Peppina Marries MiniGaggia - Page 4

[lino]

One point of "caution" on stamping...

While it is an effective and economical means of shaping metal, the tooling and machinery required to do it are both very expensive.

Generaly what I have found is that in quantities under about 500, machining (CNC) is typically the most economical way to shape metal. From 500 to the lower thousands is a grey area that depends on the specifics of the parts, and over that, the higher volume methods: casting, stamping, etc become more economical. FWIW

I would also caution that making a profit (or even breaking even) on a low-cost, low volume, manufactured item is *extremely* difficult. The last thing I would want to do is be a discouragement, but I wanted to put that unfortunate reality out there. It bites me in the backside frequently. I don't know, but I suspect that MoGoGear could second that with his experience in the camp stove business. And if that's not the case, then, Man!, more power to him!

ciao

lino

[timo888]

Lino,
I agree with you about the unlikely profitability of a low-volume operation that uses custom components and cannot be built with 100% off-the-shelf parts. But I am hoping that the operation might be able to break even if the machine were provided as a kit that used off-the-shelf parts wherever possible. Totally eliminate assembly costs.

You have probably not had any dealings with this company because you have your own shop, but maybe you could tell us if their prices are any good, bad, or so-so -- perhaps on a test piece you have already costed out?

http://www.emachineshop.com

I would like to build this machine with a photo-grey acrylic skin -- smoky gray in sunlight but see-through in indoor lighting

Regards
Timo

[espressme]

Hi Folks,
Both "mo" and "lino" have cut to the heart of the subject. How many will be produced? How will they be assembled? What is the target price?
What are the demographics of the buyers?
There are many possibilities. Depending on the scale of production, some things are just wishes and some quite possible, or hackable! eg. kettles ( new word I just learned here) made from steam table serving trays and containers.

I am a newcomer to the topic and the HB site. I have learned a fresh aromatic pot full and, of course, have more questions. I hope to fit in as a newbie and bring 40+ years of professional new product development and industrial model making to the table. At some time , toward desert, I would really like to smell the coffee and have a serving.

To restate what I believe is being done here:
1. A forum exists here to talk the benefits of two or more real neat machines.
2. Any with experience in various disciplines or able to SWAG and TLABR may contribute.
3. Part of the fun comes in describing what benefits the previous machines gave.
4. Then an extrapolation of what could, by hindsight, be done better.
5. Many suggestions will be weighed and balanced.
6. The best perceived options shall be listed and checked against sound safety, health and hazard information.
7. A drawing ( more than a sketch) shall be completed and checked.
8. At some point in time a "breadboard"/"mock-up"/"prototype" shall be be built.
9. Options shall be arranged for: temp, speed, heat, steam control.
10. Hacker/ home shop drawings produced to allow some others to build and share experiences.
11. Final toleranced drawings shall be produced
12. Look for a producer of parts to kit and/ or final assemblies to sell at five times cost ( ChEAP! )

This forum is for persons who like or enjoy producing various levels of "REAL" brew liqueur with consistent amounts of natural and processing smells, colors, textures, caffeine, and tastes available. All this to be done with a great deal of refined ritual and pomp with suitable offerings to various nature spirits and deities. In a nut shell or coffee bean, we spend more money than the average George for our "Joe"
So-- "drumroll" ---
We seem to be looking at a collective cost for 10+ guys of about $600+ each for the prototypes that we shall use to discover whether we are getting a gosh-shot or greater quality with consistency. Not bad considering the cost of anything approaching the quality and consistency!

Is that a fairly accurate summation? And, if so how many in the first lot? AND! let's get cracking!

Now, right up front, I'm on Antisocial Insecurity, Autistic, machine stuff, & bash copper for a hobby, operate a few classic stovetops, early Italian/ Spanish home machines and machinettas and a couple 15 BAR pumpers, enjoy their results and am in this for the fun of extrapolation and the mental rewards of seeing a product done "fun and right".

