Cheese press with pulleys - help with weight calculations

[staples]

Hello,

I started off with a home-made cheese press (one that you stacked weights on top of, so you knew how much weight was going onto the cheese), but was given a dutch cheese press as a gift last year. The press has two pulleys, in addition to the lever system - I've posted a photo, to give a better idea of what it looks like. The problem is that I don't know how much weight the press is putting on the cheese (my recipes all use weight, not pressure). If anybody knows the correct way to calculate the weight the press puts on the cheese, I would really love to hear from you.

Thank you!

[Schnecken Slayer]

I think we need to know the distances from the fixed pivot point to a) the pressing rod and b) the pulley.
We may also need the distance to the second pulley with the weight attsched, my maths is rough after a couple of red wines.  :D

[hoeklijn]

I think we need to know the distances from the fixed pivot point to a) the pressing rod and b) the pulley.
We may also need the distance to the second pulley with the weight attsched, my maths is rough after a couple of red wines.  :D

True. With my press the distance from pivot to pressing rod is 7 cm and the distance from pressing rod to the pulley is 35 cm. 35/7 = 5.
This means that without pulleys every 1 lbs will be 5 lbs on the pressing rod. When you use pulleys like on the picture, you multiply that by 2, so 1 lbs will be 10 lbs. Beware: This is not the same as PSI.

[margaretsmall]

Thats a great photo of your press which I intend to show to my woodworking husband. (Fortunately he was a science teacher in a former life so he will be able to work out the weights for me). I don't yet have one like this, so have 2 questions which might be naive -

- The peg under the arm on the right hand upright - is that a removable peg to hold the arm up when you are not pressing?
- How do you stop the whole thing from toppling over to the right when you put the weight on - is it fixed to the floor?

Margaret

[Tiarella]

Margaret,  you might want to show your husband the press my dad made for me.  It's in the equipment board list under something "cheese press my Dad made for me".  It has a couple of cool ideas that could be combined with other designs.  I think I could get his full plan if you wanted. 

[Boofer]

Staples, nice-looking press.

I see you've made the same mistake I made in placement of pulleys. :P

Take a look at this thread to get some ideas for proceeding.

I've attached a recent pic of my press in action, pressing Beaufort #5.

-Boofer-

[Al Lewis]

Okay, the pulley advantage should be two to one.

The fulcrum/lever calculation can be calculated like this...

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)

[Boofer]

Hey, Al, could you go back and MODIFY your message and reattach the pic as a JPEG? I don't think the forum software likes PNG.

-Boofer-

[Al Lewis]

Sorry about that.  Got it fix now.  Still learning the ropes here.  ;D

[staples]

Thank you everyone for your help.

Just to make sure I have understood:

dl = 520 mm, de = 150 mm, (I'm measuring to the centre of the pressing rod, rather than the edges - is this correct?) so:

dl/de = 520/150 = 3.47

with the pulleys, 3.47 x 2 = 6.93

so, for every pound I hang off the end, I get 6.93 lb weight on the cheese?

Also, what is the rule with the pulleys? If I was to move the one down the bottom so that it is almost underneath the top pulley, what would the increase in mechanical advantage be?

Margaret -

- The peg under the arm on the right hand upright - is that a removable peg to hold the arm up when you are not pressing?
Yes, it is. It is really useful if you just want to hang a cheese to off the end to drain.
- How do you stop the whole thing from toppling over to the right when you put the weight on - is it fixed to the floor?[/i]
It isn't fixed to the floor - the stand on the bottom seems to give it sufficient balance, at least with the weight ranges I use.

Thanks again for all your replies - it's great to know what weight I'm putting on the cheese!

[Al Lewis]

Rather than spend all of that time on the math why don't you hang a 1 pound weight on the pulley and put a scale under the foot?  That will tell you for certain exactly what teh ratio is. ;)

[staples]

I've tried - the scales count backwards when put under the press, no matter what the weight is. They work fine with anything else.

[bbracken677]

What do you mean by "count backwards"?  As in for a 1 lb weight, they register (for instance) a negative 7 lbs?

[Mighty Mouse]

What do you mean by "count backwards"?  As in for a 1 lb weight, they register (for instance) a negative 7 lbs?

Heh heh, we're gonna be RICH! CF has discovered the next diet trend! The amazing fat burning cheese press. Mwah ha ha ha ha ha!!!

[Mighty Mouse]

I've tried - the scales count backwards when put under the press, no matter what the weight is. They work fine with anything else.

How are you placing the press exactly? Could you post a pic? What kind of weight are you hanging off?