DIY Color RA4 Processor "RePrinto" A "Modern" Durst Printo clone

[elgatosuizo]

Hi everyone,

I wanted to share a project I’ve been working on: a modular, DIY-friendly RA-4 paper processor named RePrinto. Inspired by the classic Durst Printo, this is not a 1:1 replica, but rather a modern reinterpretation using 3D-printed parts, off-the-shelf components, and open hardware principles. So these here re not parts compatible with the original Printo.

As a student in the early 90s, I did some color printing when RA-4 chemistry became more accessible. After a long break, I got back into analog photography a few years ago – encouraged by my daughter, who also learned C-41 and RA-4 processing. One day, she asked me if there wasn’t an easier way to develop color prints at home (the annoying full darkness and tray temperature). I remembered those cool tabletop processors from Durst and Ilford – the kind I couldn’t afford as a student. I looked around and found the Durst Printo again… but even second-hand units were surprisingly expensive (when you find one...).

That’s when the idea struck: could I build something similar myself? I already built large format enlargers and some darkroom gear. My idea was to have:

• A modular RA-4 paper processor with at least 2 stages, but expandable up to 5.... and a feeding module.
• Fully 3D-printable parts, with standard aluminum tubing and PETG.
• Transport via 8+2 rollers (like in the Printo), using shrink tube for grip.
• Target processing time: base ~45 seconds per module, continuous feed, with option for other processing times with digital controlled motor.
• Compact and affordable – and free to use or adapt (non-commercial license)

As I had not Printo to look into, I only used the pictures, manual I could find online and the pictures from the (expired) original patent.

My Challenges & Solutions:

• Rollers: I used 20 mm aluminum tubing (for electrical installation) and found heat-shrink grip tubing (originally meant for sports equipment) to simulate the original rubber coating. The foam squeeze rollers were made from pipe insulation over 10 mm rods.
• Gearing: Durst used a custom pitch – I standardized on module 2 gears (with wide pressure angle) for the rollers and module 1.5 for the motor drive train. All gears are 3D printed. The swappable gears for speed change are not needed.
• Transport Mechanism: I designed roller ends with brass bushings (instead of ball bearings, which don’t survive RA-4 chemicals). A NEMA 17 stepper motor drives the system with a calculated gear ratio to achieve a precise and variable speed (no gear swapping needed).
• Paper Guides: In the original Printo these are made out of molded plastic (even integrated in the tray) or stainless steel. I designed 3D printed guides the will be trated with epoxy resin to be smooth.
• Heating: A small aquarium heater brings the fluids up to 35 degrees (Celsius) and have already all the needed temperature regulation built in.
• Materials & Printing: PETG was the obvious choice for water/chemical resistance. It’s tricky to print cleanly – most parts needed post-adjustment due to PETG’s shrinkage and tolerances. Also, I designed everything support-free for better quality and easier printing.
• First tests: The prototype already works with real RA-4 paper and water. The routing of the paper is working too. No chemistry yet – but the transport is smooth, consistent, and even handles wet paper well.

3D Considerations: I print on a 400×400×450 mm printer, but I’m working to downscale parts to fit 220×220×250 mm beds, so others can easily replicate the project. Printing one module takes weeks (PETG is ultra slow in print speed) and even more when testing is included.

Next steps:

• Build a second and third process module.
• Add the feed-in module and finalize light-tight features.
• Begin tests with actual chemistry.
• Publish files and documentation on GitHub (soon).
• Create BOM with part sources and instructions.

This is still very much a work in progress, but I’ll post updates as things evolve. I’d love to hear your feedback – especially if you’ve ever used the original Durst Printo or built something similar.

Cheers. Marco

 

[koraks]

That's very cool stuff! I thought about something like this, but as with so many ideas, I never even moved to a paper napkin stage, let alone anything remotely resembling getting stuff done. It doesn't help (or perhaps, it does) that I have the luxury of having a few tabletop processors, so I've never had the need to tackle this issue.

Congrats on this project; it looks great!