My best regards to All. And may your minds keep freshly brewing ideas!
Sincerely
Espressme / Richard

[timo888]

...
To restate what I believe is being done here:
1. A forum exists here to talk the benefits of two or more real neat machines.
2. Any with experience in various disciplines or able to SWAG and TLABR may contribute.
3. Part of the fun comes in describing what benefits the previous machines gave.
4. Then an extrapolation of what could, by hindsight, be done better.
5. Many suggestions will be weighed and balanced.
6. The best perceived options shall be listed and checked against sound safety, health and hazard information.
7. A drawing ( more than a sketch) shall be completed and checked.
8. At some point in time a "breadboard"/"mock-up"/"prototype" shall be be built.
9. Options shall be arranged for: temp, speed, heat, steam control.
10. Hacker/ home shop drawings produced to allow some others to build and share experiences.
11. Final toleranced drawings shall be produced
12. Look for a producer of parts to kit and/ or final assemblies to sell at five times cost ( ChEAP! )
...
Espressme / Richard

Richard, change "shall" to "might" and I believe your restatement of what we're about might achieve some consensus

Though we are a formidable presence here on H-B, we leverites represent only a sliver of real-world espresso-machine consumers; and the trend seems to be towards machines that do everything for you. Soon, no doubt, they'll have 802.11 wireless, and a LCD so you can place your coffee order online by connecting the machine to your wireless router and the internet. So who knows if we could ever afford to pay someone to produce in mass quantities, or even in collectible quantities, a retro lever machine with two boilers, one open for brew-water temperature stability, one closed for steam.

Since, as you say, you're on Antisocial Insecurity you might recall the old Twilight Zone episode where a prisoner-of-war dreams he is designing a dream-house plank by plank, pipe by pipe, nail-by-nail, drawing the blueprint in his head as he sleeps. If he can ever get that last nail in place, dream logic has it he will be once again at home safe and sound. His captors, however, repeatedly deprive him of sleep, waking him before he can finish the design in his dream. Each time he falls asleep he's able to fly through the design he knows by heart and get farther into the blueprint in his sleep.

I can't remember how it ends.

Regards
Timo

[espressme]

Richard, change "shall" to "might" and I believe your restatement of what we're about might achieve some consensus Smile

Hi Tim,
I agree and suggest we all change the "shall" to "might." This, in aviation, is called "hanger flying"

Each time he falls asleep he's able to fly through the design he knows by heart and get farther into the blueprint in his sleep.

That seems to be the story of my life! However, I shall continue to dream and sometime shall awake to peace. Actually, you know, there is a strong correlation between intense visual thought and performance. In service some guys in "boot camp" would sit up in bed during the night performing the rifle drill while still asleep! I received a patent for a operational feature I sketched after awakening in the night.

And now someone else needs take the floor so our dream may progress!
Regards
Espressme
As with a stopped clock ( old style) I may be correct twice in one day. However, I may be wrong at the time you happen to glance. :D

[timo888]

Setting aside for a moment the question of relative costs of the different manufacturing methods...

Is it possible to stamp a box-shaped (lidless) watertight vessel out of a single sheet of stainless steel? Or do you have to bend a sheet into the side panels and then weld one corner and weld a base at the bottom around the perimeter?

Or is stainless steel tube or pipe available in ~10cm inner diameter? How do you connect a base to the cylinder? Weld it?

Is there a kind of welding that is certifiably food-safe for drinking water applications?

Regards
Timo

[timo888]

Below is a picture of the Arrarex Caravel kettle. What is the nature of the seam that runs up the spine, so to speak, at the back of the kettle? How is that seam made to be watertight?

A 1.5mm wall thickness does not provide as much support for a lever as I'd like. Although the piston housing, which runs from kettle lid to the group cap at the top of the group cylinder, would provide some structural reinforcement, a boiler made from this gauge of stainless steel sheet would need additional reinforcement if it is to be robust and provide a stable platform for the lever. Perhaps the boiler could be placed inside a powdercoated steel frame to give it greater rigidity?

What is the maximum thickness of stainless steel sheet?
Regards
Timo

[mogogear]

One point of "caution" on stamping...

While it is an effective and economical means of shaping metal, the tooling and machinery required to do it are both very expensive.

