Glue and warping

The Ambroid sement I ever used was designed for use with wood and not plastic.

If you're getting warping with plastic parts you may be experienceing o ot two different problems. Plastic cement works by melting the plastic and fusing the surfices together. Drying really isn't a long term process since this process mets the plastic surfaces and they dry pretty quickly. If you are experiencing warping pver time chances are you aren't using the right glue since diferent kinds of glue have different drying times.

Irv

glue

I'm assuming your Ambroid cement is the solvent stuff, sold for use with a variety of plastics (including polystyrene) - when I've used it, I've found it to be decent stuff.

The biggest issue I'm aware of with any solvent glues is plastic softening, due to solvent vapours not being able to escape. I believe this to be a particular issue if there's a pocket created by the items being joined (effectively a hollow box) - the standard way of dealing with this is to drill a small hole, somewhere that won't be obvious after the model's fully assembled. I don't think this is the problem you're having.

Another issue concerns dissimilar materials being joined - they might expand or contract at different rates - more likely they might just "absorb" different amounts of solvent and shrink at different rates when the stuff evaporates. I encountered this a few years back when I had my first try at scratchbuilding a railcar. I used two different types of scrap plastic (I'm not sure, but suspect they might even both have been polystyrene) - the clear and black plastic parts of a scrap CD case - and solvent joined them continuously over about 5 inches. After a few weeks, I found they'd warped. I learnt my lesson - I replaced them with parts that merely rested against each other, so warping was no longer a problem.

Another approach I've read about involves using glues with a bit of "give", that don't actually dissolve the plastic - impact glues or rubber cement.

The other thing I'm wondering about is whether the plastic parts would warp by themselves after gluing. This might sound crazy, but it does happen with some plastic kits, even where all the parts are made of the same plastic. I'm not an expert on this - but I suspect that raised detail, scored lines and extra parts glued on top might set up different stresses on both sides of the parts, causing them to distort. It probably doesn't help that they're glued to further parts subject to different stresses. I've also encountered this - and the standard way round it is to add extra bracing pieces, to keep the parts a constant distance apart. I've found this works, but it probably helps if alternate braces are first joined to different sides before they're all joined together. By this I mean that, if you've got two wagon sides (left and right), the first brace is initially glued to the left side, the second to the right, the third to the left ... you get the idea. Once both ends are joined to both ends - and the joints have had time to harden - the braces get glued to the sides they weren't initially joined to.

I don't know your model - or your parts - but I can't help also wondering if there might also be some way of using screws to fix parts on from behind. This probably isn't an option, but I was just wondering if it might be possible to completely remove glue from the equation here.

I hope something here might be of some help - it would be interesting to find out what you end up doing and whether it works.

All the best,

Huw.

Thanks for the replies.  Most

Thanks for the replies.  Most of the warping was when I glued heavier backing for larger glue surfaces .  I ended up rebuilding the sides and it is all glued together now.  It is still square and straight a week later so I probably got a little heavy when I put the larger pieces on.  I'll post more when it gets farther along.