Camera turned out well, but though I would compile a list of the things I wish I could do over- and probably will have to do over at some point. Will update the list as new ones are discovered.
I cut the shaft flush with the bed, and tapped and Locktite’d 6-32 studs into each end for the focus and lock knobs. Would have been better to leave the shafts long on the focus side and pin the knobs to the shaft, as done with the gears themselves. The studs are fine for locking knobs, but probably too weak to handle the torque from the focusing knobs over time.
I made some new shafts and knobs. I got some precision ground 3/16″ stainless steel rod, which is roughly the major diameter of 10-32 thread, so I cut this thread on each end. The focus knobs are fixed on one end with a set screw, and the lock knobs will be held captive with a 4-40 screw tapped into the end of the shaft.
Collet chuck and threading die holder in the tail stock makes threading the end of rods pretty quick work on the lathe.
Boring and threading the shaft end for the locking knob captive screw. The head on the 4-40 screw will keep the knob from unscrewing all the way off the shaft and getting lost.
Boring the spur gear out for the 3/16″ shaft.
New shaft parts. I made some new knobs, the hardest part was knurling the stainless steel with my cheap knurling tool. I knurled 4″ of 3/4″ rod before turning the other features. Forgot to take pictures, but taking light passes and flooding with lots of cutting oil seemed to help. I cut a shoulder on the knurled stock, bored and tapped the 10-32 thread, parted the knob off, then repeated for the other knobs. Knobs are only 1/2″ thick, so had enough knurled stock to make a spare just in case.
Aligning the gears. I tapped the hubs for set screws first. Then I set up the shaft on each stage, locked the gears in position with a drop of threadlock, then bored the shaft and continued the thread for the setscrews. If the shaft isn’t square to the gear rack and the gears aren’t radially aligned the focusing stage will skew and bind.
I hate slop in gears, so continued the setscrew thread into the shafts, really locks them in place.
Locking knobs with retaining screws in place.
Should have made the rear bellows frame thicker to give a little more wood around the hole for the knob’s retention pin. Alternatively, I could have just located the pin in front of the frame to lock it in place. If I ever over extend the camera and put a lot of stress on the bellows, the pin may break through the weak side of the frame. Not a huge worry, the fabric’s bond to the frame would probably fail before the wood does, but I may inlay a piece of aluminum to reinforce this. Might have been better to locate the pin towards the front of the bellows frame, and just file enough of a divot in the frame so the pin would wedge the frame tight to the back.
Friction fit for the gear racks. I haven’t come up with a good way to mechanically fasten these small brass racks to the extension. Too fine and too small for screws, at least the size of screws that I can handle with my ham hands. Friction is fine to keep them from simply dropping out, but not good enough to resits linear movement under a lot of load. I inlaid these gears with high quality double-stick tape, which works ok. I usually use stopped dadoes for the racks, so the racks are captive front to back. But for a bed this short I wanted every bit of rack I could get. As is, it works fine under regular load, but if I ever try to focus with the movement locked down, it just might force the gear out of its groove. I might get some micro drill bits and just pin the rack to the wood in a few spots between the teeth.
As also shown in the picture above, I used stock black oxide steel T-nuts for the rear shift. They’re a little grabby, will probably make some out of Delrin. The head of the stainless steel screw takes all the load, the T-nuts are just to keep the screw from rotating when tightening/ loosening the control knobs above.
I did pretty well locating most of the screws considering the space restrictions. But the screws in the aluminum angles on each side of the bed are meant to easily adjust the tension on the rear extension- except I can’t reach the front and back screws without removing the focus and lock knobs.