I have looked at these clamps for holding edges of thinner material even with each other for tack welding into place. I would have bought a set of four, but a neighbor wants a hole filled in the deck of his lawnmower before I can get to a store.

Materials

1" square tubing with semi-thick walls
Flat stock
10 x 24 machine screw
10 x 24 wing nut
3/16" rod

Tools

Grinder and cutting wheel
Bench grinder
Drill and bits
Center punch
Hacksaw
Welder

Step 1: Cut 1 Inch Square Tubing

I cut 7/8 inch from a piece of 1" square tubing.

Step 2: Saw the First Side

I used a hacksaw to saw across the 1" square tubing. (I did not measure and my cut is not centered, but that works out well, too.)

Step 3: Mark the Ends of the Other Slot

I made marker cuts above the cut from the previous step so both cuts would be even with each other.

Step 4: Cut a Slot

The slot in the bottom piece will need to be wide enough to pass the flat slider piece.

Step 5: Test Fit the Flat Slider

The flat slider piece is in place and loosely fitted. I used weldor's chalk to mark the flat slider for cutting. Although it is not easy to see, the flat slider has a gap between its right end and the right half of the 1" square tubing. The gap between the pieces is approximately the maximum thickness of pieces to be welded together.

Step 6: Weld a Screw to the End of the Flat Slider

I used various pieces of scrap to align the screw and the flat slider for welding.

Step 7: Mark a Hole for Drilling

Although not easy to see, the upper half of the square tubing is under the piece with the slot. Mark the position of the screw so a hole can be drilled for the screw.

Step 8: Fit for a Hole in the Flat Slider

Here a hole has been drilled in the upper half of the square tubing. See the text box in the first photo for the location of the retaining hole in the flat slider.

The second photo shows the location of the hole.

Step 9: Use

Cut a piece of 3/16" rod to retain the flat slider.

Slip the two pieces to be welded between the two halves of the square tubing. The thickness of the flat slider will restrict how close the two pieces to be welded can be move to each other. See the second photo.

This clamp is for holding the pieces to be welded until they can be tacked together. Then unscrew the wing nut and take the clamp apart to remove it.

The piece I used for the flat slider is a it thicker than the ideal. Pieces to be welded have a little too much gap between them for welding very thin material.