Equipment Cart

Needed something to move heavier pieces of small equipment, like my Dayton hub dolly.   This seemed to fit the bill.  Somewhat overbuilt, but still manageable.  Sort of a goofy thing, but it’s good for pointing out some techniques I guess.

The Caster

The spindle, which enables the caster to revolve, is attached to the base plate.  Care has to be taken to assure it’s perfectly plumb.  Any deviation, and the caster won’t spin properly.equipment cart1

The hole through which the spindle fits is drilled exactly to the size of the spindle, allowing for an interference fit.  This simplifies fitup.  The spindle is then plug welded on the bottom side of the plate.equipment cart2

Arms, which will hold the axle, are then welded to the top plate.equipment cart3equipment cart5

To keep the arms stiff, strongbacks are added.equipment cart4

At this point the axle has been added.  The tab securing the axle is attached via a bolt, which goes into a nut welded on the inside of the arm.

Next, a gusset is added beneath the top plate.  It ties the arms to the plate, and prevents any movement.  Note that the gusset falls exactly on the edge of the outside strongbacks.  This ties the whole thing together as a unit.  Solid, from top to bottom.equipment cart6

The bluish marks on the steel are from heat straightening.  There’s always distortion when there’s welding.  It’s best to straighten the steel at each step of the fabrication process.  Heat straightening aka flame straightening is a subject for another altogether dedicated article.

It all comes together when the wheel is added.  An ordinary wheelbarrow tire.equipment cart7

 

The Swivel Assembly

The spindle has to be free to rotate.  This requires a thrust bearing.  They’re widely available.

thrust_bearingsThey’re designed to carry weight, or resist force, on the outside face of the race.

Let’s start with the bushing that allows the spindle to swivel.  I like using DOM (drawn over mandrel) tubing.  It’s sized extremely accurately.  In this case, I’m using 3/4″ DOM tubing, with a 3/16″ wall.

DOM is exact when it comes to the inside diameter.  To fit a piece of 3/4″ round stock inside this tubing requires some machining.

First, you must check the actual diameter of the round stock.equipment cart11

The round stock measures .748 (I round up a bit).

Next you must bore out the DOM to allow the spindle to freely rotate.

The DOM is placed in a vice on the milling table, and the milling machine spindle is centered.equipment cart10

The gauge is replaced with a boring bar, and the DOM is bored to size.equipment cart13

The DOM is bored to a final inside diameter of .752equipment cart12

The final clearance is .004.  While it seems a bit tight, it’s not.  A tight bushing allows for easier rotation because the spindle will be less able to wobble (I mean, were talking a few thou in runout, but it adds up over a distance).

Next the assembly the spindle will rotate in has to be made.  In this case, a piece of square tubing.

The tubing is drilled to accept the bushing.  The DOM has a 3/16″ wall, so the hole has to be 1 1/8″.equipment cart14

The bushing is inserted into the hole, and welded.  Then the weld is ground nearly flush to allow for the installation of a wear plate/pad.  This is because the square tubing is thin walled (11ga), and won’t hold up to the force applied to the thrust bearing without collapsing.

The wear plate is beveled to clear the remaining weld when it is attached to the tubing.equipment cart15

Pop the wear plate over the bushing, and weld it.  Note that the welds are on the shoulder of the square tubing, not across the width of the tubing.  This is to prevent distortion.  Welds across the tubing flange will cause the tubing to pull when the weld cools.equipment cart16bequipment cart17a

The thrust bearing I’m using is a completely enclosed 3 piece bearing.  The races interlock to prevent dirt/water from entering.

The bushing was tapped to add a grease zerk.equipment cart18
The entire assembly will be attached to the main cart frame later.  At this point, the spindle is left untrimmed.  It gets trimmed to final length later.equipment cart19

 

The Frame

There were a few notable things about the frame, but it’s pretty straightforward.cart22

Probably the most important thing is to wrap those welds.  It’s imperative that the tubing is water tight.cart21
Next, the floor, ramp, and other odds and ends were attached.cart23
The hinges are off-the-shelf door hinges, adequate for the load.cart33
Set of simple toggles to lock the ramp in the up position.cart26
A note on small wire welding machines.  I’m pushing the limit here.  I would not recommend using a 110v machine on anything heavier.  This weld, for example, is made with the machine cranked up to the max.  It’s ok, but it’s the red line.  We’re talking sch40 pipe welded to 14ga square tubing,  Pretty thin stuff.  cart27
For thicker stuff, such as round stock….it’s back to the reliable stick process.  7018 is my rod of choice in this application.cart19

Finished Out

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