Need nylon bushings for a shift lens

[Bruce B]

Hi, I know this is a large format forum, but I've had some great help here before in finding parts and lubricants, etc. I recently purchased a Pentax 28mm f/3.5 shift lens (from this forum actually) and needed to repair some looseness in the shift mechanism. I took care of the looseness with an adjustment to the shift dovetail. However, someone had repaired the lens earlier and replaced the shift ring in the wrong direction, i.e., it read 11mm of shift when the lens was at zero shift. So I rearranged that and noticed the bushings that slide in a "female" cam groove on the shift ring were worn. Also, one bushing had been replaced with a slotted screw and was beginning to wear the inside of the cam groove. I took a bit off the screw to prevent it from scoring the top of the cam groove. It will be a machining situation to replace the slotted screw, as the threads in the shift ring were retapped to a larger size than that used for the shouldered screw that mounts the other bushing. That shouldn't be too much of a problem, but first I need to find a pair of bushings. Here's a photo with dimensions as close as I could measure with calipers or mm ruler.

Note that there is some wear on the bushings and the height is probably more like 5+ mm. There is 1.5mm headspace above the bushing in the cam groove. Also, the cap of the bushing mounting screw fits into a shoulder in the top of the bushing. When machining the larger screw I'll have to take this into account.

Any suggestions for where to find these bushings would be most welcome. Thanks in advance BAB

[Tin Can]

McMaster Carr or have a watchmaker turn new ones.

[Bruce B]

Thanks, Randy. I'll try McMaster but there are no watchmakers in Maine, and these are too big for most watch repair facilities. However, I noticed a clock repairman not long ago in another town and perhaps I should pay him a visit. Cheers

[ic-racer]

Sullivan makes nylon model aircraft nylon control rods that accept 4-40 hardware. That is nominal 0.112" OD thread which works out to 2.8mm diameter. Since the hardware has to screw into the rod, I'd be the inner diameter is close to what you need.

[Bruce B]

Somewhere I would never have thought to look, thanks. I'll check Sullivan today.