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Nova1

Brittle plastic and tips for storage

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The issue of plastic deterioration has been discussed in the past on this forum so apologies if the below points go over old ground. I have several questions for those familiar with the restoration of vintage Tamiya RC namely:

1. Have any members noticed any change in the plastics used in re-release kits to those used in the 80’s?  I am wondering with the changes in technology whether newer plastics will exhibit similar deterioration in 20 plus years time just from the passage of time. 

2. Besides the usual precautions of minimising UV exposure, fluctuations in temperature/humidity, are there any tips on  treatment or storage of plastic to prevent drying out and brittleness occurring? I tend to store my collection in plastic storage boxes in the spare room.

Any feedback much appreciated.

 

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1. I unfortunately don't have the sprues to a lot of my old kits which would tell me what they were material-wise. I'm inclined to believe much of the older plastics were ABS and I'm definitely seeing an increase in the use of PC, which is an improvement. I still see ABS in re-releases here and there but more PC nowadays (not to mention more reinforced plastics on newer kits).

My experience leads me to believe there was an era where Tamiya plastic had issues. I've had old Frogs or Hotshot with little more than the typical age related issues. Somewhere around the Astute era up into the first DF01s seems to have more cracking and shattering issues. It could be the actual plastics or it could be that Tamiya designs changed a good bit and they were designing more complex moldings that the plastics simply weren't up to. It could also be they were attempting to minimize plastic usage for cost reasons. Since ABS gains strength through mass this is possible. ALL of this is mere conjecture on my part. Other than the usual fracturing at screw insertion points lacking in material, I have not seen any of deterioration of my re-release plastics stretching back to 2005. Keep in mind, mine don't see UV and are kept in a climate controlled home.

2. All I do, as previously mentioned, is keep plastics away from UV and in steady climate controlled conditions. No hot lofts, attics, cold/hot garages etc. UV leads to plasticizer mitigation, the breakdown of polymer chains and eventual part embrittlement. Once gone, plasticizers can not be replaced.

Remember, much of the splits, cracks and fractures we see are started at initial screw insertion during assembly. I exclusively use the "hot screw method" during assembly now. Impacts from use plus the loss of plasticizers simply spread these cracks until the part fails. Since ABS and PC are basically waterproof, boiling them won't rejuvenate them like nylon. You can reduce internal stress from impacts by submerging in hot water. This is why the white stress marks visible in lighter colored plastics like gray go away when submerged in hot water. It "relaxes" the part. One must be careful heating these plastics however. While ABS has a glass transition temperature of 221 degrees F (105 C), it can warp and deform at temps lower than that. I don't recommend just tossing a part into a pot of water at a rolling boil. Failed attempts at dying ABS often result in distortion (ABS doesn't really take dye anyway). A very knowledgeable Tamiya enthusiast plus discussions with engineers who dealt with plastics plus experience and research is where I gleaned most of this information

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All plastic degrades - some composites more quickly than others

Each also responds differently to UV 

Every kit then uses a different a blend of plastics, alloys + pure metals - the interaction of which changes each part + boundary with degradation + wear 

If the real question here is a formula for plastic obsolescence  - good luck !

For me, a better question is what vintage parts break, why + how often ?

For obvious reasons 👍

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Some days I feel like an easier question is "which plastic don't break?";). Tamiyas aren't like old RC10s. Between their aluminum, fiberglass and reinforced nylon componentry (which can be revived every so often through boiling/soaking), RC10s can last forever it seems barring wear or damaging impacts. 

This could gone through car-by car if we take the time. Designers don't always have the luxury of one of the best all-time test : durability over time in the hands of the consumer. People can do things designers/engineers never dreamed of planning for, like using their Tamiya models 20 or 30 years after their production date ;).

