Also posted in the P64 thread (since a P64 user requested it), but here's an adapter to grind directly to porta-basket. It should fit grinders with similar style portafilter forks, but I used a DF64 to measure so YMMV.

I got this one from Amzon.com
https://www.amazon.com/Backflush-Disc-F ... 5YF8V?th=1
I imagine any store that sells espresso equipment would carry something like this.

jpender wrote:I made a plastic piston for testing and found that it worked just as well as preheating a metal piston does. The only problem is that you can't buy a non-metal piston; you have to make your own.

I wouldn't be confortable toi use plastic. It's a good idea for temperature but the pressure... Metal atoms won't dissolve at 9 bar, how about organic polymers though? I would test it before drinking...

manu99 wrote:I wouldn't be confortable toi use plastic. It's a good idea for temperature but the pressure... Metal atoms won't dissolve at 9 bar, how about organic polymers though? I would test it before drinking...

I pulled over 40 shots with my test piston. I couldn't taste anything funny. It was coated with FDA silicone adhesive to make it hopefully food safe. You can't always taste poison though.

There are food grade materials that can be used. I was planning on using PVC as the structural part and silicone rubber on the exposed bottom part of the piston. If you're okay with the silicone Robot seal you'd probably be okay with what I have in mind, at least in terms of food safety.

My biggest concern is longevity. I'm not a mechanical engineer and I wonder about the pressure on the plastic where the axle sits. Could it crack there? Or maybe deform slowly over time? I doubt it would fail catastrophically but if I had to make a new one every 12 months that would get old.

There are other espresso machines with plastic pistons. The original Flair, for example. And I've read that some La Pavoni machines have plastic pistons. Are they unsafe? I'd be surprised if that were the case.

Pavoni use https://en.wikipedia.org/wiki/Polyphenylene_sulfide
Flair https://en.wikipedia.org/wiki/Polyoxymethylene

Both food safe and both break eventually, but should last much more than a year. In the case of Pavoni it's even inside a hot group for a considerable amount of time. I would be happy to try either on a Robot, but feel a bit uneasy about PVC.

Jonk wrote:...but feel a bit uneasy about PVC.

That's why I stopped using my test piston. Even though I slathered food grade adhesive all over it and checked it regularly to see if it was peeling off, I was still concerned about exposure. Standard PVC is used for supply side plumbing, but only for cold water. Near boiling water is a different story. Also, the glass transition temperature, where PVC becomes soft, is only 60°C. I put a little piece in a cup of boiling water and it softened and deformed pretty quickly. My piston didn't have signs of deformation but it was a larger mass and not actually in the water.

I'm planning on having around 1cm of silicone rubber between the PVC and the inside of the Robot. So the PVC won't get that hot and it won't touch the water. Assuming I can really fabricate the thing I think it will be okay.

Thanks for the link. Amazon.de did not have the 58mm and I bought the 54mm and works ok. Without pressure it leaks a bit, but it's not a big deal.

I love the coffee now. It was indeed the temperature (or better say temperature gradient in time) causing my shots to be sour. Now I get the sweetness I was looking for so long. Of course these are speciality coffees I'm talking about.

Of course in an ideal world I would not have to preheat and could just extract without any fuss, but here we are... for me preheating takes a bit of fun out of the Robot, but if you consider that the coffee you get is comparable with machines maybe 10 times as expensive and very hard to maintain... the Robot is a breeze.

I've had my Robot for a little bit now, so I suppose I'll post my preliminary thoughts in case they are useful for anyone else. I bought my Robot (partially as an impulse buy) as an effort to downsize, and given the heat-loss I expected my espresso quality to take a small hit compared to my other levers. In all honesty, that hasn't happened. My roast preference I'd consider on the lighter-end of what people are generally willing to drink, with most of my shots recently pulled being Tim Wendleboe Kiahia and Coffee Collective Kiangoi. While pre-heating is generally helpful, I also find that the slightly lower brewing temp hasn't at all stopped me from drinking these very very light roasts. The variable I've used with the largest effect has been varying my water composition, and adding a bit more bicarbonate/buffer content to it. Expect acidity to still be there, but for the harsh, lemon juice edge to be softened and integrated with the aroma and to be perceived as "juicyness/fruityness" rather than harsh acidity. Paper filters on the bottom of the basket have been the other biggest lever for taste improvement, but that seems to push shots into much greater clarity and intensity rather than changing the character of the perceived acidity. I still have a preheat routine, but it is mostly hands off, I just heat the basket + PF over my kettle while I am waking up, and I pour a bit of kettle water into the piston through the top of the Robot. This doesn't get the piston nearly as hot as a dedicated preheat would, but there are only a few things I'm willing to go through in the mornings before work. If you drink only black coffee as I do, I can give a strong recommendation to the Cafelat Robot as a great option, even if your taste preference skews towards filter roasts. Workflow for me is no more faff than it would be for a pump machine with the lack of maintenance and quick heat up time.

I recently got my Robot and an Aergrind and love both of them. However, I am having the worst time trying to dial-in a (fresh) medium roast. I've been dosing 16g and adjusting my grinder between 1.1-1.3. At 1.1, the puck cracked and channelled; at 1.3 everything came out waayy too fast. In between, I've been getting a lot of sputtering and spraying at 7-8 bars pressure. I've also noticed that pieces of the puck have been sticking to the side of the basket when I knock it out after.

What settings are other Aergrind users using? I recognize that this a somewhat meaningless exercise given that as much depends on the coffee, but still, it would make me feel better to know others are having success.

IIRC when I had an aergrind burr touch was below zero, so unless you're counting revolutions specific numbers are kind of arbitrary.

Do you pre-infuse and use WDT? Especially the latter is very helpful to avoid spraying.