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Hairline crack repair on plastic
Old 07-03-2013   #1
lawnpotter
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Hairline crack repair on plastic

Hi I have a chrome/plastic and leather Polaroid sx70 With a hairline inch long crack on the front tray corner running vertical. The crack starts at the top. I could open the crack wide enough to jam in some crazy glue probably. This is not a cosmetic problem. If I dont fix it than it may get longer and I could lose a sizable piece from the front. Does anyone recomend a place that may do plastic welding or is crazy glue my best option. Bye the way, I dont care too much if the repair is pretty, I want a strong fix. Thanks
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Old 07-03-2013   #2
Frontman
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Use two-part epoxy, you can find it in clear or black. Krazy glue will not work as well, it is too watery when applied, and is better for fastening than for filling cracks. Epoxy will give a better repair, and should cure the crack problem. I have used epoxy to fix cracks in Polaroid film backs, it works great.
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Old 07-03-2013   #3
greyelm
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I think the superglue option is worth a try but use the thin liquid type so capillary action takes it into the crack, try and clamp the piece if possible. If you want to prevent the crack from lengthening take a pin with some pliers, heat it to red heat with a lighter and poke it in the leading point of the crack, this should have the same effect as drilling the leading point of a crack.
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Old 07-03-2013   #4
lawnpotter
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Thanks for the replies so far. I dont know much about epoxy but it sounds like it may be a bit thick. The space I make will be less than razor thin, maybe the liquid super glue may work best. Greyelm, your sugestin of burning a pin hole at the bottom or the crack is interesting but why is it nesaceary ? If the crack is forged with glue than there will be no more crack to grow right? I am not arguing but simply asking.
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Old 07-03-2013   #5
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Quote:
Originally Posted by lawnpotter View Post
Thanks for the replies so far. I dont know much about epoxy but it sounds like it may be a bit thick. The space I make will be less than razor thin, maybe the liquid super glue may work best. Greyelm, your sugestin of burning a pin hole at the bottom or the crack is interesting but why is it nesaceary ? If the crack is forged with glue than there will be no more crack to grow right? I am not arguing but simply asking.
As we say in England "Belt and braces". You could omit this step and only use it if the crack starts to lengthen after the repair.
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Old 07-03-2013   #6
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Drilling a hole at the end of a crack is a classic engineering fix, it spreads the stress around the circumference of the hole instead of concentrating it at the point of the crack ... but If you aren't bothered how it looks I'd just epoxy-glue a bit of plastic over it.
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Old 07-03-2013   #7
sevo
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Cyanacrylate superglue on plastics needs a primer/etch, as it does not bond to most polymers. And where it does bond, it (and its fumes) may eat holes into the plastics or fog the surface around the repair spot. Along with its often alarmingly quick action on materials it bonds to, that makes it rather difficult to use.

Epoxy by itself won't hold on to plastics either, and the typical (rigid, high hold) epoxy glues generally list none or only few and rather specific plastics among the materials they may be used on. If the surface is not hard and microscopically rough enough to give sufficient mechanical bonding, you should avoid generic epoxy glue - but there are special plastics/polymer modified epoxies that have additives that make it bond to plastics.

For vinyl, ABS and many other "non-breakable" plastics commonly used on cameras, there are welding glues available in model making shops. These can leave welds as strong as the solid material, provided that you can identify the exact plastics type and get the matching glue - there are less particular combination glues that will cater for a whole group of plastics, but create a less good bond.
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Old 07-05-2013   #8
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What sevo said depending on what type plastic, I built models for about 30 years and these types of cement will give strong bonds.

David
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Old 07-05-2013   #9
lawnpotter
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Thanks for all the replies,
Today I dropped my camera off at a plastics manufacturer and he will drill a tiny hole at the end of the crack and bond the crack with methylene chloride. he will charge $35.00. I think this is the correct route for me.
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Old 07-06-2013   #10
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Super glue melts certain plastics and if you use the type that brushes on, you could separate the broken part, brush a small amount on to each side and then allow it to bond. Don't disturb it for 12 hours, and it should create a very good bond.

I've used this to repair cracks on several cameras, including a Pentax and a Nikon Coolpix 700. I also used it to rebond a plastic light fixture.
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Old 07-06-2013   #11
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Not sure if this helps but when I have had to fill a hole in various bits of equipment I have successfully used epoxy mixed with some appropriately colored oxide - the inert stuff used by bricklayers to color mortar when laying bricks. Its cheap and works well. (e.g. black oxide for black plastic.) It can be polished off the surface after it dries to hide the fix. Of course for a fine crack this is not the stuff you need its more when you need to fill a hole. I used to build gun stocks many years ago and the same technique with brown oxide was a good fix if wood needed a little filler - e.g. if there was a gap when metal met wood. Much more robust than commercial wood filler.
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Old 07-10-2013   #12
lawnpotter
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The plastic fabricateur did a great job . He drilled in a hole at the end of the crack and added methylene chloride in the crack. It's fixed ! Thanks for all the help
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