Not being a math major or engineer, (I'm a warranty manager), is there a formula to calculate the PSI exerted on the cheese using a lever press. How would one calculate the amount of weight required on the end of the lever to exert the required psi on the cheese plunger?
Thanks
You're talking about a couple of different concepts. It helps to separate them, divide and conquer, eh.
First the PSI. It's Pounds per Square Inch. It's a pressure unit.
Your press will deliver a specific number of pounds on the follower, and the follower will have an area. Those two combined will give you a pounds per area, and if your area number is calculated in square inches, then you'll have your PSI.
A circular area is calculated using the formula A= pi * (radius squared)
pi is 3.14159
the radius of a circular area is measure from the middle to the outside, or you can use the maximum width of the circle (the diameter) and divide by 2.
So for a 4inch mold,
A = 3.14159 * (radius of 2inches) squared
A = 3.14159 * 2 squared
A = 3.14159 * 4
A = 12.57 square inches
So, you can calculate the area of the top of your mold, now onto the weight
I haven't seen the design of your press, but I assume that it's using a lever to magnify the downward force with one end being fixed.
We'll tackle that one next.
There is probably a main horizontal lever that your design has.
On (or towards) one end is the weight, and the other end is fixed. Somewhere between those two is the place where force is exerted on the follower.
There are two distances you'll be concerned with.
1) The distance between the weight and the fixed end, and
2) The distance between the follower connection and the fixed end.
The force being exerted at the follower in pounds will be the weight in pounds (times) distance #1 (divided by) distance #2
So if you hang a 50lb weight on the end, and distance 1 is 2meters and distance 2 is 1 meter, then the force on the follower is 50 * 2 / 1 = 100lbs.
That 100lbs on your 12.57sq inch follower would be 7.9PSI on the cheese.
Good job, Groves. :)
Here is a normal lever type diagram, in the case of a cheese press the "Output" is at the base of the fulcrum.
Grove's excellent description has distance 1 to the left of the fulcrum and the weight or work end to the right.
I believe that most leverage presses will have the fulcrum at the end, and both the input and output will be away from the end, but the numbers would work the same.
More like this, excusing the fact that this isn't a press at all, but illustrating a common configuration.
(http://chestofbooks.com/crafts/metal/Applied-Science-Metal-Workers/images/Fig-13-A-Safety-Valve-A-lever-of-the-third-class.jpg)
Whew, thanks for the replies. Now if I read this correctly:
My hoop is 7" in diameter so the radius is 3.5 correct?
A = 3.14159 * (radius of 3.5inches) squared
A = 3.14159 *3.5 squared
A = 3.14159 *12.25
A = 38.46 square inches
So if my weight is 28" to the fixed point, and my follower is 10" to the fixed point, then 28/10 = 2.8 * weight hanging. Such as: 30 lbs x 2.8 = 84 lbs
So 84/38.46 = 2.18 lbs of pressure per square inch?
So to have 50 lbs of pressure on the cheese in the 7" hoop I would reduce the hanging weight to about 18lbs correct.
Thank you Groves and Coffee Joe for your assistance in this. Please correct me if I have miscalculated. I really appreciate this help. I do not have a press yet, but it is being built this week.
kim
QuoteSo to have 50 lbs of pressure on the cheese in the 7" hoop I would reduce the hanging weight to about 18lbs correct.
This is true but is this what you need? The psi would only be between 1 and 2 lbs/sq in. I am not sure what kind of cheese you are making but for some cheeses (cheddar, jack, colby) you need more pressure than this. You may already understand this, so please ignore if you do. Many times the recipes will just give a required weight and I wanted to be sure you really understand that the 50 lbs on the cheese will produce varying pressures dependant on the area/ radius of the hoop. Your math is great! You even showed your work. ;)
Here's a handy little table that shows the weights and corresponding psi for various hoop sizes. I have this laminated and keep it by my press for reference.
Find your hoop size at the top. Go down the column until you find the psi that you want to press your cheese at. Now follow the row to the left to find the weight that you need to produce that psi.
Example: You are doing a Gouda in a 7" hoop so find that at the top. A good pressing for Gouda is 2 psi, so go down the column to 2 (or close to it). To the left you will see that it takes 75-80 pounds to hit that psi target.
To put psi into a practical perspective... When using a 4" hoop, it only takes 25 pounds to achieve the same psi. Recipe books apparently assume that home cheese makers are using 4" hoops. They do NOT tell you how to adjust for larger cheese sizes.
Sailor, I do not see the chart. I appreciate your comments too. Thank you. I would love to have that chart. I just made a 3 gallon cheddar, and after pressing it is only about 2 1/4" tall. Very thin cheese. Once the rind develops, there will not be much cheese.