Generaly what I have found is that in quantities under about 500, machining (CNC) is typically the most economical way to shape metal. From 500 to the lower thousands is a grey area that depends on the specifics of the parts, and over that, the higher volume methods: casting, stamping, etc become more economical. FWIW

I would also caution that making a profit (or even breaking even) on a low-cost, low volume, manufactured item is *extremely* difficult. The last thing I would want to do is be a discouragement, but I wanted to put that unfortunate reality out there. It bites me in the backside frequently. I don't know, but I suspect that MoGoGear could second that with his experience in the camp stove business. And if that's not the case, then, Man!, more power to him!

ciao

lino

I am a poor repository of knowedge that is applicable. I only manufacture 400-500 units a year. I use recycled aluminum cans that mearly have to be cut down and reworked to save REAL tooling costs. I made all my own jigs, tools and processes and have a whopping 2.5 emplyees!!( Man that .5 person is a slow worker, ....

That is why I recommend searching existing stainless commercial boilers( most have bolt on lids) and then modify them to your needs . If one that will work can be found. I realize that stamping is not cheap or easy, but more realistic than the lost wax method. Machining is also a good option as Lino wisely pointed out.

[lino]

Hey Y'all

Yes, you can deep-draw stainless in a (nearly) square cross section, no it's not cheap (to set up). Food serving pans (knock boxes) are examples, though they aren't that deep. Cheap (and not cheap) stainless cookware is frequently deep drawn with depth to diameter ratios exceeding 1 (though I can't bring to memory any that exceed 1.5).

In the quantities you are likely dealing with a bent box with welded seams is by far the most economical. Welds can be chemically and electrically pasivated and while it's *much* harder to do, you can weld the insides of the box so there are no cavities and it is "more" food safe. Typically an open top box is made by making a cross shape (think Red Cross logo) and then bending each of the "arms" to make the sides, with that, you get 4 edges to weld.

Looks to me like the kettle you pictured is a two piece, bottom and hoop. Without seeing it better I can only speculate on the seam method, crimping would be my first guess. US made Blitz fuel cans are crimped. (that's why I use German Jerry cans...)


Stainless tubing is available in almost any size and wall thickness you can imagine. 4" (~100mm) and 6" (~150mm) are fairly common sizes. To cap the bottom your options are threading (requires a thick wall and o-ring) or welding. Again, an inside weld would be more food safe and FAR more difficult. I don't know much about NSF or other food certification requirements.

Stainless sheet is probably available in thicknesses up to a few inches... I commonly use .030", .060", .080", .090" and .120" (those and probably 1/4" are readily available)
I made the body/chassis of my E-61 machine out of .080" and it's built like a tank (that was not intentional). That's roughly 2mm. .060" (1.5mm) usually feels more than sturdy enough for me, but that's also largely dependent on its shape.




ciao

lino

[espressme]

I am a poor repository of knowedge that is applicable. I only manufacture 400-500 units a year. I use recycled aluminum cans that mearly have to be cut down and reworked to save REAL tooling costs. I made all my own jigs, tools and processes and have a whopping 2.5 emplyees!!( Man that .5 person is a slow worker, ....

That is why I recommend searching existing stainless commercial boilers( most have bolt on lids) and then modify them to your needs . If one that will work can be found. I realize that stamping is not cheap or easy, but more realistic than the lost wax method. Machining is also a good option as Lino wisely pointed out.

Hi Mo, I agree that the lost wax is a poor choice for the boiler/kettle. What it is great for is the group and portafilter. Agreed also the stampings are expensive. I would comment that there are steam table containers that are about 6"x6"x up to 1.5 X depth. Great for a kettle!

Stainless steel mechanical tubing is available in many wall thicknesses and diameters.
Welding a collar/ plate at or near one end then trueing in a lathe is a good solution to the fabrication problem and is fairly quick and simple if the mounting holes for the group and the kettle are pre-drilled.

I would kinda-sorta like to see the group head simply removeable from the pump tube collar and kettle. Sort of like the wing nuts on a brass porthole. Or, a bayonet type mounting safe'd by a wing bolt. That unit could hold and locate the dispersion screen. The tube making up the pump body could then hold the valve disk and valve as a bottom slide in element held in place by a spacer ring above the dispersion screen.
this construction would remove the need of threaded parts in the pump tube.

First time to upload graphic, here's hoping!

