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CA and photo etch coming off


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Guys, my love / hate relationship with PE is well documented on these pages, but I have persisted in using them in certain places because of the clear benefits they can bring in detail. However something that continues to occasionally frustrate me is getting the damned things to stick, and bizarrely the ones I have most difficulty with can be the ones that theoretically should be the easiest to deal with.

 

A great case in point is the cockpit sill surround on the Hasegawa F-!4A, and Eduards PE replacement. I have now had to re-attach it four or five times, as it pulls off with the absolute minimum of handling. It is a part that has a large, flat, constant gluing area, it is not a pre-printed part. I deliberately do not paint the kit mating parts, and I apply a layer of medium viscosity CA, then lay the PE over it. I use the release paper that comes with double sided tape, plus tape to hold down the part while it cures. So, large flat  area, not in an exposed area where it can be easily knocked off, no attaching parts to complicate things. Easy, right?

 

Wrong. Even using low tack masking tape, when masking off the cockpit sills for painting, off comes the tape complete with the PE. So I reattach, after scraping the PE clean of the PE and trying to do the same on the now more considerably more complicated cockpit sill area. Strangely, the remaining CA does not want to come off the PE nor the cockpit parts, so it baffles me that it didn't want to stick together. By the way, I have tried Loctite, Bob Smith industries, Zap and various unbranded cheapo shop CA's, so it isn't an issue with the CA, although there have been a few cases where it seems that the CA did not want to adhere to the PE parts. But, the re-attached part is more prone to debonding, and with each progressive release gets worse. I now am unable to get it to lay flat on the area, and the unsightly gap between it and the edge of the cockpit has me now thinking that I will remove it and close up the cockpit in order to hide it, rendering all the cockpit work null.

 

In contrast, I have sailed through putting on the myriad of wing and fuselage mounted vortex generators, landing gear cover brackets, HUD parts, external grilles and chaff dispenser type objects, all with no issue. Some get knocked off when fumble fingers here does something exceptionally stupid, and you actually feel that there has been a lot of force resulting in the part coming away. Also, masking doesn't seem to pull them off.

 

So it must be me and my technique. I lightly abrade the PE so that it has a surface that the CA can key to, but would like to know any tips, or receive any advice that can help  me.

 

Cheers

 

Les

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26 minutes ago, lesthegringo said:

Strangely, the remaining CA does not want to come off the PE nor the cockpit parts, so it baffles me that it didn't want to stick together.

Does this mean you're leaving the previous CA application on PE and plastic when you try to reattach the part?

 

If so, that would explain this next bit:

26 minutes ago, lesthegringo said:

But, the re-attached part is more prone to debonding, and with each progressive release gets worse.

Glue on top of glue is not good.

 

For flat surfaces, you really want something more flexible to deal with different expansion properties betwixt PE and plastic. Gator's Grip or Formula 560 Canopy Glue are great choices for this application.

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47 minutes ago, lesthegringo said:

I reattach, after scraping the PE clean of the PE and trying to do the same on the now more considerably more complicated cockpit sill area

 I do try, but the issue is you can't remove all the CA from the kit parts due to the geometry - there is always some bits left

 

Les

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Before attaching etched parts, it's a good idea to lightly sand both the metal and plastic contact areas so the adhesive can key on to something. This is especially helpful on (comparatively) large, flat surfaces -and a reason not to like self-adhesive etched bits!

 

Like dnl42 says, a flexible adhesive is a good move on areas like cockpit sills. Cyanoacrylate glue dries hard and brittle; very often the slightest flex of the plastic during handling will not translate to the adhesive layer, with the result that the bond simply breaks open. Gator's Grip is the best solution I've found, along with the kind of heavy duty double-sided adhesive tape used by carpet/flooring installers. The caution here is that there are many types available; you want one that is thin (for obvious reasons), grips like an Evangelist's handshake and does not lose hold if paint gets to it. I wish I knew the brand of the roll I've had for years, but it didn't have a wrapper when I inherited it...

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Thanks. I have some Gators grip somewhere, will have to use that for this - I always avoided it as I was not convinced it would cure / dry in the middle of larger areas

 

Another thought was maybe an epoxy, the slow cure types; I remember the lab guys at work explaining that the slow cure types are always better for applications where a bit of give is good as they are slightly flexible when fully cured, as opposed to fast cure types that embrittle. The fan track and ice impact linings on the engines are now held in using polysulphide epoxies to stop them detaching, and we always cure the blue filler cold and slow where possible as it is tougher and less brittle. Looks like I should have used my memory a bit more

 

Cheers

 

Les 

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another alternative could be to use tamiya extra thin or equivalent to soften the plastic and then press the pe part hoping it would stick to the soft plastic as it dries. tho with a clear part like a canopy, extreme care would be needed to avoid a mess...

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I have had the same issue with adhering PE to Styrene and it has really, REALLY pee-ed me off ... but for the last model, I prepped the PE, not by abrading the surface, because a lot of my parts were teensy weensy ... I put the 2 sheets of PE in White Vinegar ... and the subsequent bond was ... EXCELLENT!

 

I had absolutely NO bonding issue!

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21 hours ago, lesthegringo said:

interesting, did it etch the surface?

Not visibly ... it simply removed the release agents or whatever residue is on the PE.

 

I don't recall how long I left it in the White Vinegar, ( the same as you'd use in a Salad ) but it may have been a few hours. No scrubbing ... but rinsed under running water and air dried.

The bond was quick and strong.

 

I read about this online but can't locate the info right now ... but it works!

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Guys, using some ammonium persulphate, I tested the brass photo etch frets to see if it would etch the surfaces slightly to give a better key for the adhesives, whichever flavour is used. On the right is an untreated fret, on the left one that spent a minute in the ammonium persulphate solution

 

20170427_155924_zpsvezljlaq.jpg

 

you can see that the surface has been etched, resulting in a matt (or at least satin) finish that hasn't affected the quality of the details.

 

I will have to use some of it and let you know what (if any) difference it makes

 

Les

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I'm curious how they'll take to paint. I've been experimenting with a warm vinegar pickle to improve paint adhesion. The pickle has helped, but I'd be interested in something that does better still.

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Actually, gluing a flat surface to another flat surface is not optimal for CA. CA really, really does not like being shifted when drying, which is likely when you try to position the part. That's why the bond is breaking within the glue instead of on one of the surfaces. CA is best when you can mate the parts and then glue them without moving the parts.

 

I would use epoxy in the cockpit situation.

 

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Two things

1. I'm not sure that using etchant on the parts is going to have any effect. The coating that's left on the parts which may cause problems with adhesion is photo-resist, which is used in etching to protect the parts that you DON'T want eaten away by the etchant. It isn't going to be removed by that, but another solvent may do so.

 

2. Buy some of the new(ish) "shockproof" or "rubberised" superglue. It's far better in sheer strength and will hold when older types fracture

 

Shane

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