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Author Topic: Filling/stiffening vac-formed ABS parts?  (Read 385 times)

clockworks

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Filling/stiffening vac-formed ABS parts?
« on: August 28, 2019, 06:16:33 PM »

I'm building a Krick Neptun tug (about 1/50th scale I think).  Many of the parts are vacuum-formed from ABS sheet, including the superstructure.
The instructions say to join these parts using thin superglue. I'm using a mix of superglue and Polyweld (MEK), and this is working fine where the contact area between parts is a decent size.


I'm having a problem with the funnel though. It's a fairly modern tug, so has a fancy multi-curved funnel. It's moulded in 2 halves, which are sanded flat and glued together edge to edge. This doen't give much for the glue/solvent to work on, so I've done my best to reinforce the join on the inside with strips and tabs of styrene.


The funnel has to support quite a few bits and bobs, including the mast, lights, horn, radar platform etc. I'm a bit worried that the joint will crack if any of these bits get knocked.


I'm thinking about filling the inside of the funnel with some sort of resin or filler, making it an almost solid lump - maybe a core of balsa or foam to keep the weight down.


My question is, does this sound like a good idea, and what do I use as the filler? Needs to be something that won't shrink, attack the ABS, or generate too much heat as it cures.
I've got P38 and P40 fillers, and polyester and epoxy resins. Epoxy would probably be safe, but it would take a lot of expensive resin.


Anyone done something similar?
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tigertiger

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Re: Filling/stiffening vac-formed ABS parts?
« Reply #1 on: August 29, 2019, 02:56:39 AM »

One idea that does spring to mind. You could dissolve cut off of plastic into the liquid glue/cement to form a thick plastic goop, then use this to reinforce the joint. I have also seen people use this as a filler.
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Subculture

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Re: Filling/stiffening vac-formed ABS parts?
« Reply #2 on: August 29, 2019, 07:40:37 AM »

A simple and lightweight reinforcement is to use some epoxy resin and glass cloth to line the inside of the funnel. Same the inside well to key the epoxy to the plastic and use a very light cloth. However the abs should be strong enough on its own IMO.

coch y bonddu

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Re: Filling/stiffening vac-formed ABS parts?
« Reply #3 on: August 29, 2019, 08:36:02 AM »

A simple and lightweight reinforcement is to use some epoxy resin and glass cloth to line the inside of the funnel. Same the inside well to key the epoxy to the plastic and use a very light cloth. However the abs should be strong enough on its own IMO.




What I would be afraid on is that the curing resin could deform the abs......melt some plastic off cuts into a small container and add some MEK into it to form a gloop and use this to strengthen the joint....tbh if the joint in glued properly in the first place it should not come apart



Dave
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Subculture

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Re: Filling/stiffening vac-formed ABS parts?
« Reply #4 on: August 29, 2019, 09:31:15 AM »

Epoxy won't harm the abs, and any shrinkage is so minor, you don't even have to consider it.

clockworks

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Re: Filling/stiffening vac-formed ABS parts?
« Reply #5 on: August 29, 2019, 09:51:31 AM »

If the parts were made from styrene, I'm sure that a simple Polywelded joint and a few tabs would be sufficient. The ABS sheet in the kit doesn't soften as readily as styrene, so the joints don't fuse together quite as well. I managed to pop part of the joint while sanding the outside. It would be a real problem to fix after painting and final assembly, as there's no access to the inside then.


I'd forgotten about dissolving styrene in Polyweld - I used that as filler back in the day. I'll try that first. If it doesn't work, I'll pour in some epoxy.
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Subculture

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Re: Filling/stiffening vac-formed ABS parts?
« Reply #6 on: August 29, 2019, 01:11:43 PM »

Another glue I use are modified acrylics. These are extremely strong- stronger than the plastic in most cases. They lack finesse though, as they tend to be gooey like epoxy, so not well suited for fine work.

RST

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Re: Filling/stiffening vac-formed ABS parts?
« Reply #7 on: August 29, 2019, 01:50:47 PM »

ABS solvent welds perfectly well with the right product. Try MEK or some say acetone (not all nail varnish removers are acetone now). Rule no 1 as always, try it on scrap first!
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clockworks

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Re: Filling/stiffening vac-formed ABS parts?
« Reply #8 on: August 29, 2019, 02:46:26 PM »

I'm using EMA Plastic Weld (dichloromethane). I thought it was MEK, but I've just checked the label. It's a bit slower to liquify the surface of ABS compared to normal styrene - needs to be kept wetter for longer, and some pressure applied to the joint to force the liquified surfaces together.


Some test joints using scraps of the ABS worked well - as long as I applied more solvent and pressed harder than I would with a styrene to styrene joint.



Does MEK work better?


I've got some acetone in the shed, but haven't tried that. I normally use it for dissolving superglue, removing paint, etc.


I've got some Deluxe Materials Fusion 2k acrylic glue, which I've used for fitting the wood and brass parts inside the hull. Creates a really strong bond, but not easy to work with.






I've slapped some "goop" inside the joints, will see how that holds up once it's hardened.
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Re: Filling/stiffening vac-formed ABS parts?
« Reply #9 on: August 29, 2019, 04:02:04 PM »

I tried fusion glue, which is modified acrylic, but agree it's a fiddle to work with. I much prefer the modified acrylics which are mixed in tubes like epoxy e.g. https://tinyurl.com/y3oxzq6o
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