I do have a concern about the heat-shrinked aluminum rollers. I wonder to what extent it'll prove to be possible to protect the aluminum from the RA4 developer. I suspect the aluminum will survive the blix for the most part, but the developer will corrode it, and it'll be a pretty fast process that will likely also affect the developer itself. So I think you'll ensure that there's absolutely no way the developer can make its way to the aluminum.
Edit: the blix will actually also dissolve the aluminum.

The Printo does not use a foam roller; this was used on e.g. the RCP machines and it's a known wear item. Nothing inherently wrong with using one, of course. It's an effective way to make a swift transition from the developer to the stop bath.

I notice you printed the tub as well; have you considered using a stock item (some kind of storage box, tray, etc.) as a starting point? I'm asking because that would bring print time way down and it would also mean less of a headache trying to waterproof the whole thing. Then again, it'd make the project dependent on a 3rd party stock item, so there's pros & cons involved.

Also, as the owner of a Printo, I can attest to the many, many similarities between your project and the original device!

 

[elgatosuizo]

That's very cool stuff! I thought about something like this, but as with so many ideas, I never even moved to a paper napkin stage, let alone anything remotely resembling getting stuff done. It doesn't help (or perhaps, it does) that I have the luxury of having a few tabletop processors, so I've never had the need to tackle this issue.

Congrats on this project; it looks great!

I do have a concern about the heat-shrinked aluminum rollers. I wonder to what extent it'll prove to be possible to protect the aluminum from the RA4 developer. I suspect the aluminum will survive the blix for the most part, but the developer will corrode it, and it'll be a pretty fast process that will likely also affect the developer itself. So I think you'll ensure that there's absolutely no way the developer can make its way to the aluminum.
Edit: the blix will actually also dissolve the aluminum.

The Printo does not use a foam roller; this was used on e.g. the RCP machines and it's a known wear item. Nothing inherently wrong with using one, of course. It's an effective way to make a swift transition from the developer to the stop bath.

I notice you printed the tub as well; have you considered using a stock item (some kind of storage box, tray, etc.) as a starting point? I'm asking because that would bring print time way down and it would also mean less of a headache trying to waterproof the whole thing. Then again, it'd make the project dependent on a 3rd party stock item, so there's pros & cons involved.

Also, as the owner of a Printo, I can attest to the many, many similarities between your project and the original device!

I was partially aware of this, but now that you are saying this I see that it was a bit to much out of my sight. I will consider alternative materials. I guess the rollers can be made water tight, but the 8mm axes of the rollers and gears are actually made out of alluminium too. Brass it's not good for the blix, so I will see if PVC rods will do the job. Even for the rollers PVC could be an option. Existing storage boxes would be fine, but it's hard to find the right dimensions.

 

[koraks]

PVC rollers may work; the main question is whether they'll be rigid enough also at process temperature. There's quite some work done by several people in attempts to rebuild or refurbish the Durst RCP rollers, which are notorious for corrosive self-destruction (I can personally attest to this). One scenario I've considered and that may work for you as well is to start with a standard let's say 6mm stainless steel rod, print a cylindrical sleeve that fits over it and then line that on the outside with heat-shrink tubing. A friend of mine is test-running heat shrink tubing over other types of rollers; I'm not sure what the progress is on that, but I've not hear any stories about smoke & explosions yet. The question is how durable the heat shrink stuff will be over time, but it's not too bad if it lasts for maybe a few months or a few years as it's easy to replace.

Existing storage boxes would be fine, but it's hard to find the right dimensions.

I'd be inclined to work the other way around and start with a box of roughly the right size and then build the machine on that basis. However, there's a potential challenge with chemistry economy. One thing the Durst machines do very well, is being economical. An RCP20 or 30cm Printo both run on just 2.5L of chemistry, which isn't a whole lot if you think about it. It's actually pretty challenging to top that. Maybe if you used PVC drain pipe as a basis for the tank; cut it in half lengthwise and waterproof it on both ends so you end up with a trough. That might be pretty efficient.

 

[elgatosuizo]

PVC rollers may work; the main question is whether they'll be rigid enough also at process temperature. There's quite some work done by several people in attempts to rebuild or refurbish the Durst RCP rollers, which are notorious for corrosive self-destruction (I can personally attest to this). One scenario I've considered and that may work for you as well is to start with a standard let's say 6mm stainless steel rod, print a cylindrical sleeve that fits over it and then line that on the outside with heat-shrink tubing. A friend of mine is test-running heat shrink tubing over other types of rollers; I'm not sure what the progress is on that, but I've not hear any stories about smoke & explosions yet. The question is how durable the heat shrink stuff will be over time, but it's not too bad if it lasts for maybe a few months or a few years as it's easy to replace.


