Author Topic: Sturdy Press (Modified for pulleys)  (Read 5611 times)

Spoons

  • Guest
Sturdy Press (Modified for pulleys)
« on: November 12, 2014, 02:09:51 AM »
I really love Smolt's press. I've had it for 4-5 years now and it never failed. I do admit though that my cheddar types seem to be cracking a bit while air drying. So I've been wondering if this is for lack of pressure.

On Smolt's press I get 8.5 mechanical advantage, but I never add more than 22LBS of actual weight on it for safety reasons (a 10L jug of water). With that, I get 4.8 PSI on a 7'' mould.

After asking Smolt if he builds presses with pulley systems, he rather simply guided me in making my own. It was quite simple really, even if I'm very limited in tools. Basically, I drilled a hole on each leg but only halfway. I then cut a 6.25'' aluminum rod and bolted the legs back together. That's the only modification needed on this press. The rest is just 2-double-pulleys, 4 clips and some nylon rope. The whole pulley system can be easily clipped on or off if needed or not. The mechanical advantage for this setup is 2.7 on top of the 8.5 on pin B. That's ridiculous!

So 22lbs on Pin B with a 7'' mould is:
Without pulley: 8.5 MA, 187 LBS, 4.8 PSI
With 2.7 pulley: 22.95 MA, 505 lbs, 13.1 PSI

Simply amazing! Thanks Smolt for this suggestion :) A cheese for you :)

Now bring on the cheddars!
« Last Edit: November 12, 2014, 02:16:47 AM by Anonymous »

Offline smolt1

  • Mature Cheese
  • ****
  • Location: oregon
  • Posts: 246
  • Cheeses: 29
  • Default personal text
    • SturdyPress.com
Re: Sturdy Press (Modified for pulleys)
« Reply #1 on: November 13, 2014, 12:05:55 AM »
Anonymous,

I think you are short changing yourself on the total MA with your pulleys. I looked at the pics and it looks like a 2 wheel pulley on the top and on the bottom. That gives you a pulley MA of 5. It looks like 4 of the lines are pulling at about 30 degrees from vertical and 1 ( attached to the weight ) is vertical. That gives you ( neglecting friction ) [4*cos 30 +1*cos 0 ] = 4*.86 + 1*1]=[3.44+1]= 4.44 MA.  That is the portion of the pulley system pulling straight down on the lever arm and since the MA of the press is 9, the total MA is [9 * 4.44]= 39.96. With a guess for friction of press and 4 pulleys, how about a MA of 35. To check to see if this is correct, you could use a weight of 3 liters of water and you should get a pressing weight of 3*40= 120 kg. Or if you don't have a scale you could set up the press with a small amount of weight to keep all the lines stretched out and measure the distance moved by the pulley weight line divided by the distance moved by the plunger.That should give you the MA ( without any friction accounted for ).  Now for some perfect Cheddar.

Spoons

  • Guest
Re: Sturdy Press (Modified for pulleys)
« Reply #2 on: November 13, 2014, 01:39:41 AM »
You're right, Smolt! I ran some tests with a 5 LBS and a 10 LBS weight and realised a tiny bit of friction can cause some discrepancy, and also the position of the lever as the weight pushed it down.

Test 1
5 LBS on pin B with pulley system: 109 LBS
I noticed that if I tapped the lever, the weight would fall even more (friction)
New reading: 148 LBS

Test 2
10 LBS on pin B with pulley system: 265 LBS
Same thing; I tapped the lever, the weight would fall even more (friction)
New reading: 300 LBS

I did a few more readings with the ''lever tap'' and it would be a consistent 145-152 LBS readings with a 5 LBS, and exactly DOUBLE on the 10 LBS weight.

Mechanical Advantage: 30-ish

As the lever was pushed down by the weight, the angle got more pronounced (greater than 30 degrees). Now I see that the MA will vary a bit depending on the lever position.

