Making a replica of Durst RCP 20

[arturo_rs]

This is an update of the project:

I am taking inspiration from paper processors such as the Durst RCP, the Fujimoto CP31/CP32, and also current Colenta brand processors.


Initially, the problem was the gears and the dimensions. That has now been solved.


The roller shafts will use 6 mm 316 stainless steel rods. From 6 to 10 mm I will 3D print the components. From 10 up to the final 22 mm I will use NBR foam rollers used in refrigeration. With the latter, I have carried out some fairly rough chemical resistance tests over several days. The result: it resists very well, and since it is also very cheap at €0.41/m, it can be replaced if necessary.


The motor that will drive the gears is a NEMA17 using a TMC2209 driver, which allows for virtually silent operation. For communication I will use UART.


Regarding the submersible heating element, I am considering several options: passivated 304 stainless steel using citric acid, 316 stainless steel, or steel with a PTFE coating. I am also in contact with Alibaba sellers on this matter.


Regarding the pump that moves the liquid (developer and bleach-fix), I will use magnetic pumps such as the MP-6RM or MP-10RN, which are the same ones used in the Fujimoto CP31.


To reduce friction, I will use PP bearings on the roller shafts.


I will try to avoid using screws and nuts. I have carried out tests and corrosion appears very clearly within two days.


The liquid pumps, heating elements, and NEMA17 motors will be controlled by an ESP32-S3 or an STM32F411, using zero-cross SSR relays and implementing PID control. I still need to think through several aspects. The idea is to connect via WiFi and be able to control the processor and adjust parameters in real time.


Screens and indicator lights are ruled out.


The outer casing will be made of PETG. The tank and other parts that come into contact with chemicals will be made of PCTG.


I will soon begin the first tests of paper transport through the rollers. After that, I will move on to full transport tests through the tank using water.


I will keep you updated...

 

[koraks]

Very interesting, looking forward to how the project unfolds!
Personally I'd try to avoid printing too large objects because it takes such a massive amount of time. I.e. the rollers and outside housing. For the rollers I can see the reasoning of a printed 'interface' layer to bridge the gap between the shafts and the rubber liners; I've done some very brief testing with something along those lines to rebuild RCP20 rollers using heat shrink tubing for the outer layer, but I've never tested the concept for chemical resistance. One concern is that chemistry gets trapped in the printed part or between the printed part and the other parts, although maybe that's not all that much of a concern. However, also stainless steel will corrode at some point.

Did you try to find a suitable tub or tank that could be used as the basis for an outer casing? Perhaps it's possible to use a series of 3 tubs for which you manufacture inserts that act as frames for your additions. This way you could rely on the pre-manufactured parts for the waterproof outer layer and probably dramatically cut down print times. It's just a thought; I haven't done any design studies on it or anything.

The rest of your choices seem kind of sensible when taken at face value, although I wonder why you'd want to use a stepper motor to drive the whole thing. It's not like you really need the stepping function, so you'd essentially be using a stepper as if it's a continuous motor. I mean, it'll work (it has been done), but...why?

 

[arturo_rs]

I’m going to print everything in 3D because I want a specific geometry. I want it to fit perfectly with the roller rack geometry while also using a maximum of 4 to 5 liters of chemistry.


I want a very compact and externally simple block. Since 3D prints cannot be that large—because I’m planning to develop 20×30 cm sheets—I’ll print it in sections and then join them with two-component epoxy, as well as external nuts and bolts. I’ve also considered applying a thin internal epoxy coating for chemical resistance, although that is not fully decided yet.


Yes, if the heat-shrink tubing is made of polyolefin, it holds up well against RA-4 chemistry.


Regarding the motor: silent operation and very precise motion. Also, if I use multiple motors that are not mechanically linked on the same shaft, I can synchronize their RPM so they run in unison. The TMC2209 using UART also has several advantages, such as detecting paper jams and adjusting the current (mA) to provide more or less torque. I can also make them rotate in reverse, which would make clearing paper jams easier. I’ve already calculated the gears, their modules, and tooth counts as well.

In the future, I also have some ideas about implementing a replenishment system using peristaltic pumps.

 

[koraks]

I have doubts about your motor requirements resulting in the choice for a stepper motor, but it's your project!

 

[thinkbrown]

I have doubts about your motor requirements resulting in the choice for a stepper motor, but it's your project!

There's a lot to be said for just how cheap and available stepper motors and drivers are thanks to the 3d printing industry

 

[koraks]

There's a lot to be said for just how cheap and available stepper motors and drivers are thanks to the 3d printing industry

I understand the line of reasoning, but check how cheap and available sync motors are. A Nema17 costs easily 3-5x as much, without a driver. A sync motor is also easy to drive by simply switching it with a MOSFET. A simple H-bridge can be used for forward + reverse.

However, everyone throws steppers into every project nowadays so it's kind of the hammer & nail scenario. It'll work; you can also use a forklift to move the living room couch.

 

[gordrob]

I have a box of parts from a The Durst RCP 40 that I salvaged when my unit packed it in. If there are any specific Durst parts that are common to the two machine that you are looking for send me a PM and I will see what I have.

 

[arturo_rs]

I understand the line of reasoning, but check how cheap and available sync motors are. A Nema17 costs easily 3-5x as much, without a driver. A sync motor is also easy to drive by simply switching it with a MOSFET. A simple H-bridge can be used for forward + reverse.

However, everyone throws steppers into every project nowadays so it's kind of the hammer & nail scenario. It'll work; you can also use a forklift to move the living room couch.

Nema17 and TMC2209 for 8€ at AliExpress

 

[arturo_rs]

I have a box of parts from a The Durst RCP 40 that I salvaged when my unit packed it in. If there are any specific Durst parts that are common to the two machine that you are looking for send me a PM and I will see what I have.

Now I am just taking inspiration not an specific measurement. Thank you, by the way

 

[mshchem]

If you want to develop 8"x10" and smaller, get a print basket for the 1 gallon stainless tanks. IIRC these baskets hold 8-10 sheets. 10 sheets, approximately 2 minutes to get through develop stop blix.

 

[mshchem]

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