Welding Clamp for Thin Materials




About: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying posting things I have learned and done since I got my first ...

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.


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


  • 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.



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    7 Discussions


    2 years ago

    I think you could probably use a piece of thin sheet metal instead of thicker plate for the slider. The sheet metal could then be brazed into the slot of the screw head. Alternatively, you could also use, instead of a flat metal slider, a length of small dia. steel rod, e.g. 1/16" welding rod. Weld the screw to one end of the rod and use a removable clamp, e.g. small set collar, on the other end. Filing or drilling a small notch/hole in the sheet metal pieces where their edges meet would allow the rod to be passed through to the bottom half of the clamp. The small hole could easily be welded closed after tacking the sheet metal pieces together.

    2 replies
    Phil BRossL2

    Reply 2 years ago

    Good suggestions. Thank you.

    RossL2Phil B

    Reply 2 years ago

    Thank you for the Instructable - nicely done!


    2 years ago

    Back up the wide gap with some thick flat copper stock, it makes the electrode think the workpiece is thicker than it is and so fills better rather than burn through.

    1 reply
    Phil BBeachsideHank

    Reply 2 years ago

    I do not have copper, but often use aluminum for that.


    2 years ago

    I've successfully used 2 appropriately sized and fairly strong magnates to hold the thin material together for tack welding.

    1 reply
    Phil Bnseetha

    Reply 2 years ago

    I have done that, too. I wanted to try this, but did not need to use it for the job I intended. Magnets sometimes deflect or interfere with t he arc, depending on strength and proximity.