Blue is kettle, green is pump tube and welded flange with flat head mounting screws to the kettle, purple is group { not showing wing nuts for removal}, orange is portafilter, turquise is dispersion screen ( perhaps with one way valve above) in the ring that is held into the pump tube by the group.

That's all folks:
Regards
Espressme / Richard

[timo888]

First time to upload graphic, here's hoping!

Very nicely done, and I don't mean succeeding with the upload to the website.

... group head simply removeable from the pump tube collar and kettle. Sort of like the wing nuts on a brass porthole. Or, a bayonet type mounting safe'd by a wing bolt. That unit could hold and locate the dispersion screen. The tube making up the pump body could then hold the valve disk and valve as a bottom slide in element held in place by a spacer ring above the dispersion screen. This construction would remove the need of threaded parts in the pump tube.

I am not wedded to threads but I thought a threaded connection would give the pump tube more structural rigidity, which it might need given the stresses placed upon it from the piston-lever. But if the pump tube slides flush into the group cap and abuts the plate that holds the one-way valve, and if the entire assembly is adequate for the stresses it's under from the lever, then a slide-in as opposed to a threaded one-way-valve-housing is okay by me.

Note that the plate that holds the one-way valve(s) in place above the dispersion screen might have to be more than 25mm thick, depending upon the type of valve used. The bushing valves I have not been able to find in lengths shorter than an NPT 1/8" (nominal) hex coupling, i.e. about 1". A simple EPDM NSF61-compliant washer would require less vertical space, ~6mm. We want the dispersion screen to be immediately below the egress orifice of the one-way valve(s) with headroom no greater than the valve requires to open, so that only the tiniest amount of water remains unexpressed above the dispersion screen. And so the plate that holds the valve(s) has to be as thick as the overall valve length in its closed state...if the valve is other than a simple washer.

I had situated the One-Way Valve Housing (formerly 'group cap') on top of the group cylinder which protruded slightly into the kettle. My proposed group was roughly bell-shaped like an inverted Coke glass. The top of the group protruded into the kettle so that heat from the brew water could be conducted to the group. The group is this design is atypical in that it is NOT designed to be an aggressive heat-sink. The water will be in an unpressurized kettle and therefore cooler than water in a closed boiler and much closer to optimal brew-temperature range. The group must be brought up to a temperature where it would not rob too much heat from the brew-water as it is pressed down to infuse the puck (what that temperature is depends on the metal chosen for the group). And the group must be kept close to that temperature to minimize the need for warming flushes.

On seal materials: if the seal comes into contact with drinking water, it should be NSF61-compliant. That's my feeling, anyway. AFAIK, this limits the choice to to EPDM PC (good to 300F) because FDA silicone is marginal in wet-heat applications (and, again AFAIK, FDA-compliance is not as strict as NSF61 "drinking water").

Regards
Timo

[timo888]

I should add to my most recent posting that in the spirit of retro simplicity, this machine should be temperature-stable and work extraordinarily well even without the sophistication of a PID and yet support a PID for micro-management of temperatures.
Regards
Timo

[timo888]

I had situated the One-Way Valve Housing (formerly 'group cap') on top of the group cylinder which protruded slightly into the kettle. My proposed group was roughly bell-shaped like an inverted Coke glass. The top of the group protruded into the kettle so that heat from the brew water could be conducted to the group. The group is this design is atypical in that it is NOT designed to be an aggressive heat-sink. The water will be in an unpressurized kettle and therefore cooler than water in a closed boiler and much closer to optimal brew-temperature range. The group must be brought up to a temperature where it would not rob too much heat from the brew-water as it is pressed down to infuse the puck (what that temperature is depends on the metal chosen for the group). And the group must be kept close to that temperature to minimize the need for warming flushes.

What if we used thick-walled stainless tube for the group cylinder and welded a stainless collar to the bottom of the tube for locking the PF in and for bolting the collar to the bottom of the kettle? The top of the tube could protrude through the base of the kettle up into the kettle water to optimize the conductivity of heat from the water to the group. Using stainless tube avoids the need to tin plate brass. The tube is pre-shaped and so we don't have to do a brass casting. All we'd need to do is cut the group-cylinder hole in the plate that acts as the collar, tap the bolt holes, cut the groove for the PF, and weld the collar to tube. Shouldn't it be easy to weld a collar to a tube in a food-safe manner? There's no logistical difficulty of reaching an inside seam. We could also use thick-walled 100mm diameter stainless tube for the kettle if the stainless tube has the right percentage of metals to make it NSF certifiable food-safe.

