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How to Adjust for backlash/play in a Chrosziel Follow Focus?


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#1 Eric Young

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Posted 25 May 2016 - 06:36 PM

I have a Chrosziel 203-01 dual sided Film and Video Studio FF.
http://www.bhphotovi...llow_Focus.html

 

The smart side has about 0.5mm backlash/play at the drive gear meshing with the lens, which I think is probably acceptable & normal, but the dumb side has double that.

 

Ideally I'd like zero play of course, but I wondered if anyone knows how to adjust the play or point me in the direction of a service manual online somewhere?

I'm mechanically minded and could just dive in and disassemble, or have a play with that crescent cut, screw-locked dial, but prefer to have an idea of the correct procedure!

 

Mitch Gross was kind enough, in a PM, to give me some pointers for the smart side (essentially adjusting that that screw locked dial - an eccentric tensioner adjustment for the internal belt in the swing arm), but he hadn't ever adjusted anything for the dumb side, although he thought the grease might have dried up leaving some gaps and hence play.

Many thanks for any info!

Eric


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#2 Gregg MacPherson

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Posted 25 May 2016 - 08:57 PM

Did you try asking the tech guys at Chrosziel directly?  I found them quite helpful previously.  The issue is,  whether they have an eccentric adjustment for the gear clearance in the gearbox.  I always thought they did,  but that is an assumption.  If they don't,  maybe the gears don't cost too much.  But I would find that surprising,  and dissapointing.


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#3 Dom Jaeger

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Posted 25 May 2016 - 10:09 PM

Are you saying there is more play when you attach the hand wheel to the other end of the unit? If that's the case, it seems like the issue isn't about play in the gear meshing, but in the handwheel/drive shaft interface, since the two ends of the driveshaft should be solidly connected. Or if it's a second hand wheel, there might be play in the hand wheel itself. Grub screws are usually used to hold the shaft in place inside the wheel, and can come loose. 

 

The other possibility is that the driveshaft is not a single shaft but two parts held together by grub screws (as in the Arri FFs), and the grub screws are loose. 

 

I'm not familiar with this FF, so just throwing ideas out there based on others I've worked on.


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#4 Gregg MacPherson

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Posted 25 May 2016 - 10:54 PM

Dom,

do the units you've worked on have an eccentric adjustment,   or some other way of adjusting gear clearance?

 

Cheers,

Gregg

 

PS:  Your's was better logic.  If the left and right sides have different backlash then there should be a problem in the connection between left and right...


Edited by Gregg MacPherson, 25 May 2016 - 10:57 PM.

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#5 Dom Jaeger

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Posted 26 May 2016 - 12:04 AM

Hi Gregg,

 

yes usually an eccentric, some of the Panavision ones used two half housings with a gear shaft in each which could have the spacing adjusted with set screws. But often play in geared systems can be due to something other than the mesh spacing - loose shafts, lateral play in helical or worm gear spacing, play in the keyway of a gear or removeable handle, etc. Sometimes the play is an aggregate of a tiny bit of play in several different places.


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#6 Eric Young

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Posted 03 June 2016 - 01:46 PM

Hi Gregg & Dom.

 

Thanks for your responses!

 

Dom, yes there is more play on the second handwheel. I've managed to adjust to minimal play on the smart side with the eccentric tensioner at the bottom of the swing arm belt.

 

I will enquire with Chrosziel directly. If/when I have any more definitive information I will report back  :)

 

Cheers!


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