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Repairing plastic


whizzzy
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Not directly bass related but is from some stage lighting gear so it qualifies for music - ;)

Does anyone have any experience with using this product - [url="http://www.repairproducts.co.uk/page20.htm"]http://www.repairpro...o.uk/page20.htm[/url]

The item I am trying to repair is a plastic cover from a moving head and I have tried the usual superglues, one being Loctite All Plastics and none of these have been very successful. Even after bonding it and leaving it undisturbed overnight it hasn't held the cracked part together. The plastic in question is the hard but slightly flexible type, possibly polypropylene.

Watching the video makes it look like the answer to everyone's prayer but all too often with these sorts of thing the demo makes it look all too easy and it never works when you get it home.

Any advice or recommendations would be appreciated.

Col

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It looks and sounds suspiciously like a bog standard two part resin based product to me.

The catch with moulded plastics is that they are pretty strong but a break will nearly always re-occur at the point where it has previously broken.
I'm kinda of the opinion that if this product was an absolute miracle then the major players would have been selling it by now.

The repair method, or the decision to replace, really depends on the part that has broken - can you give us a clue what the part looks like?

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Depends on the plastic probably.

Years and years ago i worked for Scrivens as a hearing aid engineer. The behind the ear and in ear aids were in sealed pink or flesh couloured plastic cases which we used to cut off, then after repairing the electronics or whatever, fit a new case which was in two halves, by painting the edges with a solvent then pressing them together and the polish off the excess plastic, Different models needed different solvents though, cant remember all of them, but one was Methyl Ethyl Keytone, one was just Acetone, another was ( I think) Tri clorethyline.

Trouble with gluing plastics is that the glue need to flex, or not,in the same way as the plastic.

There are firms around that repair car trim and bumpers, by welding the plastic, dunno how the process works
but it does, and you cant see the join. Just wondering whether its worth you trying one of tese firms. Or could you use screws and nuts and fit a plate behind the crack ?

The car repairers option seems like the best bet to me though.

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Thanks. I'll get a photo of the part posted when I get home later.
Replacement isn't totally out of the question but the fixture was made by Coemar in Italy (so read that as dammed expensive and quite difficult to get hold of). Repair seems best option and I hear what you say about none of the major players selling this type of product but looking at the video it all looks a bit of a faff (not that it worries me) so this may be one reason why it hasn't caught on?

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[quote name='whizzzy' timestamp='1332512527' post='1589425']
Repair seems best option and I hear what you say about none of the major players selling this type of product but looking at the video it all looks a bit of a faff (not that it worries me) so this may be one reason why it hasn't caught on?
[/quote]

Could be that it works just fine but I just can't see 'how'.
If it has a different level of flexibility to the plastic parts that it's sticking together (which is near enough guaranteed) then I don't see how it can work... :huh:

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looks to me like fine plastic powder plus superglue or acetone to redissolve the plastic then set it hard. You can use similar method to re-build up an over-filed nut slot. Will be ok for some plastics but harder ones are often a problem since they have plasiciser content which is a little oily and glue can't stick to it. The plasticiser helps with moulding and any brittleness.

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Thanks for the response guys. Below is a shot of the part in question. The split has been held open with a screwdriver blade just to emphasise it.
It's probably a heat stress related as these things get pretty warm over several hours. Checking with someone who repairs car bumpers may be an option but its always a challenge to do these sorts of things by yourself.

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Looking at that I think I'd be inclined to make a thin metal plate the same shape as the side facing us (and maybe one for the other side(s) before the same happens again?).

A thin layer of evostick to fix the plastic to the plate and then rely on the existing screw holes to hold it all together.

As for the metal - I'd go for an old tin can, tough, thin and quite easy to cut - but mind your fingers. :)

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Those 'two-part' glues can be very strong in themselves but rely on their 'stickiness' to hold stuff together. If the materials to be glued are slightly unclean or naturally 'slippery' then even the strongest glue won't hold things together.

Probably the best solution is a glue that effectively 'welds' the plastic together, as BRANCINI described, but the trick is to find the right solvent for the type of plastic. A quick and cheap thing to try would be plastic model glue.

Failing that, reinforcement of the entire piece seems a good idea, as icastle described above.

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For a start I'd drill a hole at the end of the split to top it getting any worse.

Airfix glue, but it depends on what type of plastic it is, its much like using solvent really, as from my youth I remember the plastic in Airfix kits used to melt a bit.If uts something that gets hot its unlikely to be the same type of plastic though I reckon..

Or if you can find some scrap bits of the same type plastic, weld it....Fumes can be a bit dody though, so I'd do it outside if I were you. Re inforce it by melting in bits of stiff wire, or a plate with holes in it.



[media]http://www.youtube.com/watch?v=NuA6d49Z7Rc[/media]

Edited by BRANCINI
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Ok, a bit of an update on the plastics repair.

Although I'm probably one of the worlds worst sceptics when it comes to these sorts of things I did go ahead and order one of the plastic repair kits on line. Well what can I say, I'm really very impressed with the outcome. As icastle mentioned in an earlier post the kit does seem like it is resin based as the liquid has that characteristic smell about it. However I followed the instructions and used a small Dremel type tool to cut a groove along the break and then filled the channel using a drop of the mixture at a time as they demo in the video. Left it overnight and it's a proper job and I would go as far as saying that the repair is as every bit of strong as the plastic itself.

I did consider the other suggestions before going with the repair kit but none of these were really practical for a number of reasons. But anyhow thanks for the suggestions chaps.

So there you have it. If you have any awkward plastic parts to repair on your bass then I would seriously consider looking at this repair kit as an option.

Mrs. W. may even get the plastic nozzle repaired on the vacuum cleaner now! :D

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