FarmenrJd - thank you as well.
I think I need to go to a deeper and small diameter hoop. What do most of you use for a hoop standard size?
There was quite a discussion of this previously:
https://cheeseforum.org/forum/index.php/topic,4026.msg30656.html#msg30656 (https://cheeseforum.org/forum/index.php/topic,4026.msg30656.html#msg30656)
I have included my latest calc sheet for my press as an additional data point for you. :)
-Boofer-
Thanks Boofer, I will definitely read that thread. Thanks for the chart too. It's on my desktop.
I know I attached the chart last night - Don't know what happened.
Anyway, here it is again in both Acrobat and Excel formats.
Excellent chart Sailor,
Now, I'm always in doubt as to the proper PSI for different cheeses, Cheddar, Parm, colby etc
I was warned that the PSI I was using for cheddar was low so I increased my arm (MA) to 5.22 with 6Kg and 22 Kg on 8" mold
so am now running 1.43 PSI for 20 Min, then Flip over in mold and go to 5.23 PSI for 24 Hours, change cloth and turn over at same weight for another 24 hours.
I have a single pulley on my press( not using) as well so that would double the PSI
I think I did this math correctly :-\
Fixed point to Fulcrum point 223mm
Fulcrum point to weight end 1210mm
1210/223 = 5.42MA
6 Kg weight *5.42 = 32.52Kg/.454 = 71.63 total weight (Lb) on follower
8" follower is 50.3 Inches²
71.63/50.3= 1.42PSI ( theoretical)
22 Kg weight *5.42 = 119.37Kg/.454 = 262.93 total weight (Lb) on follower
8" follower is 50.3 Inches²
262.93/50.3= 5.23 PSI ( theoretical)
Now, is the weight given enough for a cheddar?
Quote
Fixed point to Fulcrum point 223mm
Fulcrum point to weight end 1210mm
1210/223 = 5.42MA
This is not exactly right. The MA is actually the total length (1210+223) divided by the distance from fixed to fulcrum. I have always tried to follow the University of Guelph (http://www.foodsci.uoguelph.ca/cheese/sectionf.htm#firmtohard) guidelines. They suggest 10-20 psi for cheddar. Peter Dixon (http://www.dairyfoodsconsulting.com/recipes_cheddar.shtml) says to use 25 psi initially and then 40 psi until morning. I know these are difficult :o
to achieve at home but I am just pointing out the general practice in commercial settings. The more the better. IMHO
Sailor, thank you for getting the charts for me. I will print and laminate them as well. I really appreciate your assistance.
Quote from: FarmerJd on July 28, 2010, 01:33:21 PM
I have always tried to follow the University of Guelph (http://www.foodsci.uoguelph.ca/cheese/sectionf.htm#firmtohard) guidelines. They suggest 10-20 psi for cheddar. Peter Dixon (http://www.dairyfoodsconsulting.com/recipes_cheddar.shtml) says to use 25 psi initially and then 40 psi until morning. I know these are difficult :o to achieve at home but I am just pointing out the general practice in commercial settings. The more the better. IMHO
You know, in the back of my mind, I often considered this to be a mistake...a typo, or something.
25psi to 40psi? Really?
That makes the top end of my cheese press spreadsheet a reality!
- 45lbs on the arm to reach 1100lbs applied theoretical for an end result of 25.5psi calculated.
- 70lbs on the arm to reach 1700lbs applied theoretical for an end result of 39.6psi calculated.
OMG!! ::)
I haven't tried that to see what would happen. I guess I will...even though I have no real method for measuring the applied force at the business end of the ramrod.
What could I use as a test to press the
living daylights out of? (I know...don't end a sentence on a preposition.) I'd like to know whether the press can even
do that before I start down the make process.
-Boofer-
Yeah Boofer, I wondered myself until I saw Peter Dixon's site confirm it. I have always wanted to achieve that kind of pressure without feeling like I was endangering my family so I am picking up a set of suspension air bags this week. i won't be able to put a setup together for a while (fall maybe) but I finally figured out how I could do it. I am going to stack 2 bags on top of each other to get the travel (14 inches) I need. Then I will just hook up my air hose and with 7 inch diameter bags, I can produce enough pressure to satisfy even Sailor. ;D We'll see.
We shall see who comes up with more Monster Pressure >:D this is going to get interesting!
