Assessing caster mount design

The object to be studied is a table saw with two wheels on one side of it.  To make it fully mobile, two additional caster mounted wheels will be added to the opposite side of the table saw (location circled in red below).

The design goal of the structure was to ensure that the deflection of the caster mount would not be significant.  In addition, the structure was checked for areas of high stress, to ensure that yielding would not occur.

The total weight of the table is 250 lb, and each of the casters should be able to support the full weight of the table saw.  Normally the weight would be equally distributed, but when moving over a crack or bump a wheel could carry the entire weight of the table saw.

The corner of the table saw was modeled in Rhino.  It was then intersected with a sphere, producing the object shown.  This is to reduce the modeling size of the structure based on distance to the area of interest.  In addition, the sphere intersection produces a single surface in Rhino, so applying the restraints is simple.

The proposed design is shown above.  An angle iron will be welded to the side of the saw cabinet, and square tubing will be welded to the angle iron.  The caster will be welded to the bottom of the square tubing, as seen above.  The structure was then modeled as an assembly using the Scan&Solve Work-In-Progress.  Modeling the caster mount as an assembly allows for easier design changes based on the results of a simulation, as the individual components were not joined with Boolean union.

However, the wheel itself does not need to be simulated, since the deflection and stress in the mount are the most concerning. The 250 lb (1100 N) force will be applied to a small area on the caster mount, and the cut face of the model is fully restrained.

A small cylinder was created and positioned on the bottom face of the mount and the force was applied to this cylinder.  The small cylinder is positioned to correspond to the location of the contact patch of the wheel on the ground.  Use of the cylinder in this manner is similar to creating a point force.  With its location near the edge of the plate we should expect to see bending and twisting of the tube.  With the loads and restraints applied, the scenario was solved.  The Danger Level is shown below.

The stresses in the structure are quite low.  While there are some stress concentrations near the weld points, they are low enough to not be of concern.  The maximum Danger Level is 0.0967:  less than 10% of the material strength.  So, the mount will not fail under the specified force.  The magnified deflection of the structure is shown below; the original structure is shown in wireframe.

The shape of deflection is a combination of bending and twisting in the caster mount.  However, the maximum displacement in the mount is only 0.005 in (0.127 mm).  This deflection is quite low, so the mount should work effectively.

If you are interested in working with assemblies in Scan&Solve, the new Work-In-Progress version is available for download here.  All you need is a valid Scan&Solve license and you will be able to simulate composite assemblies and orthotropic materials.

Thanks for reading!

Will