timo888 wrote:Henry,
There was a calculation posted a little while ago by Brooklynshot.

http://www.home-barista.com/levers/calculate-how-much-pressure-is-needed-to-pull-shot-on-lever-machine-t1859.html

You calculate the force applied to the piston rod by the lever.

Then you calculate the pressure exerted upon the puck by that force (Pressure = Force / Surface Area).

Thanks, I got that part, what I don't know is whether the same applies for spring levers.

Maybe the answer is too obvious that's why nobody is replying?

Henry

hbuchtel wrote:Thanks, I got that part, what I don't know is whether the same applies for spring levers.

Maybe the answer is too obvious that's why nobody is replying?

Well, despite being recently thrown by the horse of Physics, I will climb back on and venture an explanation

If we can measure how much force is being exerted upon the lever at a given point, we can calculate the force being applied to the compressing spring. We can safely assume, I think, that very little of the lever's energy is lost in the process, as heat say, and so virtually all of the lever's kinetic energy is being transferred to the spring where it is stored as potential energy. When the spring expands, it releases that potential energy. So the force applied to the lever, multiplied by the advantage, ought to be a very close approximation of the force of the decompressing spring.

Regards
Timo

timo888 wrote:Well, if open-boiler Beast becomes a reality, we won't need a lot of brass for the group to accommodate our 58mm basket. The water will be at temperature and the group will be made of something that takes little heat from the water. The outer bell is mainly a bracket for the portafilter and won't come into contact with the water because it will be separated from the inner cylinder by an insulating gasket.

Regards
Timo

Keep me in mind, I'd love to own an open boiler Peppina style machine that does 58mm baskets and 9 bar pressure

another_jim wrote:Keep me in mind, I'd love to own an open boiler Peppina style machine that does 58mm baskets and 9 bar pressure

Will do, Jim. Nothing I'd like better than to send you a Beast, since your comments on Peppina's temperature stability and simplicity of design were what got me interested in this in the first place.

Slowly zeroing in on the geometry of the fulcrum.

Regards
Timo

Hey Guys, been gone a while...

The diameter that you need to use to calculate the brew pressure is the diameter of the piston. It has nothing to do with either the puck or the spring.

I had some notes somewhere on both the cylinder diameters and the spring forces for LaPeppina and for a MicroCasa. Can't seem to find them. I think I posted before, but with my pressure gauged LaPeppina, I saw brewing start at 6 bar and drop to 3 over the course of a shot. I suspect that a MicroCasa has a very similar profile.


Sadly figuring out the force on the spring by measureing the force on the lever is a litlle tricky, because the fulcrum moves. As a result, your mechanical advantage ("gear ratio") changes thru the swing of the lever. It's not impossible to solve though, and you only need data at two points because these use linear springs. You just need to measure and calculate the force ratio at each point.



ciao

lino