My Dutch cheese press...hooyah!

[Boofer]

On Sunday I made a Gouda following Dave's (aka. likesspace) recipe. On this occasion I used my Extech pH100 meter for the first time. I also used my new small (450g) Kadova moulds for the first time. But the real kicker was that I got to use my newly-built Dutch press.

Following visuals from Alex and others I built my press out of 2"x8" and 2"x3" hemlock stock. I decided I wanted something fairly hefty so I used 1" square steel tubing for the lever arm and 3/4"square steel tubing for the vertical ramrod. The majority of the construction is complete but I still have a few finishing touches to add.

Using a combination of a 5-pound and a 10-pound weight, I am able to deliver 200 pounds to the pressing point. I used a scale to check the actual press weight. The most I've checked is 25 pounds on the lever arm...delivers 300 pounds. The scale only goes to 350. According to my Excel "Lever & Pulley Worksheet", I should be getting close to 400 pounds. Need to investigate a little further why my actual falls short of my calculated.

I am encouraged by the results I've experienced so far. I was using a stack of 5, 10, 10, 25, and 25 pound barbell weights to reach a maximum press weight of 75 pounds. This was unwieldy and an inconvenience using all those heavy weights. Now I use fewer actual weights combined with a little advantage to gain a much larger applied weight.

The cheese was pressed when the curds were cooled down. I put the moulds in the pot with warm whey and held them for an hour, then pressed at 4psi (15 pounds actual). It helped to form a better closed knit to the curds. You can see one of them still is a more open knit.

-Boofer-

[wharris]

Very nice looking press.  I am impressed.
Question:  What kind of PSI are you looking to achieve?
My math says that with 200lbs of downforce accross all your moulds  there, you get about 8.5psi. 

That is just about where you want to be in my book.  Perhaps a touch more, but not much.

[Sailor Con Queso]

Press looks really nice Boof. You will be taking a big leap in your learning curve with that press.

I believe your theoretical differs from the actual because you have the fixed end of the pulley line attached near the middle of your lever. You are losing some of your mechanical advantage and would have stronger force if you moved that line out to where the block is at on the lever arm. Some blocks have a connection point for exactly that purpose. (Sailboat blocks take advantage of that )

The other thing I notice is that your ram rod is not actually attached to the lever arm. I wouldn't trust that with 300 pouinds of force. You are probably losing some power here as well. The lever has a force vector that is pushing forward as well as down.

See what I mean about using scales to test and calibrate your press?

You get a cheese from me. A+ for making the leap.

[FarmerJd]

Great pics. You really did a great job designing the press. I can tell you why your values are off but I don't want to sound negative, so please don't take it that way.


First, the MA of the arm is 4.8 not 3.8. You divide the total length by the distance to the rod. It is a common mistake to use only the extra length (in your case 38 in).


Sailor pointed out the source of the second problem; you actually have 2 connection points on your arm for the pulleys. This actually creates a complex situation where you have to figure 2 separate forces and add them together; one for the weight on the end (25 lbs X 4.8 = 120 lbs) and another for the weight applied at the second point where there is a lever mechanical advantage of about 2.5 ( a guess from the pic) and a pulley advantage of 3 (even though there are more pulleys, 1 is simply changing direction for you). This means the second force is 2.5 x 3 x 25 = 187.5 lbs. If you add you get 307.5 lbs. I figured that the distance from your pivot to the first eye bolt is 24-25 inches which would make the mech advantage at this point 2.4-2.5.


You really don't have to even figure it mathematically since you have a scale but i thought I would throw it out there.



The other question I have is about the psi generated on your cheese. I figured each mold at 4.375 inches and get an area of 15 square inches for each one. Is this right? If so, and there are 4 separate molds, then the psi would be the total wieght (300lbs) divided by the total area (60 in2) which equals 5 psi. I could be wrong about the sizes and even the math, so correct me if I am wrong on this.


Sailor mentioned the pin being a problem. You might try using a u bolt and bolting all the way through. Just a thought.


It is obvious from the pics that you are a craftsman. I wish I was more patient with the details like you and Alex. You get a cheese from me too. Thumbs way up!

[wharris]

I guessed at 3.75 inches diameter per mould.  That is why my math came to about 8 PSI
I could be off in that guess.

[Boofer]

The other thing I notice is that your ram rod is not actually attached to the lever arm. I wouldn't trust that with 300 pouinds of force. You are probably losing some power here as well. The lever has a force vector that is pushing forward as well as down.

How do I lose power? I've tried to minimize any forward effort by having the lever push more-or-less directly downward.


