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How to Make a Spot Welder for Cheap!

Dec 21, 2012 03:48 PM
Dec 26, 2012 04:20 AM
Welding process demonstration with a close-up of electric arcs.

A typical resistance spot welder can range in price from about $200-$800, but with a little resourcefulness and a bit of free time, you can make one like this for about $10 or less.

Before starting on this project, there are a couple of videos you should check out, because you may want some background on how the device works. Firstly, check out how to make the Metal Melter, then see what it can do.

Spot welders are used to fuse thin sheets of metal together.

Hydraulic tool with yellow handles on a work surface.

They are most likely used in the auto industry, as well as HVAC for welding metal duct.

Electrical arc between metal contacts.

Measuring the base of my Metal Melter, I found it was about 4-1/4".

I found a 6' length of 1x6 common board for about $4, which actually measures out at 5-1/2", so it will work just fine.

Two pieces of the board will need to be cut to 12" lengths (5-1/2" x 12"), but the rest can be pushed through a table saw to trim the width down to 4-1/2" (1/4" wider than the transformer base).

Measuring a mechanical component with a tape measure.
Wooden plank with measuring tape on a workbench.
Woodworking table saw cutting a wooden plank.
Measuring a mechanical component with a tape measure.
Wooden plank with measuring tape on a workbench.
Woodworking table saw cutting a wooden plank.

The piece of common board that you just trimmed down to 4-1/2" wide can be cut into 3 pieces measuring:

  • 4" x 4-1/2"
  • 12" x 4-1/2"
  • 24" x 4-1/2"

The other 2 pieces of the common board should measure:

  • 12" x 5-1/2" (x 2 pieces)

You'll also need 4 pieces of 2x2 measuring;

  • 2" x 2" x 13-1/2" (x 2 pieces)
  • 2" x 2" x 4" (x 2 pieces)

This is all of the wood you'll need for building the casing.

Woodworking jigs and blocks for precise cuts
Wooden boards with measurements of 4", 12", 24", and 4-1/2" on a miter saw.
A person using a miter saw to cut a piece of wood.
Woodworking jigs and blocks for precise cuts
Wooden boards with measurements of 4", 12", 24", and 4-1/2" on a miter saw.
A person using a miter saw to cut a piece of wood.

I used a 3/4" rounding bit and my router to smooth the edges and give it a cleaner look. This is roughly how it will look when it's assembled.

A notch needs to be cut on one of the 2x2 arms, and you'll see what this is for later on. I found a piece of scrap can be used as a template.

Woodworking tools and wooden pieces being joined together.
Woodworking tool creating a groove in a wooden piece.
Woodworking tools and wooden pieces being joined together.
Woodworking tool creating a groove in a wooden piece.

The notch can be cut out with a bandsaw, wood saw, or any other saw you can get creative with. I used a jig-saw, but wouldn't recommend it as the safest option.

The back panel (4" x 4-1/2") also gets holes cut that will accommodate an electrical light switch, and a notch for a power cable.

Wooden frame with a cutout, being held by hand.

The pieces get sanded, primed, and painted. I chose to paint this black and yellow.

When I salvaged the Microwave Oven Transformer in this previous project, I saved some of the other components that can be used for our Spot Welder:

  • The power cord
  • The door handle
  • Wires for the transformer terminals, with insulated spade connectors
  • Power switch, with wires and insulated spade connectors
Electrical wiring and connectors on a table.

Aside from these, the only other items you'll need are:

  • Simple light switch, with faceplate
  • Copper offset terminal lugs that will hold (x 2)
  • 1/4" hex screws (x 2)
  • Small nails (x 2)
  • Length of solid copper wire (4AWG is better, but I used 6AWG in this project)
Electrical switch components including a switch, faceplate, screws, and packaging.

The solid copper wire can be snipped into 1" lengths, that fit nicely into the terminal lugs.

Pliers cutting a copper wire.
Copper connector in a person's hand.
Pliers cutting a copper wire.
Copper connector in a person's hand.

The lugs have a mechanism that can be tightened with a screwdriver to secure the connection with the wire. The tighter the better.

Now that the wood is painted, finished, and dry (I gave it about 2 days), the unit can be assembled.

The back panel is for a light switch and a power cord.

Before screwing the panel into the base, make sure your cord goes in first. The thick piece at the end of the cord prevents it from pulling back though the hole.

Power switch assembly with mounting screws.
Electrical connection with wires and a connector on a workspace.
Electrical transformer mounted on a wooden base with connecting wires.
Power switch assembly with mounting screws.
Electrical connection with wires and a connector on a workspace.
Electrical transformer mounted on a wooden base with connecting wires.

This is also the time to add the 2 pieces of 2" x 2" x 4" support blocks to the base. Be sure of your measurements before you screw them down. You want them to end up flush with the side panels when it's done.

The Metal Melter can be placed inside now, and when a good position is found, can be screwed to the base with a couple of small screws.

