Re: Shop Crane Revisited

"Bob La Londe"  wrote in message news:vk7mtd$9buc$1@dont-email.me...
...
Anyway, out by the back fence I found several fairly large I-beams
setting up off the ground on wood beams.  I think I just found my gantry
crane.  Now if only I can stumble across some big steel casters out
there somewhere I'll be set.  Maybe they are under the old gas pumps
over by the south fence.  ;^)
Bob La Londe
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If you don't need to roll a loaded gantry you can use trailer tongue jacks for retractable casters. Position them so you can crank both at one end up and down simultaneously. You can still travel with a load above their rating in steps, moving the load and gantry alternately.
Adding outrigger wheels to the casters lets them roll better on dirt but then they don't swivel well. They can be linked and controlled with steering knuckles made from strap steel, drilled to go on the axle, with a pull handle.
Custom axles are a use for a lathe.
I've seen boat trailer winches on commercial gantries to raise and lower the unloaded beam. I use them on my tripod supports, attached to a leg with muffler clamps. I would want a lowest beam height that allows hooking on the chainfall without a ladder, they are heavy and awkward. I modified my trolleys with connecting rod sleeves that the chainfall hook fits over (endwise), increasing the working height and allowing the nuts to be tightened without restricting the hook. I put the chainfall on a table and lower the beam to match so I have both hands free to assemble the trolley to them.
Unbreakable rubber farm buckets are good for storing and carrying a chainfall, and in use they can keep the hand chain out of the dirt/mud.
The sleeves were a lathe job, water pipe bored to fit over the trolley rod. Much of what I make could be done on a small inexpensive hobby lathe, the shafts and bushings, but not the gears and pulleys. My small lathe turns much faster than my larger one, which is handy to drill deep grease holes in axles. I use the little one for grinding, sanding and polishing to keep grit off the ways of the good one.
The tripods stand upright without the beam, which makes one-man assembly easy. Published specs suggest that some sizes of water pipe, EMT and chain link fence post may telescope together, I haven't tried with the 2" sizes appropriate for a tripod gantry support. You can check their column strengths with on-line calculators, I know what loading my rigging gear has proof tested to but can't guarantee it for someone else's likely different construction. Single post uprights with free rolling bases would need to be much stronger. The conventional rolling design makes sense on level pavement, mine is for uneven ground outdoors and disassembles for storage.
https://www.amazon.com/Klau-Industrial-Hanging-Display-Factory/dp/B0CFFCSFJW/ref=asc_df_B0CFFCSFJW?
On-line calculators can give you the load capacity of a simply supported standard structural beam with a single centered load, the worst case. The first number is the nominal height of the beam, the second the weight per foot, determinable from the dimensions. I used 1/240 deflection as the limit, the beam can handle more but the load may roll toward the center.
I didn't specifically include loading the truck in my gantry design because the towable shop crane that moves in all directions is more convenient for slung loads, the platform lift for others. Plus I can mount the bed crane to lift on or off anywhere.
For the heaviest log loads (>3000#) I moved and secured the trolley with two blocks-and-tackle, operated from outside the danger area. They gave fine control to center a maximum sized log within 1/2" on the sawmill and should help to position a heavy lathe chuck or workpiece.
jsw