I started playing with welders with a Lincoln AC "crackerbox". I had built a cart, sort of like a hand truck, and I had a homemade welder's vise on the top, even with the top of the welder. It made a pretty good table when working on something small.
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[Linked Image from live.staticflickr.com]

Fast forward a few years and I now have an inverter welder, wire flux welder, plasma cutter and toolbox on a cart built from an old pressure washer chassis. The old welder and cart were traded to a friend for a favor.

Time to add a vise and work table to the top. First, the frame
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Then to add the sliding vise jaw. The center strap of the frame is to reduce the spatter getting on the lead screw. The old vise screw simply went in and out with the jaw, this one moves the jaw along it so the screw would otherwise be exposed. This way you don't have to close the vise to get the screw and handle out of the way when storing it.
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From the top. There are two fixed jaws, so you can clamp something at either end of travel. Whichever side you are standing at, turning it clockwise winds the moving jaw towards you.
[Linked Image from live.staticflickr.com]

Coming next, a buttweld alignment jig, paint and attaching it to the cart.