). Definitely needs something like wha your talking about before i lift anyting heavy

 

Ya looks like a nice build but def do something about the leg extensions. Id say they shouldnt be stand alone like that.

 

I fast forwarded to the end pic so apologies if you covered this - but why didn't you just go up from the top and make it adjustable?

I do not like the modifications as they are right now.

Edit: I decided my post was not strong enough.
I seriously dislike the modification - I wouldn't even use it.
I've watched too much metal bend, buckle, twist and deform under load to consider your modifications safe.
Could just be I'm too hard on stuff, so it's just my opinion.

 

I fast forwarded to the end pic so apologies if you covered this - but why didn't you just go up from the top and make it adjustable?

I do not like the modifications as they are right now.

I've built and modified a few gantries over the years. I've always added or removed from the top. You do realize you used twice as much material as required?

The biggest risk with gantries occur when moving. A gantry can shift quickly if the load moves while lifting or as the gantry squares up. Any surface abnormalities can put uneven stress on the crane. The spindly legs only exaggerate this risk. As a rule I try not to move any gantry loaded although wheels make it tempting and I'm always super cautions when moving. I prefer to lift onto a pallet and then move the item with the pallet jack. Or us cross bars on the crane and set the load down while moving. Dynamic loading on a gantry crane can easily make it unstable and/or over limit. The extension may be ok if they were bolted to the floor but with wheels I don't think so. Listen to Dave put your extension on the top.

 

Without casters, your main support column transfers the load directly to the ground. Adding the casters forces the bottom part of the triangle to act as a support at its very ends, where the casters are. You've turned it into a support beam. Not a big deal for a static load.

I'd be more stressed about side to side motion, than fore/aft motion. Weakest point of any crane of this type is the mid point bending stress on the column, and the stress at the top juncture between carrying beam and column. It's more likely to collapse from side to side motion, than motion when rolling forward/backward.

Your critical moment will be below the 45 degree kicker on the main beam, not on the leg extensions. The leg extensions merely add more leverage to the critical area. Adding to the top would yield the same results. 1/4" tubing is 1/4" tubing........doesn't matter how long the "span" is, matters how resistant to bending it is. Legs on bottom, or addition on top...........same same (Assuming all welds are good)

Forget about the "spindly" legs you added, and focus on stiffening the main support column, or not. Might be, it's strong enough to take side load, but I wouldn't count on it in a pinch.

Stress, leading to failure, has more of a tendency to manifest itself at the terminus of longer members rather than short members. Leverage.

 

I suppose the lower extensions could torque on the support tubing, but it's something that's up for debate I guess.

To put it in perspective......take a look at the support columns at just about any gas station canopy......pretty thin, yet resist a lot of lateral load. Boils down to what you feel comfortable with.....give it a shake when it's loaded, and see how much it deflects.....then decide whether you feel comfortable enough moving it under load