Mini spot-welder for the workshop - some help please? - Page 1
Forum section: electronics / projects

author: Inflex
author_rank: Regular Contributor
timestamp: January 27, 2017, 05:15:07 am
content: For years I've considered getting/making something, but now it's really upon me.I have a laptop display assembly that's broken the long moment-arm and it simply is not able to be repaired with the usual judicial application of JBWeld, as much as I want it to be. So now I have decided my best bet is to spot-weld a length of similar metal as a splint across where this one is broken. I have searched around a lot for replacement hinges/arms because I'd prefer that option, but so far nothing in AU (and i've checked quite a few suppliers - HP 15-g036AU is the laptop ).So... getting to the point of this thread, how hard is it to make up a small spot welder? Charge up a bank of caps and use some old multimeter superflexible leaded probes ?

author: Paul Moir
author_rank: Frequent Contributor
timestamp: January 27, 2017, 05:42:41 am
content: It works, replacing your probes with really heavy copper wire. However, beyond very thin metal the energy needed means you need unreasonably large capacitors.* (* supercap bank notwithstanding).Consider an alternative: splint it with a section of silver-soldered metal. The real stuff, which is ~40% or more silver and only melts at about glowing hot. It is structurally very strong and although you have to make the investment in it and some flux, it makes up for it by being handy around the shop. It will bond a bunch of dissimilar and unweldable metals. As a testament to it's strength and utility, I have a HSS drill bit soldered onto the end of a steel rod as an extension.

author: Inflex
author_rank: Regular Contributor
timestamp: January 27, 2017, 05:52:22 am
content: Quote from: Paul Moir on January 27, 2017, 05:42:41 amThat's probably not a bad suggestion at all. I used to have a small spool of genuine silver-solder but never had a suitable heat source to suitable use it ( much to my chagrin )... just not sure where it is now. Might well be worth the investment as you have said.Any links/recommendations?

author: Ian.M
author_rank: Super Contributor
timestamp: January 27, 2017, 06:48:54 am
content: The issue will be if it has any tempered parts you cant remove before silver soldering - e.g. hardened pins or springs.It may be worth taking a look at:http://hackaday.com/2014/09/21/a-professional-spot-welder-made-out-of-a-microwave-transformer/

author: Inflex
author_rank: Regular Contributor
timestamp: January 27, 2017, 07:02:07 am
content: Quote from: Ian.M on January 27, 2017, 06:48:54 amThanks Ian, I had seen that one in the past when I was digging around the trashcans of the internet for some interesting items.The breakage this particular hinge has suffered is indicated in red on the attached photo, so hopefully a split running on the outside, silver-soldered/brazed should work.The retention pins holding the arms on to the hinge assembly itself are likely hardened.

author: Ian.M
author_rank: Super Contributor
timestamp: January 27, 2017, 07:31:58 am
content: At least there's a reasonable distance between the break and the pivot. It should be doable if you keep the pivot immersed in a tray of water while you silver solder it so it doesn't loose temper. Some creativity with aluminium foil and a plumber's fireproof mat may be needed to keep steam and spatter from the water tray away from the joint.

author: jpanhalt
author_rank: Super Contributor
timestamp: January 27, 2017, 11:09:01 am
content: 1) Silver soldering or brazing is one good option. Water to keep cool as suggested. But that can be inconvenient too. Welding sheet metal is common in body shops, and heat distortion is a problem. There is a heat absorbing putty/clay made (used to be asbestos) that you can apply around the joint to keep the heat affected zone small.2) My first choice, if you have access, would be TIG welding. Your material looks like plated mild steel. One can TIG weld very thin materials. If you also flow the argon along the back side (i.e., protect it from oxidation), you can get a full depth weld that looks great from both sides and is very strong. TIG inherently gives a small heat affected zone, because the heating is very quick compared to a gas torch; although, some putty or a damp towel would be advisable to protect any plastic parts that are adjacent.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 27, 2017, 02:32:01 pm
content: Silver brazing is a very high temperature process, not much different than any other brazing. We're talking red heat. You might want to try something a bit less risky- Harris "Bridgit" solder. It has a high nickel percentage and is stronger than most regular and low percentage silver solders. Use their flux for it. I've used this to repair the hollow beam on a drafting instrument with good results and no damage to graduations and such.BTW, pure C-D spot welders aren't the best. A better way is capacitor discharge through a transformer having about 1 heavy turn on the secondary. That's how the better thermocouple welders work, Ewald and such.

