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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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8th Dec 2019, 4:34 pm | #41 |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,587
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Re: Damaged vintage variac
Have just read some of the earlier posts again and looked at the time lapsed section of JW's video part 3. Am I right in thinking that it's the grub screws holding the collar to the insulating tube that you've been unable to shift? I wonder if these are the things on which to concentrate your efforts. If the collar can be freed it'll be much easier to remove the rotor from the top end of the tube. Just thinking aloud really.
Alan |
8th Dec 2019, 4:54 pm | #42 |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
Posts: 2,535
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Re: Damaged vintage variac
I will make the decision on replacing the brush nearer when it comes to re-assembly, which may be some time yet as everything needs to be cleaned thoroughly and re-painted before it can be re-assembled. This will give me some time to think about it, although I am now inclined to go with the 'leave well alone' advice until proven otherwise.
The top plate and rotator are made of aluminium/mu-metal or similar. The insulating material I think is phenolic resin. I initially thought it might be Bakelite, but not sure. I seem to remember PlusGas being mentioned before. I don't have any, or anything similar, so just used what I had to hand. I did wonder about thinning some cycle oil with with white spirit? Regarding PlusGas, which to go for: the spray can or the 'oil can' with the nozzle? I am inclined to go with the the nozzle as that would make it easier to direct the fluid rather than using a spray can, but I am a little worried about the potential for spillage if the consistency is as thin as WD40? Sorry but I have not used PlusGas so am not familiar with its properties. |
8th Dec 2019, 10:08 pm | #43 | |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
Posts: 2,535
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Re: Damaged vintage variac
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8th Dec 2019, 10:32 pm | #44 |
Dekatron
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
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Re: Damaged vintage variac
Plusgas is a similar viscosity to WD40 - it has to be so that it can creep.
To be honest though, the reason it has gone tight on the shaft is probably due to the phenolic shaft swelling - be warned that this may well end up going horribly wrong if too much force is applied. a proper puller is best, you can apply a constant pressure to the shaft, and hopefully this controlled method will be kinder to the parts.
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8th Dec 2019, 11:18 pm | #45 |
Octode
Join Date: Nov 2011
Location: Manchester, UK.
Posts: 1,874
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Re: Damaged vintage variac
I have a couple of these 8A jobs. One came very corroded, and the 'plastic' tube in the middle had swollen and gone very tight - I think they swell if they are stored anywhere other than dry. It lives outside in a shed now and is going a little tight again. The grub screws came out on mine and the steering wheel pulled off, but as I remember it was a bit of a nervous moment. Your brushes look a lot newer / less worn than anything I have - I suggest they're fine.
cheers Mark |
8th Dec 2019, 11:27 pm | #46 | |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,587
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Re: Damaged vintage variac
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Alan |
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9th Dec 2019, 1:04 am | #47 |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,587
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Re: Damaged vintage variac
Worth noting that the top plate should just slide off (in theory!) once the collar is out of the way but the rotor is held in place by more grub screws as it has to rotate with the tube. I think you will only be able access the grub screws once the top plate has been removed. This would explain why it's not possible to shift the rotor towards the bottom of the tube. Might not need the penetrating oil after all.
Alan |
9th Dec 2019, 11:38 am | #48 |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,587
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Re: Damaged vintage variac
The attached sketch illustrates how I think the whole thing goes together and comes apart. You will notice that drawing was not one of my better subjects at school. Hope it helps anyway. Good luck!
Alan |
9th Dec 2019, 2:28 pm | #49 | |||
Nonode
Join Date: Mar 2013
Location: Leicester, UK
Posts: 2,535
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Re: Damaged vintage variac
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Thanks for that sketch. After you mentioned the collar, that is how I now see it. Hopefully I might have some time later to have a crack at it. Last edited by WaveyDipole; 9th Dec 2019 at 2:38 pm. |
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9th Dec 2019, 4:38 pm | #50 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,934
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Re: Damaged vintage variac
I think it might well be the case that phenolic materials could swell or even be embrittled by agents like WD40 or Plusgas. Certainly, cracks in many materials (all?) can be made worse by wetting the tip of the crack.
As for the question of which is the best releasing agent, I suspect no one can supply some hard data on that matter? I've got cans of the traditional WD40, the newer WD40 penetrating stuff and a tin of Plus Gas. I have no strong inclination to say that any one is better. B
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9th Dec 2019, 6:03 pm | #51 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,395
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Re: Damaged vintage variac
Another problem I've seen in association with damp and variacs is that the winding doughnut often sits on a ring of insulating fibre material against the base frame (seems like a sort of dense compressed card, though it may even be an asbestos-type gasket material with bigger or older ones). This can absorb moisture if it's kept in damp conditions and eventually the enamelling fails in places and results in problems that can result in write-off, such as shorted turns and fusing, or nuisance such as leakage to earth or serious corrosion. They really are devices that ought to be kept in dry conditions.
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9th Dec 2019, 6:43 pm | #52 | |||
Nonode
Join Date: Mar 2013
Location: Leicester, UK
Posts: 2,535
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Re: Damaged vintage variac
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I dug the puller out but unfortunately it will be of no use for now. Having had another look today, I realised that the top end of the isolator is wider than the bottom end by about 5mm. It seems that the tube has been moulded with a lip (and narrower inner diameter) at the top end which would make it impossible to remove the top plate and rotor via that end of the isolator tube. Even if it were possible, there is only the tiniest of gaps below the collar and some insulating material, the presence of which also makes applying any leverage impractical as the material would almost certainly get damaged. It would therefore seem that the only way the parts can be removed is along the full length of the tube via the bottom end. Last edited by WaveyDipole; 9th Dec 2019 at 6:51 pm. |
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9th Dec 2019, 7:03 pm | #53 |
Heptode
Join Date: Jul 2014
Location: Boston, Lincolnshire, UK.
