Author Topic: Eric's over-the-top home made cheese press  (Read 33872 times)

Sailor Con Queso

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Re: Eric's over-the-top home made cheese press
« Reply #30 on: October 05, 2009, 08:20:37 PM »
Since the piston is not making actual contact with the cheese, I don't understand why the bore size comes into play. On a French press, the shape or size of the ramrod pushing down on the follower doesn't (to me at least) make any difference. It's the follower that's pushing on the cheese.

For simplicity, assume my mold has a surface area of 50 sq. inches. If I put a 50 pound weight on the top of the follower, the FOLLOWER, not the weight, would be transferring 1 psi (50 pounds / 50 sq. inch = psi) onto the surface of the cheese. The shape (or diameter) of the weight doesn't make any difference. The ramrod from the hydraulic unit is just a different source of "weight" i.e. pressure. Without the follower, the ramrod would easily go right thru the cheese, but the follower disperses that weight evenly over its surface area.

The end location mark on the lever of my French Press delivers a 5 to 1 mechanical advantage. If I hang 10 pounds of lead, sand, or whatever, I get 50 pounds at the ramrod. (I have used a very accurate commercial scale to take measurements). So, if I used a hydraulic ram to push down the same 10 pounds at the end of that lever, I would still get the same 5 to 1 advantage with 50 pounds pushing down on the cheese. The bore size doesn't have any effect. Neither does the lever. It's the surface area of the follower as determined by the diameter of the mold. The PSI for 5o pounds applied to the follower of a 4" mold is very different than the PSI on an 8" mold.

It is obvious that recipes need to talk about PSI and not just weight.

wharris

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Re: Eric's over-the-top home made cheese press
« Reply #31 on: October 05, 2009, 08:42:33 PM »
Agree with you sailor on the french press. (damn I want one of those.)

But I think the piston bore size in this case does matter, because I first need to  determine how much force, in lbs, is being applied to the follower, before I can determine the PSI being applied to the actual cheese.


The larger the bore, the more force.
The smaller the boor, the less force.

Why?

With a larger bore, that same 150PSI of pressure inside the cylinder has more square inches to push against.  Thus  the larger the bore, the more force than can be applied by the cylinder to the push rod, then to the follower, then to the cheese. 
Ultimately the rod pushes with a force that is measurable in lbs. That force would be exactly 150lbs if the surface area of the bore was exactly 1 sq inch. (and 300lbs if 2in and so on...)
In Eric's case, the actual bore surface area is a bit less than 1/2 sq inch. That yielded about about 73lbs of force applied to his follower.  Kinda like stacking 73lbs of rocks on the follower.  Instead of rocks, he used a cylinder. 
So the size of the bore determines the actual force applied.

Make sense?

So...
Step 1 was determining force applied by the cylinder in lbs. (function of cylinder PSI and bore size)
Step 2 was dividing that force across the surface area of the follower yeilding PSI in lbs/sqin


I think I'm right here.  I hope.  I trust the pros here will set me straight if not.
The reason I am going through these lengths is because this is the path I would like to go down at some point. I'm still trying to mature my own thoughts about these topics and will use these basic assumptions as i go forward.


FarmerJd

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Re: Eric's over-the-top home made cheese press
« Reply #32 on: October 05, 2009, 08:56:52 PM »
Once again I took too long to post! Wayne said the same thing but here goes anyway.

Sailor,

The reason you need to know the bore size is so that you can figure the force exerted by the cylinder to start with. Just like the weight on the follower is distributed so is the pressure inside the piston. To determine how much force is exerted by the piston when the pressure inside it is 40psi, the bore size has to be known. A piston with a 4 inch bore produces 32 times more force than a 1 inch bore under the same pressure. That 40 psi inside the piston is producing 40 pounds of force on each square inch of the piston bore. More bore = more force. 

You are right about the size of a ramrod being unimportant on a french press. In your example you said, " So, if I used a hydraulic ram to push down the same 10 pounds at the end of that lever, I would still get the same 5 to 1 advantage with 50 pounds pushing down on the cheese." My point is that in order to know what pressure to put the piston under to get that 10 pounds, you have to know its bore size.

Quote
The PSI for 5o pounds applied to the follower of a 4" mold is very different than the PSI on an 8" mold.

