Marcelnl wrote: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 !

Hi there, someone above has already mentioned this, and erroneously calculated the area using the basket diameter. This is not the case...you need to use the pipe diameter for calculations. I assure you, I do not weigh 500 lbs, and I don't need to stand on the device.

You can also check out the video for a proof of concept as it were...although pressure may be a bit lower than I expected at the downward force I calculated (due to a variety of reasons most likely), but you can see that I get up to 100 psi (~6.8 bar). With some mods I've already done, going over 100 psi is much easier for me, but I would like to improve things even more for those that don't want to put 50 lbs pressure continuously on the device. A smaller pipe will decrease the force needed.

Also, as to my above post, I've found an exact grouphead seal match looking around a bit more. Surprising that Strega seal is the same as E61, but according to my calipers everything will match up. http://www.espressoparts.com/faema-e-61 ... ter-gasket

Unless I have missed some changes in natures laws I would think that the 9atm required for espresso need to be present on the surface of the coffee puck and therefore I'd say you need to calculate the surface area of the filter basket you are planning to use and not the diameter of the bit of pipe you happen to use, pressure equals force divided by surface area and you need 9atm on the filter basket.

Just trying to clarfy the dimensions of what we are looking at:
My faemina uses a lever with a ratio of approx 2cm to 24 cm in order to compress its internal spring which in its turn is delivering something like 9 atm on a tiny 48mm filter basket...I need a car jack in order to compress that spring when I need to remove it for repairs and am pretty much unable to compress it much using my weight.


Following your logic all levers would be using a longish piston chamber and a very narrow piston. long piston chamber in order to hold enough water to create enough espresso volume, and a tiny diameter piston in order to keep the force required to push the piston down low.


May the force be with you

EspressoForge wrote:Hi there, someone above has already mentioned this, and erroneously calculated the area using the basket diameter

+1

I can vouch that the cylinder calculation is correct because I had the same misconception before (and I find it really hard to believe until I think deeper). I used to think that home lever has smaller basket so it must be the reason. But no, cylinder/piston is the contributor here since they're the one moving the volume of water. It is using the concept ofhydraulic press to compress water for creating pressure. With a bigger piston = it moves more water/per distance travelled = more force needed. Inversely, if you have a smaller piston, you need less force. Also, it is similar to bicycle shock pump, by just manipulating the piston diameter, you can create up to 40 bar with bare hand (albeit less volume/stroke).

The force in spring lever is another story because it stores the total force required for the whole piston travel, where as in manual lever force is provided continuously(spread out).

Really interesting project there Andre, I have been watching this since you posted and am only posting now. I'm all interested for this project and almost wanted to bite for the preorder, but realize shipping may tip the scale for me.

The pressure part is considered solved and I don't doubt your gauge/calculation. With Rossa HC, it's amazing how easily I can reach 13 bar or more. So with the right design, I don't think it's impossible at all. I would be interested to see how the two issues are addressed.

i) Preheating & intrashot temperature
ii) Clean up

Good luck and keep the updates coming.

Marceini,

EspressoForge is correct in using the diameter of the piston, instead of the puck, in calculating the necessary force to generate a given pressure (ignoring friction, of course). As the diameter of the piston and cylinder increase, so does the force required to generate the same pressure. If you look at it in reverse, it makes sense. If your puck is exposed to 9 bars of pressure, that same 9 bars will be pushing against the piston above the puck. If the area of the piston is small, then you apply the formula and you will see that you can get a lot or pressure with less force.

Lever machines need the lever for mechanical advantage since they are exerting force over a much larger area. You'd need to be a weight lifter otherwise, just as you suggest. Lever machines could dispense with the lever if they made the cylinder a small diameter and very tall, but that would be an awkward design for a countertop espresso machine, so they use a shorter, larger diameter cylinder. They need that mechanical advantage, or a barista who is built like Hulk Hogan.

I believe the reason that other machines don't use my small pipe design is that it would make the lever machines too high. It's also likely that springs just don't work so easy with that kind of distance...I'm not too familiar with coefficients of springs used in lever machines. Also, since a lever is used, it's really not needed.

The other thing about this design, is the balance between cylinder diameter (smaller being better for pressure) and travel amount needed to push the required amount of water for a double shot of espresso. If I reduce the pipe too much, not enough water would be available without an extremely tall pipe, not to mention having to start from a very high distance.

Right now, on the current 3/4" pipe, I've taken off 3", which has helped with the height of the device. It's harder to press the required force when the handle is at a certain height, of course this depends on how tall the person is, and how tall counters are. So here I'm trying to balance between a happy medium. For production I'm thinking to keep the device on the taller side, allowing for maximum shot volume...but were a person to want to increase their mechanical advantage because they were a bit on the shorter side, or their counters pretty tall...they could trim the pipe and/or piston down a bit.

My overall vision with the device is that it becomes a platform for mods. I'm sure many other creative people will come up with interesting ways to make pressing easier...but similar to the Pharos in the grinder world, I hope that I can bring this device to the community with the goals that it will make the best possible espresso for the lowest reasonable cost.