Thanks for clarifying, smolt! I am now a little scared of my press  ;) Now I need to figure out a way to avoid destroying my mould lid...
« Last Edit: November 13, 2014, 01:52:45 AM by Anonymous »

Offline awakephd

  • Old Cheese
  • *****
  • Location: North Carolina
  • Posts: 2,351
  • Cheeses: 240
  • compounding the benefits of a free press
Re: Sturdy Press (Modified for pulleys)
« Reply #3 on: November 13, 2014, 02:06:42 PM »
Keep in mind that you can cut the MA down by threading only one of the pulleys on each end, instead of both.
-- Andy

Spoons

  • Guest
Re: Sturdy Press (Modified for pulleys)
« Reply #4 on: November 13, 2014, 07:26:41 PM »
Keep in mind that you can cut the MA down by threading only one of the pulleys on each end, instead of both.

Yeah, thanks. Those knots are tight and the ends are burned. So I'm not taking it apart. But good point though, I'll make a single pulley set. I really like the fact that it simply needs to be clipped on or off.

Offline awakephd

  • Old Cheese
  • *****
  • Location: North Carolina
  • Posts: 2,351
  • Cheeses: 240
  • compounding the benefits of a free press
Re: Sturdy Press (Modified for pulleys)
« Reply #5 on: November 14, 2014, 02:53:00 PM »
Good point. Clip on/clip off is an extra-good feature ... though it sounds a little bit like a late-night TV ad for some reason ... :)
-- Andy

John@PC

  • Guest
Re: Sturdy Press (Modified for pulleys)
« Reply #6 on: November 16, 2014, 09:30:17 PM »
Nice modification Anonymous.  IMO Bob makes the best dutch-style press in the business when cost vs. performance is weighed (no pun at all intended :)) and your rigging adds to it.  Smolt1:  Have you considered adding a pulley system to your sturdypress as an option?

Offline smolt1

  • Mature Cheese
  • ****
  • Location: oregon
  • Posts: 246
  • Cheeses: 29
  • Default personal text
    • SturdyPress.com
Re: Sturdy Press (Modified for pulleys)
« Reply #7 on: November 17, 2014, 05:08:24 AM »
Thank you John, BUT,

I have thought many times about adding pulleys, but have decided against it. Here are some thoughts.

1   The Sturdypress will already press to above 500 lbs without breaking ( see http://cheeseforum.org/forum/index.php/topic,9821.0.html  ).

2 To keep friction to a minimum the legs would need to extend about 6 inches. The reason for the longer legs would be to have the pulley system pulling straight down (not at a 30 degree angle). This has the effect of increasing the force of the pulley system, but more importantly it removes the horizontal force( from the pulley system 30 degree angle )  pushing the lever back into the press causing lots of friction between the plunger and its square guide holes.

3    As demonstrated by 'Anonymous ', it is easy to modify the press yourself if you want to go head to head with a pneumatic press.

And, you know how we get stubborn as we get older ;)

« Last Edit: November 17, 2014, 05:16:10 AM by smolt1 »

John@PC

  • Guest
Re: Sturdy Press (Modified for pulleys)
« Reply #8 on: November 17, 2014, 01:07:04 PM »
And, you know how we get stubborn as we get older ;)
True but in your case Bob I think it's "if it ain't broke, don't fix it".  I'm still tweaking my "compact" press but as you know we get slower as we get older  :) ;).

Sailor Con Queso

  • Guest
Re: Sturdy Press (Modified for pulleys)
« Reply #9 on: November 17, 2014, 05:43:50 PM »
There is a simpler way to increase the pressing weight on the Sturdy Press. Just slide a length of 2" PVC pipe over the existing wooden lever arm and hang the weight from the end of the PVC extension. I haven't done the math, but you can easily double the mechanical advantage. One caveat though. The press WILL tip over so you have to clamp down the rear of the press to your work table.

Spoons

  • Guest
Re: Sturdy Press (Modified for pulleys)
« Reply #10 on: November 18, 2014, 05:03:44 AM »
huh, That is indeed quite simple yet effective. Thanks Sailor!

John@PC

  • Guest
Re: Sturdy Press (Modified for pulleys)
« Reply #11 on: November 19, 2014, 10:27:06 PM »
Just to add to Sailor's overcoming the tipping problem:  If you're using on a counter-top like in Anon's picture you don't have anything to clamp at the rear.  An option is to add weight to the back of the press.  If you attach a thin (1/4") plywood rectangle to the bottom of the press that extends out each side of the press 8" or so you can place a gal. jug of water or a couple of bricks on each side.  May not be pretty but it will gain you some press weight if clamping isn't an option :).