For a mostly plastic Tamiya, let's take the Lunch Box. Driven within its means (like not launching it down a flight of stairs, lol) a Lunch Box doesn't break from component failure over time except for the ridiculously under spec'd body mounts. Granted if it sat in the sun in a hot attic it might, but otherwise, no. Why? A good part of the front suspension that takes impacts is made from PA which remains flexible and absorbs impacts. The tub is traditionally ABS. The tub has enough mass in important areas not to break through normal use. The gearbox is PC, but again, is properly designed with enough mass in important area to withstand use over time. Unlike the body mounts, the the gearbox is actually over spec'd (especially considering the basic gear train design (all be it not identical) functions durably in the far large/heavier Clod Buster as well). The oldest versions of the gearbox (pre-Lunch Box usage, I believe) did suffer cracks in the "axle tube" area but Tamiya rectified this early on. That's not to say holes won't strip out from tear downs over the years or things won't break in freak accidents, but overall, plastic-wise, its safe to say the Lunch Box has few, if any, Achilles heels aside from the body mounts. So in this case, there's less of a need to stock up on Lunchie spares ;).

edit: obviously when abused or overpowered beyond original design-intent anything can break.

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It seems to me like storage is probably the biggest contributing factor, stuff that gets left in sheds or lofts for decades fares worse than brand new unbuilt kits that have been kept more or less at room temperature.

It's the same with tyres I suppose. Just like plastic, they aren't going last forever even in an ideal world but the differences you see between 2 of the same tyres of the same age but stored differently can be drastic. One can be virtually as good as new and the other can be like slimy goo or dust.

Hard to say if newer stuff is going to last better at this stage although ABS does seem to feature less prominently these days which helps.

I don't have a ton of vintage Tamiyas but one thing I've noticed with my sizeable collection of Nikko stuff is that things made in the 90s seems to hold up better than stuff from the 80s in terms of being brittle. I know you could easily say that's just because the plastic isn't as old but I think by now, stuff from the mid 90s would be starting to show it's age too but that isn't always the case.

The Dictator family of cars in particular, every 80s example I have seems to have one part or another broken in high stress areas but I've never had any of signs of undue fragility with any of the later versions even though many of those are 25+ years old. It's actually quite common to put the bodies of the earlier and more iconic versions onto the chassis of a later model to make it hold up better if you want to run it.

So I'm sure less than ideal storage plays a role but I believe improved manufacturing methods can have a significant effect too.

I expect simply by keeping the models out of direct sun and in average living room conditions you'd be helping the plastic a lot vs an attic or garden shed etc.

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18 hours ago, Saito2 said:

I exclusively use the "hot screw method" during assembly now.

I'm intrigued. Please elaborate.

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2 hours ago, Otis311 said:

Please elaborate.

When self tapping screws are inserted into rigid ABS/PC, there is a great deal of outward pressure. If there is not enough material surrounding the hole, stress fractures immediately produce a potential weak points. You might drive a buggy for months or even years until one day the part just fails inexplicably. The truth is, the constant impacts of normal use gradually caused these cracks to grow until the part fails. The screw pins used in Fox suspension arms are a good example. 

By heating the screw prior to insertion you can relieve some of this stress. The heated screw will "move" the material out of the way easier allowing the threads to form under less pressure. Some start the screw, apply a soldering iron to the end of it and drive it home after it has gotten hot. I've seen the same trick done with a lighter and magnetic screw driver. I try not to go too hot, as you still want threads to form as the screw goes in. Also, stop the second the screw is fully installed as a heated screw will quickly strip threads. Once cooled, it will act as any normal self tapper (just hopefully without the microscopic stress fractures from initial insertion).

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Makes sense. Basically you are using the screw as a tap that melts threads into the plastic. I can see how some trial and error may be involved.

Makes me rethink my new habit of lubricating screws before insertion into untapped plastic. I'm probably doing more harm by not letting the screw cut into the plastic.

On my trf201 with reinforced plastic and machine screws I used a piece of threaded rod in a small power drill and drove it in and out until it was hot, even when lubed with grease. This worked very well and didn't remove material as would a traditional tap. Tamiya sells a thread forming tool for this but it is expensive and hard to find.

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19 minutes ago, Otis311 said:

Makes me rethink my new habit of lubricating screws before insertion into untapped plastic. I'm probably doing more harm by not letting the screw cut into the plastic.

I don't think lubing the screws would hurt anything (unless the lube attacked plastic). I used to put a little grease on the tips of my screws to make them easier to install. I always use lube when tapping metal at work. I'm probably doing it overkill. Like I mentioned earlier, I've run Lunch Boxes not assembled with hot screws for decades without failure. On the other hand, I've had a rear inner upper control arm screw pin split the the mounting boss on a Thundershot rear gearbox while sitting on a shelf. It was fine one month and split the next when I went to dust it.

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