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home made spot welder

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  • home made spot welder

    Has anyone made, or have knowledge of making a spot welder.I used to use a small one sometimes during the construction of orthodontic dental appliances it was foot controlled and bench mounted and was a real help in holding small pieces of metal together long enough to solder or weld.I have seen bigger bench mounted ones for making other objects lamp shades etc.I understand that a set of plans is available to make your own spot welder but wondered how difficult this would be anyone tried it please let me know thanks Alistair
    Please excuse my typing as I have a form of parkinsons disease

  • #2
    Check out in their Build it Yourself board archives. There were several designs one of which used a car battery for the power source.


    • #3
      The Eastwood Automotive Tools Co. ( sells a small spot welding attachment for a conventional stick welder. $49.99, takes about 50 amps to operate. I have one, currently loaned out for the last three years. I recall using it and found it to be a good tool.

      Perhaps it's time for me to reclaim that tool.


      • #4
        Here's two, one smooth and one rough. I did a search on Google for

        "spot welder" (project OR projects)

        and these two turned up in the first page. There were 843 total hits. I scrolled through four or five pages of results without seeing any more that looked relevant to your question, but they might be in there.


        • #5
          You should make a field trip to Sweden and go shoping in the scrap yards. Or check local sals, theere is bound to be one show up sooner or later.

          With the amount of copper in one, it is cheap er to buy one at a sale than to build one, but if you had a big welder power supply you could fake one. you can still fake one with your Mig, but it will not work very well for sheet metal. Mot enough jam. And if you were thinking of Aluminun - forget it, it takes many kiloamps to do a half assed job even on thin sheet.


          • #6
            The stuff that Eastwood sells is a "spot" welder in that it welds a spot (but then you can do that with just about any welding technique). It is however not a resistive welding in the truest sense, since it doesn't use the resistance of the sheet metal to create the heat.

            In order to resistive weld, you need lots and lots of current. Small portable spot welder are capable of deliver 1000-2000 Amps. P = I^2R. Because R is very very small for sheet metal (we're talking fractions of milliohms), you need lots of current to dissapate the required power (i.e. heat).

            Another critical aspect of resistance welding is to apply pressure at the point of welding. This is best done using some type of clamping device. There are two reasons for this. The obvious is to press the two sheet metals together so that they will fuse when the temperature has been elevated to a melting point. The not so obvious is that if the contact is not good, the resistance will be higher, and although according to P=I^2/R, this may be good, the open circuit voltage on these welder is very low (around 1-2 volts) so I = V /R becomes the limit.

            Trying to convert existing welder to a spot welder cannot be done effectively simply because of their inability to deliver the current.

            Also, using car battery is very ill advised because it's difficult to switch such high current reliably. Most switches will arc weld instantly when you're trying to open a circuit that's conducting hundres of Amps. Not being able shut of the welder, you have a very dangerous situation where the battery may heat up and explode

            The best way to build spot welder is to modify an existing transformer, which usually means replacing the second winding with a heavy gauge wire with perhaps 2 or 3 turns. The transform need to be large enough to handle the power, which should be at least 1000W.

            Good luck.



            • #7
              Uncle Dunc I would say the spot welders shown in your reply look simple enough to make whether they would be effective I don't know

              Dave (thrud)I dont intend to use it for aluminum but see were you are coming from as I always ask about aluminum(I guess you will all be glad when I finally use what little I have left of the that)

              Albertwhat did you think of the ones shown by Uncle Dunc?
              Please excuse my typing as I have a form of parkinsons disease


              • #8
                I think both the of link provided by Uncle Dunc are very viable means of making a spot welder. I would have tried to use a heavier gauge copper wire since maximum power power transfer is achieved when winding resistance equals the sheet metal resistance. It's difficult measuring such low resistance, but you can use a AC volt meter to do the same. Meaure the open circuit voltage and then measure the voltage under load (ie. when welding). If the voltage under load is 1/2 that of the open circuit, you're achieving maximum power transfer.



                • #9
                  I work at a university and get old high voltage transformers and cut the high voltage winding off then put two raps around the core using several thin sheets of aluminum.The best one I made draws 50 amp at 220 volt will weld 1/16 sheet very well. I use ooo welding cable off the transformer and it gets hot in 10 to 20 welds



                  • #10

                    If all you want to do is light stuff that first one in Dunc's link is a beautiful job. I would use bigger stranded copper cable for the secondary though, it looks on the dinky side - otherwise I am impressed. I might even have to build one of those myself...

                    Thanks Uncle Dunc for some inspiration!


                    • #11
                      Alistair: A microwave oven transformer (large ones) are good for 1500 watts continous, would do 3000 watts short term with a fan.
                      No experience making a spot welder but I think, I would try to buy the "tongs", then disassemble a Microwave oven for the Xformer.

                      Every one I have used (and it has been several) has primary and secondary on seperate legs of the core. The secondary has the smaller wire. Cut the secondary off (it has maybe 10,000 (minus 1000 plus 5000 turns). I cut off with a wood chisel. Each had one volt per turn voltage out put. so two turns of your biggest welding cable, with short leads to the tongs, will give you two volts. you should get in excess of 1500 amps woth ease. THe primary at full rated load will draw about 15 amps- which can be supplied by most circuits in the USA. A series resistor just before the transformer, can be used if it too hot. Piece of cake buddy!!!!
                      BTW the link from dunc looks like it tells you every thing else excepting the transformer.

                      Say hi to your nice from all of us.



                      • #12
                        Thanks Steve you are as always very kind. She is out of hospital and so far doing better,thanks again my brother.
                        Thanks guys for the help with the spot welder question this is really fascinating to me . I think it would be a real worthwhile project as they are so expensive to buy.I just missed one at an auction several years ago don't come up too often so I would like to make my own.Alistair
                        Please excuse my typing as I have a form of parkinsons disease


                        • #13
                          Steve incidently would a motor from an old microwave make a good slow sharpening machine? similar to a Tormek.
                          I notice it goes lovely and slow when in operation but have never been able to tell if has any real torque as the door is always closed when in operation.
                          But this has been an idea of mine for a while to test the one I have when it breaks down.If you say it will work I may be tempted to help it on it's way just kidding dearest wife oops she heard me .Alistair
                          Please excuse my typing as I have a form of parkinsons disease


                          • #14
                            Alistair,what did that dental spot welder look like? I bought a bunch of things at an auction of an old dentist and one item might be a spot welder or resistance soldering machine. I've never done anything with it.


                            • #15
                              Alistair: I have never tried on of thoseturn tables.
                              I tell you :from experience, a phonograph turn table will not do it . Neither spring wound, 78 nor 33.3333. they slip or stall. Tried it as a kid with grindstone from a hand cranked grinder.