FarmerJD, so my real MA is 6.42, (1210+223)/223 this is a small help towards attaining 40 PSI. X50.3"² = about
2000 Lb on an 8" follower - ok - crazy but OK
2000 Lb/6.42MA = 311lb X .454 = 141Kg
141 Kg /2 for 1 pulley = about 70 Kg weight, should be close at least theoretical...
Going out to pour a 70 Kg bucket of concrete
If I don't break something, I feel like I'll have linguine cheese coming through the holes in the mold!
Quote from: coffee joe on July 29, 2010, 02:38:15 AM
If I don't break something, I feel like I'll have linguine cheese coming through the holes in the mold!
I've got the feeling that the plastic moulds I'm using weren't designed for that kind of pressure and they may just bust a seam. Now stainless steel might make the grade, but then I don't have any of those. ;)
-Boofer-
I'm thinking that I will have to build a beefier press too. I don't think that my press lever arms will support the weight required to reach 19 or 20lbs psi required for a cheddar. As boofer said it could be scary hanging that much weight.
Boofer - It's not about weight. It's about pressure. As I pointed out above if you are pressing a Gouda at 2 psi it would take 75 pounds on a 7" hoop or just 25 pounds for a 4" hoop. On a larger hoop the weight is spread out over a larger surface area but the downward pressure is still the same. So the outward pressure on your molds is not as much as you think. Good quality molds are made to handle commercial pressing, which is MUCH higher that what we use.
Mr. Kim - I wouldn't jump into a really monster press too quickly. The problem with cheddar is that it is a salted curd cheese and the curds don't want to meld together very well after salting. So higher pressures are used to force the curds together. However, there is always more than one way to skin a cat. For 5 gallon batches, I use a technique I call Pressing In The Pot. (search the forum). Keeping the curds at 85-90 degrees during pressing will make a huge difference. So for example you could build a warming box around your hoop or use a heating pad wrapped around the hoop. By keeping the curds warm, I never have to go over about 8 psi on a 7.5" hoop and I get great results. Food for thought.
Thanks Sailor, I read that post and was already planning to do exactly that. The cheddar's that I have made previously in my 7" mold turned out okay with just the 50 lbs that I used on them, then again, they were hooped warm for the initial pressing and flipping. I think that the press that I am having built will be adequate for my needs for a while. I was just amazed at the weight requirements from the chart that you so graciously shared. Thank you again.
Here is a pix of the Swiss wheel that I did a couple of weeks ago. This is after the initial pressing, not the final press before brine.
Quote from: Sailor Con Queso on July 29, 2010, 02:22:34 PM
Boofer - It's not about weight. It's about pressure. As I pointed out above if you are pressing a Gouda at 2 psi it would take 75 pounds on a 7" hoop or just 25 pounds for a 4" hoop. On a larger hoop the weight is spread out over a larger surface area but the downward pressure is still the same. So the outward pressure on your molds is not as much as you think. Good quality molds are made to handle commercial pressing, which is MUCH higher that what we use.
I agree. My spreadsheet allows for my 7" and 4" molds. The only shortcoming of the sheet is that I have to be using four of the 4" molds with a "spreader"(cutting board). I don't have it broken out for a single 4".
So you believe that 1100 or 1700 lbs applied to my 7.375" mold will be just fine then?
-Boofer-
Mr Kim - I know this wasn't the final pressing, but the texture looks really open. As you can see from the chart, 50 pounds is really light for a 7" mold.
Boofer - just so you know, I have never pressed over 200 pounds on a 7.5" hoop.
It doesn't look like that now. I will get a pix of it tonight and post it. It is in day 6 of the plumping stage now. Hope that it swells like it is supposed to.
I managed to get the weight up quite a bit.
35 Kg raw weight pass through 1 pulley
MA of 6.42 (math in previous post)
35 X 2 X 6.42 = 449Kg/.454= 989Lb
8"follower =50.3 In²
989/50.3= 19.67PSI if all the math is correct
I now have 3 raw weights 6Kg, 22Kg and 35Kg so I can start adding in increments
With the big weight, the result was a slight pressing of the curd up around one edge of the follower because the plunger was a little bit off plumb. This happened real quickly! fixed this but need to add a second spacer bar so it doesn't happen again ( saw this here on someone's post).
Will be turning over in the mold this afternoon and will have pics then.
Otherwise nothing broke! :D
Wow my head is spinning. ???
I am very new to cheese making, and as such I bought the easiest, dumb guy press I could find. It uses springs for the pressure and has a gauge to show how much pressure is being applied. My question is, if my recipe says 20 pounds, and I push this thing down to 20. Am I using the right pressure? Or will it vary with the size and type of mould I am using?
