DIY Film Drying Box

[IanBarber]

Ive been thinking of making a simple wooden box with a door for hanging the wet 5x4 negatives in, something similar to my mockup below.

172428

On the top I was going to drill a hole in the centre and place a heppa filter over the hole which would be the intake.
On the bottom, I was going to drill the same size hole in the centre for the output.
Around the front where the door would close, I was going to place some draught excluder tape so the door would fit nice and snug up against it.

I am not overly concerned about force air or heat drying.

Question:
Can anyone see any flaws in this setup?

[Bob Salomon]

Where will the moisture go and how will you get rid of the moisture?

[IanBarber]

Where will the moisture go and how will you get rid of the moisture?

I was going to add a small removeable tray on the bottom

[xkaes]

Looks OK, but -- if for some reason you need to dry film fast -- there are faster, easier, simpler alternatives.

[Randy]

My method - I have one of those spring-loaded telescoping closet rods in the shower. Have a bunch of plastic close-pins that have hooks on one end to hang over the rod. I just hang my film in the shower, pull the shower curtain closed, close the floor heater vent almost all the way to minimize air movement and close the bathroom door.

[George Richards]

You'll need a fan to make sure the air flows the right way, something to pull the air down thru the filter and out the bottom. Just the filter and hole in the bottom won't do much in fact since warm air rises it might actually go the wrong way. You'd be better off with no hole or filter just a closed box.

[Pere Casals]

Ian, as Bob Salomon and George says a little fan would be necessary, at 20ºC 1000L of 100% water saturated air only contains around 17mg of water (17gr/m3), this is half a drop per L. If original air is at 50% humidity you need some 5 L of air for each drop. So some air forced circulation is interesting to not depend on the natural circulation across the HEPA filter. https://www.engineeringtoolbox.com/maximum-moisture-content-air-d_1403.html

Evaporation speed depends on temperature, air speed and air humidity. The most pratical way is that you simply mantain internal humidity low by injecting some fresh air. I'd use a fan from an old PC box.

[IanBarber]

Ian, as Bob Salomon and George says a little fan would be necessary, at 20ºC 1000L of 100% water saturated air only contains around 17mg of water (17gr/m3), this is half a drop per L. If original air is at 50% humidity you need some 5 L of air for each drop. So some air forced circulation is interesting to not depend on the natural circulation across the HEPA filter. https://www.engineeringtoolbox.com/maximum-moisture-content-air-d_1403.html

Evaporation speed depends on temperature, air speed and air humidity. The most pratical way is that you simply mantain internal humidity low by injecting some fresh air. I'd use a fan from an old PC box.

I like the idea of a computer fan which could be easily mounted on the inside at the top. Does the size of the box have to be mathematically worked out for it to be effective

[Pere Casals]

I like the idea of a computer fan which could be easily mounted on the inside at the top. Does the size of the box have to be mathematically worked out for it to be effective

No... just use the volume amount you need for the film, a little fan moves a lot of air and with that air circulation won't allow humidity to get high. You can be sure that ventilation is enough by placing a cheap weather humidity sensor inside to see that it is not much higher that in the outside.

At 80% air humidity evaporation may be 2x than at 90%, because in the first there is 20% until saturation and in the second there is 10%.

So if in exterior you have 60% and in the interior you have 65% then I'd say ventilation it is good enough.

If you were wanting a fast film drying (like in minilabs) with high speed hot air you would require a more complex design, but I understand you simply want a clean space to not take dust, so I'd take just the volume I would need, with moderate HEPA filtered ventilation, that's all...

[domaz]

I made a simple horizontal drying box for drying carbon tissue which is actually much much wetter than typical LF film would be (since the gelatin soaks up a lot of water). I made a box with the same basic design as you. I used a computer fan with a stovepipe duct adapter on one end to step up from 4" duct to 12" duct. The 12" duct end is in the interior of the box. The carbon tissue sits horizontally on screens and on the other side of the box I have a right-angle duct that the air exits out of.

It seems to work fine and cuts my carbon tissue drying time at by over half (used to take several days now I can dry fresh tissue overnight).

[Jac@stafford.net]

Consider using a cardboard box with a modest sized HEPA filter on top, a couple more holes in the sides with HEPA filters and a 60W lightbulb inside for a little heat which helps dehumidify the air.

A low volume fan on the side at the bottom to evacuate air.

[Robert Brazile]

I did something very similar recently for drying silver gelatin plates after pouring, or after development. Allows them to dry in a relatively dust-free environment, and dries them somewhat more quickly. Just threw it together out of some scrap wood, a small fan (of the same sort as on a computer), and furnace filters. Seems to work well enough...

https://farm5.staticflickr.com/4524/37883057524_04f8e3579d_c.jpg (https://flic.kr/p/ZHAzbd)
IMG_3472, Fan installed (https://flic.kr/p/ZHAzbd) by Robert Brazile (https://www.flickr.com/photos/rbrazile/), on Flickr

https://farm5.staticflickr.com/4579/37883039914_18712909a4_c.jpg (https://flic.kr/p/ZHAtWA)
IMG_3471, Starting to look like a drying box (https://flic.kr/p/ZHAtWA) by Robert Brazile (https://www.flickr.com/photos/rbrazile/), on Flickr

On a suggestion from Mark Osterman, I plan to line it with cardboard (just using double-stick tape, so it can be removed/replaced). May consider heating the air slightly by putting a small light bulb near the inlet filter, but it's not necessary.

Robert

[IanBarber]

Robert, how dust would you say you have eliminated with your new box

[Robert Brazile]

I cannot quantify it precisely, but the amount of spotting I have to do (generally digitally on the scanned images) has decreased significantly. That is, before I had to do a lot, so far with the new box, I don't have to do much at all.

Newly poured plates used to take most of the day to dry completely; now it's down to about 5 hours, and I suspect I can get it a bit lower still.

Robert

[HMG]

I was thinking a hepa filter might be overkill. The paper style furnace filter (per Robert Brazile) might work fine. I've used these in smaller openings but just cutting them up.