I'd be inclined to work the other way around and start with a box of roughly the right size and then build the machine on that basis. However, there's a potential challenge with chemistry economy. One thing the Durst machines do very well, is being economical. An RCP20 or 30cm Printo both run on just 2.5L of chemistry, which isn't a whole lot if you think about it. It's actually pretty challenging to top that. Maybe if you used PVC drain pipe as a basis for the tank; cut it in half lengthwise and waterproof it on both ends so you end up with a trough. That might be pretty efficient.

Thank you so much for your help! I’ve done a bit of "research" at our local home improvement retailer. I found 20 mm water pipes rated for 95 °C, so I guess deformation at 34–35 °C processing temperature won’t be an issue. They’re quite rigid too. I think the softening point of the pipe is around 120–140 °C. If I insert a wooden rod during the heating process, it should stay dimensionally stable while shrinking. With a 25 mm shrink tube I might not even need to heat that much.

I’m fairly confident that I could also seal the aluminum rollers properly if I dip the tube ends 10 mm into the right sealant (epoxy resin or some PU-based primer). I possible I run some tests and submerge them, maybe in a high-alkaline solution (Sodium hydroxide) to see what happens. Another issue I’ve re-discovered thanks to my "material compatibility amnesia" are the brass bearings I use – these will definitely be eaten by the Blix. I’ll replace them with nylon, some other polymer, or maybe just go with a hole in the PETG wall.

For the rotation axles I’ll need a solid solution. I may not get around using stainless steel (I bought a rod and will test how it goes), but I also have an idea to print the axles in PETG and reinforce them with a metal core to prevent breaking. Maybe a stainless steel M4 threaded rod – it’s way cheaper than a precision-ground one. Right now, the axles don’t run through the whole roller: I’m only using two stubs at the ends, inserted into a printed endcap that seals the 20 mm aluminum tube.

High cylindrical prints with small diameter (<60mm) are risky: no printer handles them well unless you go ultra slow, and even then small shifts can happen due to wobble. Adding supports might help, though.

That’s actually the spirit of these kinds of DIY projects – it’s always the unexpected things (even if they’re entirely my own fault) that turn into problems. But that’s also the fun part: trying to solve them. I’ll use the current build for some water-based testing anyway. Many parts will still be reusable, no matter what. Thanks again for sharing your ideas.

 

[Neal]

Nice!

 

[koraks]

I found 20 mm water pipes rated for 95 °C

Is this PEC (usually white)? What may be a problem with PEC is that it bends fairly easily (which is nice for its intended purpose) - so it's difficult to keep it nice and straight. You may find a PEC-based roller will easily start to wobble even if it starts out straight. You could 3D print something around it to prevent this from happening, but you're pretty much back to the lined-steel concept, just replacing the steel with something else. The other material commonly used here for water lines is copper, which is evidently unfit in this case.

I’m fairly confident that I could also seal the aluminum rollers properly if I dip the tube ends 10 mm into the right sealant (epoxy resin or some PU-based primer).

This is essentially how the original Durst/Termaphot rollers were also made. In that case, some kind of plastic/polymer lining was fitted over the ends of the rods. Ultimately, that failed; I'm not sure whether it's just due to creepage (the lining only extended for a short length IIRC) or the more aggressive nature of the RA4 chemistry compared to the perceding chemistry for which the older RCP machines were originally made.
Anyway, I find the main challenge with this approach is to not damage the sealant when further assembling the rollers. There may also be challenges with the processor when it's opreating, with the lining potentially getting damaged by the roller working against its bearing. Not necessarily deal-breaker problems, but things to keep in mind when working out a solution.

Testing would be a good idea and indeed a solution of sodium hydroxide (something like 1-5% will do just fine for this) can be a good test. You'll notice if everything holds up well if there are absolutely no bubbles coming from the rods. As aluminum corrodes under influence of hydroxide, hydrogen gas is released, which is an easy way to tell whether this is happening as long as everything is kept submerged.

