Engine hoist capacity beware

[whateg0]

Helping the local makerspace move this past weekend. Roughly 1800# welding bench about a foot in the air, when the caster broke, causing the bench to swing in that direction and downward, then bend the leg on my old HF engine hoist. We were using safe lifting practices (aside from relying on a HF tool), so nobody was hurt.

While looking for casters for another project, I found that there was little in a 1000# rating available in anything smaller than 4" or 5" and even those were pretty beefy looking. The casters on all of the common engine hoists have very thin webs and fairly small axles.

That got a buddy and me wondering where they get the 2T weight rating for these engine hoists. Even with the boom fully retracted, the CG of the load is well forward of the middle of the casters, but even if it was centered, that would be 1000# on each caster. With a safety factor, each caster ought to be able to handle far more than that.

What I surmise happened here is this. Some years back, I got tired of fighting 4-wheel uncontrolled steering and used the original front wheels to make fixed casters. The cast web being as thin as it is won't withstand much lateral loading. If the caster was able to swivel, then the lateral load becomes not a lateral load fairly quickly. Since these were made fixed, perhaps the welding bench swayed slightly left, and in doing so increased the load over that caster while simultaneously loading it laterally. As the weight started down the sort distance until the caster frame hit the floor, the table gained some momentum and when the caster frame hit the floor, the additional force on the leg caused it to bend at its weak point where there is also a point load. Compared to the old engine hoist my dad has that has 3/16" wall tubing for every piece, these little thin wall tubed machines always seemed rather flimsy to me.

I've always avoided moving things around up in the air until the last moment. I've also always tried to make any necessary movement with loads in the air a straight forward or rearward movement. Still seems a good practice. Be careful with these things!

I'll add for anybody tempted to call this a Chinese POS, yes, it was a Chinese machine. No, I don't think it was a POS. This machine has served me well for many years. The fact is, like anything, as long as you stay within the proper design criteria, it's probably fine. The problem isn't that it's Chinese. The problem is that it's sold at a price point. To design an engine hoist that is truly good for 4k would require far more expensive casters and far more steel. Both of those cost money. This machine is probably really good for about half its rating. Most users probably never get close to even that. So, it isn't a COO issue. It's a sales and marketing thing.

Dave

[LIALLEGHENY]

Just out of curiosity what wall thickness is the tube that bent?

No the ratings on the casters or the entire hoist don't make sense. I haven't broken the wheels on mine, but I have had the casters separate at the swivel. I have a Carolina hoist,it has a one piece welded bottom frame, it is rated for 5000lbs, had it for over 30 years....there's no way it is going to lift 5000lbs, not even new. A friend of mine bought one a few years after I did, same hoist , and it was down rated to 4000lbs. I wound up replacing all the casters with 5" ,1000lb casters. Took some 4" wide 1/2" plate , bent the end at 45 degree, cut the ends of the tubes to 45 degree and welded them on flush to the top of the tube. The hoist sits at exactly the same height and rolls around much better than it ever did with the 3" casters.

Nyle

[whateg0]

Don't recall the thickness but it's less than 1/8". Maybe closer to 0.100". Not very thick at all. I have to go down to the makerspace later where I left it for now. I'll check it then.

[warmstrong1955]

I have an old Horror Freight lift, and the legs are 40mm x 60mm x 4mm wall.
It's the fold-able 2-ton, so it may be different than yours.

Bill

[Russ Hanscom]

Years ago, I undertook to design an engine hoist. After applying reasonable safety factors and reinforcing wear points, I determined I could not buy the metal for the price at which imports were selling. A bit of reverse engineering suggests that their safety factors are about 1; no allowance for wear, unequal loading, or other than perfect use conditions. Castors are about the same way - consider the source.

For an eye opener compare a good commercial one to a typical import.

Regardless, you never want to be where the bits will land when they come down.

[Magicniner]

You put side load on the caster wheels which they were not designed for by re-mounting them as fixed wheels.
Entirely your own fault for using a component in an application it was not designed for!

[STRR]

Being a crane operator knowing what the OSHA specs. are, I can tell you HF would not be allowed to sell those in the US if they didn't meet OSHA specs. Having said that, I am also sure that the just barely meet the specs.

Concerning the load rating on the casters. When hoisting 2,000 lbs, there are less than 1,000 lbs on each front caster. OSHA specs dictate how much weight minimum has to be on the rear casters so the rig doesn't tip over front ways. Considering the safety margin in the casters, in the design, in the materials, and in the construction, a 1,000 lb caster will be fine for the front casters. HF usually uses the same casters all the way around.

Loading. The design and OSHA specs are based on a free-hanging load directly under the hook. The biggest problem with engine hoists is the load does not remain directly under the hook/connecting point on the boom. When you move the hoist (rolling it around) the load always swings this causes side-loading. While HF uses square tubing which is less prone to failure from side loading, side loading must be minimized so the weight is evenly distributed between both front casters and less on both rear casters. When your caster failed, the load swung to the side, side loading, and the load exceeded the maximum load the horizontal leg could bear. When that leg bent, it added to the side loading and actually bent more although you probably didn't see it happen.

It was mentioned the caster most likely failed due to side loading. Looking at the photos, I agree. Over time, a hairline crack might have developed thus weakening the web.

IF you choose to replace the casters, look for thick webs and wide treads. All things considered, I recommend scrapping the hoist. If you want to keep it, be sure to replace BOTH horizontal legs. You do not have to use the same tubing HF did. You can, but I recommend using at least the next size heavier. It will give you a larger safety margin which is always a good thing.

