Midtone Machines - Automatic Film Processing Machine

[Duolab123]

For a variety of reasons I'm currently going to use pinch valves, essentially the valve is a section of silicone tube that is squished to prevent flow. It's a fairly common technique in medical/chemical applications where pressures are very low and chemical compatibility and a lack of trapped volume or places where contamination can collect is important.

I feel they're good for this application for the following reasons:

- Based on the design I need a valve that positively blocks flow in both directions, common direct acting solenoid valves tend to only really block flow in one direction and will pop open when pressurised in the reverse direction, which I can't have in this case
- Pinch valves are quite simple and there is no material exposed to the process fluid other than the tube material
- They don't trap any fluid volume or present any cavities where deposits could form, which is good for minimising potential chemical contamination

The tube itself should be good for several hundred thousand cycles (potentially ~ 1 million rolls of film) and replacement should be easy and cheap.

That's a good idea. Silicone should work well with dilute photo chemicals. I would double check it with E6 color developer. Decades ago, when I was a analytical chemist I tried to transfer cool 35% NaOH with Silicone tubing. Very dumb.

[Duolab123]

Here's a possibility dumb idea. Could you transfer chemistry by gravity. To use "cock" the tanks in a up position, manually. After dispensing, trigger a latch that would drop the chemistry bottle below the developing tank.
The chemistry could syphon in and out pretty quickly????

Another point from working in a laboratory with silicone tubing, be careful of pressure. The tubing gets slippery.

[AndrewBurns]

Peristaltic pumps? I used them with salt-water aquariums for years. The maintenance boils down to replacing the tubing every few years.

Same principal as peristaltic pumps except just closing or opening the tube rather than pumping liquid. Not using peristaltic pumps for the actual pump part of the machine because they're not commonly available with a flow rate as high as I'd like (the slower the fluid transfer into/out of the develop tank the higher the possibility of uneven development).

That's a good idea. Silicone should work well with dilute photo chemicals. I would double check it with E6 color developer. Decades ago, when I was a analytical chemist I tried to transfer cool 35% NaOH with Silicone tubing. Very dumb.

Will check it out, but yeah on the whole standard photochemicals are pretty benign.

Here's a possibility dumb idea. Could you transfer chemistry by gravity. To use "cock" the tanks in a up position, manually. After dispensing, trigger a latch that would drop the chemistry bottle below the developing tank.
The chemistry could syphon in and out pretty quickly????

Another point from working in a laboratory with silicone tubing, be careful of pressure. The tubing gets slippery.

Definitely sounds possible but a lot less flexible as a system and probably more complicated and expensive than just using a pump. I know some people want to use chemicals from large bulk containers for example, which is easy if you can pump up from below the machine but you're not going to be swinging large tanks of liquid up and down easily.

Yeah as far as pressure goes although the pump is capable of generating reasonable pressure it should never have to as it's only ever pumping into containers that are vented to atmosphere. It's a good point though, I might have to think of adding a pressure relief valve though in the failure-case where one of the valves has broken and the pump is trying to pump through it.

[Duolab123]

I hope it all works out. I like the idea of using the bottom half of the tank as a "trough" of sorts to spin the reels in. I have a bunch of Jobo stuff, my littlest is my dear little Duolab, it only spins in one direction, but if you're only developing a couple rolls of film it works perfectly well. It's about the size of a old typewriter. The heater is from a Mr. Coffee type pot. Couldn't cost more than a couple bucks.

Something about that size would be great. Paterson reels are great, but make no provision for loading 2 rolls of 120 on one reel, it can be done but it's tricky. For 35mm Paterson are unbeatable.

[AndrewBurns]

New post is up, showing off some 3D printed parts I got for fit-checking the develop tank and a few other parts of the machine:

http://midtonemachines.com/news/3d-printed-goodies/

Everything is fitting together pretty nicely and looks like it should work fine, so some good solid progress!

[Duolab123]

Looks pretty neat. It would be great if the market was big enough to justify injection molding tooling. You could make 10,000 tanks in a week or two. There's so darn much used stuff out there, even the new darkroom products typically use decades old tooling.
Keep going!
Best Regards Mike

[AndrewBurns]

Looks pretty neat. It would be great if the market was big enough to justify injection molding tooling. You could make 10,000 tanks in a week or two. There's so darn much used stuff out there, even the new darkroom products typically use decades old tooling.
Keep going!
Best Regards Mike

Cheers. I got some quotes early on and once you include tooling costs it seems that the cross-over point where injection molding starts to make sense is about 350 parts. Honestly I'm not sure I'll be selling that many machines but who knows, once I have working prototypes I might use Kickstarter to see how much interest there is and if I get enough I might go down that road.

[calebarchie]

Just a thought; since the design of the tank is pretty much identical to the phototherm, perhaps you should also make it compatible? Just retrofit the probes and contacts and sell the same part as a replacement tank?

There would be even more interest and users to justify that volume if you did so. I have a phototherm machine and willing to assist with design and testing if you decide to do so.

[AndrewBurns]

Just a thought; since the design of the tank is pretty much identical to the phototherm, perhaps you should also make it compatible? Just retrofit the probes and contacts and sell the same part as a replacement tank?

There would be even more interest and users to justify that volume if you did so. I have a phototherm machine and willing to assist with design and testing if you decide to do so.

Yeah it's very similar to the Phototherm. I originally wanted to go along a different route but as I was designing I realised that there's a lot of good reasons for it to look that way and if made what I thought were good design choices my tank ended up looking a lot like theirs, so kudos to the Phototherm people I can definitely see why they did what they did.

That said there are a few things about their tank that I'm not too keen on, I don't really like the massive light trap they use for their chemical inlet or the idea of having a temperature sensor inside the tank with electrical contacts or using hot air to maintain tank temperature. If I were to make the tank designs cross-compatible I'd have to compromise on other aspects of my design that I think are important, like size and functionality. We'll see how it goes as I get into live testing over the next few months though, maybe I'll find more reasons to change my design closer to theirs in which case it could end up being something I do, never let it be said that I'm somebody too stubborn to change my mind when it makes sense to do so.

[calebarchie]

Can you elaborate on the light trap? I haven't had any issues.

Your designs look about the same size as a 4-roll tank I mean I don't see how it could be any smaller or larger regardless. Sorry I think you misunderstood, I mean if you make any tooling or molds, have design provisions to allow it to be retrofit for Phototherm compatibility, eg have a spot for the contacts or, but in your version simply omit them. The probes and magnets are very, very basic stuff (infact they just drilled holes into the tank to fit/glued them in) do you need me to take some pictures?

It would be a bit of a shame if if you were to make a tank with such minor changes from the phototherm without considering cross-compatibility, there is a pretty high demand for these things. Others would ask sooner or later, just sayin'.