16.2 Dollies, Skates, Rollers and Horizontal Control
Key Takeaways
Calculate actual reactions rather than assigning total weight equally to devices.
Check floor capacity for concentrated wheel or roller forces.
Provide suitable braking or restraint on slopes and low-resistance systems.
Carrying capacity is only one requirement
Dollies, machinery skates and rollers support loads while allowing horizontal movement. Their suitability depends on rated reactions, support geometry, floor condition, steering, speed and a controlled means of starting and stopping. A device that can support the weight is not necessarily suitable for a ramp, joint or curved path.
Determine the actual contact points on the payload. Its base must transmit reactions into the devices without bending or local failure. The floor must carry concentrated wheel or roller forces, including at joints and edges. A broad machine footprint does not distribute load if only a few narrow wheels touch the floor.
Read each product’s rating and conditions, including whether ratings apply per unit or to a set. A set capacity cannot be assigned equally to every skate without the manufacturer’s sharing assumptions and the actual CG. Keep units clear; metric tonnes and short tons can differ materially.
Support geometry and CG
A three-point arrangement can provide a defined support plane for a rigid body, while a four-point arrangement may be sensitive to unequal heights and stiffness. This does not mean three supports guarantee constant load distribution, continuous contact over every surface or immunity from tipping. Terrain and the payload’s CG still control stability.
Draw the effective support region and locate the CG projection. During slope, acceleration or turning, the relevant forces can shift the tipping tendency. A high CG or narrow support triangle can be vulnerable even if all devices are below their individual capacity.
| Route condition | Handling consequence |
|---|---|
| Floor joint or depression | Can change contact and reactions |
| Ramp or slope | Adds downhill force and stability concerns |
| Sharp turn | Changes steering and lateral demand |
| Weak floor area | May not carry concentrated reactions |
| Obstruction | Can stop one support while others continue |
Do not assume a four-point arrangement always places all weight on exactly two diagonal skates. The distribution depends on stiffness, geometry and the approved system. Use the actual manufacturer's arrangement and a qualified assessment where needed rather than a universal chair analogy.
Plan motive and stopping forces
The required pull depends on rolling resistance, grade, starting behavior and obstructions. A supplied coefficient can be used in a training calculation, but generic coefficients are not reliable site design values. Floor finish, wheels, bearings and contact condition all affect resistance.
For a simplified level-floor exercise with given coefficient 0.03 and load 100,000 lb, estimated steady pull is 3,000 lb. This omits grade, startup, losses and other specified effects. A winch and anchor need evaluation for the actual force and direction, while blocks may impose larger anchor resultants.
Low resistance can increase runaway risk on a slope. Provide an approved controlled means of restraining and stopping the load. Taglines and workers’ hands are not automatically adequate brakes for a heavy machine. Do not release restraints because the load was difficult to move on the previous level surface.
Select and install the arrangement
Use approved contact pads, turntables and steering components. Keep devices beneath intended support points and prevent escape or slipping as specified. A machine lowering onto skates can change reactions as contacts occur; coordinate the jack-to-skate transfer.
A steerable front unit and rear supports may suit a particular product’s system. Another load or route can need different equipment. Do not copy a standard three-point sketch without checking load shape, CG, base strength and turning clearance.
Joint-crossing scenario
A loaded skate reaches a floor joint beyond its approved surface capability. The rigger must stop before crossing and establish an approved route preparation or alternative. Adding more pulling force can cause a sudden release, loss of support or wheel damage. The problem is the route condition, not merely inadequate effort.
Air bearings and slide systems
Air bearings support a load on an air film under specified supply and floor conditions. They can reduce movement resistance dramatically, but floor cracks, porosity and supply loss can affect operation. A generic pressure or air-film thickness is not an installation instruction. Use the product manual and controlled restraint method.
Jack-and-slide systems move loads on rated shoes and tracks, often with hydraulic push-pull units. Track alignment, support, friction interfaces and end restraints are system requirements. There is no universal PTFE coefficient or track-alignment tolerance for all products. The manufacturer and approved plan establish the permitted conditions.
Monitor the moving system
Assign observation of devices, floor condition, payload attitude and the path. Keep personnel outside crush zones and away from the line of a loaded pull. Stop for support migration, wheel binding, unexpected tilt or uncontrolled movement. Do not reposition a skate beneath a fully supported load without the planned safe transfer.
At the destination, move onto approved stable supports and secure the load before removing transport devices. Inspect units for wheel, roller, frame and bearing damage after use. A successful arrival does not erase damage incurred at an obstacle.
Sources: CCO horizontal-handling topics, CMCO industrial handling catalog.
A training level-floor move gives 100,000-lb weight and resistance coefficient 0.03. What simplified steady pull results?
30,000 lb
333,333 lb
3,000 lb
300 lb
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