Friction fit help

[Jinxr]

Has anyone ever had any experience with making friction fits in plastic parts? And could you offer me some advice?

This is the first time I've ever designed a plastic part and I'm having problems with a friction fit. The part I'm trying to make is a push-pull stop using a micro toggle switch. The push pull knob operates the toggle. My problem is that the switch they decided to go with (due to the cheaper price) doesn't take much force to toggle it, but they want it to have a nice, firm feel when pushing and pulling the knob.

Right now I have 4 small tabs about 3/8" long with 4 deg of draft sticking into 4 holes with 5 deg of draft. In the 3D model, it has a tiny amount of interferance because I want those tabs to deflect a small amount to make a solid feel when pushing the knob in. I also have to keep the switch from rattling in it's normal (pushed in) position.

I'm having problems because the mold guys are concerned with the overlapping tolerances and aren't being very helpful with any advice on what to do. I also have to keep the total depth under 1.063" which is causing plenty of headaches on my part.

Thanks.

 

[bvanhiel]

Jinxr,

It sounds like what you really want is a detent. Just putting in a small amount of interference will cause problems because of the tolerances and creep. A detent allows a large interference during actuation without loading the plastic when you're not actuating the switch.

Another approach would be to try to eliminate the tolerance and creep by making a large, low stress interference. You'll need to involve a lot of plastic, because what you are creating is a large low stress cantilever spring.

-b