Got a cheap 120v mig and needed a cart for it. Started looking around and found this and this and turn it into this Total cost zero dollars It's still a little rough , but works well. It is much more stable than it looks. The weight of the tank more than offsets the weight of the welder. I plan to add another chain for the tank and to hold a commercial fire extinguisher that will sit next to the tank. I'll tack on a couple of hooks for my helmet, gloves, and welders pliers. My buddy is a commercial blaster. I'll let him hit it and then give it a coat of paint. I have to get my regulator mounted and convert the welder over to gas. I did this with some .35 flux core. I haven't welded in years and it shows. This was good practice. sorry for not flipping the pics - couldn't right now.
Be careful trying to weld old bed frames. They tend to be very brittle and will crack next to the weld. Ask me how I know.
You can't tell in the pic, but the weight of the welder is centered over the axle. The cart does not tip over when the bottle is removed. It is very stable once the bottle is on. Also not shown is the support from the outer edge of the shelf to the center of the cart.
Go to a Goodwill type of store, and buy a very long belt to use in securing the bottle to the uprights. I used an old audio-visual cart from a former employer (tossed out), and all my welders are on it; just have to make a tank holder for the oxy/acet cylinders. Recycle and reuse works. Butch/56sedandelivery.