Film-Tech Forum ARCHIVE: Gate Maintenance

This is topic Gate Maintenance in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Ian Bailey (Member # 1752) on 08-02-2004, 08:34 PM:

I have 2 Simplex 35 projectors whose gates have never had any parts replaced in them.They would have to be 25-30 years old and still running.I will be replacing the tension springs.The bars that rest against the film edge are worn but still appear to be in useable condition.Are there any other parts that would need replacing?
Could someone explain to me how you adjust gate tension correctly(I know you turn the KNOB but how much tesion is required?)
What indications on the projected image do you get when gate tension is not correct.
I can wind the gate tension knob from zero to full on these gates and not see any difference in the stability or look of the projected image.
Any help will be much appreciated
Ian

Posted by Steve Kraus (Member # 476) on 08-02-2004, 08:50 PM:

Generally, the lowest tension that keeps the picture steady under all normal conditions and film stocks (snipes, trailers, feature). Lower tension reduces wear on the intermittent sprocket and on the intermittent movement that drives it.

Posted by John Pytlak (Member # 331) on 08-02-2004, 09:17 PM:

quote: Steve Kraus
Lower tension reduces wear on the intermittent sprocket and on the intermittent movement that drives it.

Lower gate tension also reduces wear on the print, including a reduction in the scuffing projector abrasion of the SDDS and Dolby Digital soundtrack areas and sprocket tooth deformation of the film perforations. As Steve says, just enough tension to get a steady image.

Posted by Michael Schaffer (Member # 1204) on 08-02-2004, 09:23 PM:

If adjusting the tension doen't make any difference (at one point when you turn the tension down, the image should start jumping unless the gate bands are new), you can also check how far the gate pushes into the trap. There is a stop screw just beyond the aperture which you can adjust. When you install new gate bands, you can work with that and see that you put as little tension on the film as is just necessary.