Building a Dutch Press

[OlJarhead]

I hope there isn't a thread dedicated to this already, if there is I apologize, I just couldn't find it.

So, I started this thread, rather then hijack my own on the topic, to discus particulars of building a dutch press like calculating weight and PSI for the cheeses and how to get those numbers right when building the press along with how many different settings a person might need.

So here goes:

To calculate PSI:

When reading other threads on the topic I cam across this formula (after making my press and trying to figure it out) which I will put here but later correct -- or at least correct my interpretation of it and any confusion there might be:

To calculate this you need:
Length of press arms (helpful to have so you can play with the numbers and decide where to put your holes).
Length of fulcrum to pivot (Edit: this will be corrected later in the thread)
Length of fulcrum to weights
Weight of the empty press
Area to be pressed (follower)

Now of course you might not have all of these right away but you can certainly begin to estimate needed distances using a simple spreadsheet that might look like this:



I created this in excel and it was pretty simple.  Once you plug in the numbers you will need to add the formulas to see it work.  Here they are:
1.  pressing weight =D4*D5+D8 Where D4 is the weight you want to add to the end, D5 is the Fulcrum Ratio and D8 is the empty press weight
2.  Area to press  =(3.1415928*(D9*D9)) where D9 is the radius
3.  PSI on Cheese =D11/D12 where the pressing weight is divided by the area to press.

Of course those row/column numbers are based on my spreadsheet but I hope it helps you.

Once you do this you can plug in numbers and watch them change.

First question:  Anyone see any glaring mistakes?

Now what I've done is taken my 32" arms and removed 1" from either end to give me 30" from pivot to hanging bolt.  Now I can move the fulcrum around and assuming a weight of 5 to 6.5lbs empty I can determine what will give me 10psi to press cheddar by inserting numbers into the formulas and letting excel do the work for me.

[OlJarhead]

Running the numbers a few times I came up with this:


So with a 30lbs weight hanging off the end of the press with a fulcrum to pivot distance of 5" and from fulcrum to weight of 25" I should get 156.5lbs of force and 9.84PSI on the cheese.

[Cheese Head]

Math looks right to me, compounding ratio of 25/5 gives you 5X gearing on your 30 lb weight making it 150 lb + 6.5 lb empty weight of press = 156.5.

Area calc is correct, resulting in 9.85 psi for your 4.5" diameter mold.

It would be interesting to check this with actual measurements as I expect friction will errode that psi a little.

[OlJarhead]

Something wasn't working out with this formula so I did some research and this is what I found:

A 2.5lbs weight with a 7.75lbs empty weight gave me 18 lbs on the scale.  Something didn't add up as the formula said it ought to be about 15.5lbs with all my measurements.  Then I decided to try this:

A = Distance from Fulcrum to Pivot
B = Distance from Weight to Pivot
Ratio of B divided by A = B/A
C = Weight on end
D = Radius
E = Empty weight

Formula for Weight on the scale is:
[(C*(B/A))+E/((3.1415928*(D^2))]

This resulted in the correct weight.  So....

These measurements are from my current roughed press.

[OlJarhead]

So taking my press and changing the weights to match what I want and viola:

[OlJarhead]

I keep seeing a different calculation in these forums so I went to an engineering website to check my results and discovered that the calculation being used on the forum here is for a different scenerio then what a Dutch Press presents.  In reality the Dutch press PIVOT is really the fulcrum -- they are one and the same.

Maybe I was just mixed up but to be sure I've decided to include this

A lever mechanism where the input effort is higher than than the output load is often characterized as a third-class lever mechanism.

third-class levers
Example - Third-Class (Order) Lever

A force (weight) of 1 pound is exerted at a distance of 2 ft from the fulcrum.


The effort force at a distance of 1 ft from the fulcrum can be calculated as

    Fe = Fl dl / de

        = (1 lb) (2 ft) / (1 ft)

        = 2 (lb)

So the distance from the PLUNGER to the Fulcrum/Pivot is used to calculate the ratio in my formula.

So if DI represents the weight to the pivot and DE the plunger/cheese to the pivot then my calculation makes sense

[OlJarhead]

http://www.engineeringtoolbox.com/levers-d_1304.html
This is were I verified my calculation after discovering my error...I'll change the spreadsheet to look like this:

[OlJarhead]

So now that I have a working spreadsheet I'd like input as to how many PSI different cheeses need.  If I can have that I can adjust the press to accommodate different cheeses and different sized molds.

For starters I'll make calculation for 4" ID molds as well as the 4 1/2" ID mold I started with and larger molds.  If anyone has a specific mold and PSI they need to see on it I can calculate those into the press and come up with a press arm length that will accommodate all of them

[OlJarhead]

While waiting for replies I calculated the following:

As you can see changing from a 4 1/2" mold like the one I got for Christmas (my wife got from Cheesemaking.com) to a 7.75" mold they also sell (large hard cheese mold) makes a dramatic difference in PSI on the cheese press follower.

So to get about 10PSI which I hear is needed for good cheddar I need ~25lbs placed at 30" from the pivot/fulcrum and a plunger set at 5" from the pivot.  This gives me 157.75LBS when adding in the weight of the press empty and considering the multiplier.  PSI is actually 9.92 PSI 

To get something similar on a 7.75" mold I need 65lbs at 36" from the pivot with the plunger at 5" giving the 7.2x multiplier and a pressing weight of 475.75lbs with PSI right at 10.09PSI

My current arms are only 32" long with 30 inches of usable arm so I couldn't do this...I'd have to stack on 80lbs to get 10.34 PSI and a pressing weight of 487.75

Will a simple press like this take the pressing weight?  Good question and I might have to go to some span tables to see if the oak can handle the stress -- seems like a LOT of force but I suspect that because the weight is only 80lbs maybe it isn't that hard on the lever.