Posts: 995
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Re: Damaged vintage variac
A long bolt straight through the centre of the insulator, with appropriate oversized washers (at the bottom), and something like a very large 'socket', big enough to clear the diameter of the metal collar at the top, could be used as a 'puller' - that's how we used to 'pull' new small-end bearings, or some gearbox bearings, into / out of place on older motorcycles.
Nuts at each end can be just tightened to provide a controlled 'pull', possibly with the aid of oven heat, and penetrating oil. If the insulator is phenolic, then 100°C shouldn't damage it, but may be enough to expand the metal sufficiently to free it off... |
9th Dec 2019, 8:27 pm | #54 | |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,934
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Re: Damaged vintage variac
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B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |
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9th Dec 2019, 8:49 pm | #55 | |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
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Re: Damaged vintage variac
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Alan |
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12th Dec 2019, 7:01 pm | #56 |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
Posts: 2,535
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Re: Damaged vintage variac
Its out! The PlusGas arrived today so I gave it a try. It did loosen the rotator after it got stuck again when using WD40. I managed to wiggle it about an inch forward using the PlusGas, applying it, leaving it to soak and then wiggling a bit more, but then it got stuck again. Still, an inch was now enough to get my fingers though and use both hands.
I clamped it to a workbench and again using the PlusGas and wiggling managed to get it to within 2 in or so of the bottom end. At this point it needed more drastic action so out came the socket and hammer. I took my time using generous squirts but not overflowing of PlusGas and managed to get the rotator off, but not before a bit of damage occurred (see photo). At this point things got rather worrying as I still needed to get the top plate off and didn't want to do any more damage. I tried the PlusGas on it but this only moved it a little bit and I could move it no further by hand, brute force seemed the only way was brute force again, but this time I tried using a piece of wood between the insulator and socket. This worked and I got the tube down about 3 inches of the way which was enough then to get the puller on. The puller did the rest. Now can begin the work of cleaning up! Fortunately the damage does not look too severe and it should still rotate when re-assembled. I was hoping that the single piece that came off can be glued it back on with either superglue or epoxy adhesive and got back down to original thickness using some fine sandpaper? Or should I just leave it off? Hindsight is a wonderful thing and perhaps I should have used the piece of wood in the first place. In my defence, I tried every option before resorting to brute force. Although I would have preferred to have gotten it out intact, things could have been much worse and I am content with getting this far. |
12th Dec 2019, 8:24 pm | #57 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,934
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Re: Damaged vintage variac
I'd say that was a pretty good outcome . Also sounds like you'll be joining the PlusGas fan club?
B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |
12th Dec 2019, 8:43 pm | #58 |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,587
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Re: Damaged vintage variac
Well done indeed. I'd be inclined to use super-glue on the small chip but don't think it'll matter much if you decide to leave things as they are. All plain sailing from now on.
Alan |
12th Dec 2019, 9:44 pm | #59 | |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
Posts: 2,535
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Re: Damaged vintage variac
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I hope so! Last edited by WaveyDipole; 12th Dec 2019 at 9:50 pm. |
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11th Mar 2020, 3:31 pm | #60 |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
Posts: 2,535
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Re: Damaged vintage variac
I haven't been able to do much with this variac over the winter months except to remove dirt and crusty flaking paint, and give the parts a general clean. Some parts still need a much deeper clean. For example, the circular metal contacts to the centre of the rotator have so much oxide on them that Brasso penetrates only with difficulty and will take some perseverance to clean thoroughly. Now that we are getting more light and the conservatory at least is getting a bit warm at times, I have started re-painting some parts of the chassis. In the meantime, I would like to ask for advice regarding cleaning the brush track at the top of the winding.
The track is dirty and dark as can be seen in the photo. I am not sure whether this is crusted dried out grease, oxide or some other deposit, but the resistance is vary high (varying between 10's of kΩ and 10's of MΩ when I run the probe across the track or even hold it down firmly. I have already cleaned it by wiping down with IPA but the track remains dark and resistance high. In the repair video I referenced earlier in the thread, there is a point where the top of the winding is visible and it looks shiny and copper-like. I am wondering whether it is safe for me to go over this with emery cloth or fine sandpaper until the metal begins to show through? I obviously don't want to damage the winding but am unsure how to proceed. The other problem I still have is removing the large knob from the shaft. The grub screws are firmly seized in the Bakelite and no amount of Plusgas or heat has helped. Since the knob is loose, it does need to be removed and re-seated properly. It had evidently been forced by the previous owner while the unit was still seized and I myself probably didn't help things by wiggling it when I firt received the unit in order to try and get the rotator to move. Any ideas as to how these grub screws might somehow be removed other than drilling them out (which in itself seems a tricky proposition as the Bakelite is easily damaged) would be greatly appreciated. On the other hand if there is no other way than drilling them out, what is the best way to proceed and what can I replace them with? So far, no amount of effort has enabled me to move them by even the slightest amount. Last edited by WaveyDipole; 11th Mar 2020 at 3:59 pm. |