I make my own axles out of car parts. I get spindles, hubs, and wheels from AMC cars at the junkyard (they're getting hard to find!). The AMC spindles bolt on. I weld a 1/2" plate onto a 2" square tube, with however much drop I desire (usually 4"), then bolt the spindles on. I've hauled a 3500# machine, plus the weight of the trailer without any problems. Bear in mind, I'm a skilled machinist and welder. If you can get the parts cheap enough, and like to make stuff, it's worthwhile. I can also make the axle to the exact length I want, instead of building the trailer around what's available. You can buy a similar axle with hubs and springs for $250 or so, so it's barely worth it unless money is an issue. In fact, it's pretty hard to build a trailer for much less than you can buy one, unless your labor is free. I like to build my own, both because I like to build stuff, and I can make it the exact size and type I want. Many commercially made trailers I look at are made of angle iron, and seem very flimsy. If you stand on one corner, they twist a lot. I use 4" channel all around. They don't move!