[Boofer]

Congrats on your efforts so far. Been there, done that! 

I think the weak point in this whole scenario will be the stress point of the mold. How much pressure can it sustain before it splits. A little caution may be needed.

I derived a lot of satisfaction out of my press-making process, including the spreadsheet and other tweaks. I have been told, and have learned on my own, that most cheeses I intend to make will not need the excessive pressures I am able to deliver to them with my press. It's somewhat of a comfort to know that I could squeeze the holy heck out of a lot of things if I had to, but probably will never need to. For me, it was a decided improvement over stacking my barbell weights up and hoping they didn't crash to the floor again. (Sorry, Honey!)

Here's a cheese for your vigorous and industrious efforts. Now, go squeeze some cheese! 

-Boofer-

[OlJarhead]

Congrats on your efforts so far. Been there, done that! 

I think the weak point in this whole scenario will be the stress point of the mold. How much pressure can it sustain before it splits. A little caution may be needed.

I derived a lot of satisfaction out of my press-making process, including the spreadsheet and other tweaks. I have been told, and have learned on my own, that most cheeses I intend to make will not need the excessive pressures I am able to deliver to them with my press. It's somewhat of a comfort to know that I could squeeze the holy heck out of a lot of things if I had to, but probably will never need to. For me, it was a decided improvement over stacking my barbell weights up and hoping they didn't crash to the floor again. (Sorry, Honey!)

Here's a cheese for your vigorous and industrious efforts. Now, go squeeze some cheese! 

-Boofer-

Thanks Boofer,

One of my quests was to get input on PSI required by cheese (anyone have this?) so I could devise and share the data with others.  I figure that making a dutch press should be pretty straight forward once you have these and know what kinds of weights you have and what you need to press etc.

So far it looks like 40 inch levers will press a ton (no pun intended) if the materials are up to it however that's pretty big...so I'm aiming for something in the 32-36" length that could be used to make any and all cheeses without too much extra weight.

[FarmerJd]

Technically, a dutch press is a second class lever, but it is upside down from the normal examples like a wheelbarrow. In a third class lever (like a baseball bat) the intention is to increase the speed/distance of the load/resistance end. When you swing the bat you are applying a force between the fulcrum (your bottom hand) and the resistance force (the end of the bat) with your top hand which is the effort force.


In a dutch press, the effort force is the weight on the end of the arm, the resistance force is the plunger and the fulcrum is the pivot. The correct way to calculate mechanical advantage is to divide the arm length (from weight on the end to pivot point) by the distance from pivot to plunger. It looks like this is what you are doing if I understand your formula correctly so I am not sure what error you were referring to when you quoted the engineering site.


My press has about a 40" arm and about 10" from pivot to plunger for a mech advantage of 4. The arm is made of 2 1x4" mahogany boards with spacers in between and it will hold 350lbs at least on the end for a weight of 1400lbs+ on the cheese. This is necessary for my 12" and 10" hoops of cheddar. If you are limiting your hoop size to 6" or less everything is muchhhhhhhhhh easier. I was an idiot 10 years ago and started my equipment accumulation with a monster 12" stainless steel hoop and then had to build everything big enough to use it. I'm happy to be making 20lb cheeses but it was difficult getting here.


I use the university of Guelph guides for psi per cheese info. They are commercial numbers but they give good info to work from.


Good luck.

[OlJarhead]

Technically, a dutch press is a second class lever, but it is upside down from the normal examples like a wheelbarrow. In a third class lever (like a baseball bat) the intention is to increase the speed/distance of the load/resistance end. When you swing the bat you are applying a force between the fulcrum (your bottom hand) and the resistance force (the end of the bat) with your top hand which is the effort force.


In a dutch press, the effort force is the weight on the end of the arm, the resistance force is the plunger and the fulcrum is the pivot. The correct way to calculate mechanical advantage is to divide the arm length (from weight on the end to pivot point) by the distance from pivot to plunger. It looks like this is what you are doing if I understand your formula correctly so I am not sure what error you were referring to when you quoted the engineering site.


My press has about a 40" arm and about 10" from pivot to plunger for a mech advantage of 4. The arm is made of 2 1x4" mahogany boards with spacers in between and it will hold 350lbs at least on the end for a weight of 1400lbs+ on the cheese. This is necessary for my 12" and 10" hoops of cheddar. If you are limiting your hoop size to 6" or less everything is muchhhhhhhhhh easier. I was an idiot 10 years ago and started my equipment accumulation with a monster 12" stainless steel hoop and then had to build everything big enough to use it. I'm happy to be making 20lb cheeses but it was difficult getting here.


I use the university of Guelph guides for psi per cheese info. They are commercial numbers but they give good info to work from.


Good luck.

Thanks for the reply -- I'll check that site out.

The original formula that I read here (though I might have misread it) seem to say from Fulcrum to Pivot which I took to mean 'Plunger to Pivot' and Fulcrum to weight -- this caused confusion in me perhaps.

I now read it as Plunger to Pivot and Weight to Pivot (the pivot is the fulcrum )

[steampwr8]

Great work and great teaching on the physics of the cheese press. Thank you.

Could you please post your spreadsheets.

[Pondering Turtle]

Great work and great teaching on the physics of the cheese press. Thank you.

Could you please post your spreadsheets.

If you really wanted to have some fun you could calculate how the angle of the arm effects leverage.