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> Best Way To Crack Apart Seamed Plastic?
Lil-Ozzy
Posted: January 24, 2012 08:29 pm
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Hey,

I'm working on opening up a travel mug to put some electronics inside it. The seam that I'm talking about is at top along the rim, where the insert that holds the liquid meets the outer shell.

When I did this before, I opened it up by sawing through the seam with a thin hobby saw, and that seemed to work alright, but it took forever and my hands were sore for a few days. I was wondering if there might be a better way to go about this.

From when I opened up another mug before, the insert's lip comes up and around a small rim on the top of the outer shell, so the seam actually has 3 sides to it, and I think it's put together with a solvent or glue. Both plastics involved are pretty brittle, although the insert isn't so bad.

Thanks,
Oz


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kellys_eye
Posted: January 24, 2012 08:35 pm
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'Glue' is rarely used. Most plastic jointing is done using ultrasonics. It's also unusual to have a 'complete' joint too (Tek excluded.... laugh.gif - sorry, in-house pun there... wonder if it'll get picked up?)

As a consequence, finding those small areas that are actually 'joined' is important. Try running a sharp blade around it first - careful levering may indicate where you have to make the real cuts.

Of course, a Dremmel drill with appropriate disk cutter is 'the' defacto solution to all problems of this sort.



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Lil-Ozzy
Posted: January 24, 2012 08:37 pm
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Thanks for the advice. I'd be using a dremel, but it might draw too much attention in my dorm room!


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AwesomeMatt
Posted: January 24, 2012 08:46 pm
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QUOTE
Thanks for the advice. I'd be using a dremel, but it might draw too much attention in my dorm room!


Turn some porn on to disguise your activities, then turn some loud music on to appear as if you're disguising the porn. Both should mask your true activities.

Go to the arts building, find the bottom of a stairwell and use the plug there? Noise shouldn't be noticeable to anyone. Parking garage might be good too.

Your hand was sore for several days after sawing through a plastic mug? Keep sawing, you could use the exercise. Hacksaw perhaps, if your hobby saw is too wimpy?

Sometimes I've had luck with a chisel. Stuff pops apart. Other times it shatters the plastic and makes a mess of things.
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Lil-Ozzy
Posted: January 24, 2012 08:54 pm
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The soreness was due mainly to a lack of a vice to hold the mug in place. The hobby saw is wimpy, but the hacksaw is too wide.


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tekwiz
Posted: January 24, 2012 11:41 pm
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A saw is still the best option. Try a cheap coping saw with a very narrow blade. Most coping saw frames will accept stardard scroll saw blades, & these are available very thin...down to ~.010" or so, by .025" wide.
None are expensive & a dollar store saw frame will accept top quality blades.
Look: http://www.leevalley.com/en/wood/page.aspx...902&cat=1,42884


BTW: What about cutting a hole in the bottom & covering it with a false glued on bottom? A tiny end mill style cutter in the Dremel would make short work of the cutting. Do it in the bathroom & if anyone asks, tell them you're fixing a tooth or a toenail. tongue.gif


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MacFromOK
Posted: January 25, 2012 12:08 am
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I generally use a trim knife (those with the snap-off blade sections), and just keep going over and over the same cut. The last wallwart I opened was in this manner, and it worked very well.

This method usually works better on soft-ish plastics than hard/brittle ones though. beer.gif


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Jimthecopierwrench
Posted: January 25, 2012 12:46 am
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Quite surprised not to see my method of preference mentioned...

Hammer and vise - swear to god. Takes some patience and practice but I can split the average lappy supply so cleanly now that they can be put back together invisibly with the original surfaces undamaged.

I use a vise to clamp right even with one side of the split line and apply pressure slowly until you hear the first light sound of cracking, then tap a bit with a small soft hammer (or the end of a small ~1/2 x 1/4 end profile piece of soft wood as a punch) on the other side of the split line with sharp blows, moving the unit's relative position often, and swapping the vise/hammer sides of the line.

Hmm, mebbe I should do a video. Works like a charm and once you get the feel and sound you can do all kinds of those ultrasonic odd shaped joints. I've done everything from clear plastic neon shifter knobs, to wall warts. It also actually takes far less time than any other method I've seen.


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Lil-Ozzy
Posted: January 25, 2012 02:27 am
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Thanks for the ideas, guys! Considering my equipment, I think I'm going to stick with a saw, but I want to try the vise and hammer method when I work on stuff at home.


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kl27x
Posted: January 25, 2012 02:46 am
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http://www.amazon.com/Dremel-199-High-Spee...7455819&sr=1-17
I have always used this, in a Dremel. Gotta try that hammer and vice trick!
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tekwiz
Posted: January 25, 2012 09:45 pm
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QUOTE (Jimthecopierwrench @ January 24, 2012 03:46 pm)
Quite surprised not to see my method of preference mentioned...

Hammer and vise - swear to god. Takes some patience and practice but I can split the average lappy supply so cleanly now that they can be put back together invisibly with the original surfaces undamaged.

I use a vise to clamp right even with one side of the split line and apply pressure slowly until you hear the first light sound of cracking, then tap a bit with a small soft hammer (or the end of a small ~1/2 x 1/4 end profile piece of soft wood as a punch) on the other side of the split line with sharp blows, moving the unit's relative position often, and swapping the vise/hammer sides of the line.

Hmm, mebbe I should do a video. Works like a charm and once you get the feel and sound you can do all kinds of those ultrasonic odd shaped joints. I've done everything from clear plastic neon shifter knobs, to wall warts. It also actually takes far less time than any other method I've seen.

I use that method myself. It helps to have a nice big bench vise. I didn't mention it in this case because the OP indicated that the two halves are both snapped & glued together. The vise may break the glue joint, but the snapped together pieces likely won't resond well to this. It'll likely take prying to separate the halves, & this will invariably cause visible damage. wink.gif


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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Hamlet
Posted: January 26, 2012 05:44 pm
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QUOTE
Hmm, mebbe I should do a video.


That'd be cool, sounds like a good method. The dremel is a bit violent for cutting plastic, since the cutting disk tends to melt the plastic due to high rpm heat friction (at low rpm, the torque is not really there), which covers the disk with the melt and then follows like a hot knife trough butter, Jack the ripper style. Though this does depend on the kind of plastic you work with.
I have used a hammer without the vice, smashed the enclosure like a chestnut thumbsup.gif


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