Your plans for the axes, rods & bearings sound fine to me; it's a matter of trying a couple of things out, I think. Around here, 6mm stainless steel rods are pretty affordable; if you just use stubs, the material costs will be minimal.

As to print quality - I've always had trouble printing something that was watertight to begin with, LOL! I tried printing stops for the drain tubes on my Printo and miserably failed. So you're miles ahead of me anyway!

 

[RalphLambrecht]

Hi everyone,

I wanted to share a project I’ve been working on: a modular, DIY-friendly RA-4 paper processor named RePrinto. Inspired by the classic Durst Printo, this is not a 1:1 replica, but rather a modern reinterpretation using 3D-printed parts, off-the-shelf components, and open hardware principles. So these here re not parts compatible with the original Printo.

As a student in the early 90s, I did some color printing when RA-4 chemistry became more accessible. After a long break, I got back into analog photography a few years ago – encouraged by my daughter, who also learned C-41 and RA-4 processing. One day, she asked me if there wasn’t an easier way to develop color prints at home (the annoying full darkness and tray temperature). I remembered those cool tabletop processors from Durst and Ilford – the kind I couldn’t afford as a student. I looked around and found the Durst Printo again… but even second-hand units were surprisingly expensive (when you find one...).

That’s when the idea struck: could I build something similar myself? I already built large format enlargers and some darkroom gear. My idea was to have:

• A modular RA-4 paper processor with at least 2 stages, but expandable up to 5.... and a feeding module.
• Fully 3D-printable parts, with standard aluminum tubing and PETG.
• Transport via 8+2 rollers (like in the Printo), using shrink tube for grip.
• Target processing time: base ~45 seconds per module, continuous feed, with option for other processing times with digital controlled motor.
• Compact and affordable – and free to use or adapt (non-commercial license)

As I had not Printo to look into, I only used the pictures, manual I could find online and the pictures from the (expired) original patent.

My Challenges & Solutions:

• Rollers: I used 20 mm aluminum tubing (for electrical installation) and found heat-shrink grip tubing (originally meant for sports equipment) to simulate the original rubber coating. The foam squeeze rollers were made from pipe insulation over 10 mm rods.
• Gearing: Durst used a custom pitch – I standardized on module 2 gears (with wide pressure angle) for the rollers and module 1.5 for the motor drive train. All gears are 3D printed. The swappable gears for speed change are not needed.
• Transport Mechanism: I designed roller ends with brass bushings (instead of ball bearings, which don’t survive RA-4 chemicals). A NEMA 17 stepper motor drives the system with a calculated gear ratio to achieve a precise and variable speed (no gear swapping needed).
• Paper Guides: In the original Printo these are made out of molded plastic (even integrated in the tray) or stainless steel. I designed 3D printed guides the will be trated with epoxy resin to be smooth.
• Heating: A small aquarium heater brings the fluids up to 35 degrees (Celsius) and have already all the needed temperature regulation built in.
• Materials & Printing: PETG was the obvious choice for water/chemical resistance. It’s tricky to print cleanly – most parts needed post-adjustment due to PETG’s shrinkage and tolerances. Also, I designed everything support-free for better quality and easier printing.
• First tests: The prototype already works with real RA-4 paper and water. The routing of the paper is working too. No chemistry yet – but the transport is smooth, consistent, and even handles wet paper well.

3D Considerations: I print on a 400×400×450 mm printer, but I’m working to downscale parts to fit 220×220×250 mm beds, so others can easily replicate the project. Printing one module takes weeks (PETG is ultra slow in print speed) and even more when testing is included.

Next steps:

• Build a second and third process module.
• Add the feed-in module and finalize light-tight features.
• Begin tests with actual chemistry.
• Publish files and documentation on GitHub (soon).
• Create BOM with part sources and instructions.

View attachment 400526 View attachment 400531 View attachment 400532 View attachment 400530 View attachment 400527 View attachment 400528 View attachment 400529



This is still very much a work in progress, but I’ll post updates as things evolve. I’d love to hear your feedback – especially if you’ve ever used the original Durst Printo or built something similar.

Cheers. Marco

applaus!

