Film-Tech Forum ARCHIVE: uses for different sprocket and pad roller types

This is topic uses for different sprocket and pad roller types in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=010141

Posted by Scott Norwood (Member # 30) on 10-19-2009, 11:42 AM:

The Century projectors in my screening room were built in 1970 and have CS-type sprockets. I assume that these are original to the machines (they had been lightly used when I got them a few years ago). They work fine with KS-perf film. They also have plastic pad rollers.

[side question: when ordering a new projector, is one given a choice of sprocket types?]

I see that one can purchase VKF, CS, "standard," and "posi-trol" sprockets. Also, both metal and plastic pad rollers are available.

What are the relative advantages of each sprocket type? Why would one choose one type over another (other than CS sprockets for CS-perf prints)? And which pad roller type (plastic vs. metal) is preferred?

Posted by Tim Reed (Member # 137) on 10-19-2009, 02:26 PM:

Scott, I wouldn't even consider CS sprockets today. VKF (Very Kind to Film), have teeth which are a better fit to the perf, and I think they will also handle CS perfs, too. Not sure about specifics of Positrols...

Nylon pad rollers don't require lubrication - you only have to make sure the shaft is clean and dry.

Posted by Robert Minichino (Member # 3495) on 10-19-2009, 02:57 PM:

From the literature I've seen, positrol sprockets have a wider sprocket on one side that improves horizontal stability by completely filling the perf. The VKF sprockets are wider than CS sprockets (the VKF-2 wider still), and have radiused edges.

Posted by Kenneth Wuepper (Member # 1174) on 10-19-2009, 03:09 PM:

Scott,

I can assure you that VKF intermittent sprockets WILL DAMAGE the CS perfs.

A film festival at our theatre did not exchange the VKFs for the CS intermittent sprockets and destroyed a full reel of mag 35mm.
The VKFs are a snug fit in the holes of standard prints so they would tear open CS sized holes.

KEN [Frown]

Posted by Tim Reed (Member # 137) on 10-19-2009, 04:13 PM:

Maybe I'm thinking of the first-issue VKFs... seems like I remember one of their selling points was that they would work with Fox holes? This was late 70s, of course.

Posted by Robert Minichino (Member # 3495) on 10-19-2009, 04:45 PM:

Based on the published dimensions, the VKF sprockets should fit CS perfs so long as it's not badly shrunken. Positrols look like they'd make a big mess out of CS perfs, though.

Posted by Ian Parfrey (Member # 5122) on 10-19-2009, 05:13 PM:

Whether you go the C/S, VKF or Positrol sprockets would surely depend on whether you either intend (or are equipped) to run Foxhole mag/mag-opt prints. If you dont have the intention of running foxhole, then go the VKF or Positrol route. They generally run quieter anyway.

Cheers
Ian

Posted by Mark Gulbrandsen (Member # 72) on 10-19-2009, 06:55 PM:

Its the other way round. You can't use Posi-Trol sprockets with CS type perfs at all!!! It'll ruin the print. VKF, especially the latest gestation VKF-2 work well as long as the print is not badly shrunken. If it is then use CS type sprockets.

I ran Positrol sprockets on all my dailies projectors Centurys) and the image from them is lke it's nailed up on the wall. They remove the last vestage of lateral film movement completely. You can remove all the lateral guidance rails (which really do nothing at all anyway) and just use the lateral guide roller by itself. One side of the sprocket teeth are full fitting and copntrol the lateral movment of the film. The sprocket hole is also the best place to do the controling of the film. If you are running an old Super Simples the image can actually be frighteningly dead steady... The old Super Simplex and E-7 movements were the best of the best ever produced. Too bad the rest of the projector was so-so. If you run Positrols I reccomend the MNR4-22(?) LaVezzi steel pad rollers that have the oilite bushings in the ends. Aside from lasting really long the groove better matches the wide Positrol tooth.

Mark

Posted by Scott Norwood (Member # 30) on 10-19-2009, 10:45 PM:

Wow. Now I am more confused.

I have no intention of running anything with CS perfs. I also had no intention of changing out my sprockets when I started this thread, but would consider it if someone can explain exactly why CS sprockets are not a good choice when running KS-perf prints.

I guess the source of my confusion is that there are at least four different types of sprockets for these machines, and I am curious as to the typical application for each.

Posted by Ian Parfrey (Member # 5122) on 10-20-2009, 03:39 AM:

Scott.

If this were my Screening room, here is what I would use.

If there was any chance of C/S Mag-mag opt fox hole prints to be run, I'd go with the C/S sprockets. Im assuming here that these would be older, original prints anyway.

Of course, the majority of 35/70mm machines will come equipped with C/S 35mm sprockets as standard.

If there was any chance of running older, shrunken prints with standard KS sprocket holes, VKF sprockets would be my choice.

If there were only new prints or new archive prints from original negs, then Id go with the Positrol.

But for a general, all round solution for the majority of prints available, then the VKF would be my choice.

C/S sprockets on the whole aren't really "bad" for KS holes, it's just the wider VKF and Positrol tooth spreads the driving load over a wider area of the sprocket hole, thereby theoretically reducing potential print damage.

I hope this helps. I'm sure that the others will chime in with their personal preferences.

Cheers
Ian

Posted by Dick Prather (Member # 1136) on 10-20-2009, 03:53 PM:

It all boils down to what kind of prints you will be running. Century's have less of a problem with shrunken film because of their 16 tooth sprockets and only one pad roller per sprocket.

VKF sprockets were designed to run mag with no problems. Tim is correct. The problem here is shrunken film especially mag. VKF's don't work here with XL 24 tooth sprockets and two pad rollers. The VKF II and Positrol sprockets will not run mag at all. I do run mag and other older films and did replace my VKF's in my XL's and RCA soundheads with new C/S sprockets. No problems since.

Suggestions:
Only new prints - VKF, VKF II, or Positrol
All around no old mag - VKF
Everything - VKF or C/S

LaVezzi metal pad rollers are the best but require some maintainance. Machined PVC rollers will work fine as long as the shaft is kept clean.

I think all new machines come from the factory with VKF or
VKF II sprockets.
Dick