EspressoForge wrote:It's a piston and cylinder design (no pump, you can change pressure near instantly). You just press on the top (a rod of aluminum, it goes inside the pipe),

I have never used one but i thought thats how the rok worked?

day wrote:I have never used one but i thought thats how the rok worked?

I was referring to the other person who asked if my device was pumped with a bicycle pump. Although it looked like your question was similar I can see the difference.

I also haven't used a ROK, or the old Presso...but my understanding of it's design based on research is:

1. a plastic piston/cylinder and a gasket that allows water to flow one way when pumped
2. dual levers on a gear interlock to give leverage and stability
3. Generates approximately 3-5 bar as a max pressure (~40-70 psi)

The above could be wrong, but was based on my research before deciding not to buy one a long time ago, maybe it has changed. The lower pressure and plastic piston/cylinder were the main reasons I looked elsewhere for a manual press. I love the dual levers, and while on the ROK it doesn't give a lot of piston travel capability, it does look like a nice ergonomic design. Ultimately I believe most levers would add too much complexity and push the price point of this device a lot higher, but maybe there is some ratcheting or other type of device that could fit on the top to help with leverage.

This morning I just pulled a shot, starting at 60 psi for about 5s, ramp up to 100 psi quickly for 15s, finish out shot at 60 psi for another 10-15s. Turned out great...it's making me think that some of the harshness I sometimes get on my Strega might be due to it's default high-pressure infusion. I've played around with stopping the Strega pump early, but it seemed too much of a hassle at the time...looks like I'll have to revisit that again.

troposcuba wrote:if it is awkward to see the gauge as you press, I am sure you could just use a 90* fitting to face the gauge upward so you could see it from above.

I was thinking of this and since I have the 90 fitting I'll try it out at some point. But the way it is I do like that the gauge fits more with the diameter of the device, which seems to help during travel. Currently while pressing I can see the gauge enough to know the pressure, but I don't get the full dial in view. If the gauge stuck out (in this case most of the 1.5" diameter would be off the side of the device), does anyone feel this negative would outweigh being able to see the gauge more easily?

Also, as a general note about the gauge...I was originally thinking that a gauge would be an optional accessory, but at this point, it seems like almost a necessary addition. A small change in pressure on the top can change the brew pressure considerably around 0-80 psi, but more significant force is required to get up to and break 100 psi currently. I think without the gauge, shooting in the dark would be a bit of a hassle.

I see what you mean. This is just me more being interested here, and I am no engineer, but a quick look online brought out that F=PA, and in this case we want 131psi, and so at lets say 50.8mm group you have A=3.14si, thus it would take like something like 411 pounds of pressure to make 9bar wouldnt it? I think some type of lever is a must isnt it?

EspressoForge,

I just took a look at some pipe dimensions online. If you are using ¾" aluminum Schedule 40 pipe (6061-T6), it has an OD of 1.05" as shown on this website: http://alcobrametals.com/resources/pipe-schedules

On Engineering Toolbox, 1" PVC Schedule 40 Pipe has an ID of 1.049", which would probably be a very snug fit as a sleeve, to insulate both the aluminum cylinder and protect the user's hands from excess heat. http://www.engineeringtoolbox.com/pvc-c ... d_795.html

We used to build and repair huge pumps for the Pulp & Paper industry. To install large roller bearings, we would chill or freeze the outer race of the bearing to make it contract in size. We'd heat the bearing housing to expand it. This made it much easier to insert the bearing, and when temps normalized, it was a very tight friction fit. You might be able to use the same trick if the above dimensions are accurate. I'd think a rubber mallet would be all you need to gently drive the PVC sleeve over your aluminum cylinder. If it is a tight fit, you probably wouldn't need adhesive or fittings to secure it. Fast, cheap and no machining, if the dimensions work out.

If you use a smaller diameter cylinder and piston, that will reduce water volume unless you make them longer. I wonder if you could find an inexpensive ratchet assembly you could adapt to drive the piston (like a home caulking gun). It would give you good control and would need less muscle. I'd think walk thru Home Depot might yield some possibilities.

Lou

If you can drill a small enough hole in the piston or if it's hollow, run a very thin tube to the top, a gage at the top might be the best location. It has ergonomic issues as it's then part of the handle but it would be the smallest diameter. Or just a put a spring and a piston as then the spring compression is pressure and making an indicator is just some rings turned on one of the shafts.

Ira

day wrote:I see what you mean. This is just me more being interested here, and I am no engineer, but a quick look online brought out that F=PA, and in this case we want 131psi, and so at lets say 50.8mm group you have A=3.14si, thus it would take like something like 411 pounds of pressure to make 9bar wouldnt it? I think some type of lever is a must isnt it?

You should use the diameter of the cylinder for calculations. Since it is a 3/4" pipe (schedule 40) this is 0.804" ID, not 50.8mm. As you can see in the video, pressure over 100 psi can indeed be had without more than 2 of myself standing on the top of the machine.

