Intrepid View Camera - Extendable Focusing Knob

Magnetic Extendable Focus Knob Replacement

My primary motivation for this model was to print my own knob with slightly less-aggressive knurling, as I found that my thumb and forefinger were basically shredded after any small amount of focusing when using a heavier lens on my Intrepid 8x10.

Replacement Knob

This is a two-part and easily customizable focus knob replacement for the main focus knob for the Intrepid 8x10, 5x7, and 4x5 cameras. The first part is a replacement for the stock 3D Printed knob that comes with the camera that fits into the same footprint to avoid interfering with the front and back standards or bellows as the camera folds for storage, or while the standards are tilted. This enhanced knob adds four new holes for registration pins, allowing for a second extended shaft to be connected, as well as two pockets intended for press-fitting two 6mm disc magnets that help hold the extended shaft in place.

The replacement knob comes with a single variant .stl. I've found that this prints well with nearly any printer settings. This should be printed with the flat face on the print bed. This face will be against the bushing at the end of the focus screw that the knob is fastened to. A .20mm layer height with a 0.4 nozzle seems to match the stock print quality, but the print comes out just fine using the DRAFT setting and a 0.6 nozzle, and prints in just minutes. You may need to tweak the tolerance for the magnets depending on your print quality settings.

The included .scad file is commented and has the flexibility to allow you to control the pockets for the magnets, the registration pins, and fastener holes, as well as the knurling around the outer knob. The larger diameter nozzle you use, the less pronounced the knurling will be. Rather than proper knurling, the texture is approximated by cutting small-diameter cylinders out of the perimeter of the main knob body at regular intervals based on the number of “knurls” configured. The default settings use 54 knurls. 

Extended Shaft / Ergonomic Knob

The second part is an extended shaft that couples with the replacement knob using two magnets and some registration pins that ends in a much larger knob that allows both finer adjustment and a more comfortable experience in focusing.

There are two .stl files included here for two types of knobs. The first type ends in a knob similar to the base knob - a plain cylindrical knob with some configurable knurling texture around the outer edge of the knob. The knurling is approximated in the same way as the base knob, and this basic knob uses small diameter cylinders are more regular intervals.

The second .stl file has an ellipsoid/spherical knob, and is a trickier print due to needed support material, but is slightly more ergonomic and comfortable to turn, using larger, less frequent cylindrical cutouts around the knob perimeter for easier grip.

When printing the ellipsoid knob, I find it's best to print in a SPEED/DRAFT mode, using organic supports, with the knob laid on the print bed. The supports should peel away relatively easily from the round surface of the knob, but the center of the knob will have variable print quality as the material here will never be well supported. If printing with a smaller diameter nozzle, lower layer heights, or higher print quality settings in general, I recommend painting on supports in a sort of “Bullseye” pattern, where the center of the knob explicitly does not have support material, and the outer ⅓ perimeter of the knob does have supports.

I have included a sliced file using settings that I was able to get to print in PLA reliably using a 0.6 nozzle, as well as a .3mf file you can load into your slicer to customize.