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rb auto loose focusing rack

 
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jerryg



Joined: 04 Apr 2017
Posts: 65
Location: spokane wa.

PostPosted: Sat Jan 23, 2021 7:29 am    Post subject: rb auto loose focusing rack Reply with quote

i have a 3x4 and 4x5 auto rb, they have the two focusing knobs, and they both are loose to where when the camera is moved the lens will move on it's own. any neat tricks to adding a little tension to the knob to keep the lens from running away on it's own lol
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45PSS



Joined: 28 Sep 2001
Posts: 4020
Location: Mid Peninsula, Ca.

PostPosted: Sat Jan 23, 2021 5:01 pm    Post subject: Reply with quote

Remove the rail guide blocks and the rail from the bed. The focus pinion should now lift out.
Inspect the gearing on the bottom of the rail and the pinion for wear. There is likely a brass spring on the underside of the focus pinion that may be compressed.

The body focus should be similar in build. The bellows are attached to the body with a frame and 4 screws if memory serves correct and easy to disengage from the body for servicing.
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jerryg



Joined: 04 Apr 2017
Posts: 65
Location: spokane wa.

PostPosted: Sun Jan 24, 2021 4:45 am    Post subject: Reply with quote

I didn't find any springs. what i found were a brass dowel that is riveted to the rail and has a hole in it for the geared pinion . the top half is split in the middle, a simple pinch together adds enough tension to keep the front standard from running away.

https://i.ibb.co/C77c7n2/20210123-180552.jpg

https://i.ibb.co/6n8bh5H/20210123-183626.jpg


https://i.ibb.co/T2Mp7ZX/20210123-180643.jpg
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45PSS



Joined: 28 Sep 2001
Posts: 4020
Location: Mid Peninsula, Ca.

PostPosted: Sun Jan 24, 2021 7:50 pm    Post subject: Reply with quote

I see some wear on the pinion in your first photo. The focus knob is attached with a taper pin, drive it out from the small end. Put a .010 to .020 shim between the knob and the side mount or between the side mount and the bed to pull the pinion over to an unused section of the pinion to the rail.
use a light amount of grease on the pinion and its pivot points.
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jerryg



Joined: 04 Apr 2017
Posts: 65
Location: spokane wa.

PostPosted: Mon Jan 25, 2021 1:03 am    Post subject: Reply with quote

thank you
always great help
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