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How to unstick plastic parts.


PatW

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Although I sometimes use enamel thinners to dissolve plastic cement, I have read in a website Hints and Tips somewhere, that putting the parts into a domestic frezeer sometimes does the trick. Does anyone really know, having tried it themselves?

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If there's EXCESSIVE tube-type glue between the parts, and / or if the solvent-action of the glue hasn't thoroughly "welded" the plastic parts to each other, then freezing will indeed embrittle the glue and allow the joints to snap more easily.

Unfortunately, if a solvent-type glue HAS achieved good penetration and "welding" of the plastic parts, about all you'll get is an embrittlement of the whole mess, and the parts may or may not snap on the glue-line.

Misting or dipping assemblies in water prior to freezing can sometimes be beneficial as well, because water MAY penetrate into gaps between ill-fitting parts, and as it freezes and expands, it MAY force the joint apart.

These are trial-and-error methods, and don't always work equally well, or even work at all.

Edited by Ace-Garageguy
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Thanks Bill for your prompt reply. I had a kit from ebay 'already started' and the first owner stuck both the bonnet and bootlid on! I used enamel thinners but had to resort to a craft knife in the end. This model is in the Nascar thread just now. AMT UPS Taurus...... didn't work out too bad!

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Thanks Bill for your prompt reply. I had a kit from ebay 'already started' and the first owner stuck both the bonnet and bootlid on! I used enamel thinners but had to resort to a craft knife in the end. This model is in the Nascar thread just now. AMT UPS Taurus...... didn't work out too bad!

I bought a rare AMT '68 Firebird off eBay that has the hood glued on so solid that there's nothing to do but cut it out...very carefully. I work at it a little at a time when I want to do "something" but only have a few minutes to work. I'll get it out of there eventually!

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Thanks guys. Al as I'm in the UK mineral spirits doesn't ring any bells.

White spirit (UK) or mineral spirits (US, Canada), also known as mineral turpentine (AU/NZ), turps (AU), turpentine substitutepetroleum spiritssolvent naphtha (petroleum)varsolStoddard solvent or, generically, "paint thinner", is a petroleum-derived clear liquid used as a common organic solvent in painting and decorating.

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... had to resort to a craft knife in the end...

Sometimes mechanical cutting is the only solution. I'm currently separating the cam-covers from the cylinder head of a 1/8 Pocher Alfa Romeo. The builder used almost enough tube-glue per-cover to do one whole 1/25 scale model.

DSCN0255_zpszj08pmsl.jpg

The tool of choice for this is a set of photoetched saws from Model Car Garage. They're only .007" thick, and work a treat...but you HAVE to go slow.

                                                                             Image result for MGC photoetch saws

And sometimes, there's just no substitute for brute force with a grinder (another 1/2 tube of glue holding this 1/25 '32 Ford grille shell to the hood, and the hood to the body shell):

DSCN1100.jpg

DSCN1102.jpg

 

Edited by Ace-Garageguy
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White spirit (UK) or mineral spirits (US, Canada), also known as mineral turpentine (AU/NZ), turps (AU), turpentine substitutepetroleum spiritssolvent naphtha (petroleum)varsolStoddard solvent or, generically, "paint thinner", is a petroleum-derived clear liquid used as a common organic solvent in painting and decorating.

I wouldn't use anything that had naphtha (lighter fluid) in it to weaken plastic for un-gluing. Naphtha does something very odd to styrene--it doesn't melt or warp it, but it soaks into it and makes it as brittle and crumbly as a cookie. Put any stress on it at that point and it will crumble and disintegrate. Later, after the plastic has dried out for a few days (or weeks), it's more or less normal again.

Please don't ask me how I know this. The story is too painful. :(:angry:

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I wouldn't use anything that had naphtha (lighter fluid) in it to weaken plastic for un-gluing. Naphtha does something very odd to styrene--it doesn't melt or warp it, but it soaks into it and makes it as brittle and crumbly as a cookie. Put any stress on it at that point and it will crumble and disintegrate. Later, after the plastic has dried out for a few days (or weeks), it's more or less normal again.

Please don't ask me how I know this. The story is too painful. :(:angry:

That is VERY interesting...

I soaked an old AMT Indycar frame in brake fluid to attempt to strip it, and it did exactly the same thing...except it never regained its strength. Every time I'd glue a repair section in, something else would crumble. One of the few times I've actually given up trying to repair something. It's pretty much just a pile of powder in the bottom of a box of loose parts now.

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I use Naphtha on styrene and on ABS all the time (usually to clean/degrease it) with no ill effects. But I don't soak them in it.  But I use 99% Isopropyl alcohol on clear styrene parts as Naphtha does seem to slightly dull clear plastic's surface. Alcohol does not.

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I use Naphtha on styrene and on ABS all the time (usually to clean/degrease it) with no ill effects. But I don't soak them in it.  But I use 99% Isopropyl alcohol on clear styrene parts as Naphtha does seem to slightly dull clear plastic's surface. Alcohol does not.

I've used it to clean parts, too, but I found it can leave a very slight "oily" residue, so, like you, I use isopropyl alcohol mainly for that.

Don't bend or stress anything you have naphtha on, or it will crack and crumble. And if it's clear plastic, even if it doesn't crumble, it will get internal "stress cracks" that can't be repaired.

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The photoetched saws from Model Car Garage...they are a "pull cut" (like a coping saw), not a "push cut" (like a hack saw), correct?

Actually, they cut equally well in both directions, neither direction being as aggressive as a regular razor saw.

Examination of the teeth under magnification shows the rake to be symmetrical, which accounts for this.

Because these things are only .007" thick and unsupported by anything but the handle at the end. cutting on the push stroke requires care and finesse to avoid bending the blade.

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I've used it to clean parts, too, but I found it can leave a very slight "oily" residue, so, like you, I use isopropyl alcohol mainly for that.

 

That's odd. And the Naphtha was fresh(not reused)?  I used both, Ronsonol lighter fluid and VM&P Naphtha, and when fresh out of the bottle they leave no residue at all.

Now most of the time I use Naphtha for degreasing N scale model locomotive parts. Those are made from Delrin or similar plastics (resistant to most solvents).

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.....this has always  been an interesting topic over the year's, and this particular thread is no exception...over the year's I have used several method's  to get model part's to come apart .....I found that the yellow can, full strength Easy Off oven cleaner usually help's , or at least weakens the original glue so that a blade can usually get thing's loose for you. however, as Bill mentioned earlier on, if liquid solvents have welded part's together , it becomes tougher.  failing that, I  try locating new parts if possible, but we all know that can be tricky in many cases. glad I read this thread so far,,, some great ideas here from our member's..........the Ace.....;)

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