How to slit film w/o tearing it?

Is there a trick to this, like bolting the film slitter to a bench and doing a continuous, steady pull? I initially tried working in the confines of a daylight film changing bag but only succeeded in ripping my film to shreds. Next I tried in a darkened closet but still couldn't do it in one continuous pull, and tore the film once again, though in longer, more usable pieces than before. My film slitter is configured to cut 1-16 mm and 1-9.2 mm strip from 35 mm film.

I clamp my slitter to a countertop in the darkroom. One long pull and it is done. I wouldn't do it in a darkbag. Too much trouble. You might want to check the blades too since they can chip, or maybe they aren't sharp, if you are having problems.

Film slitting requires a steady, continuous pull at a constant angle of attack. That is hard to do in a changing bag. I tend to start slowly and slowly pull it slightly faster until I feel it suddenly "glide" on the cutting blade and keep it at that speed no matter what the rate. If you have changeable blades, like single sided razor blades, change them often; they are a lot cheaper than film...

Patrick Robert James said:

I clamp my slitter to a countertop in the darkroom. One long pull and it is done. I wouldn't do it in a darkbag. Too much trouble. You might want to check the blades too since they can chip, or maybe they aren't sharp, if you are having problems.

Click to expand...

Thanks, let me try one continuous pull next time. Blades are brand new Stanley carpet blades and more akin to box-cutting blades than shaving razors, but I took the extra step of a few passes over a #800 stone.

4season said:

Thanks, let me try one continuous pull next time. Blades are brand new Stanley carpet blades and more akin to box-cutting blades than shaving razors, but I took the extra step of a few passes over a #800 stone.

Click to expand...

Those are pretty thick blades; single sided razor blades might work better.

Kino said:

Those are pretty thick blades; single sided razor blades might work better.

Click to expand...

I'll try better technique, and if that doesn't work, I'll look into using some other type of blade. I now see that the original designer of the film slitter (on Thingiverse) didn't specify blade type, save for dimensions including 0.2 mm thickness, which is about the same as a single-edge razor, about half the thickness of my carpet blades.

yeah I had this trouble and I was using a Gami slitter. As others have said dont do it in changing bag, make sure its firmly secured, I found I had to pull film past and above the blades then push it down onto the blades so that the blades pierced the film then it would pull through easily. Then I would just trim off the unslit leader. Trying to pull it straight through the blades always ended in problems for me personally.

I use the very thin double edge style razor blades. Fortunately I have my windowless laundry room that, after dark, with all the house lights off, is suitable for a darkroom. As others have said, one smooth continuous pull on the film. I only pull through a 20 inch length at a time. Then roll and load that before pulling the next strip through.
I measure the 20 inch length of film from the bulk loader with a cord with a knot at 20 inches so I can tell how much to pull out. The sequence to cut and load film is;
Checklist items needed to load film,
1. Empty cartridge, bulk film holder, scissors, film slitter, spinner stick.
2. Remove cap of feed chamber.
3. Turn off lights.
4. Open lid and release light trap of bulk loader.
5. Find knot in string and end of film, holding knot and film pull out film until string stops. Close light trap of bulk loader.
6. cut off film at bulk loader with scissors.
7. Place start of film in slitter and push onto blades with press block/lid leaving 1/2 inch film overhang to grasp onto.
8. Pull film through slitter in one continuous motion.
9. Cut off end of film not slitted.
10. Place film end, emulsion side in, in spinner stick slot and rotate stick letting your thumb and forefinger ride on edge of roll keeping it tight.
11. Pull roll from stick and place in feed side of cartridge, cap cartridge.
12. Turn on lights and secure lid with low tack masking tape. (Hint, you don’t need much tape.)
Do the next cartridge the same way.

After you have loaded the feed chambers of as many cartridges as you need, then attaching the film to the take up spool and putting that in the take up chamber and securing the cap can be done in room light.

Gotta go steady with it. I use the thin 'safety' razor kind of razors. Double sided. They tend to wear out fast as film seems to really dull the blades. No jerky action, just a slow and steady pull. Even then I do shred my film once in a while.

Cholentpot said:

Gotta go steady with it. I use the thin 'safety' razor kind of razors. Double sided. They tend to wear out fast as film seems to really dull the blades. No jerky action, just a slow and steady pull. Even then I do shred my film once in a while.

Click to expand...

Good thing is you can flip the blades 3 more times. I use a fine point sharpie to mark the corners 1 through 4 and as soon as I notice them getting dull then I flip to the next number.

ciniframe said:

Good thing is you can flip the blades 3 more times. I use a fine point sharpie to mark the corners 1 through 4 and as soon as I notice them getting dull then I flip to the next number.

Click to expand...

Or I just buy new ones. They're .99 for a pack of 10.

Biggest thing is the blade has to be sharp, especially with PET/polyester film base. A fresh #11 blade, fresh carpet knife blade, fresh utility blade, or fresh single edge blade should do the job well, but as noted above, the film base wears out the blade fairly quickly.

One other thing that makes a difference is the design of the slitter -- the more perpendicular the blade edge is to the film, the more you'll notice any dullness. I've cut film still on the 120 roll with a not overly sharp pocket knife, or a fairly used snap blade, but because I was spinning the roll in my lathe, the blade was slicing rather than chopping as it would be if I held the blade edge vertical and pulled the film horizontally.

Progress! Among other things, I was making the mistake of trying to scavenge every possible bit of film, and not giving myself enough of a leader to hold onto as I pulled the film through the slitter. First test with longer leader and a smooth, continuous pull worked without a hitch. Emulsion side of film looked flawless, but I noticed fine scratches on the film base. I then stuck a couple of pieces of black velvet where I thought the film base was likely to rub against the lid of the slitter, and the subsequent trial run looked perfect, so I think this problem is solved.

As for the carpet blades, since I had my Japanese sharpening stones out in order to sharpen my kitchen knives, I gave the carpet blades a few passes over my Japanese sharpening stones too. I don't know that it made a make-or-break difference, but it certainly didn't hurt either.

Nice. You're in the game!

Whole lotta shooting in the dark...

Just trimming to size?
Slitting from sheet film or roll film?
Typical cut sizes expected?
Just "one or two now and then", or a "bunch for a big project?"
Using a flat bed guillotine paper trimmer?
Or a straight edge and a box cutter on the kitchen table?

To much: "try this, try that"...
Without understanding your set-up, we're just shooting in the dark...