Regards
Timo

[espressme]

A simple EPDM NSF61-compliant washer would require less vertical space, ~6mm. We want the dispersion screen to be immediately below the egress orifice of the one-way valve(s) with headroom no greater than the valve requires to open, so that only the tiniest amount of water remains unexpressed above the dispersion screen. And so the plate that holds the valve(s) has to be as thick as the overall valve length in its closed state...if the valve is other than a simple washer.

I am partial to a replaceable washer type valve. They may seal better in a gritty environment and may provide less dead space in the head

The spring loaded safety valves for Stovetop Machinettas are only about 8-10 mm, 3/16ths" to 3/8ths" in length. with a .09 (2.1 mm bore) They may be available in S.S.

The group is this design is atypical in that it is NOT designed to be an aggressive heat-sink.

I thought that the idea was to make the whole kettle, group and group head + portafilter to be at ~ 200°-207° F. That may make all group head parts S.S. and the portafilter of plated brass. That would allow the porta filter to come quickly to temp after being refilled with grounds. And serve as a heat source through the brew process.

By the way, I am partial to a submerged calrod or similar element. The reasons being that the outside of the kettle is easily insulated and convection really will keep the kettle evenly heated. You may look at some of the cheap home deep fat friers with stainless kettles and see how the element hinges into the kettle or passes through the kettle wall. I believe that element would be foodsafe.

On seal materials: if the seal comes into contact with drinking water, it should be NSF61-compliant. That's my feeling, anyway. AFAIK, this limits the choice to to EPDM PC (good to 300F) because FDA silicone is marginal in wet-heat applications (and, again AFAIK, FDA-compliance is not as strict as NSF61 "drinking water").

A man after my own heart, looks for the toughest reg and says so! Another reason to have an immersed heating element! no very hot metal near the gaskets, all at about ~ 200°

What if we used thick-walled stainless tube for the group cylinder and welded a stainless collar to the bottom of the tube for locking the PF in and for bolting the collar to the bottom of the kettle?

That will take some thought. I really would wish to hold the valve and screen in place with a strong removable member. for maintenance

* 'Could we possibly have another ¼ turn slot in the head above the portafilter?

By the way, my math is poor and I wonder would be the force at 15 bar pressure on the 51 mm portafilter? 15 bar x 15Lbs per square inch =~ 225 Lbs per square inch. Area = Pi* r² so,
1xPi = 1x 3.1416= ~3.2 in² That being 225x 3.2 =~700 lbs. Whew?!?! Am I close? Then, what would be the force on an arm of reasonable length?
Keeping in mind that this should be a short stroke for a single and a long stroke for a double. ( That is why the pump tube extends so far into the kettle and the fill holes are so high { that allows the pump piston to breath through its one way washer and fill the shot space in the tube.[ That does mean a pint or so of water left in the kettle at the bottom level limit ]}) That could allow a stable temp due to its mass.
Whew
Regards
Espressme / Richard

[hbuchtel]

Hey folks, I just found out a friend of mine is the boss of a CNC machining company (doing iron and steel). . . if y'all figure out which parts could be manufactured this way I can get an estimate from him.

Henry

[timo888]

Keeping in mind that this should be a short stroke for a single and a long stroke for a double. ( That is why the pump tube extends so far into the kettle and the fill holes are so high { that allows the pump piston to breath through its one way washer and fill the shot space in the tube.[ That does mean a pint or so of water left in the kettle at the bottom level limit ]}) That could allow a stable temp due to its mass.

Others may be, but I am not partial to the partial pull ... It's sort of like the BigEndian-LittleEndian controversy Yet it's more than a philosophical position on my part: the ability to draw multiple fractional-shots of water into the piston cylinder by jacking the lever would earn the machine an undeserved reputation as a SuperSoaker water gun, a sneeze-machine. Water pressure would build up as users jacked the lever... I'm in the one pull one shot camp. Water from the kettle should flow into the piston cylinder only when the spring has been fully compressed and the piston is fully retracted. The gross amount of water that flows from kettle into piston cylinder should be sufficient to net a single shot. A double would require two pulls, not a long pull.

