8mm Forum: Claws on dual 8 machines

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Posted by Martin Jones (Member # 1163) on August 24, 2009, 02:08 PM:

Can anyone offer a simple explanation (or point me in the direction of one or a previous discussion) on how the different claw positioning and pulldown standards are implemented on dual machines?

Posted by frank arnstein (Member # 330) on August 24, 2009, 09:25 PM:

Hi martin
there is a thread that has a reference to the guage changing on a dual 8mm Elmo GP-E, some weeks back.
It was about focus problems after changing guages.
It mentions the 2 side guides in the gate and how they can be moved sideways by the selector to locate the film correctly, in relation to the aperture & sprockets.
As for the claw movement, it remains the same for both guages.
The claw sweep is dependent on the profile of the cam that drives it. You can't alter that. The depth that the claw penetrates into the film sprocket is usually adjustable by sliding the shutterwheel along the shuttershaft.
The sideways location of the claw tip is adjustable by a small cam near the claw pivot.
The framing is simply done by sliding the pressure plate up or down the gate, moving the frame till its perfect.
Hope that helps.
dogtor pufferfish [Smile]

[ August 25, 2009, 12:31 AM: Message edited by: frank arnstein ]

Posted by John Whittle (Member # 22) on August 25, 2009, 01:35 PM:

Note to Frank,

Actually the claw travel has to be different for Super8 and Reg8. The pitch of regular 8mm is .1500 (half of 16mm release print pitch of .3000) and the pitch of super 8 is .1667 so it can be seen that the claw set for a regular 8mm pull down will not position itself for entry in the super8 perforation on return.

Most of the dual machines I've seen will position the claw slightly toward the outside edge (guide edge) of the film thus getting a little more pull down for Super8 than regular8. Also the claws for these machines are really very small pins and all are single claw units. That way some of the error for over pull down on 8mm will be made up by entering the claw into clear space on the return and just sliding into position on Super8. Also an adjustment has to be made for framing since the frame line on regular 8 is on the center of the perforation whereas Super8 perforations are in the center of the frame.

John

Posted by frank arnstein (Member # 330) on August 25, 2009, 05:57 PM:

Thanks John,
for that in depth explanation of claw operation.
I was trying to keep it simple but it ain't that simple & the points you raised & explained are much appreciated.
We never stop learning more about this great hobby & we try to help each other on this forum.

dogtor pufferfish
[Smile]

Posted by Alexander Lechner (Member # 1548) on September 06, 2009, 03:46 PM:

Hi John!
I have to correct you here: having a closer look at my Eumigs Mark 501, 602 D and 610 D, I have to tell you that they are all projectors for Super 8 and Standard 8 and they all have dual claw systems.
The clue is that the two claws are quite far apart (I measured 37.5 mm) because that's where the sprocket holes of Super 8 and Standard 8 meet again; so actually one claw is above the gate and the other one below ...

Posted by frank arnstein (Member # 330) on September 06, 2009, 09:21 PM:

Hi Alex,
An interesting point you raise....
I have had a close look at the Eumigs to see how they work.

The Eumigs you speak of do not have the usual top sprocket to push film towards the aperture.
So they use a special reciprocating, sliding claw mount setup using 2 fingers wide apart. The top claw finger is reponsible for catching the film as its loaded & then dragging it into the film gate & pushing it past the aperture towards the 2nd claw finger. Once its caught there, the film is secured between 2 pins, one above and below the aperture. The top claw finger does what the top sprocket used to do. The bottom one is responsible for pull down as is usual.
So it really only uses a 1 fingered claw for pulldown, mounted onto the same sliding claw bracket as the top claw finger, which catches then pushes down film & also holds each frame stretched flat as it passes the aperture.
The 800 series of Eumigs went back to the conventional Top Sprocket setup. The claws on them were 2 fingered & close to each other. The pins are like thin needles so they will do Super or Reg & still get into the film sprocket holes, using either guage.
A different gate is used for sideways location of reg. 8 film.
Both of these needle like fingers do pulldown only, as the top sprocket pushed film down to it.
When the 900 series Eumigs came out, the Sprockets went away again and the weird, sliding claw mount had returned.
So this is 1 reason why your claw fingers are so far apart. They have to be that far apart or it wouldn't self thread itself.
They also happen to coincide with either guage at that distance apart, as you have pointed out.

dogtor pufferfish
[Razz]

Posted by Joerg Niggemann (Member # 611) on September 07, 2009, 02:12 AM:

Hi all,
one more reason why these Eumigs have to use an additional claw under the gate: since they don't have any sprocket wheels, the film has to be pulled out of the gate by the second claw at its end to avoid burning of the last frame. The takeup reel won't do that because the torque is adjusted very low with these machines, again because sprocket wheel is missing and takeup directly affects claw transport.

Joerg

Posted by Martin Jones (Member # 1163) on September 07, 2009, 04:50 AM:

Well, that provoked a most interesting discussion. I learnt a lot, and I hope others did too. It's interesting also to realise from such a discussion the wide range of expertise in other fields that exists in the fraternity; is this because cinematography embraces so many other disiplines by virtue of it's very nature?
Martin

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