author: DTJ
author_rank: Super Contributor
timestamp: January 27, 2017, 02:43:32 pm
content: Where in Oz are you?This guy in Vic park WA had hinges that got my old lappy going again.http://itclearance.com.au/contact/

author: james_s
author_rank: Super Contributor
timestamp: January 27, 2017, 07:11:41 pm
content: I have a capacitive discharge spot welder that I built for welding battery packs. It consists of a capacitor bank of just over 1F, a simple variable power supply based on a LM317 and the biggest stud mount SCR I could find on ebay.A friend of mine made a more conventional spot welder using a large microwave oven transformer with the HV secondary replaced by a turn or two of very heavy copper wire. For the electrodes he used copper ground rod bent to shape and ground to points. I forget how the controller works, triac I think, counts the number of mains cycles to switch on for.

author: lilshawn
author_rank: Regular Contributor
timestamp: January 27, 2017, 07:42:00 pm
content: not to toot my own horn... but... I did make a spot welder from a microwave oven transformer.it's capable of outputting ~1300 amps at ~2 volts it's probably more than enough to spot weld some crummy metal like a lappy frame.half ass build and an explanation here:http://forum.arcadecontrols.com/index.php/topic,130330.msg1333493.html

author: Paul Moir
author_rank: Frequent Contributor
timestamp: January 28, 2017, 03:39:01 am
content: I use a simple butane torch for small stuff and a MAPP torch for bigger stuff. I'm too cheap to use an oxy-anthing.If shopping for a propane and/or MAPP torch, look for the kind that have a flameholder up about an inch inside the nozzle. They're invariably entirely stainless steel because they get orange hot at the tip during use, since the combustion begins inside the tube. I find these much better than the common external combustion type.I silver soldered by glasses back together when the kids broke them. How nerdy is that?

author: Inflex
author_rank: Regular Contributor
timestamp: January 28, 2017, 03:40:57 am
content: Quote from: Paul Moir on January 28, 2017, 03:39:01 amThe lack of tape disqualified you

author: SeanB
author_rank: Super Contributor
timestamp: January 28, 2017, 07:17:42 pm
content: Quote from: Inflex on January 28, 2017, 03:40:57 amJust fixed mine, using a piece of copper wire to fabricate a rivet to replace the screw that decided to snap. polished it down to size with a file in the dril, and then pushed into the hole, and used the tiny hammer and a steel rod anvil to spread it out a bit to hold in the hole.

author: Ian.M
author_rank: Super Contributor
timestamp: January 28, 2017, 08:02:04 pm
content: If there's enough bond area and the parts are closely fitted, soft solder works fine for wire frame glasses repair. Fabricate broken hinge parts by drilling and hand filing brass strip, 'black' them in a flame to prevent solder wetting where you don't want, lap on 400 grit wet&dry paper to get bright metal for the joint, tin and sweat into place. I've done 'field expedient' repairs that way that have held up for well over a year's daily use.However if you paid a premium for Titanium frames, you are FUBARed - repairing them is rather specialised:http://www.thefabricator.com/article/arcwelding/adventures-in-titanium-3-questions-about-repairing-titanium-eyeglasses-by-welding

author: SeanB
author_rank: Super Contributor
timestamp: January 28, 2017, 09:10:57 pm
content: Yes, titanium frames are not all they are touted for, took me 2 years ( funny enough the same lifetime as regular brass frames) to corrode them to pieces. Second set broke when dropped. Hard to find frames I fit, and i detest frameless glasses, but have a very nice Optometrist. Last visit was a check up , had a CT scan of the eyes, automated check of script ( he has some nice new toys, I am envious, want to get some broken ones if he has any in the back) and a confirmation with the old fashioned chair and big frame set to top it off. Stable, just the eyes getting old, and really nice to see the CT images picking up ultrafine details in the eye structure as well.