Are all old playfields bowed?

[femto]

I placed a steel ruler across my 36yr old Card Whiz playfield which I am trying to fix up and noticed a distinct bow in the playfield. The gap in the middle is about 1 to 2 mm and I figured gravity etc is bound to bow these. So my question is are all old playfields bowed to some degree or do I have a shitty one?

[andtan]

I just checked my WH20 playfield, which has been sitting in a rotisserie for the last few months, and it doesn't have a bow. It is however a bit more junior than your Card Whiz.

I have been worried that it may start to bow because I have had all the hardware off it over winter, and at times I have had the heater on in the garage when I have been working.

[Strangeways]

They are basically planks of timber and they do bow, crack and plank over time. Laying them on a flat surface can minimize this. Leaning them against a wall promotes bowing and warping. Having said that, they do straighten up once the timber sides are screwed into the topside of the playfield.