Specifying Flatness for Appearance of Plastic Control Panel

[goldenfab]

I'm working on the design of a control panel that goes in a vehicle that is approximately 6" square with the front face having a 2" by 6" area being flat that will be an arms reach from the operator. The part is going to be injection molded. On the reverse side of the flat area there are cavities in the design and I'm afraid shrinkage during cooling will result in a visible indentation on the face of the flat area. I'm worried about the aesthetics of sunken in areas. The part will be painted matt black and will mostly be viewed normal to the surface. I would share a picture but those pesky NDAs... What would be the best way to spec the flatness without being too restrictive and what would be a reasonable value?

Thanks,

Adam

 

[3DDave]

Go find a cheap plastic item which the decision team agrees is the worst product you feel like selling, then buy it and measure its flatness. Dollar Store or Home Depot, for example, have plenty of plastic, not all of it needing perfection to function. Yeah - there's a reason not to put intersecting ribs behind good appearance panels; probably why over molding is so popular on portable power tools.

 

[TheTick]

Flatness alone probably won't get you the quality you are after. Shadow lines can appear without significantly impacting flatness.

Texture helps, but relying solely on texture never gets you all the way.

Redesigning ribs to work in harmony with other visual elements on the control panel can also help.

Most injection-molded part problems are caused by designers not believing that basic laws of plastic design do not apply. Among the most common issues is ribs that are too thick, which cause sink.