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Forum Index : Electronics : Relays: Carbon contact refurbish
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bigmik Guru  Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Hi John, To my eye it doesn’t show any sign of being rolled, I think you see the chamfer on the hex that most bolts/nuts have. I would think that rolling onto the graphite would risk it cracking but it might be possible..the carbon may be stepped to allow it to be rolled but I think that method is less likely than heat shrunk onto the rod.. at least the electrical junction won’t be liable to arc as the rod can’t loosen, it would have to crack for that to happen.. Of course there are more than one way to most results.. Unfortunately the picture is blurred right at the business end. If the carbon pad is deemed to be still serviceable you might be able to get the thread phosphor bronze braise welded and re turned/threaded.. I don’t know what the application of heat for the braising would do to it.. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1032 |
Better Piccie. I don't think it is rolled. I initially did though.  ChopperP |
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| Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1032 |
Hey Mick, not sure what you mean by this. ChopperP |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Thanks Brian, I think it’s almost certainly not rolled.. you said the rod went about 3mm deep, is it a plain bored hole or does it look like it’s stepped? It could be the rod is bonded onto a steel/brass pin that is press fit into the screw.. like i said there are mor3 than one ways to skin a cat. Mik Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Brian, Phosphor bronze braising is done with an oxy-acetylene torch with a special hand held rod of brass like material (phosphor bronze???), dipped in a braising flux, the idea is to build up the worn thread so that it is larger in dia than the thread. The hex head is then clamped in a lathe chuck and turned down to size I am assuming it may be a 3/16” thread so in that case that is the size to machine down to.. and the thread re formed onto the newly turned shaft.. Another method would be to cut the old shaft off and drill and tap into the base of the hex head and screw a new threaded brass rod into it.. this may not be possible due to the depth the carbon rod penetrates.. or a touch of braising to secure it if you can only get a few turns into the head. Regards, Mick Here is a you tube clip of the process of brazing (my spelling* was wrong) Youtube Mik Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1032 |
Mik / Mick  I have not attempted to remove the carbon pad yet, (but it looks like I will have to), so I don't know what is beneath the surface. BTW, I've been in contact with David from Graphite Aust. He will get back to me next week. (In S Africa ATM) Re the brazing. The bolt etc is OK. Just the pad is about 3 - 4mm too thin. I hadn't actually given much thought as to what the bolt was made of. Interesting though. Thanks for your input & give your dog a pat for me Brian ChopperP |
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| Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1032 |
FYI, photos of both sides of the armature contact part way through being redressed. Each totally different 'wear' paterns   ChopperP |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Chopper, Really? The first picture seems to clearly show a stripped thread and the rest of the thread seems pretty ordinary as well. Anyway.. Just about to take him down to post another package this will be interesting this time its to Coonabarabran.. I will give him a pat from you. If it took 12 days to Toowoomba, god knows how long it will take to get to there. Here he is in his warm coat.. Damn cold here today (guess about 11degrees.)  Kind Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1032 |
Nice Doggie . You like your Sunday walkies to the postbox or are you driving today?About 14 Deg here & @#$% windy. Better Piccie. Old one blurry. Thread is OK. Must remember to upload better quality photos in future.  Our old dog, Emma. Sadly no longer with us. Took me ages to get around to watching Shane Jacobson in "Oddball". Same breed. Not allowed to get another dog (or a cat)  . Regards Brian ChopperP |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
I have to agree you could not blame anyone for thinking the thread is stripped in the first photo. But it is just an illusion. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I think I would pay a visit to my local happy smiling nuts and bolts sales person, and see if he/she had some nice new shiny brass bolts of the same size. Then I wold experiment with some of these carbon rods people here are talking about. If it takes a few goes to get something that ends up looking reasonable, at least the original brass prototype contacts were not destroyed in the process. Cheers, Tony. |
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| Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1032 |
Yeh Madness, looking at the photo again, the threads did look bad. Good Idea Warpspeed. They do have a rather large head for a small thread though. One can only ask. ChopperP |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Chopper, I stand corrected, I had to have another look. It sure is an optical illusion.. Sorry to go on about brazing when not needed.. Sorry about Emma, I have a few sob stories I could add but I will try to stick to context.. I would suggest the thread is a WHITWORTH thread which have bigger heads than other imperial and metric threads have.. Of course it could have been a custom made job. Mik Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1032 |
No worries Mik. The blazing stuff was interesting Thanks. Been a while now. Better stick to the topic. Could be WW but more likely a custom made job but then it might not be. Thanks for the input. Hope your parcel gets to Coonabarabran in record time!!!  Brian ChopperP |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Thinking a bit more about all this, and looking again at the original. If you start out with some larger brass bolts that had a similar sized head, then reduce the shank diameter down in the lathe, and re-threaded to the correct thread form. If its Pommy, it may well be Whitworth, but if its Aussie or American its more likely to be UNC. And of course the The Europeans always used those funny coarse metric threads. If you know where this regulator originally came from, that could be a pretty good indicator. With the oversized head, that will give you more material to work with when boring out the hole to final size. A shrink fit would be my first choice as previously suggested, although it might be difficult to get consistent results that way. Second choice would be boring out to a close slip fit, then hitting around the top of the head with a sharp centre punch in six places. That will spread the material and shrink the hole. If you leave the carbon rod long, you can turn it to judge how it tightens up with successive centre punch hits. If you go at it too hard, it will probably crush and shatter the carbon. It probably just needs to be nipped up tight. Cheers, Tony. |
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| Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1032 |
Good idea, Warpspeed of getting the right size head (1/2" AF) & then reducing the shank which is bout 3/16" or 4.5mm. Thread not critical as long as there is a corresponding nut to fit. The unit is made by GE in the US of A back in the early '50s I think. I have a guy (David) from Graphite Australia looking for some suitable material for me. Once I get some, there will be some experimenting with fixing the stuff. I'll keep in mind what you suggest. Just got an email saying he has suitable stuff 10mm x 300mm for $20. Will go with that & see what happens. Thanks again Brian ChopperP |
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| Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1032 |
Getting a 10mm x 100mm of Grade PCCX2 from these people. Very helpful. They reckon it should do. Thanks all. Will update when things happen ChopperP |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Yet another idea.... How about fitting some really small grub screws sideways through the flats on the bolt head. The tips of these grub screws could screw into a shallow groove turned into the carbon rod thus locking it into position. Cheers, Tony. |
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| Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1032 |
Or maybe a very small roller pin. Interesting idea though Tony. Worth considering. Thanks ChopperP |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Lads, The problem with grub screw and pin is the graphite would almost certainly crack, especially as these will ‘pound’ into another contact when activated.. I think your only option would be a heat press fit into the bolt. You still need to be mindful of the electrical conductive property. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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