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0.12m=12cm diameter with 40kg gives  5028511.21 psi
Thats a bit of an overshoot....

It should give 0.47411096 psi.

I think I see where we are off base.
My tool only knows mm, not m or cm.

So your example of 0.12m would need to be bumped to 120mm.
Just enter the numbers and select metric don't put mm.

so 120/2 = 60 give us our radius in mm
60/25.4 to convert to inches = 2.36"
2.36 X 2.36 X 3.14 for the area = 17.52"

Then we take 40Kg x 2.204 to convert to pounds = 88.16

weight / area = psi, so 88.16/17.52 = 5.03 psi
we can the multiply 5.03 by 6.89475729 to convert to Kpa which is 34.69

Probably should make a note on the tool to use only mm, Kg, Kpa, psi, lbs, inches
The only drifting I've found is due to pi not being a whole number so the decimal place comes into play for rounding.

This is exactly why I was asking for input from my Metric friends.
I do not know what the preferred method of entry or the expected output.
All of our Metric molds are listed in mm so I assumed that was the expression of choice.

Oh I see.... that makes sense.
Thanks.

Aside from clarifying some of the verbage in the tool.
So as to make entry clear so predicted outcomes are as expected.

I do plan another add on.

a resistance/tare weight factor.
Every press has a certain amount of resistance to overcome which must be subtracted from it applied force, and likewise the assorted resting weight of the lever or other bits weight must be added to the force.
All of this will effect the predicted weight/pressure needed.

If you have any ideas let me know, and I will see how it can be added.

The formula for the Arm weight is:  ARMWEIGHT=(PRESSINGWEIGHT-TAREWEIGHT)/MECHANICALADVANTAGE.

Figuring the friction is not easy for a wooden lever press because it changes at different weights. Also the coefficient of starting friction is much different from the moving coefficient of friction especially if there is any ware on the wood at the fulcrum. Some presses can be modified to overcome most of the friction problems by fitting a plastic or metal plate at the fulcrum.

Hope this helps.

Yep, not to mention moisture causing wood to swell, and not slip against other parts well.

And pneumatic cylinders have a minimum operating pressure which drops off quick once it starts moving.
then comes on again at rest.

This is going to be one of the close, but not perfect issues.
The static resting weight should be easy and will be the starting place.
The cylinders issue I will need to do some real world testing, and an engineer buddy of mine
is advising me a bit on the friction issue.

But I just want the predicted weights and pressures necessary for a good press to be as close as possible.
I figure most recipes are ballpark figures anyway.

Even in the retail presses that use pressure springs there's a huge variance.
Temp, and mold to follower tightness, spring age, spring rate, etc...
I dare say 50lbs is not really 50lbs.
At least with a lever press or a pneumatic you can throw a scale under your pressing board zero it out.
and get a nearly 100% accurate weight of press.
Unfortunately they generally only go up to 350-400lbs, after that it's all math based calcs.


Hmmmmmm, Perhaps I should intigrate a load cell into my press.

Quote from: Fatman on August 01, 2011, 03:54:01 PM
Yep, not to mention moisture causing wood to swell, and not slip against other parts well.

And pneumatic cylinders have a minimum operating pressure which drops off quick once it starts moving.
then comes on again at rest.

This is going to be one of the close, but not perfect issues.
The static resting weight should be easy and will be the starting place.
The cylinders issue I will need to do some real world testing, and an engineer buddy of mine
is advising me a bit on the friction issue.

But I just want the predicted weights and pressures necessary for a good press to be as close as possible.
I figure most recipes are ballpark figures anyway.

Even in the retail presses that use pressure springs there's a huge variance.
Temp, and mold to follower tightness, spring age, spring rate, etc...
I dare say 50lbs is not really 50lbs.
At least with a lever press or a pneumatic you can throw a scale under your pressing board zero it out.
and get a nearly 100% accurate weight of press.
Unfortunately they generally only go up to 350-400lbs, after that it's all math based calcs.


Hmmmmmm, Perhaps I should intigrate a load cell into my press.

HAhahaha, just picked up a 3000lbs load cell.
If I can figure out how to use it, I will have the worlds first cheese press with intigrated scale.
You might ask why on earth 3000lbs!
I have two 8.5" mold I got from Ullmers dairy.
Pressing them side by side @ 20psi ~ cheddar pressure takes over a TON approx 2300lbs.