The Long and Winding Road to a Balanced Shutter in Mitchell 46

After winning last week’s struggle with the rear bearing race, I could actually move on to properly aligning the shutter in the camera casting. I hope you will all forgive the tedious details of this process, but it seemed important to me to outline the many steps it took to achieve this. Several things had to be considered in order to ensure that the shutter would line up parallel to the aperture, and the two adjustable bearings would line up with each other in the horizontal and vertical planes all at the same time. The vertical axis was pretty much established when the dovetails were indicated true and parallel to the camera’s aperture. To indicate the shutter shaft along its vertical axis, the camera casting was set up so the dovetails rested on a set of precision ground parallels on the granite surface plate. Tolerance was +/- .001”.

The shutter system on a Mitchell Standard or GC is made up of 2 shafts or axles. The main shutter shaft is hollow and has been fitted inside with brass bearings at either end. The variable shutter shaft rides inside the main shutter shaft on these bearings. Neither shutter shaft was long enough for me to indicate the front and rear bearing positions at the same time. I left the variable shutter shaft protruding out of the front of the camera so I could indicate that position. Then I installed a precision ground gauge pin inside the rear bearing of the main shutter shaft. I now had two points that I could indicate to. With much fussing and fiddling, I was able to get both ends of the shutter shaft to indicate to the same height from the surface plate. That resolved the vertical positioning of the shutter shaft.

Then I moved on to checking and setting the horizontal position of the shutter shaft. The problem with this is, there are no true surfaces on the camera casting to assure parallelism between the granite plate and the where the true position of the shutter shaft needs to be. I turned the casting on its side, put it on top of a set of parallels, and indicated the machined flats that the movement mounts to. Careful shimming of the parallels made the camera casting  true and parallel to the granite plate. I repeated the indicating process in the horizontal position so that, if I got extremely lucky, the shutter shaft would be true and parallel on both the vertical and horizontal axes. After what seemed like an endless amount of indicating and re-indicating both the vertical and horizontal axes of the shutter shaft, I was finally satisfied that the shutter shaft was now truly parallel and within tolerance to the casting.

Without any way to clamp or fixture the rear bearing support in place now that it was indicated, I temporarily super glued the rear bearing support (spider) into place so I could drill and tap new mounting holes. No dowel pins at this point, that will come later, after I break the temporary super glue joints apart. All that done, I assembled the main and variable shutter shafts, installed the main shutter shaft drive gear and the variable shutter shaft drive gear, and ran everything by hand. Success! Please enjoy the attached video which shows much of my process, step by step.