Absolutely right. And for the same reason, the pressure applied to a 4" bore pneumatic cylinder produces a very different force than 1".

I especially agree with your last statement. Very frustrating at times. I wonder if the reason weight is given in recipes instead of psi is:

1. These recipes were created by home cheesemakers not industry and the recipes reflect that, or

2. A lot of people just don't understand the math but still make great cheese and pass on the process minus the science. Just a thought.

Hope I explained that ok.

Offline DeejayDebi

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Re: Eric's over-the-top home made cheese press
« Reply #33 on: October 06, 2009, 12:05:53 AM »
This holds true because it is not the pressure AT the follower end of the piston that is being measured (in this case in PSI) but the pressure that is PUSHING the piston rod out of the canister that is being measured in PSI. The pressure in the canister to force (and hold) the piston out uses energy so it is not a direct tranfer of force.

Sailor Con Queso

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Re: Eric's over-the-top home made cheese press
« Reply #34 on: October 06, 2009, 12:35:26 AM »
To determine how much force is exerted by the piston when the pressure inside it is 40psi, the bore size has to be known. A piston with a 4 inch bore produces 32 times more force than a 1 inch bore under the same pressure. That 40 psi inside the piston is producing 40 pounds of force on each square inch of the piston bore. More bore = more force.

OK, Wow, I got it. Cool.. Between Wayne & FarnerJD it makes sense now. No question that with equal pressures a larger bore will exert more pressure (weight) than a smaller bore. I was looking at the metered PSI on the air feed line as being an absolute at the end of the piston - it's not. That PSI is spread over the area of the piston, just like a follower.

I have always thought that science has to be applied in a practical way to be meaningful to the masses. So, here is my practical solution. When I made my French Press I needed to know for certain the true weight applied to the follower. I did the math to figure out the mechanical advantage of my lever, but then used a commercial weight scale to calibrate 3 to 1, 4 to 1 and 5 to 1 set points. Why not just do the same with the hydraulic piston? Put a scale under it and turn up the air. Just check the scale to see how much weight is being applied at at various PSI readings? THAT is the weight being applied to the follower.

FarmerJd

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Re: Eric's over-the-top home made cheese press
« Reply #35 on: October 06, 2009, 03:09:26 AM »
Wayne, I sort of had an "epiphany" studying those double levered presses. It really is simple to add another lever to a press with one arm already. I am not sure if you have one of these but I think it was either you or sailor that did.

You simply attach another post ( call it Post B )on the side opposite of the original fulcrum post (post A). then attach a short connector from the first lever (about 1 inch away from Post A) to another lever (arm) above the first one that attaches to the new post B. In the middle of the new lever, bolt through the ramrod which extends through the first arm but doesn't attach.

ok- i just reread that and it makes no sense. I am attaching a pic of my current press with proposal added. i'm kind of giddy about it and the wife and kids just roll their eyes when I try to tell them. i hope someone on here appreciates it. :-\

MA = Y/X times W/Z x 2 (if I add the pulley too.) I know I can make it out of metal but if I can just add to my existing press ...walah! The idea of having a press with just a few small weights and no hoses or regulators or electricity that sits snug in a corner and can produce an MA of 70, a force of  2800 lbs with only a 40 lbs weight is really appealing. I just have to find out the shearing strength of my screws! Like John said, there's a lot of tensile strain.

memkuk

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Re: Eric's over-the-top home made cheese press
« Reply #36 on: October 06, 2009, 03:10:23 AM »
Wayne - Txs for the spreadsheet.
Farmer - I believe you are absolutely right with the statement you made:
1. These recipes were created by home cheesemakers not industry and the recipes reflect that, or
2. A lot of people just don't understand the math but still make great cheese and pass on the process minus the science. Just a thought.
The unscientific way I calibrated my press kind a reflects your statement: originally the press was hand-cranked (see attached pics). I used a stainless steel spring between the rod and the follower. The first pressing was done with the spring half compressed. For my second pressing, I cranked it up until the spring was fully compressed. The Gouda produced like this turned out fine. So when I later fitted the press with the pneumatic cylinder, I put the same spring underneath it and applied pressure until it was half compressed, then fully compressed. I simply read the meter readings on the pressure gauge on both occasions and that gave me my callibration: not a scientific way to do it, but effective nonetheless.