 

[Lachlan Young]

PVC rods will do the job. Even for the rollers PVC could be an option.

Chemical grade PVC is about as good an option as possible for resilience against photo chemicals - with 316 stainless (or better) for metal parts. The SPSE handbook has an extensive table covering materials suitable for processor construction.

Printers' engineers will be able to make roller squeegees of the right durometer & chemical resistance on a suitable core that you supply.

 

[mshchem]

Fascinating. Welcome to the forum!!!

 

[koraks]

Printers' engineers will be able to make roller squeegees of the right durometer & chemical resistance on a suitable core that you supply.

Kind of cost-prohibitive for a hobby project, though. At least last time I checked. Recoating existing rollers with a suitable PU lining was north of €40 per piece. Costs won't be much lower if you supply a brand new rod/core. It might be worth it if you order a batch size of 1000pcs or so in China.

 

[elgatosuizo]

Kind of cost-prohibitive for a hobby project, though. At least last time I checked. Recoating existing rollers with a suitable PU lining was north of €40 per piece. Costs won't be much lower if you supply a brand new rod/core. It might be worth it if you order a batch size of 1000pcs or so in China.

I was thinking the same. The spirit of my project is to make everything affordable and DIY-like. Building an industrial grade Printo copy is not really the goal here. In the meantime I think I have a valid axes material altarnative by printing them in PETG with a metal core. I made a fist test and it seems a possible solution. I will consider POM rods too as option. Another problem are the brass bushings I'm using: The alloy is a bit more chemical ressiatant than plain brass, but RA4 chemistry is really too aggressive for these. I will see if I find precise POM or stainless steel ones.

 

[koraks]

Yeah, sounds sensible; we're on the same page. Given where you are now, I'm convinced you're going to get this to work. I'm already looking forward to the point where the first people start copying your project and the whole issue of unobtainable table-top processors starts to solve itself!

 

[Lachlan Young]

Kind of cost-prohibitive for a hobby project, though. At least last time I checked. Recoating existing rollers with a suitable PU lining was north of €40 per piece. Costs won't be much lower if you supply a brand new rod/core. It might be worth it if you order a batch size of 1000pcs or so in China.

Maybe so - but they are arguably the most failure-prone part in the machine, and bodging them seems like a false economy (at least beyond working prototype) on something that as it already stands has the potential to at least equal the Printo if not outright better it - especially because I'd like to see this project succeed well enough that a version of the 20" Printo becomes feasible too.

 

[koraks]

I think you're losing sight of the crucial bit of information here:

The spirit of my project is to make everything affordable and DIY-like. Building an industrial grade Printo copy is not really the goal here.

Anyway, since the building plans are apparently going to be published, nobody will be stopped from having their own super-durable rollers made if they so desire.

 

[elgatosuizo]

I think you're losing sight of the crucial bit of information here:


Anyway, since the building plans are apparently going to be published, nobody will be stopped from having their own super-durable rollers made if they so desire.

Correct. My words.

 

[elgatosuizo]

An update. After some research, I have compared the RA4 compatibility of various materials. I am certain that there will be no problems with PETG and heat-shrink tubing. Sealing the 3D prints with epoxy is also compatible.

As it turns out, exposed aluminium and brass are not suitable at all. I am now proceeding with two variants consisting of partial solutions that can be combined with each other:

- PETG 3D-printed rotation axes (with metal core) and a phenolic epoxy (the classic rust converter sprays) coating (2x) on the aluminium tubes of the transport rollers. This will then be sealed with silicone at the end and covered with a heat-shrinkable tube. This gives me almost triple protection. The bearings will be made of stainless steel rings (both solutions have this in common).

- POM (derlin) axles and 316 stainless steel tubes for the rollers. I will order these in 250 mm lengths, but I don't necessarily need grip on the 2.6 cm at the end of each roller. So I will make the PETG end caps longer and it should work. Then I will put heat-shrink tubing on them. Bearings – as mentioned – with stainless steel rings.

The cost of the second option is around 30-50% higher, but still within the DIY-range.

The question is whether the aquarium heater will survive the RA4 (it has an unknown housing, but it may be aluminium). However, this problem can also be solved with an epoxy coating. Glass/plastic aquarium heaters would be better, but they are more bulky.

