I wanted to build a self contained portable welding station that is complete, yet small enough to be safely pulled by my jeep. The 4'x8' trailer will be built around a Miller Bobcat 250NT and will include a torch setup and typical welding tools.
50' 3" channel
Millermatic 210 welder
I needed a level place to lay out my pieces and since this project is as big as my welding table, I decided to take the project outside and ended up using an existing trailer as my table. Not only does this keep the work pieces off the ground, but it also provides a perfectly level surface (frame rails).
I decided to use a 50° A-frame coupler and instead of welding the tongue underneath the trailer frame I decided to bend the frame rails into the A-frame coupler. I called in a few friends to help me with the trigonometry involved in determining the length and angle that each frame rail would need to be. Knowing that the outside frame rails would be 4 feet apart and that the coupler was 50°, we determined that each frame rail would need to be bent into a 155° angle and that the length of the each tongue half would need to be 4.7 feet long. I cut it a couple inches short since it isn't necessary for the two rails to touch. The bends were accomplished using a heavy duty pipe bender and a protractor to know when to stop. While not made for bending 3" channel, the 16 ton jack made easy work of the bend.
The trigonometry worked just like it was supposed to. The frame rails came together with the A-frame coupler in a perfect fit. I used 4 vice grip c-clamp pliers to hold the coupler to the frame rails to ensure lateral and horizontal positioning and tacked the coupler to the rails. After tacking I removed the clamps and ran a continual bead along every point of contact.
With the coupler welded on its time to install the cross members that will support the flooring. Since the outside frame rails are 4 feet apart and the 3" channel is 1.5" thick, the cross members were cut to 45 inches. Instead of just cutting a flush piece for the back I took the extra effort to cut the frame rails and the rear cross member at 45° angles to form perfect 90° joints at each corner. While this wasn't necessary for function, attention to detail makes you a true fabricator. The cross members were boxed in and the top beads were ground down so that the flooring would fit flush against the frame.
With the frame welded up its time to install the spring hangers. The trailer bed is 8 feet long and I wanted the axle to be positioned exactly in the middle. To accomplish this I first marked the halfway point on the frame. Since the springs are 24 inches bolt center to bolt center, the front spring hanger would be mounted 12 inches in front of the halfway point. After welding the first spring hanger I took a measurement from a central point on the coupler. I measured the same distance from the same point on the coupler to the opposite side of the frame to ensure the axle would be perfectly square. In all reality this isn't necessary. As long as the axle is straight the tires will wear normally. The only difference axle position (in relation to being square with the trailer frame) makes is how well it tracks behind the vehicle pulling it. I took the extra step because once again, attention to detail is what makes a true fabricator.
With the frame, coupler, and springs perches welded up, 2 hours into the project we decided to call it a night. The next morning I bolted up the axle and put the wheels and jack on. There are many axle options from pre-measured, cut, and assembled to buying the parts individually and assembling it yourself.
Since I would be using non-standard wheels I chose to assemble my own axle so I bought the tubing, spindles, hubs, springs, etc. I assembled the hubs and bolted up the wheels to determine how much backspacing I needed to clear the frame. I decided to run 31x10.50 tires to match the tow vehicle and this required a wheel with a larger offset than a typical trailer wheel. After determining that I needed 7" clearance, I welded my spring perches to the axle and bolted it all together. The frame grind marks on the close up picture are because I decided to move the axle forward 2" from my original design to decrease the tongue weight a little. The multi-lap bead was to fill the cut areas where I cut the hanger off the frame. After getting the tires installed it was time to put down the decking plate. This required multiple clamps and plenty of tacking the plate into place before running the continual bead.
With the basic assembly complete, its time to get the new machine. $2640.82 later my new Bobcat 250NT came home. Mounting is simply a matter of positioning the machine for the desired tongue weight and bolting it directly to the bed.
With the machine bolted to the trailer its time to mount a few tool boxes. I decided to mount the larger toolbox inside the A frame pillars and it required a sub frame to support the toolbox. With some leftover angle I fabricated a cage for mounting my oxygen bottle.
Instead of wrapping my welding leads around a few pegs, I decided to put my 150' of 1/0 welding cables inside of a tool box to offer some protection from the elements when not in use. While this isn't necessary, I felt it would also clean up the looks of my welding trailer. As the cables leave the machine they are routed through holes drilled into the bottom of the toolbox. I coiled the cables (50' work cable, 100' electrode cable) in the box and cut notches under the lid so that the box could be closed while welding. This will aid in air flow through the vents in the welding machine.
I welded the tank bracket to the trailer at an angle and mounted the oxygen and propane tanks to the bracket. The oxygen tank is held in place by a U shaped strap I built out of 1"x1"x.125" square tubing and the propane tank bolts to the trailer bed. The bungee straps are in place to help prevent vibrations. The hoses are routed through a hole I drilled into the bottom of the toolbox directly in front of the welding machine, and the hose, torch, and accessories are kept inside.
I welded a 2" receiver hitch to the back of the trailer frame. This will allow me to pull an additional welding trailer if need be, and it also allows me the flexibility of using hitch accessories such as the basket pictured above for hauling additional tools and equipment. I mounted my vice onto a piece of 2x2x.125 tubing that I'll keep in the large toolbox. When I need a vice, I'll simply slide it into the receiver. I've done the same thing with my bench grinder, and even a small portable welding table.
This left me with a functional, strong, and lightweight welding trailer that can be pulled with confidence by my little quarter ton.
Nathan W. Collier
AWS D1.1/D1.5 Certified Welder