Sailor Con Queso

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Re: Eric's over-the-top home made cheese press
« Reply #37 on: October 06, 2009, 04:07:29 AM »
Farmer - A block & tackle could be rigged from the press base to the lever end. 2 pulleys at the base and the lever end would be give a 5 to 1 M.A. So hang 40 pounds on the upper pulley rope. That would give 200 pounds pulling down on the press lever. Now if the lever arm itself has a 5 to 1 M.A. That would be 200 x 5 = 1000 pounds out of a 40 pound weight. Is that right??? College Physics was more than a few years ago. ;D

Sailor Con Queso

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Re: Eric's over-the-top home made cheese press
« Reply #38 on: October 06, 2009, 04:15:28 AM »
OK. Here is a spreadsheet that I created showing press weights and the resulting PSI for various diameters of molds/followers. This was actually very enlightening. Makes me feel like I should be pressing a lot harder than I am. BUT.... my concern is that higher press weights would extract too much whey and result in cheeses that are really dry.

FarmerJd

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Re: Eric's over-the-top home made cheese press
« Reply #39 on: October 07, 2009, 12:35:12 AM »
Sailor, I actually thought about pulleys but i would still have the same problem of my press not handling the stress out on the arm.

I tried my upgrades tonite and I guess I should have thought it through a little more. Law of conservation of energy and Work = force X distance.

i forgot about distance shrinking at the same ratio that the force is increasing. That is why those double levered presses had the threaded bolt with a big steering wheel on it down the middle - so they could keep the force on the hoop because they only had about an inch of play in the ramrod. With a 70 to one MA your weight would move 70 inches down while your ram would only move 1 inch. Ouch. Oh well, back to drawing board.

Sailor Con Queso

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Re: Eric's over-the-top home made cheese press
« Reply #40 on: October 07, 2009, 03:26:28 AM »
You might have guessed that I'm also a sailor. On a sailboat we use lots of cam cleats to lock loaded lines in place. I've thought about installing a triple pulley block & tackle system from the forward face of my press base to the end of the lever. I envision an inline spring scale to accurately measure line load. With a cam cleat you could apply whatever force that you want and then lock the line in place. With enough mechanical advantage, you could just pull down on the block line by hand until the scale shows the force that you want - WITHOUT using any mechanical weights. The obvious disadvantage is that the pressure would decrease as the cheese compresses.

Cheese Head

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Re: Eric's over-the-top home made cheese press
« Reply #41 on: October 07, 2009, 09:54:19 AM »
All, just wanted to say great discussion and especially like Farmer's drawing! Have fun y'all!

Baby Chee

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Re: Eric's over-the-top home made cheese press
« Reply #42 on: October 19, 2009, 06:18:59 PM »
This thread makes me want to build my own wood mold.  It seems impossible to find any good, tall molds for cheese, or good, strong, wide molds.  This way I could make my own to my own specifications.

FarmerJd

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Re: Eric's over-the-top home made cheese press
« Reply #43 on: October 19, 2009, 06:46:17 PM »
It really isn't rocket science. I used some Spanish cedar for mine so that I didn't have to worry about it getting wet. The screws and bolts are the main cost factors. I used a piece of corian countertop that was leftover from a cabinet shop in the bottom that lifts out easily for cleaning. I have already drawn up plans with a welding buddy for my double levered metal press and I can't wait to use it. The only problem with building these things is that it is yet another piece of "furniture" to put somewhere along with the heating tank, assorted large pots, draining cooler, stirring device, cave, and assorted hoops and weights! I wish I had a spot like Wayne where I could attach a couple of 2x6's to the wall and have a long wall-mounted press that wasn't in the way. The problem with that is the potential for the curd to "float" the hoop and come underneath because there is no way of pinning the hoop down. I would love to see your plans if you decide to make one. Good luck.

Baby Chee

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Re: Eric's over-the-top home made cheese press
« Reply #44 on: October 19, 2009, 07:09:08 PM »
There is a simple, not too attractive, way to keep hoops from floating... hang weights from both sides.

2 10lb. weight lifter weights on hooks will do.

My camembert hoop floats, being very thin and light, but I just put a weight on it.