Author Topic: Compound Lever Press Design  (Read 10933 times)

Offline NW Fromager

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Compound Lever Press Design
« on: November 01, 2011, 02:35:57 PM »
So after perusing the numerous threads here and googling images of old presses, I think I've settled on the design below.

It's a slightly modified version of this press, designed for making briquettes out of waste material.  After watching the video and seeing how much force it generates (watch the 2"x6" lumber bend), I figured it would do the job on cheese.  Pressure can be adjusted both by altering weight on the press arm and by moving the cheese to the right or left.

Any thoughts appreciated!

« Last Edit: November 01, 2011, 02:42:38 PM by NW Fromager »
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Offline smolt1

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Re: Compound Lever Press Design
« Reply #1 on: November 01, 2011, 10:39:00 PM »
   Just guessing the dimensions of the press would give you a MA of 10 (left side of bottom lever) to 50 (right side). So hanging 20 lbs on the arm would give a pressing weight of 200 lbs to 1000 lbs. With a 4 inch mold 16 to 80 PSI. That is a lot!!
   To keep the top of the cheese level with the bottom in the mold you will need a plunger that moves along the bottom lever and is kept vertical. Also check to see if you have enough vertical movement so you won;t have to reset in the middle of the night.

Offline NW Fromager

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Re: Compound Lever Press Design
« Reply #2 on: November 02, 2011, 06:33:21 PM »
Thanks smolt1.  I left the plunger off to clarify the design. I'm thinking it's going to be similar to the one in your press, and there will be a series of holes placed horizontally along the bottom lever.

There will also be a drip pan with a drain to catch the whey.

This is about 2.5 feet wide, made from 2x4s.  If it works out, I'd like to make one out of birch, with a copper drip pan.
« Last Edit: November 03, 2011, 03:12:23 AM by NW Fromager »
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Offline NW Fromager

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Re: Compound Lever Press Design
« Reply #3 on: November 03, 2011, 02:38:35 AM »
Okay, so now I'm trying to calculate the final dimensions of this thing and I'd like to factor in the mechanical advantage with the spacing of my holes, but I'm at a loss as to how to calculate it (math is not my strong suit).  I know that I have two class two levers and that the "load" of the upper one, by way of the linkage, becomes the effort of the second, but I'm not finding a set of equations that matches up with this configuration.  Units shown are hypothetical.

Here's the press in a leverage diagram.  Any tips?

« Last Edit: November 03, 2011, 02:47:34 AM by NW Fromager »
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Offline psearle

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Re: Compound Lever Press Design
« Reply #4 on: November 03, 2011, 06:53:53 AM »
Using the notation in your diagram:

F1 = W x (A+B)/A

F2 = F1 x (C+D)/D = W x (A+B) x (C+D) / (A x D)

Using your sample numbers:

F1 = W x (2 + 18)/2 =10W

F2 = F1 x (6 + 4)/4 = 2.5 x F1 = 25 x W

Hope this helps

Pete

Offline smolt1

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Re: Compound Lever Press Design
« Reply #5 on: November 03, 2011, 10:57:55 AM »
Now you have the mechanical advantage ,and the press design minimizes the friction compared to a dutch style press ( so it should be quite accurate), but I would change the copper to stainless ( copper reacts with acid ) .

Offline FarmerJD

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Re: Compound Lever Press Design
« Reply #6 on: November 04, 2011, 06:53:24 PM »
Remember that a MA of 50 means a distance decrease of 1/50th. In other words the weight on the end would have to travel downward 25 inches just to get the plunger to move down 1/2 inch.


I built one of these but got so frustrated with the travel issue that I went back to a single lever. I am sure it will work but it just means a lot of tinkering to determine if you actually have enough play at the plunger end to make it work. It would be great if you could begin with a single until the curds are fairly compressed and then switch to the double lever for the final pressing. Just a thought. Great graphics by the way. Good luck.

Offline NW Fromager

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Re: Compound Lever Press Design
« Reply #7 on: November 15, 2011, 05:59:09 PM »
@FarmerJD:  Actually, the travel varies with how much to the right or left you place your cheese.  That's what the horizontal series of holes are for. There is much more travel to the left side of the press.  The vertical series on the plunger allows me to adjust the depth, so that as the curds compact, I can lower the plunger.  Or, simply add another follower which is even easier.

I corresponded with the inventor of the briquette press and he was so pleased with my re-purposing of his design that he shared his spreadsheet with me, making adjustments for where I changed proportions.  Depending on horizontal placement and the weight used on the arm, with a 4" hoop I can get:
 
2.5 lbs: 3psi to 10psi
5 lbs: 6psi to 20psi
10 lbs:12psi to 40psi
15 lbs: 18psi to 60psi

Obviously the larger the hoop, the fewer psi I get, but the range is still from 2.70psi to 27psi with the same weights.  Using more weight can get it up to 60psi.
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Offline FarmerJD

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Re: Compound Lever Press Design
« Reply #8 on: November 15, 2011, 10:28:12 PM »
The travel varies because the MA is varying as you move from right to left. I just picked an MA of 50 as the extreme example.


I also added holes to my plunger every 1/2" which helps but I still ran into the same problem because the short distance that the arm can move reduced by a factor of 50 (or even an MA of 25) is still less than the distance between the holes. Your setup is a little better at managing that since you also have the horizontal holes but I would imagine that you may have issues when you actually start using it. The way that cheesemaker's dealt with this in the old days was to add a threaded rod and wheel to the double levered press to keep the pressure up. Here is a pic and here.


No criticism here. I just wasn't sure if you had considered it so I thought I would mention it. Good luck.

Offline NW Fromager

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Re: Compound Lever Press Design
« Reply #9 on: December 09, 2011, 07:45:02 PM »
Well, I finally got this thing built.  It's not complete yet, still have to add the plunger and feet, but it's entirely functional and of course I couldn't wait to try it out.  My first pressed cheese was a gouda, which I'll have some comments and questions on elsewhere.

The press works brilliantly!  Most of the needed variation in pressure can be had by simply moving the hoop from the left to the right.  With ten lbs of weight on the lever, the pressure at the far right could easily damage a hand.  With a simple downward pull, by hand, you could crush a coconut.

I have no worries that this will be just fine for my upcoming cheddars!
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Offline smolt1

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Re: Compound Lever Press Design
« Reply #10 on: December 09, 2011, 10:40:35 PM »
That is a beauty. Looks like you can easily press a 10 inch diameter cheddar. I'm curious, what is the pressing weight on the left side and on the right side with no weights on the lever arm.

Offline NW Fromager

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Re: Compound Lever Press Design
« Reply #11 on: December 09, 2011, 11:39:24 PM »
Thanks.  Empty, it's roughly .84 psi to 4.22 psi.

With 5lbs it's 2.11 psi to 10.54 psi.  With 10 lbs, it's 6.32 to 21.08.
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Offline smolt1

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Re: Compound Lever Press Design
« Reply #12 on: December 10, 2011, 01:08:07 AM »
On what size mold?

Offline NW Fromager

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Re: Compound Lever Press Design
« Reply #13 on: December 10, 2011, 01:18:28 AM »
Six inch.
“Poets have been mysteriously silent on the subject of cheese.”
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