What I have noticed is that calculations are nice, but ergonomics play a large part in how easy it is to press as well, including the handle shape etc.

I'm planning to step down to a 1/2" schedule 40 pipe just to see how much easier it will be, ID is a 0.602", so generating over 100 psi maybe only a little easier apparently, or maybe a whole lot easier.

lbdina wrote:EspressoForge,

I just took a look at some pipe dimensions online. If you are using ¾" aluminum Schedule 40 pipe (6061-T6), it has an OD of 1.05" as shown on this website: http://alcobrametals.com/resources/pipe-schedules

On Engineering Toolbox, 1" PVC Schedule 40 Pipe has an ID of 1.049", which would probably be a very snug fit as a sleeve, to insulate both the aluminum cylinder and protect the user's hands from excess heat. http://www.engineeringtoolbox.com/pvc-c ... d_795.html

We used to build and repair huge pumps for the Pulp & Paper industry. To install large roller bearings, we would chill or freeze the outer race of the bearing to make it contract in size. We'd heat the bearing housing to expand it. This made it much easier to insert the bearing, and when temps normalized, it was a very tight friction fit. You might be able to use the same trick if the above dimensions are accurate. I'd think a rubber mallet would be all you need to gently drive the PVC sleeve over your aluminum cylinder. If it is a tight fit, you probably wouldn't need adhesive or fittings to secure it. Fast, cheap and no machining, if the dimensions work out.

If you use a smaller diameter cylinder and piston, that will reduce water volume unless you make them longer. I wonder if you could find an inexpensive ratchet assembly you could adapt to drive the piston (like a home caulking gun). It would give you good control and would need less muscle. I'd think walk thru Home Depot might yield some possibilities.

Lou

Thanks again Lou, I've been looking into these suggestions...need to try the PVC as I'm hoping I'll be able to come up with something perfect there. As you mention, less need for custom fitting or wrapping etc.

I did have a look at my caulking gun...interesting idea for sure. I haven't yet thought of a way to integrate it without a lot of machining.

ira wrote:If you can drill a small enough hole in the piston or if it's hollow, run a very thin tube to the top, a gage at the top might be the best location. It has ergonomic issues as it's then part of the handle but it would be the smallest diameter. Or just a put a spring and a piston as then the spring compression is pressure and making an indicator is just some rings turned on one of the shafts.

Ira

Also a cool idea, I hadn't thought to use the piston...likely I couldn't do a solid rod design for this to work out, as I'm really not sure that a whole could be drilled economically. I'd have to make the end of the piston a drilled piece with a pipe travelling up. Possible...but it does seem like quite a bit just to relocate the gauge. Also the handle may not be the best for the gauge, but just below it might work ergonomically.

So in the name of science (and potential cost savings), I tried today to pull a shot without the shower screen. Disaster. Puck fractured majorly and I got a nice watery mess.

Right now I'm using the gasket and screen from my Strega, since it was on-hand, and I was reasonably sure it would work. It does work great, but the main problem may be getting multiples of them for production since there's only 1 supplier here in the US. EPN seems to have a good shower screen that I'm planning to look into instead:
http://www.espressoparts.com/parts/espr ... oup-screen

Any other suggestions welcome for screen or the group gasket (73mm OD on the square cross-section gasket...thickness isn't critical, ID only needs to match the screen). My main goal here is something replaceable as these 2 parts, along with the piston O-Ring are really the only parts to wear out on the device as I see it. Similar to 58mm baskets, aftermarket support would be more desirable than choosing either the cheapest or something just because it was on hand.

Hoping to have more goodies and time to shoot more video by this weekend. Thanks everyone for following along.

Interesting project!

i do not like to dampen your enthousiasm and empirical approach yet I think you may be lacking some fundamental understanding of pressure and force...
https://en.wikipedia.org/wiki/Pressure

It's a long time ago since I did my chemical engineering but it seems quite hard to believe that you would reach 9 atmosphere or 900000 pascal by hand without using some sort of lever or other mechanism.

Assuming a typical body weight of users of your device at 100 kg ( 220 lbs or thereabouts,certainly no lightweights) would mean they can create a force of 1000N by sitting on your device, calculating on how big a surface area they could create a pressure of 9 Atmosphere or 9.10^5 (900000) N/m^2 on a surface by;

The formula A=F/P or 1000/900000 equaling 0.00111 m^2 or 11 square centimeter.
A regular portafilter basket of 58 mm has a surface area of 26 square centimeters, I think this explains why the smaller levers have small filter baskets...

Calculated the other way round: the surface area of a regular 58mm pf basket would and aiming for 9 atm would require F=P*A or 900000*0.00264 or a whopping 2376 Newton which is a hefty 237 kg or 500 lbs ( think that is close enough, did not look up the labs to kg conversion rate)

So unless you and your customers are morbidly of supra obese they'll have to do with less pressure OR you have to revisit your design by including a lever mechanism in some form or shape and or decreasing the filter basket surface area.

Still, an interesting project !