Whenever I try to scratch bodge a flat wagon or something, they warp. What causes it and how can I prevent it?

I have the frames for 3 3d printed warflats and I thought I would use them for a bit of scratch bodging. They were slightly warped to start with, so I taped them down to a flat surface and poured some hot water on them,  which straightened them up.
I've tried scratch building flat wagons in the past, (I guess it is one of the first things that you try when exploring this Rabbit hole), and I knew that the moment that I glue the deck down, it will warp again. No surprises there.
So I tried the hot water method again last night and it worked. But this morning I looked at it again and it has gone back to as it was. I can't win.

Is there any way to stop this or is this just a job for the bin?

Roberto.

Warping is usually a combination of the base material and either environmental conditions or solvents/glue it is subsequently exposed to...

Guessing from your description 3d print of some kind but what material and what are you doing with it apart from the warm water bath? What glue are you using, what paint etc?

If this is purely a 3D print problem then the title needs amending to reflect that, and the thread needs moving.
Could someone let me know please?

Some of it is down to the material type, thickness and size of the part.  Some if it is down to the design, where larger thinner components will benefit from framing / ribbing on the inside to keep things rigid.

Are these resin prints? And if they are, is the resin fully cured?
Maybe clamping them down to a flat surface and placing them in the sun for some time may help.

Jan

Hi Rob

I notice that a lot of RTR flats depend on their ballast weight for rigidity. Maybe try to copy that with your scratch builds?

Mike

If you can hide some T section metal (flat bottom rail) under a longitudinal spar that will definitely not flex in the direction that your print wants to flex, provided you fix the base of the rail to the main structure. You may have to design into your print the space for the rail, but it will definitely give strength as well as weight.

Bob