If everything will work out I think a 50cm/20" Version could be possible. But this is for the future. Still a lot of challenges till there.

 

[skaSmith]

Hi everyone,

I wanted to share a project I’ve been working on: a modular, DIY-friendly RA-4 paper processor named RePrinto. Inspired by the classic Durst Printo, this is not a 1:1 replica, but rather a modern reinterpretation using 3D-printed parts, off-the-shelf components, and open hardware principles. So these here re not parts compatible with the original Printo.

As a student in the early 90s, I did some color printing when RA-4 chemistry became more accessible. After a long break, I got back into analog photography a few years ago – encouraged by my daughter, who also learned C-41 and RA-4 processing. One day, she asked me if there wasn’t an easier way to develop color prints at home (the annoying full darkness and tray temperature). I remembered those cool tabletop processors from Durst and Ilford – the kind I couldn’t afford as a student. I looked around and found the Durst Printo again… but even second-hand units were surprisingly expensive (when you find one...).

That’s when the idea struck: could I build something similar myself? I already built large format enlargers and some darkroom gear. My idea was to have:

• A modular RA-4 paper processor with at least 2 stages, but expandable up to 5.... and a feeding module.
• Fully 3D-printable parts, with standard aluminum tubing and PETG.
• Transport via 8+2 rollers (like in the Printo), using shrink tube for grip.
• Target processing time: base ~45 seconds per module, continuous feed, with option for other processing times with digital controlled motor.
• Compact and affordable – and free to use or adapt (non-commercial license)

As I had not Printo to look into, I only used the pictures, manual I could find online and the pictures from the (expired) original patent.

My Challenges & Solutions:

• Rollers: I used 20 mm aluminum tubing (for electrical installation) and found heat-shrink grip tubing (originally meant for sports equipment) to simulate the original rubber coating. The foam squeeze rollers were made from pipe insulation over 10 mm rods.
• Gearing: Durst used a custom pitch – I standardized on module 2 gears (with wide pressure angle) for the rollers and module 1.5 for the motor drive train. All gears are 3D printed. The swappable gears for speed change are not needed.
• Transport Mechanism: I designed roller ends with brass bushings (instead of ball bearings, which don’t survive RA-4 chemicals). A NEMA 17 stepper motor drives the system with a calculated gear ratio to achieve a precise and variable speed (no gear swapping needed).
• Paper Guides: In the original Printo these are made out of molded plastic (even integrated in the tray) or stainless steel. I designed 3D printed guides the will be trated with epoxy resin to be smooth.
• Heating: A small aquarium heater brings the fluids up to 35 degrees (Celsius) and have already all the needed temperature regulation built in.
• Materials & Printing: PETG was the obvious choice for water/chemical resistance. It’s tricky to print cleanly – most parts needed post-adjustment due to PETG’s shrinkage and tolerances. Also, I designed everything support-free for better quality and easier printing.
• First tests: The prototype already works with real RA-4 paper and water. The routing of the paper is working too. No chemistry yet – but the transport is smooth, consistent, and even handles wet paper well.

3D Considerations: I print on a 400×400×450 mm printer, but I’m working to downscale parts to fit 220×220×250 mm beds, so others can easily replicate the project. Printing one module takes weeks (PETG is ultra slow in print speed) and even more when testing is included.

Next steps:

• Build a second and third process module.
• Add the feed-in module and finalize light-tight features.
• Begin tests with actual chemistry.
• Publish files and documentation on GitHub (soon).
• Create BOM with part sources and instructions.

View attachment 400526 View attachment 400531 View attachment 400532 View attachment 400530 View attachment 400527 View attachment 400528 View attachment 400529



This is still very much a work in progress, but I’ll post updates as things evolve. I’d love to hear your feedback – especially if you’ve ever used the original Durst Printo or built something similar.

Cheers. Marco

Wow, Marco! I remember those Printo units, boy, did I want a set! Thank you, I'll keeping an eye on this.

 

[armadsen]

This looks amazing! I'm excited to keep an eye on your progress. I've wanted to start color printing (I've never done it, only B&W), and maybe it'd be fun to build one of your units after you've finished it and published everything.