Now it's time to wire up the electrical system.

Starting with the power cord coming into the casing, I stripped the black wire, and attached it to the bottom terminal of the light switch.

Next, I attached one of the wires I had salvaged, to the right terminal on the transformer.

Then stripped the other end, and attached that to the top of the light switch.

The electrical could almost be finished here, but I wanted to add another switch, for safety and convenience, and that's where the salvaged switch from the microwave hack comes in.

The two wires attached to the switch can be wrapped with electrical tape to secure the connection and help insulate from electric shock.

The both ends of the wires are stripped so the copper wire is exposed.

One wire connects to the left terminal of the Metal Melter's primary coil, and the other wire connects to the white wire on the power cable that runs back to the house.

The electrical system is complete!

Electrical device with exposed wires and components inside a wooden case.
Electrical tool with a handle, shown from the side.
Electrical device with exposed wires and components inside a wooden case.
Electrical tool with a handle, shown from the side.

The sides can be screwed on with 6 wood screws on each side. I used 2" wood screws after drilling pilot holes to make sure the wood didn't split.

The trigger switch is attached near the tip of the top welder arm, and at a bit of an angle so it can be pressed easily. I found that 2 small nails held this in place perfectly.

Both arms can get inserted into the front of the casing, and with a bit of guesswork, a hole can be drilled through the side of the casing and into the end of the arms, so that when a nail is inserted, it will pivot.

Now you can see why we needed the notch in the arm.

Woodworking tool demonstrating a heat source applied to wood.
Close-up of a black electrical connector on a yellow device.
How to Make a Spot Welder for Cheap!
Woodworking tool demonstrating a heat source applied to wood.
Close-up of a black electrical connector on a yellow device.
How to Make a Spot Welder for Cheap!

To help the arm stay in an upright position, I added a couple of screws and rubber bands to keep the tension. This also provides a little back pressure, and stabilization when using the welder.

The copper lugs can be added to the tips of the arms.

I drilled pilot holes with a 3/16th drill bit, then secured the lugs by pushing the hex bolts first through the hole in the lugs, then through the lugs on the the Metal Melter terminals.

One in the top, and one in the bottom. It shouldn't matter which way they go, but I chose to make my top cable on the same side as the switch because it was easier to handle.

If the electrode tips don't line up perfectly, it's easy to bend them a little until they do.

Close-up of a yellow mechanical device with a wooden piece attached.
Hand holding a tool against yellow blocks.
Electrical connection components with a yellow connector and copper terminal.
Electrical connections on a yellow device.
Close-up of a yellow mechanical device with a wooden piece attached.
Hand holding a tool against yellow blocks.
Electrical connection components with a yellow connector and copper terminal.
Electrical connections on a yellow device.

When finished, it should look like this.

An electric hand tool with a yellow handle and black casing, used for sealing or welding.

It will only work if the safety switch on the back is turned on, and even then, no power is delivered until the thumb operated switch is pressed.

To use, place thin sheets of metal between the electrode tips, then press the button with your thumb for about 3-4 seconds. The massive electrical current pushing through the metal, heats it up to the point where it fuses with the other sheet. You can release your thumb from the switch and wait until the weld cools enough to handle.

Welding these metal washers worked so well, I couldn't break them by hand. I had to use 2 pairs of pliers to get them to snap.

When the energized electrode tips touch each-other, you can see the high-amp sparks.

Note: Burning galvanized metals may release zinc-oxide fumes. Welding should be done in a well ventilated area.

The electrode arms are only held in with nails, so if the nails are removed, the arms can be removed to extend the welders reach, and access difficult angles.

They go back together very easily, and the elastic can be conveniently replaced when necessary.

When the electrode tips are spent, it's easy to unscrew the bolt holding them in place, and add a fresh piece of copper wire.

Close-up of a mechanical component being adjusted with a screwdriver.
A hand holding a wire with packaging and tools in the background.
Close-up of a mechanical component with a metallic copper pin.
Close-up of a mechanical component being adjusted with a screwdriver.
A hand holding a wire with packaging and tools in the background.
Close-up of a mechanical component with a metallic copper pin.

Copper wire is relatively cheap. You can get a pice of 12" 4AWG wire for about a dollar. That means each tip is less than 10 cents each!

The power of the metal melter is still evident in the way this can bring iron metal to a boil! Be careful running the welder too long because there is a chance the wires will get so hot that the insulation on the cables will start smoking and melt.

Welding process with a hand-held spark generated tool and metal workpiece.
Spark emitted from a lighter igniting a flame.
Welding machine with yellow arms in a workshop setting.
Welding process with a hand-held spark generated tool and metal workpiece.
Spark emitted from a lighter igniting a flame.
Welding machine with yellow arms in a workshop setting.

Now you know how to make my version of a cheap Spot Welder.

If you haven't seen the step-by-step video, you can still see it here.

If you like this project, perhaps you'll like some of my others. Check them out at www.thekingofrandom.com.

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