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An engineering challenge for you

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An engineering challenge for you

Old 17th May 2020, 12:46
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An engineering challenge for you

I have inherited a very posh torch - a P17 Led Lenser which has been lying around for years. It does not work (!) and I cannot get the end cap off to access the battery compartment.

Any brilliant ideas? I have progressively moved to holding the cap in a vice and trying to turn the body, it does not budge. I have tried soaking the end in boiling water for a few minutes - hoping to expand the end cap. I have tried gentle taps with a hammer.

My next thought was to really heat the end cap by standing it on a hotplate!

(and yes, I have tried getting in from the bulb end - no go)

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Old 17th May 2020, 12:54
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Does this help?

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Old 17th May 2020, 12:56
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Hopefully you haven't distorted it in the vice. Try putting elastic bands around the cap to help get a grip. Or a squirt of good ol' WD 40.

Caveat, I'm not an engineer.
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Old 17th May 2020, 13:08
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Do you have a strap wrench? Try one after the WD40 has had some time to penetrate.
And, stating the b obvious, the batteries seem pretty corroded.
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Old 17th May 2020, 13:09
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Strap wrenches are very useful for things like this:


Not hard to make a couple up with some cord loops and screwdrivers as levers. Combined with some rubber around the torch to add some grip you should be able to get the thing apart without damage, I think.
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Old 17th May 2020, 13:11
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Originally Posted by TURIN View Post
That does help. It shows how to get in from the other end. Unfortunately that won't budge either and its hard to get a grip on without damaging the LED.

Clearly the inside is a horrible corroded mess, the outside looks pristine.

I'll try the WD40 thing next.
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Old 17th May 2020, 13:21
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wrap ice around the male end and hot towels around the female end.

If this doesn't work, give it to some monkeys and come back later
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Old 17th May 2020, 13:38
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Originally Posted by lomapaseo View Post
wrap ice around the male end and hot towels around the female end.

If this doesn't work, give it to some monkeys and come back later
I do have access to liquid nitrogen that might usefully shrink the end piece. The video above shows that I need to shrink the end not expand it! It's a plug that fits inside the tube.

(I also have access to monkeys...)
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Old 17th May 2020, 14:03
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Originally Posted by double_barrel View Post
I'll try the WD40 thing next.
And if WD40 doesn't work, try some proper penetrating oil like Plus-Gas.
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Old 17th May 2020, 14:33
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Drill a hole in the bottom cap and attack from the inside. Plug the hole later with a rubber plug, you do not throw away stuff, do you? If bottom cap is beyond salvation, buy a new one. Still cheaper than 80/90 USD.
If everything fails, hand torch to old school merchant ship engineer. He will have two functioning torches in half an hour.
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Old 17th May 2020, 15:32
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Generally I find if I spend hours trying to take something apart to mend it, once it's in bits I find it's totally stuffed anyway. Or I break it in the process...

Just trying to remove a plastic ceiling rose so I can paint the ceiling and remove the pendant and wire for cleaning. Two problems, 1) one of the screws fixing the whole fitting to the beam above the ceiling is clearly missing - I must have forgotten to use two when I installed it 25 years ago; 2) the bloody plastic cover won't undo even with my largest molegrips applied lovingly to its delicate carcass... Never found a plastic fitting I couldn't undo before... It's double pole switched so I don't really want to replace the whole fitting as I'll probably get the wires arse about face and I hate fiddling with the damn things while balancing on a stepladder! Painted round it and I'll clean the gubbins in situ...
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Old 17th May 2020, 15:33
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Failing a strap wrench, I have a scrap toothed cam belt which works a treat if you want a good grip on a stuck lid. Might be worth a try.
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Old 17th May 2020, 15:45
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45 degrees and then freeze the cap (if plug) with electronics aerosol. Strap on a bar is easy to make. Strap on two bars will put a delightful twist into the torch if you're enthusiastic enough.

Boot sale. Sexy torch. Precise reamer. Let white power out. Reengineer switch. Find new springs. Put in megga batts. Shine it on something. Throw it away cos it's crap.
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Old 17th May 2020, 15:45
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I've got a rubber grippy thing for taking lids of jam jars I got for my late mum, irritatingly just a smidgen too small for ceiling roses. Thought I'd found a use for it, I rarely have jars of stuff...
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Old 17th May 2020, 17:09
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Aluminium to aluminium? It can sometimes almost weld itself together, especially if corrosion is involved. Id say heating the cap and freezing the body is the most likely way to succeed.

Im surprisingly no one has mentioned a bigger hammer yet...
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Old 17th May 2020, 18:02
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My maintenance tips these days extend only to this;

Is it meant to move and it's not? - Use WD-40

Is it moving and it isn't meant to be moving - Use Gaffa Tape.

Has worked so far...
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Old 17th May 2020, 18:05
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Forget it! From your efforts so far it's obvious the opposing torsional forces on cap and body necessary to separate them are greater than either will be able to withstand. In any case, judging by your descriptions you'll find the insides are totally screwed anyway. Brass contacts, switch gear etc will just be a uselessly corroded mess. Had the same problem a couple of months ago with a battery-powered mobile phone charger. Managed to force it open but the interior looked like reactor no.4 at Chernobyl.
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Old 17th May 2020, 18:16
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It's likely that thebattery has leaked and caused internal Corrosion.
I would try a few heating cycles with a heat gun interspersed with soaking the end in a cup of diesel, it will move eventually
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Old 17th May 2020, 19:07
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Or just file it in b1n,and get a new one.
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Old 17th May 2020, 21:10
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Yeah, bin is the smart choice. Have you tried boiling water, obviously need gloves. Failing that, junior hacksaw.
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