Remember, the load ratings are based on two things: Structural Strength, and Tipping. You must keep the boom labeled with the original capacities. The capacity of the hydraulic hoist jack will ALWAYS be more than the maximum capacity of the hoist. This is due to the amount of lifting pressure required with the geometry of that particular design. Because the jack is rated at 8,0000 lb DOES NOT make the hoist and 8,000 lb capacity. I've seen many hoists advertise on sites like Craig's List as 4-ton capacity when the hoist is actually a 2-ton capacity.

Good Luck,
Terry

[Steggy]

No, I don't think it was a POS.

I do. That thing was meant to be cheap, not good, which automatically qualifies it as a POS.

The holes through the leg created stress risers than any first-year mechanical engineering student who was staying awake in class would have immediately recognized as bad design. The bottom hole elongated from tension on the leg, and the tube kinked through the top hole. That failure was 100 percent predictable, and avoidable. Had an injury resulted from this failure almost any lawyer could have taken the manufacturer to the cleaners in a product liability lawsuit.

It is worth noting cranes, derricks (n.b., a typical "cherry-picker" is a derrick) and hoists are rated statically, not dynamically. If the manufacturer says it will lift a ton, it will lift a ton—when both lifting device and load are stationary. As soon as movement gets into the picture the one ton rating will no longer apply.

[STRR]

It is worth noting cranes, derricks (n.b., a typical "cherry-picker" is a derrick) and hoists are rated statically, not dynamically. If the manufacturer says it will lift a ton, it will lift a ton—when both lifting device and load are stationary. As soon as movement gets into the picture the one ton rating will no longer apply.

NOT true at all. Every mobile crane has an "on rubber" static and travel load charts, along with "on outriggers" load charts. Derricks are a fixed point hoist that are not capable of moving from one site to another. A cherry picker can be used as a derrick OR it can be used to transport a load to a new location.

[whateg0]

First, yes, I am wholly aware that I altered the design of the product. The change actually should have made it safer as the side to side movement is far less than when trying to kick the front around to get the casters to point in a direction. When traveling in a mostly straight line, the majority of the swinging is fore and aft, which assuming the front wheels are placed out far enough to prevent tipping should be far safer than something that can actually swirl around.

Yes, I am aware that the design of these casters is probably sufficient, albeit barely, for static loading. But, as somebody else pointed out, really eliminates the usefulness of such a lifting device.

Somebody also suggested extending the legs farther, but that makes the span between casters very long and while the casters themselves are subjected to more evenly distributed weight, the thin wall tube is more likely to bow, and eventually kink, I would think.

The tube did not kink at the hole on top. The location of that hole is far enough back to make the hole far less of a problem. Had that been in the middle of the span, that would be a different story. No, if you look at the photo, the kink occurred at the front edge of the C section that partially surrounds the tube. There is the stress riser in the sharp corner of that piece of formed strap. When I take it apart, I'll see how much the hole in the bottom elongated.

I think the design is sufficient for the load that the casters can reasonably support in real use, which is to say, it's vastly over-rated. I said that the casters were probably barely sufficient. If you look at similarly sized casters, such as these (http://www.steelcasterstore.com/3-x-1-1 ... -capacity/), you can see that there is far more material going across the width of the wheel in the web area. Had the original casters had a 3/8" section there, failure would probably have not occurred. Also note that these much heavier casters are only rated for 350#. With a safety margin, they are probably good for 1000-1250#, which is the minimum working load the casters on the engine hoist should be rated for. If you can honestly look at these two different casters and tell me that you think the ones on the engine hoist are stronger, you should probably see a doctor.

If I keep this hoist, and I may, I will definitely be replacing both legs. These are a bit over 1/8" thick, so going to 3/16" would be an improvement. There used to be a scrap yard here that sold new and used steel. You could get new steel for great prices. They have closed now as the old man is retired. To build a similar one would be silly, as it is barely adequate for lifting the machinery I use it for. For the same price as a new HF engine hoist, and for far less than a "good" one, I can build a good one, and that is more likely the route I'll take.

Some have said that these shouldn't even be sold, but I disagree. I just think they should be rated a bit more realistically for the components used. I have no problem pushing machines to the limit. I know when I am doing so, and I stand back. There is risk with any operation, but managing the risk is the key to not dying.

Dave

[Steggy]

NOT true at all. Every mobile crane has an "on rubber" static and travel load charts, along with "on outriggers" load charts.

I should clarify I was referring to advertised capacity, which is invariably stated as a static rating.

Derricks are a fixed point hoist that are not capable of moving from one site to another.

Not so, sir. "Derrick" refers to the lifting apparatus, not the supporting means. To wit:

Definition of derrick

1 : a hoisting apparatus employing a tackle rigged at the end of a beam

The above is from Merriam-Webster. Note that the description does not mention how the derrick is supported. A derrick may be stationary, as you describe, or may be mobile, an example of the latter being the wrecking cranes employed by railroads. Incidentally, "crane" is generally used to refer to any mobile lifting apparatus, which could be a derrick or a gantry. The cranes seen in factories are not true cranes in that sense, as they are ultimately supported by an immovable structure.

[liveaboard]

could not buy the metal for the price at which imports were selling.

I often have this problem.
Maybe the material isn't quite as much as a readymade thing, but it's so close that I don't feel clever.

Then I look at those thin steel parts with cheese bolts stuck through, get some steel, go home, and start welding.

When I worked in a garage in the 70's we had a fairly solid engine hoist, and the boom would arc like a banana when it had a big block on it.

I have used a tree and chainfall.

I have used a wooden tripod.

A bipod + chain

A 100 year old dutch barge crane.

Now I have a swinging gantry beam in my garage with a rolling electric 1 ton chain hoist; it was a lot of work to build that in, money too, but I recommend it highly.
Safe, easy lifting is priceless.