Adjustments of a Century backplate

[Peter Mork]

I have a Century SAV, and I'm trying to figure out the right way to set the film guide at the top. There's a shaft with two flanges that can rotate, and a couple of screws to hold the pins that hold the shaft in place that you can loosen to give it a bit of left-to-right positioning.

I've had a problem with the non-soundtrack edge of films getting a crimp in them in the sprocket hole area, along the length of the print, which doesn't seem to affect the projection but causes the film to wind loosely on take-up. I suspect it could be the flange on the far side running over that part of the film. The flange is spring loaded to push against the film's edge, but it possibly could snap in too far and make this crimp. Is that plausible? How should that flange-thing be adjusted? You can loosen the screws and give a tiny bit of left/right swing but there must be a standard way to do it.

pins.jpg

While we're here, what's the best setting for the strap tension knob, which you can turn with the backplate in place? straps.jpg

Thanks for any advice. PM

[Tony Bandiera Jr]

The ONLY correct way is with a trap alignment gauge..Lavezzi made one, and IIRC there are a few others out there. You'll have to look online to find them. Instructions on how to use it were on the old forum IIRC.

An alternative I used (but less precise, and took a LOT longer to do) was 35mm steel alignment film.

Another important thing is to clean all that gunk off of the left side roller in the first pic. Make sure the roller can freely (under the spring tension) move laterally. After cleaning put ONE very tiny drop of oil on each end of the shaft and ONE very tiny drop of oil on the shaft as you push the roller "open" placing the oil in the gap between the two rollers.

I had one of those alignment gauges at one time, but all of my film stuff went to the late John Eickhof and I have no idea who has it now.

[Ryan Gallagher]

The SAV trap is a bit different from my JJs, but yeah best with the alignment tool, the JJ manual describes setting the lateral guide rollers using a piece of film pulled tight between the intermittent and (??), but that seems pretty inaccurate and requires extra hands.

Basically the non sprung side should be set to the proper alignment, the sprung side moves to allow for the gate to seat and to accommodate splices and various condition of film.

The two rails affixed with the flat heads (studio guides) could also be pinching the film, it is safe to run with those removed if all other alignment is happy, otherwise they help mitigate lateral film weave.

And yeah, lots of cleaning needed in there! The JJ lateral rollers pivot on a tiny jeweled bearing, stupid easy to lose I’m told, not sure if that applies to the SAV trap. A good read of the relevant manual sections advised.

Also here is an archive thread about those alignment methods (Strong vs Lavezzi tool vs metal film vs stiff leader and normal film)

https://www.film-tech.com/ubb/f1/t003857.html

[Mark Gulbrandsen]

I borrowed an actual Century made gauge back in the 1980's and had a friends machine shop make three of them for me. He didn't charge much to do it. It was around $250 for the three gauges. The curved gate gauge works in a century straight gate as well.

[Ryan Gallagher]

I borrowed an actual Century made gauge back in the 1980's and had a friends machine shop make three of them for me. He didn't charge much to do it. It was around $250 for the three gauges. The curved gate gauge works in a century straight gate as well.

Personally I’ve never seen a Strong or Lavezzi one, I can imagine steel film though. Would you mind sharing some pictures if they are handy?

[Tony Bandiera Jr]

Personally I’ve never seen a Strong or Lavezzi one, I can imagine steel film though. Would you mind sharing some pictures if they are handy?

Pictures don't seem to exist on the mighty webs anywhere, so draw the following in your mind:

35mm steel alignment film: (Lavezzi AFG-1) Strip of thin mild steel about the thickness of 2 layers of acetate regular film, with precision perfs (KS Style, standard film stock perfs), where the width is precision ground/slit to 35.0000mm It was a 4 foot length that you could thread up through any point in the projector (or printer or dubber) path to check alignment of the film trap, sprockets or pad rollers.

Lavezzi AG-1 (Film trap gauge) Plate of hardened aluminium, precision ground to width (IIRC when I measured mine it was ever so slightly over 35mm, the number 35.025mm comes to mind.) with on end of the plate notched to the width of the inside dimensions of a KS sprocket's teeth and the other end to the width of Lavezzi's VKF (Very Kind to Film) Sprocket teeth. Those notches ensured the sprockets were exactly centered to the film trap.

Both were reasonably priced (under $100 each) and were invaluable for all of the work I did, including building reversing Simplex XL's for studio screening rooms. (And mine worked without the stupid gate release that Wrong built.)

[Ryan Gallagher]

IWhile we're here, what's the best setting for the strap tension knob, which you can turn with the backplate in place?

I think we skimmed over this question. Gate tension adjustment needed is "just enough to stabilize the film". On a properly set up machine (there other things that impact how far the gate closes), the knob should not need more than 0/12 o'clock (home position, no additional tension), and 1 o'clock (slight additional tension). Adjusting that knob is primarily to mitigate side to side film motion, there is often another place where you adjust for film bounce. (On the JJ's it's the spring tensioned intermittent sprocket shoes).

If the film "flaps" a bit in the gate at the home position turn the knob until that noise goes away, then watch the screen for weave to see if the print needs any more than that, noting that studio guide alignment (for all condition film) also combats weave too.

Minimum gate tension, the better for film preservation. So essentially start with it minimum and increase to needed amount for each print? And if you have to go ham on that knob it indicates other mechanical adjustments are needed.

[Mark Gulbrandsen]

Personally I’ve never seen a Strong or Lavezzi one, I can imagine steel film though. Would you mind sharing some pictures if they are handy?

I probably have pictures... gonna take a while to fins them though.

[Peter Mork]

Well, I ruled out the trap as the source of that edge crimp. Running some virgin film through the Century has allowed me to pin down the point where the problem happens.

Picture shows the crimp and where it stops.

crimped.jpg


And here's the culprit -- the pad roller past the intermittent.

roller.jpg

I wonder if anyone else has had this happen. Next step will be to take out that assembly. It looks like that nylon roller may not be original.

[Gordon McLeod]

It may be you have a pad roller to tight to the sprocket.There needs to be 2 thickness of film clearance

[Mark Gulbrandsen]

1. The nylon roller should look like the the one in Image, and have a tiny amount of end play to it and rotate freely. About .025 end play should be ok
2. You can measure the inside width with a caliper if you have one handy. Should be a tiny bit wider than 35mm, or 1.378 inches.
3. Be sure the closed clearance is set for two thicknesses of film.

If you still have issues and all the above is good. Check for a slightly bent sprocket shaft.

[Ryan Gallagher]

If it is the correct one, and alignment/spacing checks out. Look for damage to it, a bent flange or a nicks/scratches can “grab” the film and take it places it should not go. However usually that causes sprocket skips and your lower loop shrinking while running, which is not exactly your symptom.

seems weird that it could bend the film over the edge of that sprocket without pulling it off the teeth entirely though?

[Mark Gulbrandsen]

The way it's damaging film is also strange. When I made the above post, I am assuming the sprocket and shaft are not damaged...

[Sean McKinnon]

Steel Alignment Film

[Sean McKinnon]

more steel film