See what I mean about using scales to test and calibrate your press?

You mean it's a good thing...that it helps to validate my assumptions, correct?

Thanks for the corrective advice on my pulley setup. I moved it, but I don't see any difference. Perhaps on a sailboat where the distances are greater there would be a significant change.

Great pics. You really did a great job designing the press. I can tell you why your values are off but I don't want to sound negative, so please don't take it that way.

No, not at all. I welcome and need all the help I can get. Never was good at physics.


First, the MA of the arm is 4.8 not 3.8. You divide the total length by the distance to the rod. It is a common mistake to use only the extra length (in your case 38 in).

What I read online says differently: "The mechanical advantage of a lever is the ratio of the length of the lever on the applied force side of the fulcrum to the length of the lever on the resistance force side of the fulcrum." Is that incorrect?


Sailor pointed out the source of the second problem; you actually have 2 connection points on your arm for the pulleys. This actually creates a complex situation where you have to figure 2 separate forces and add them together; one for the weight on the end (25 lbs X 4.8 = 120 lbs) and another for the weight applied at the second point where there is a lever mechanical advantage of about 2.5 ( a guess from the pic) and a pulley advantage of 3 (even though there are more pulleys, 1 is simply changing direction for you). This means the second force is 2.5 x 3 x 25 = 187.5 lbs. If you add you get 307.5 lbs. I figured that the distance from your pivot to the first eye bolt is 24-25 inches which would make the mech advantage at this point 2.4-2.5.

As I replied to Sailor, I moved the rope at the midpoint out to the end of the lever by the top pulley block. I saw no difference in performance. Using 25 lbs with my original configuration, I was able to deliver 300 lbs to the ramrod. You are correct: the rope at midpoint was 24 inches.


You really don't have to even figure it mathematically since you have a scale but i thought I would throw it out there.

The other question I have is about the psi generated on your cheese. I figured each mold at 4.375 inches and get an area of 15 square inches for each one. Is this right? If so, and there are 4 separate molds, then the psi would be the total wieght (300lbs) divided by the total area (60 in2) which equals 5 psi. I could be wrong about the sizes and even the math, so correct me if I am wrong on this.

I figured 15 sq in for each of the small moulds. Using a 10lb weight gave me 200 pounds on the ramrod for 3.3psi.


Sailor mentioned the pin being a problem. You might try using a u bolt and bolting all the way through. Just a thought.

I don't see what you mean with the u-bolt. Can you explain, please?


It is obvious from the pics that you are a craftsman. I wish I was more patient with the details like you and Alex. You get a cheese from me too. Thumbs way up!

No, not a craftsman at all...just trying to solve a problem.

I guessed at 3.75 inches diameter per mould.  That is why my math came to about 8 PSI
I could be off in that guess.

I measured mine at 4.375 inches. That gives 3.3psi using a 10lb weight.

Thanks, guys, I appreciate the feedback so I can tweak my setup and be correct.

-Boofer-

[FarmerJd]

Ok several things to address:


1. When Sailor said you would lose power, I think he was referring to the fact that the piston might tend to lean more heavily on the side closest to the arm and increase friction on that side leading to a decrease in downward force. I do think this is possible. My solution of a u-bolt would not change that though. The only way to really address it would be to have a dual arm on either side of the piston. I am not sure it is necessary.


2. You quoted a statement from a website as follows: " The mechanical advantage of a lever is the ratio of the length of the lever on the applied force side of the fulcrum to the length of the lever on the resistance force side of the fulcrum. This is the MA for a 1st class lever like a seesaw. In that case, the resistance and applied force are on opposite sides of the fulcrum. In your press, they are both on the same side like a 2nd class lever; therefore the applied force is the whole length of the arm.
To prove the point, consider when the MA would be exactly one. It would be if you put the weight right where the piston is. If you worked this according to the method you were using, the MA would be zero which is impossible. (i.e. my way: 10 inches / 10 inches = 1 MA   Your way 0 inches/10 inches = 0 MA)

3. Are you saying that you moved the eye bolt from the 24 inch mark to the 48 inch mark? If you did and you left the anchor point way back underneath the 24 inch point, then the pulley advantage would have been decreased because of the angle. Part of the force was pulling the arm toward the piston and not downward. If you move the bottom anchor point to the point under the 48 inch point, you will see a difference. If not, then you may be trapped in a wormhole and the laws of physics don't apply.


4. The u-bolt was just an idea to keep the arm from sliding off the piston. I was thinking you could drill another hole in the piston above the bolt that is there now and stick a u-bolt through these 2 holes with the arm inside the U. Kind of hard to express but a simple idea. But it would not help address Sailor's issue.


