spring rate and ppi? same thing?

[4x4junkie]

Shouldn't be any calculating needed. Once the machine has compressed the spring exactly one inch, whatever force it took to do so is your PPI (as Bray D mentioned earlier in the thread, PPI = Pounds Per Inch). If the machine doesn't have a readout in pounds of force for whatever reason, then I couldn't help you, you'd have to consult the machine's manual (or the guy running it).

 

[gwaii]

if you know the diameter of the piston in the ram,it's easy to figure out total force.

take half the diameter,multiply that by itself,then multiply the answer by 3.14.take the resulting number and multiply the pressure reading by it.
this is total force on the spring.compress the spring a few inches,then divide the force by how many inches you compressed the spring(one inch compression won't give as accurate a reading as more compression)

as an example...say the piston is 4" diameter,half that is 2.multiply by itself,2x2=4.
multiply this by 3.14.......4x3.14=12.56.

now say the reading on the pressure is 200lbs-multiply this by 12.56.

200x12.56=2512.now,say you compressed the spring 10",the rate is 2512/10=251.

so your spring rate is 251lb/in.




edit-the ram is the part that moves out of the cylinder,it should be easy to measure.

 

[bobbywalter]

i run 140-60 springs with airbags at one point.

best compromise....tune on the fly for good road manners and awesome on the trail.


but you have to customize the buckets or lower seats to mitigate the coil bow.

 

[Bray D]

edit-the ram is the part that moves out of the cylinder,it should be easy to measure.

The size of the piston (that the pressure acts on) doesn't necessarily have the same area as the rod (ram). You need to know the ID of the cylinder, which would be a bit harder to measure.

 

[gwaii]

not always,especially on general purpose rams,but on press rams they usually are.they want to make them as big as possible to take up side loads and give end surface area..

 

[JohnnyU]

This machine probably uses a bottlejack. Bottlejack pistons are typically just a solid piston, with seal grooves machined into the last inch or so. Pressure is durectly applied to the end of the rod (piston). As gwaii said, this is done to maximize the piston area while minimizing the need for lateral support. Also, since it is single-asting, there is no need for a working suface onteh opposite end, gravity and the load typically force the piston back into the cylinder.

 

[gwaii]

This machine probably uses a bottlejack. Bottlejack pistons are typically just a solid piston, with seal grooves machined into the last inch or so. Pressure is durectly applied to the end of the rod (piston). As gwaii said, this is done to maximize the piston area while minimizing the need for lateral support. Also, since it is single-asting, there is no need for a working suface onteh opposite end, gravity and the load typically force the piston back into the cylinder.

those with bottle jacks are this way,but the big industrial machines are like this too(though the cylinder is generally inverted so the ram exits the bottom)on these some are multi-stage machines where the central piston is surrounded by cylindrical piston "extensions" that increase the working diameter of the piston-the middle stage is fast acting,but lower force,as subsequent stages come into play the speed goes down,but the force goes up.in this case you need to measure the stage that is actually working on the spring.

 

[spdcrazy]

hmm. good info. i'll stop by the spring shop. and see how their machine is built. im getting frusterated trying to find some springs locally. I don't mind rebuilding my coil buckets at all. in fact i look forward to putting my new welding skills to the task. but i still need a spring to start with!!!