Re: Shop Crane Revisited

"Bob La Londe"  wrote in message news:vk9gnn$mv2t$2@dont-email.me...
Actually their individual load times four.  Just like any other caster.
Trailer jacks is not a bad idea, and I have seen this sort of thing done
on other equipment.  They are also available (at a substantial cost) at
much higher ratings.  Having seen a few failures generally the
limitation of most lighter ones is the plastic wheel.  I've seen them
break.
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I've seen advice to select casters rated for 1/3 of the load instead of 1/4, floors aren't always flat and level. 1/4 should apply to a gantry that isn't torsionally rigid as long as the load is secured in the center, 1/2 if it can roll to an end while moving. Unlike square tubing, H, I and C section beams are made from the least metal that will be strong in one direction. They are relatively easy to bend sideways or twist, as I found from straightening salvaged ones.
My source of strong steel wheels and casters is second-hand, obviously removed from machinery from the tread nicks and grit on them. Thus I can't give a reference to buy them. I've picked them over and already bought most of the good ones. I'll know the capacity if I break one.
When I had a new section of driveway paved I asked them to level it as best they could, as the old section has a considerable slope and I jack up and work under vehicles on it. The new part looks level but when I set up and leveled the sawmill track on it I found a drop of 9" in 16'.
A vehicle on downhill end ramps on the sloped section will be nearly level. I push the ramps against the low end tires and chocks against the upper end ones, measure from the center of the ramp top depression to the wheel center, and advance the chocks that far to stop the vehicle when in place on the ramps.
I looked into the size and weight of a one piece end supported gantry track for my sawmill but I couldn't lift or store it. The compromise is a track in shorter manageable sections supported at the splice for heavier loads. This is a rough guide to the size of a one piece beam for load weights and span lengths.
http://www.cousesteel.com/AndysPlace/SteelChart.html
The quick estimate can be refined for other spans, loads and the weight per foot of the beam.