If any of this doesn't make sense, I am sure it is my fault. I just reread it a got a headache. Good luck.

[Alex]

Good work Boofer!!!
My pulleys system is delayed, because being a cabinet maker, my pulleys "have to" be made from wood. I hadn't time to turn them on my lathe.

My English is too poor to use so many words to explain, so I made a sketch.

According to physics, W1 * L1 = W2 * L2. Kooking at the system you've built, the actual force you apply is W3, applying less pressure than from W2. Therefore the difference between the weights and the reading you make. To solve this, just cancell the fixed point of W3 and you'll be fine.

I built the lever arm of my press as a ladder, because in this way I can change the point to hang the weights and get an even bigger versatility, of course using the pulleys system.

[Boofer]

  I'm a little slow, but I'm catching on!

Taking the combined advice given to me today, I moved the rigging and here are my revised readings:

Using an applied weight of:

• 5 lbs ====> 157 lbs . . . a force multiplier of 31x
• 10 lbs ====> 265 lbs . . . a force multiplier of 26.5x
• 15 lbs ====> 350+ lbs . . . a force multiplier of around 23.3x (topped out the scale)

That makes me much happier! Now I need to figure out how to clean up the modifications. I'd like to be able to hook up and go when I need to press.

The strange thing is, the 1-inch square tube bends with applied force. I guess I didn't expect it to

give so much. I also need to goose the hanging weight to arrive at the final terminal applied force. The goosing ensures that the rope isn't cinched on the pulleys and that the full pressure is brought to bear, otherwise the whole system creaks and creeps, applying pressure a little at a time until it reaches its terminal point.

Farmer & Alex - You're right about the length of the lever. I knew it was a class 2, but for some reason my mind plugged in that division at the ramrod point. I stand corrected. You're right too, Farmer, this burns out brain cells. I'm toasted...but better informed now.

Farmer - I understand your u-bolt visual now. There isn't a lot of lateral play in the lever arm so I'm not too worried about it slipping off the pin in the ramrod. I will monitor it though.

Alex - I admire your ability with cabinet-making/woodworking. Your press is closer to artwork. I'm afraid I'm limited in those areas and so I have to settle for a more brute-force approach.

-Boofer-

P.S. I sleep better tonight.    Guys, thanks for the steerage.[/list]

[Nonius]

Hi

I was just wondering about the profiles you used: isn't it much overkill? I am currently trying to design a 2 level dutch press to build when time is available, but using some stress formulae a 50x18 mm wooden beam (.2" x .07") would be more then enough to transfer 8 Kg to 100 Kg pressure. (all horizontal beams are double)
This flat structure will be clamped in the base, I designed two parts for easy storage, but not sure it will hold...
BTW: how much travel do you need during first and later pressing?

Amnon

[Alex]

Boofer, replace the lever arm with a 2"x1" RHS.

[Alex]

Amnon, as you can see on my smaller press, the plunger is long enough and drilled, to be adjustable according to the different hoops heights.

[FarmerJd]

nonius, the travel is the problem with a double levered press. I tried it and the lever has to fall a long way to produce a small movement of the piston. It basically bottoms out too quickly. It would work if the press was very tall like the ones people use to build. You need about 8 inches of travel total at the piston which translates to 32 inches of travel on the end of the arm with just a mechanical advantage of 4. As Alex said you could have multiple holes, but you still need enough travel to apply pressure and this is difficult with large mechanical advantages.


Boofer, I agree with Alex that the arm needs to be bigger. You could probably get by but to really be able to load it up you need to replace it.
As far as the total mechanical advantage, the best I can figure is 24. That is 5 (pulley advantage) times 4.8 (lever advantage) = 24. I can't see any other factors except maybe the weight of the arm itself. I think I would figure a 25 MA and just go with that. Good luck and hang in there. We are all learning with you.

[FarmerJd]

Nonius, I think your design is the same thing I tried. Here is a sketch of what I tried to do.

[Sailor Con Queso]

Boof,

5 pounds of weight with 157 pounds at the plunger is going to be overkill on a lot of cheeses depending on the mold that you use. For example, I do an overnight pressing of my Stiltons (phase 1 prior to salting) at just 1 psi. In your case 157 pounds on a 6" hoop (28.27 sq inches) would be 157/28.27 = 5.55 psi. I press Goudas at just 2-3 psi. So you need to figure out a way to really back off when you need to.

What is the bare pressing weight (measured on a scale) when you have no additional weight attached?