In my earlier drawing, when the retracting piston's lower o-ring reaches the location directly above the ingress holes in the cylinder wall, water from the kettle can flow into the cylinder into the space vacated by the piston head and so down to the dispersion screen and to the puck. Your design seems to have water already in the cylinder above the piston head before the piston retracts. Like the All-Clad Presso? I don't regard the Presso as a paradigm of excellent design. It has the air problem, and the other parts seem designed to wear out, either from metal fatigue or tearing from constant abrasion.

Apart from the avoiding the double-pull, I don't see the benefits of locating the holes higher up on the wall of the cylinder. A double-pull is not a problem with the one-way valve that prevents backflow from the puck. Where are the temperature benefits? The additional metal contact of immersed spring and immersed piston shaft have added a heat sink to the mix, probably reducing the temperature stability of the water in the kettle. Locating the ingress holes higher up introduces an additional valve, makes the piston seal design less robust, and doesn't advance temperature stability.

Do you have a link for the miniature check valves you mentioned? I'd like to check out their effective orifice specs and NSF61 compliance.

Regards
Timo

[timo888]

I really would wish to hold the valve and screen in place with a strong removable member. for maintenance

The washer-type one-way valve, as I described in an earlier posting, is readily accessible from below. Remove the dispersion screen and there's your washer, screwed into the plate in the 'group cap' right above. Maintainable without having to take the kettle lid off. The bushing style valve, on the other hand, screws into the plate from above, i.e. with the inflow orifice towards the top of the machine.

... my math is poor and I wonder would be the force at 15 bar pressure on the 51 mm portafilter?...

Why are you assuming 15 bar? Why not 9 bar?

Regards
Timo

[espressme]

A 1.5mm wall thickness does not provide as much support for a lever as I'd like. Although the piston housing, which runs from kettle lid to the group cap at the top of the group cylinder, would provide some structural reinforcement, a boiler made from this gauge of stainless steel sheet would need additional reinforcement if it is to be robust and provide a stable platform for the lever. Perhaps the boiler could be placed inside a powdercoated steel frame to give it greater rigidity?

My take on that is the idea that the kettle is only that, and the force resisting structure is formed by the framing of the machine to accept the forces where they are present. In this case between the lever and the pump tube while supporting all from the counter and countering any vector forces brought to bear. ( The Hot, Wet Peppina Tummy.)

Others may be, but I am not partial to the partial pull ... It's sort of like the BigEndian-LittleEndian controversy v

I can understand that. I like a double in the morning

I'm in the one pull one shot camp. Water from the kettle should flow into the piston cylinder only when the spring has been fully compressed and the piston is fully retracted.

Aha, Now I may get a glimmer. You want a spring machine and I am thinking direct lever action. One of my local shops has an older three group direct lever machine and with the right Barista it pulls some totally awesome shots.

Do you have a link for the miniature check valves you mentioned? I'd like to check out their effective orifice specs and NSF61 compliance.

No, Some types are available at http://fantes.com. One Asian machinetta I have has a S.S. valve. Bye the way, they are simple to make and may be as easy as elastomer balls in stopped holes in the valve body. Washer still seems best!?!?

In my earlier drawing, when the retracting piston's lower o-ring reaches the location directly above the ingress holes in the cylinder wall, water from the kettle can flow into the cylinder into the space vacated by the piston head and so down to the dispersion screen and to the puck.

Here I am confused. How does one pull a piston out of the wet tube with the one way valve closed to the puck? Seems a vacuum would form making withdrawal difficult. That's why the OWV on the piston in my thoughts.

The additional metal contact of immersed spring and immersed piston shaft have added a heat sink to the mix.

It may be we have a difference of definition? To me any mass at a stable temperature is not a sink but a source to any thing at a lower temperature.. Therefore it would seem that with more mass at temperature the less the whole is affected by transients such as a shot at that temp, or a stray breeze from a window.

Why are you assuming 15 bar? Why not 9 bar?