Any suggestions for naming the device?

samuellaw178 wrote:I would be interested to see how the two issues are addressed.

i) Preheating & intrashot temperature
ii) Clean up

I'm hoping to record a demo video this weekend that would explain both the machine, as well as a full routine...last weekend I was feeling a bit under the weather, but wanted to get out a quick shot video. I could probably split up the videos too, one to explain what it is and how it works. And the other as a full routine.

Preheating is pretty simple...put the top part of the device in a bowl, and fill tube with water until the level goes up to just below the gauge. Only the bottom ring and basket isn't preheated. You can do 1 or 2 rounds of this preheating, I find that 1 works best for darker roasts, 2 is needed for light roasts. Also, I'm working on getting intrashot temp. I have a thermocouple for roasting, but it goes to my laptop and artisan...I was hoping to get something a bit less confusing for the purposes of a video so I could just show the temp, similar to the pressure gauge you see.

http://hyperphysics.phy-astr.gsu.edu/hbase/pasc.html may be of use, it seems my knowledge is a bit rusty as i completely overlooked the hydraulic press principle in your application...

i think that indeed temperature management is the main issue, as well as the volume displacement you need in order to have a meaningful output volume (a single at 25 ml seems doable)

Following the underlying hydraulic press principle I'd like to propose 'hydrospresso' as a starting place for a name.

Just started wondering if folding the tube in one or more series of u turns would help keeping a lomg enough column in combination with a low working height....would make the temperature issue more difficult to manage AND cost would go up a bit.

Btw Springs typically have only a small distance over which they can maintain a given force.

You might want to consider wrapping a heater coil around the tube as a way of preheating the tube in case you can keep the mass of the used material low...probably not practical for camping purposes but at home or in the office preheating with hot water might be a bit of a pain and a safety issue.

Resistive heating wire Is not expensive and you would likely not need high power, my Faemina only needs 200watts to keep 10 kg of brass and a liter of water at 93'C but you can likely easily calculate the required power rating.

After making a double shot (17g coffee) with my original 12" pipe length, I not only had about 4-5" of travel left at full compression, but also a lot of water to pour out to get the puck nice and dry. I could just pull out the piston and pour out the water, but I would guess this would make a sludgy mess. I'm guessing once the smaller pipe arrives, it may need to be the full 12" length, or close to it because of the reduced water volume.

Temp management is similar to most pour-over devices...a bit hard to get super-hot, especially I would imagine if you were camping at high altitudes...but for most coffees it should be anywhere from perfect to possible with longer preheat regimens. Still I'll try to get real recorded data for temperature.

For naming...I'm really not sure what direction to go. Lot of machines with presso in them already, Portaspresso, MyPressi, Presso (now ROK). Not to knock their naming, because I do like them, but I was thinking something different. Best I've been able to come up with is "Model T Espresso Press" as a homage to Ford's Model T, "comes in any color you want, so long as it's black." Kind of a long name tho...

One of the more exciting aspects of the device for me has been the pressure profiling, I've played around a bit with profiles, but as of yet I haven't been able to determine what is best. May have to have a look around the recent Vesuvius threads I've been seeing.

Marcelnl wrote: Btw Springs typically have only a small distance over which they can maintain a given force.

I'm guessing this is why levers use both larger diameter cylinders, which as a by-product, makes a lever a requirement.

Marcelnl wrote:You might want to consider wrapping a heater coil around the tube as a way of preheating the tube in case you can keep the mass of the used material low...probably not practical for camping purposes but at home or in the office preheating with hot water might be a bit of a pain and a safety issue.

Resistive heating wire Is not expensive and you would likely not need high power, my Faemina only needs 200watts to keep 10 kg of brass and a liter of water at 93'C but you can likely easily calculate the required power rating.

My vision is that add-ons like this that would be a major expense, would be offered by others in the community. Both in order to allow me to focus on the basics of the device, as well as to keep costs down. This sort of open source platform is what I'm hoping to achieve with the project, and why I'd like others to be involved with the design process (as opposed to just releasing what I think of is best).

Also, I'd like to apologize to anyone who gives their suggestions here (both past and in the future), that I decide not to implement. Most of the reason to not implement will be cost related (either parts or machining costs), so it's really not that they aren't good or even amazing ideas. But I'll try my best to research cost effective ways to add any suggestion, especially ones that many people seem to be interested in. Also if anyone can think of ways to add their idea at a low cost, would be more likely to be added. Overall, although machining and assembly will be done in the US upfront, I still think we can make it for a pretty low price comparatively.

Not sure exactly how levers were developed, yet I think their design mainly originates in repeatability as in multiple shots...hence using a boiler etc. so I think you really can not compare these.

The idea behind your machine and others like aeropress, handpresso, rok etc etc is imo a single shot design without internal heating, which opens up a whole new wealth of possibilities ...and challenges.

Personally I am not yet sure what the advantages of your current aproach are, no harm intended but I think I'd prefer something like a faema baby which is a lot smaller for camping or even office use ( having used the aeropress and the handpresso in office I ended up with nespresso in my desk drawer), or even a handpresso (though the results of the hand presso haven't been that great imo).

Have you seen what Strietman is doing btw?

Having said that, It's great to see initiative!