hi

does anyone have answer to how to define nr. of layers to obtain desired strength of object.

i would like to do seat post tube for my MTB.
so how to define what would be the minimum amount of layers that tube will still support my weight and not to have too much of not needed weight.

i know there is no 100% accurate way, but at least a point to start

My main worry is that it's potentially a dangerous thing to make, so you don't want to take any chances with it. Maybe it would be safe though if you deliberately make it weakest just over the point where it leaves the frame so that if it does break it will go there without leaving a shard sticking up. If you can do that, it may be okay to risk going for a big weight saving.