That would be a test figure for a lever machine. Because I find that I have a great crema on the shots from my machines at that pressure. Remember, I am a newby and brew to my satisfaction. Luckily, I live alone. I am willing to be taught though.

Since you would like the spring machine which has been very!! successful, the brewing force / pressure is determined by the spring. Remember the hysteresis of a spring, strong pressure to start and a tapering reduction to its lowest at the max extension. That may be a plus for the application?!

Also I am thinking about the suggestion some one made about using a stepper motor driving a screw to drive the piston. That would be a very accurate method of setting the time of a shot with the portafilter tamped mechanically and consistently. The holy grail! Consistent tamp, time of shot, temperature of shot . All variable at will.only

We do have a commonality of parts for all the types and hole in a different place or the pump tube a different length as not really a problem.

Enough for tonight!
Regards
Espressme /Richard

Post Script: How about some others getting in on this??

[timo888]

... and the force resisting structure is formed by the framing of the machine to accept the forces where they are present.

Fair enough. The kettle wouldn't have to bear the forces of the lever. On the MiniGaggia, the lever is bolted to the lid of the (thick-walled) box-shaped kettle.

I like some of the features of 100mm stainless tubing for kettle and same material with smaller diameter for integral group cylinder protruding into the kettle, and for the piston tube; am looking more into the banded heaters of the type Mathias originally suggested or the rubberized heaters you brought into the picture. The seal material for the o-ring for the threaded base remains a question; back in the day they would have used Viton. EPDM might melt. Silicone might not last long. [Have since been assured that EPDM will work and a material called Aflas was also suggested to me.]

Aha, Now I may get a glimmer. You want a spring machine and I am thinking direct lever action.

Yes, the offspring of Peppina and MiniGaggia inherits that particular trait. (Not that I am a spring-machine bigot: the Caravel and Cremina make a nice espresso too.)

How does one pull a piston out of the wet tube with the one way valve closed to the puck? Seems a vacuum would form making withdrawal difficult. That's why the OWV on the piston in my thoughts.

In the Peppina, the one-way valve that prevents backflow from from the puck is a simple pliable washer. A slight vacuum occurs when the piston retracts, but the retraction of the piston draws water down from the kettle, situated directly above, to fill the void. In the MiniGaggia, there is no backflow prevention valve, and the retraction of the piston draws crud from the puck, situated directly below, back through the dispersion screen into the boiler. For their love child, I've proposed two backflow prevention designs: (1) a simple EPDM washer and (2) an array of small spring-type check valves. The backflow prevention seal of the washer-type valve is good but not perfect and might not pass muster today if consumer-safety regulations are strict; that possibility led me away from a simple EPDM washer to the more sophisticated spring-activated check valves that are used in drinking-water-safe systems.

In a piston cylinder with a 51mm inner diameter the piston has to retract only 25mm-30mm to create volume for water sufficient to yield a single shot. When the piston reaches the ingress ports just above that ~25--30mm mark, water from the kettle would be sucked quickly in to fill the void. There should be some audible feedback. If the force on the lever is sufficient to compress a spring capable of producing 9 bars, shouldn't the force be sufficient to overcome that vacuum? We do have to make sure that the valve and piston o-ring are both up to withstanding the pressure.

Also I am thinking about the suggestion some one made about using a stepper motor driving a screw to drive the piston. That would be a very accurate method of setting the time of a shot with the portafilter tamped mechanically and consistently. The holy grail! Consistent tamp, time of shot, temperature of shot . All variable at will.only

This machine is conceived as an homage to best features of the vintage gravity-fed open-boiler spring-driven-piston lever machines, with some willingness to incorporate a few contemporary conveniences, like maybe an autofill from reservoir when the kettle reaches 80% depleted, a PID option, and a removable drip tray. Oh, and at night, when the photo-grey acrylic is transparent, you can see the works inside.

Occasionally Untamped,
Timo

[timo888]

I was just talking with a fellow with long experience in o-ring applications and materials, and he opined that an EPDM seal for the threaded base of a cylindrical kettle for boiling water would work without any trouble. He also suggested a material marketed under the name Aflas, which is used in applications requiring high heat and purity.
Regards
Timo