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2nd Jan 2020, 09:04 AM #1Senior Member
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spotwelder advice sought - lots of heat, no weld
A few years ago I picked up a cheap 240VAC spotwelder - it looks fairly similar to the picture attached. It was an impulse buy based on a price "too good to pass", and it pretty much went into storage as I was building my shed at the time.
I actually used it the other day, and found that the sheet metal (pieces of sheet - basically lids from a milo tin) would get quite hot, but the weld (nugget) was practically useless, it had no strength - mainly just the plating melted and oxidised.
this welder has a paddle switch under the handle which the operator holds to the side for current to flow - I tried weld times ranging from 1 second to 15 seconds, the handle was down tight each time, and I could not move the metal in the tongs when pulled with pliers.
the contact spot is approximately 5mm in diameter, and the OCV is around 3.5 V
any ideas or suggestions?
thanks,
Descheap_spotwelder_example.jpg
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2nd Jan 2020, 09:13 AM #2Philomath in training
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For those to work, the current density has to be up. I'd try getting the point diameters down to around 3mm (or even less if you are going to be doing milo lid regularly). The other critical thing is clamping force. I adjust mine so that it clamps up with no gap when empty. Commercially we usually have a clamp force in the kN range - ie thousands of Newtons, so don't worry about it being 'too much'
Michael
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2nd Jan 2020, 12:33 PM #3Senior Member
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Michael,
thanks for the pointers, I'll try reshaping the tip for a smaller contact area. The handle is nearly bottomed out with the tips touching, so I'll adjust that as well. I haven't had the handle "over centre" yet, ie self locking, so I'll see if it's meant to, or if it's a case of "squeeze really hard". Should the handle "click" or lock?
Thanks,
Des
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2nd Jan 2020, 03:24 PM #4Philomath in training
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I would expect so, but my tong welder is an old Dorman, so while it does the same thing, it does not look like yours. However, that pressure needs to be there through the whole welding process, so locking would be good.
Another thing that the movies get all wrong - if you have sparks shooting out when spot welding it usually means that something is not right. Those sparks are the (molten) nugget of weld forming. Obviously if the stuff that forms the weld can squeeze out, there will not be a weld...
Michael
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2nd Jan 2020, 05:19 PM #5Most Valued Member
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Are they a 10A or 15A plug?
As with all welding equipment - if you're having issues with low output give it the best power supply you can. I.e. Close to the switchboard and definitely not on the end of a long thin extension lead. It might even benefit from some heavier cable on the 240v side.
Check all the output connections are clean and tight and also check for any that are unusually warm after the welding attempt. That would indicate they have high resistance and you're losing power there.
Steve
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2nd Jan 2020, 05:27 PM #6Senior Member
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2nd Jan 2020, 07:14 PM #7Intermediate Member
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2nd Jan 2020, 07:31 PM #8Diamond Member
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I've got one of these that I have actually never used, if you get stuck could have a look at it for you.
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2nd Jan 2020, 07:47 PM #9Most Valued Member
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From memory, the tips need to be bright and shiny to work properly, otherwise you end up with a resistance, resulting in poor joints.
HTH.
KrynTo grow old is mandatory, growing up is optional.
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2nd Jan 2020, 07:58 PM #10Golden Member
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G'day Des,
It sounds to me like you might have a high resistance connection in the output circuit. The point you are welding should be the highest resistance in order to generate the heat required to produce a good weld.
It looks like the contact tips are a screw in fit so it might be worth removing them and making sure the threads are clean, it might also be worth removing the arms and again cleaning them too, they need to be bright and shiny so a good wire brushing should do the trick. Also make sure all connections, tips, arms and any high current side cables are tight.
Make sure there are no coatings on your sheet being welded, anything like paint or lacquer will usually stop any weld but some platings might also prevent a decent weld, give both sides of your Milo lid a clean with some emery just to be sure.
For reference, my little Tecna 2kVA unit will form a good weld in sheet from a 20lt oil drum in less than a second with approx 4mm electrode tips. It will do 1.5mm stainless in a bit less than 2sec. The arms on my unit (20mm dia) are considerably shorter than yours though at around 100mm so this might affect the weld times to some degree.
Cheers,
Greg.
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2nd Jan 2020, 08:09 PM #11Senior Member
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Thanks all, you've given me some thing to look at this weekend, and I'll report back with what I find, and pictures.
Thanks,
Des
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3rd Jan 2020, 05:34 PM #12Most Valued Member
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Something else that no one has mentioned yet. When you file up the tips make sure they come together flat at the thickness you will be welding. I have one a similar size to yours that I've had for 45 years. The timer is the person holding the switch in. lol. I file my points so that one is roughly 3 mm in dia (no bigger) and the other is a flat surface. I find this allows for any mis alignment when you close the arms.
The other thing to keep in mind when you do get it working ok is to keep that point filed up and clean and don't let the points over heat. You will know when you have done that. If you do any sheet metal work, once you master the welder, you will wonder how you ever did without it.
I bought mine used in 1975 for $150 which back then was a lot of money to me as I was only earning about $45/week as an apprentice. I bought it to use repairing a smashed up vehicle that I had bought cheap with the idea that once I had finished the vehicle I'd re sell the spot welder. Here we are all those years later, the vehicle is long gone but I've still got the welder.
I've even welded aluminium with it. Just to see if it would work and it did after a few false starts.
Best of with it
Peter
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5th Jan 2020, 12:37 AM #13Senior Member
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now working!!!!!!
Results are IN - Thanks to all for the suggestions
I checked the welder over and found marks from excessive heat on the tips and arms, the tips were not 5mm as I said, but rather a smeary 6+mm, and obviously misshapen.
I took the tips out of the arms (M8 thread) and cleaned then up in the lathe. I set one tip (top) as 3mm, and the bottom as a 16mm radius as per the suggestion for alignment concerns. I also adjusted the handle links so the handle bottomed out on the overcentre links with the tips touching empty (and some slight tension).
A new test of the milo tin lids material showed that 1-2 seconds resulted in a strong weld which needed pliers to peel, the nugget did break through the centreline, but quite roughly.
DN-100E_welder.jpgmanky_tip.jpg3mm_tip.jpgtips-redone.jpgtest_weld.jpgpeel_test.jpg
A very big thank you to everyone for their advice and offers for assistance.
Thanks,
DesLast edited by desbromilow; 5th Jan 2020 at 12:38 AM. Reason: correct typo
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5th Jan 2020, 01:36 PM #14Most Valued Member
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Hope you used the correct tool grind for turning copper, otherwise your results will be null and void.
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5th Jan 2020, 03:24 PM #15China
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Good to see it is working out
( I have most likely done many null and void copper turning jobs by the sound of it )
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