User Experience with the Strietman CT2 - Page 47

#461: Post by **Chrikelnel** » May 24th, 2022, 6:22 pm

Alestz wrote:Pulled the trigger for a new CT2 yesterday! Lead time is only 1 week currently, so super excited to try it out in the near future. I've been trying to scan this thread many pages back but any quality of life tips or quirks that a new owner should know about?

These are off the top of my head: Keep the lid on while brewing to increase temperature stability, it seems like most people do these days but there's a few holdouts. On the topic of temperature don't be afraid to mess with the dial, when I first got it I set it to max and left it there but I've found I get better results around 94 for most coffees. Don't pull up on the lever too fast or you'll limit your shot volume, I try to take at least 5 seconds.

You'll need a short scale and cup to fit under the grouphead, I use a Lunar now but a Weightman style scale works as well. It can be hard to find cups short enough, I like Inker Ischias, they stopped making them a while ago but some deadstock cups have been popping up on eBay recently. Don't be afraid to underdose the baskets, I put 16 grams in the 18's as I found that anymore would overfill them. A funnel makes puck prep a lot easier, especially a tamp-through one. I've been using one from creativewerks, but I have a 49mm Sworks funnel on pre-order. Wouter just released one as well but it looks too short to me.

The CT2 makes experimenting with water recipes extremely easy, I recommend trying some out and seeing what you prefer.

#462: Post by **truemagellen** » May 24th, 2022, 9:37 pm

Chrikelnel wrote:Keep the lid on while brewing to increase temperature stability, it seems like most people do these days but there's a few holdouts. .

Early machines didn't have lids. I finally bought one for my ES3 but it isn't a perfect fit so I modified it.

#463: Post by **Chrikelnel** » May 30th, 2022, 12:21 am

Does anyone have the weight to bars numbers for the Strietman? I found an analog scale and thought I'd see what pressure I'm really pulling at.

#464: Post by **renatoa** » May 30th, 2022, 2:51 am

You should first find the piston area, from the diameter.
Let's assume it is 49mm, but it's smaller. Using 49 just for example.
Area = PI * diameter^2 / 4 = 18.9 square cm. 1 bar = 1kg per square cm.
So you need about 19 kg for one bar, 114 kg for 6 bars, 170 kg for 9 bars. A baby elephant would do this job

Kidding, this is the force to be applied on piston shaft, we have a lever there, with a reason...

Next you should compute the leverage ratio, as the ratio between the the short arm of the lever and the full length, from rotation point to handle.
Lets use 1/10, as for Pavoni, so 17 Kg is the force you need to apply at the handle for 9 bars.

#465: Post by **John49** » May 30th, 2022, 7:31 am

Chrikelnel wrote:Does anyone have the weight to bars numbers for the Strietman? I found an analog scale and thought I'd see what pressure I'm really pulling at.

OK. The mechanical advantage, if you apply the force at the very end of the handle is
38.5 cm/5 cm = 7.7. The piston radius is 2 cm so the area of the piston is 1.948 square inches (my scale is in lbs). 9 bar = 130.5 psi
F = P X A = 130.5 X 1.948 = 254 lbf and the lever load (scale under the CT2) is 254/7.7 or 33 lb.

#466: Post by **renatoa** » May 30th, 2022, 7:38 am

The piston diameter is 2 cm...

Maybe the radius...

What scale can be used to be placed under the machine, to measure piston applied force ?
The bathroom scales here are mostly limited to 120 kg...

May the force...

#467: Post by **John49** » May 30th, 2022, 9:38 am

Oops yes, 2 cm radius.

#468: Post by **Chrikelnel** » May 31st, 2022, 1:00 am

Thank you both for the math! I pulled my first shot on the scale tonight and with one arm pushing pretty hard I peaked at 38 pounds. I don't usually pull that hard for most shots but I was surprised at how high it got, I hadn't been sure if I've been coming close to 9 bars but I guess I have been. Going to try and get a feel for 3, 6, and 9 bars while I'm using the scale and hopefully avoid the impulse to buy a gauge.

#469: Post by **erik82** » June 2nd, 2022, 10:47 am

Just buy the gauge as it makes everything so much easier. I wouldn't want to live without it as I can pull every profile I want with great ease. And as the shot progresses flow and pressure becomes a bit different so I don't know how good that method works. I made over 1000 shots without the gauge but after I bought and installed it my espresso became even better as you're totally in control and no more guessing.

#470: Post by **renatoa** » June 2nd, 2022, 11:28 am

renatoa wrote:...so 17 Kg is the force you need to apply at the handle for 9 bars.

Chrikelnel wrote:Thank you both for the math! I pulled my first shot on the scale tonight and with one arm pushing pretty hard I peaked at 38 pounds.

38 pounds = 17.24 kg... pretty darn close...

You can do it different, and a bit smarter, imo... instead a bore in the piston and all that circus... given the amazing good guesstimation above, about the pressure and lever applied force, a $5 worth 50 kg luggage scale load cell (i.e. sensor) can be adapted inside the lever handle, and having under your eyes permanently the force measurement during extraction.
I means something like the attached image. It works for pushing forces too, already done something similar.