C-mount extender by Dreide1

Last crawled date: 3 years, 1 month ago

C-mount extension tubes of different lengths.
Update 08/2018
Fixed thread pitch of the outer thread (was 0.75mm, corrected to 0.794mm=1/32").
Added more tolerance (0.2mm on the thread diameter instead of 0.1mm, for each of the threads).
Reduced model resolution in order to bring down the file size.
Printing
Because of the relatively fine threads, a layer height of 0.15mm or smaller is recommended. Obviously, for the thread to work smoothly, the dimensional accuracy has to be quite high. Over-extrusion should therefore be avoided by all means. If the threads don't fit, one can fix this by changing slicer parameters, either or both the XY scaling factor and the "Surface inset" or "Horizontal size compensation" parameter (or whatever it is called in your slicer). Be aware though that just re-scaling has different effects on the inner and outer thread; one will have more clearance, the other will have less. If you need to get more clearance for both threads, "Surface inset" is the right parameter to play with.
The nominal diameters are 25.2mm (outer thread, most outer diameter) and 24.74 (inner thread, most inner diameter). The average of both numbers is 25mm (exact: 24.97mm), the difference is 0.5mm. If the measured average does not match 25mm, this can be fixed by changing the XY scaling factor. If the measured difference does not match, this can be fixed by changing the surface inset.
Notes
The models have high resolution and that is probably why some slicers see model errors. Simplify3D does not, KISSlicer does (but the slicing results are just fine anyway).
Small changes in tube length can be realized by scaling the part along Z in the slicer, possibly in combination with an accordingly adjusted layer height. Obviously, the threads won't fit anymore if the change was too big. Moreover, if the thread pitches don't match, the forces impacting on the thread are not evenly distributed. Therefore, spacers might be the better solution, for bigger changes like 0.5mm or 1mm anyway (see https://www.thingiverse.com/thing:2802119). Spacers can also be Z-scaled, of course.
The 5mm extender is somewhat critical in that the wall between the inner and the outer thread is rather thin, which makes the part mechanically weaker than the longer tubes. So be careful with heavy lenses. Moreover, light might shine through the thin wall section if the filament is not opaque enough. BTW, the thin wall is basically caused by having an overhang of just 60° instead of 90°, which makes the part printable without support.
Painting the inside of the tubes with black matte color helps reducing stray light. Don't paint the threads though. Normal wall paint actually works pretty well for that.
Material can rub off the threads, especially when being used the first couple of times. Make sure that such debris doesn't land on your lens or the image sensor. I haven't tried, but I guess putting a tiny bit of oil or grease on the threads might help to prevent the debris from flying around.