By the way, the big drawback to this press is that you have to watch it, As the cheese compresses the weight decreases, kind of a pain in the butt. :-\
Boise,
I'm sure most of the folks on this forum have been exactly where you are today. The drawing in this thread is probably the cheapest way to resolve pressing in higher weights. This thread is about PSI. As the diameter of the mold grows the total weight must increase to maintain equal PSI. How much weight really needs to be applied per square inch of follower is one of the principle questions we all have.
There are a couple of us here that are wondering how high we can manage to go without busting something! You will find a few posts in other threads referring to broken sink tops, so far no bodily harm. As we move into attempting to put 1 full ton on a cheese, well...
I believe the broken sink incident resulted from a stack of weights that toppled over. It wasn't from excessive pressure in a press.
The need for great pressure in a cheese press is limited to a very few cheese styles. The majority of cheeses will probably see less than 100 lbs.
-Boofer-
But we are having fun in the process!
Quote from: Boofer on July 30, 2010, 02:22:15 PMThe need for great pressure in a cheese press is limited to a very few cheese styles. The majority of cheeses will probably see less than 100 lbs.
Some cheeses like cheddar require more pressure anyway, but the real need for greater pressure is related to hoop size. For cheeses 7" or larger, you definitely need to go to 150 pounds or more. At 100, that's only about 1.5 psi (don't have my chart right now), so that is inadequate psi for most hard cheeses. MIGHT be passable for a light pressed Gouda, but very difficult to do a perfect cheddar at that weight.
More results for my 19.67 PSI( theoretical) experiment. 8" form with Cheddar
The Tube on the follower that allows for stacking, concentrated the pressure in the middle giving me a warped follower and a concave top on my cheese. For this pressure, the follower must be significantly more rigid. For next cheese a piece of 1" hardwood as a follower.
Otherwise, I am very pleased with the results. The cheese is noticeably drier and denser. I don't think more pressure, than applied, is needed by any means!
For the Record, I went 20 Min with 6Kg, turned over, went to 22 Kg for 1 hour then overnight with the 35Kg weights, all on the same setup, same MA.
Very cool Joe. 19.67 is getting up there, but you can see a difference in the results. I personally don't think you need to go over 10 psi if you are managing curds properly prior to pressing. A warming box around the hoop or a way to apply heat at 80-90F would make pressing a lot more effective. Your block/pulley setup to multiply the weight is simple but effective - I like it.
Definitely a case where the simplistic recipes (online or published) are jusy way off base. Hope the chart helped.
The fact that your follower warped is an indication that the molds might not be able to withstand commercial pressing. That's what LB was asking regarding plastic quality.
Coffee Joe, I see the cable and pulley on your press. How much does that help vs no cable and pulley. Cheese wheel looks great too! I have read some of the posts regarding single and double pulley gizmos, but don't really understand the resultant effects. Do you have an suggested reading?
The pulley in his setup simply doubles the weight already produced by the press.
Sailor,
the mold held fine, the design of the follower, which allows for stacking, is not suitable for 20 PSI over the 8"mold area because it was actually closer to 100PSI concentrated on the 4 " diameter riser. Felt pretty "tenderfoot"when that dawned on me!
Need the 20 PSI to be evenly spread out, scratch one bent follower up to experience.
As to results, I like what I saw but won't be going for higher PSI as I just don't see the need. That may change :-\
I have a feeling I'll end up getting talked into adding another pulley and going for 40PSI! The Peter Principle on Pressure.
Mr Kim,
Farmer JD said it all, one more pulley on the same cable would double it again - theoretically as there is loss to friction etc
Quote from: Mr. Kim on July 30, 2010, 07:30:05 PM
Coffee Joe, I see the cable and pulley on your press. How much does that help vs no cable and pulley. Cheese wheel looks great too! I have read some of the posts regarding single and double pulley gizmos, but don't really understand the resultant effects. Do you have an suggested reading?
I can hang 5lbs on my press and deliver 157lbs to the cheese. That's a 31x upgrade from just pressing with 5lbs. Granted, that's not necessary for a lot of cheeses, but when I need the extra OOMPH!...it's there. I used to stack up two 25lb barbell weights, two 10lb, and one 5lb to get 75lbs on my cheese. That was unwieldly and dangerous (It toppled off onto the floor one night and got my wife out of her chair!).
I attached my MS Excel spreadsheet on the first page of this thread. It shows the calculated pressure and what I
really saw on my bathroom scale. I have calcs for two pulleys and for four pulleys. There are pics somewhere of my press. The expert engineering tutors here helped me tweak it in.
Using 75lbs I can theoretically deliver 42+psi at 1811lbs. Never tried it. I've got a strong feeling the mold would burst.
-Boofer-