Straightening warped plastic kit parts

[ejstubbs]

Unpacking one of the polystyrene lineside building kits that I've had hanging around for ages waiting to be built, I've discovered that one of the key components appears to be slightly warped.  I don't know whether it was like that when it came from the shop, or whether it happened while the kit was in storage.  Might it be possible to coax it back to its correct shape eg by careful application of heat?  (Or maybe just warmth?)

[Dunsignalling]

Unpacking one of the polystyrene lineside building kits that I've had hanging around for ages waiting to be built, I've discovered that one of the key components appears to be slightly warped.  I don't know whether it was like that when it came from the shop, or whether it happened while the kit was in storage.  Might it be possible to coax it back to its correct shape eg by careful application of heat?  (Or maybe just warmth?)

Hot water, just off boiling, usually does the trick.

 

Dunk the part for a minute or so then manipulate it to shape. Don't forget that it will be hot!

 

Repeat as necessary.

 

If it's (supposed to be) flat, it can help if you put a weight on it while it cools.

 

 

John

Edited February 23, 2018 by Dunsignalling

[ejstubbs]

Thanks, I suspected something like that would be the best way to go about it.  I think may experiment with some pieces of scrap/sprue to see what sort of temperature I need.  And yes, I'll probably clamp or weight it flat while it cools.

Edited February 23, 2018 by ejstubbs

[34theletterbetweenB&D]

If you have a thermometer, it is worth getting a temperature established that permits easy reshaping, but does not cause complete flabbiness! The proposed experiments with the scrap to this end strongly endorsed.

[Andy Hayter]

Vicat softening point for Polystyrene is 90 C although the melting point is around 240 degrees.  What this means in simple practical terms is that above 90 degrees mouldings are likely to be distorted rather easily.  This can work two ways, so I would be tempted to work at a temperature below 90 (say start at 70 and work up to 80 as needed) to avoid unintended distortion while you are trying to correct the warping.

[The Johnster]

If you have a thermometer, it is worth getting a temperature established that permits easy reshaping, but does not cause complete flabbiness! The proposed experiments with the scrap to this end strongly endorsed.

 

In my case, 50 years of beer and chips has caused complete flabbiness, and reshaping is not easy...

[royaloak]

In my case, 50 years of beer and chips has caused complete flabbiness, and reshaping is not easy...

A treadmill works wonders as long as you keep temperature below 50 degrees, heart rate below about 100, and breathing this side of unconscious, or just accept it!

 

Edit-

How did you stop the chips going soggy?

Edited February 25, 2018 by royaloak

[The Johnster]

Ate them before they had a chance to get soggy!

 

Just accept it is the way I seem to be going; to old to worry much about it now and I'm chubby rather than full on obese, and fairly healthy for 66.  I have given things up; sugar in tea, white bread and so on, and cut down on other things, such as grilling instead of frying and restricting myself to my beloved chips once a week (I cheat with sweet potato oven chips).

[wirey33]

Hot water would be my route too.

 

I'd clamp the part to a flat piece of sheet aluminium or brass to give it a "home position" to achieve. 

 

Getting it pliable and trying to flatten it by hand would probably lead to more warp than you already have.

[ejstubbs]

The kit in question is a Dapol turntable.  It turns out that two of the components making up the turntable deck are slightly warped.  I'm just wondering whether it would be better to assemble the deck first, and then use careful warmth to take any remaining warpage out, or try to straighten the individual pieces first?

 

At the end of the day it's not a major issue - it's cheap enough to buy another if I can't fix these bits.  It's part of the risk you take with these ancient ex-Airfix kits.

[AdamsRadial]

I am building that very kit (Dapol turntable) and have had to straighten the girders for it using the boiling water trick. The curved pieces do also show some warping, and my current plan is to assemble them on a large steel sheet, warming them first, holding them tightly down to the sheet with strong magnets, and once I am certain all water has evaporated from the parts, adding liquid poly with a small pipette. I did have a go at trying to straighten two of the curves individually, and saw that the lugs with the holes and fasteners were causing as much of the distortion as the remainder of the part, hence the plan with the magnets.

Edited March 4, 2018 by AdamsRadial

[Andy Hayter]

Unless putting the bits together is going to correct the warping, I would straighten them first.

[ejstubbs]

I managed to get the warpage out of two of the three deck parts.  I clamped the warped part to the flat base of a steel bookend, and used a 3litre plastic food container for the water bath.  Monitoring the water temperature closely, I dunked the components in when it had cooled down to 85°C.  The metal of the bookend seemed to absorb quite a lot of heat, with the water temperature dropping to 80°C quite quickly.  The bit that stuck out of the water probably acted as quite a good radiator as well, with the temperature dropping to 70°C within a minute or so.

 

What didn't work so well was putting the component clamped to the bookend into the container and then pouring in water straight from the kettle.  That nudged 90°C before starting to cool down, and the result, although flat, was a little out of shape:

 

 

Lesson learned!

 

With a replacement part from a second kit I now have the three non-warped parts I need to build the turntable deck.  They do have a very slight end-to-end bow but I am expecting that will largely be cured once the side girders are in place, and the track glued to the deck.

 

I am planning to plate over the sleepers and from the rails to the inner face of the deck girders using something like the Wills chequer plate, to give the sort of finish to the deck that you can just about see in this photo of the turntable at Minehead on the West Somerset Railway:

 

[The Johnster]

A neat layer of gravel in the pit, while it looks lovely at Minehead, is not at all prototypical practice for the working steam era; filth and oil puddle are the order of the day...

[PatB]

Not really relevant for a turntable, but I'm currently building a Dapol signal cabin and have dealt with the warpage by installing additional styrene sheet floors to hold the thing properly rectangular. Hopefully creep, over the course of the next Western Australian summer, will take any residual stresses out.

[steviesparx]

Hot water would be my route too.....

 

Getting it pliable and trying to flatten it by hand would probably lead to more warp than you already have.

 

'It's no use Ted, you'll never get it absolutely right ! '...

 

Edited April 3, 2018 by steviesparx

[retiredoperator]

Hi Modellers. I have got a similar problem but, with the Dapol Presflo Wagon Kits 

but so far it is the end of the first Wagon doesn’t match the sides as it appears to on the straight side. If I was to glue/ cement/ or use solvent on the part that fits, once it has set could I bend with the hot water treatment the offending part into shape without affecting the already glued part? (Okay it is a silly question)

Happy Modelling Kev 

Edited August 29, 2019 by retiredoperator
Omitted word but

[John Tomlinson]

I'd say its usually simpler to bend the warped part while it is on its own.

 

Part of the difficulty of this is holding the warped part and being able to apply pressure to straighten. If something else is attached the holding gets trickier plus you might damage the other, unwarped part in the process.

 

John.

[michaelp]

On 03/04/2018 at 20:49, steviesparx said:

 

'It's no use Ted, you'll never get it absolutely right ! '...

 

Looks like he has got it pretty darn close though!!