Spring design: Adjustment mechanism

[rufus121]

i am wishing to design a drawbar spring mechanism.

however i would like to adjust the spring in such a way that when not adjusted it can cope with loads of 2kg and when adjusted to its maximum it can cope loads of 30 kg, while never reaching its solid length.

So my main question is what type of spring to use. i.e. should it be a long compression spring or a colonocal spring.

Space restrictions also exsist. 300mm length restriction and spring can not have an outside diameter exceeding 4mm.

 

[desertfox]

Hi rufus121

I doubt you will get a spring to do what you require with an outside diameter less than 4mm.
A sketch of your drawbar may help us find a solution.

desertfox

 

[israelkk]

Theoretically it may be done with a compression spring but the D/d ratio will be smaller than the normal. However, it depends how many times the spring will change position from 2kg to 30kg. This is by no mean standard spring design and manufacture and the price may be accordingly. You should take into account that such slender spring will buckle and rub into the hole walls causing friction.

What do you mean by "colonocal spring"

http://sites.google.com/site/israelkk/home